C5AE

5CGR

The Journal of the Canadian Society of Agricultural EngineeringLa Revue de la Societe Canadienne du Genie Rural

CAE 38(4) 241-317 (1996)CN ISSN 0045-432X

Soil and Water

ESTIMATION OF HYDRAULIC PROPERTIES OF AGGREGATED SOILS USING ATWO-DOMAIN APPROACH

B. Wagner, V.R. Tarnawski, G. Wessolek and R. Plagge 241

RESPONSE FUNCTIONS FOR GRAIN YIELD FROM SPRING·SOWN WHEATS GROWN INSALINE ROOTING MEDIA

H. Stcppuhn, K. Wall, V. Rasiah and Y.W. Jame 249

Power and Machinery

ROUND BALE ENSILAGE OF INTENSIVELY CONDITIONED FORAGEP. Savoie, D. Tremblay, E. Channley and R. Theriault 257

MODELING AIRFLOW INSIDE AND AROUND HOODS USED FOR PNEUMATIC CONTROLOF PEST INSECTS. PART I: DEVELOPMENT OF A FINITE ELEMENT MODEL

M. Khelifi. J.-L. Robert and C. Lagu~ 265

MODELING AIRFLOW INSIDE AND AROUND HOODS USED FOR PNEUMATIC CONTROLOF PEST INSECTS. PART II: APPLICATION AND VALIDATION OF THE MODEL

M. Khelifi. J.-L. Robert and C. Lagu~ 273

WIND TUNNEL FOR SPRAY DRIFT STUDIESM. Farooq, D. Wulfsohn and RJ. Ford 283

Energy and Processing

METHOD TO EVALUATE THE AVERAGE TEMPERATURE AT THE SURFACE OF AA HORTICULTURAL CROP

B. Goyette, C. Vigueaul~ B. Panneton and G.S.V. Raghavan 291

Structures and Environment

RECIRCULATION OF FILTERED AIR IN PIG BARNSAK. Lau, AT. Vizcarra. K.V. 1..0 and J. Luymcs 297

Food Engineering

DYNAMICS OF DRYING BENTONITE IN SUPERHEATED STEAM AND AIR AS AMODEL FOOD SYSTEM

S. Cenkowski, N.R. Bulley and C.M Fontaine 305

Volume 38 Number 4 OctoberlNovemberlDecember 1996

CANADIAN AGRICULTURAL ENGINEERING1996

October/November/DecemberVolume 38, Number 4

EDITOR

J.J.R. FeddesDepartment of Agricultural, Food

and Nutritional ScienceUniversity of Alberta

Edmonton, Alberta T6G 2P5

ASSOCIATE EDITORS

R.L. KUSHWAHA(Power & Machinery)Department of Agricultural

and Bioresource EngineeringUniversity of SaskatchewanSaskatoon, Saskatchewan S7N 5A9

JJ.LEONARD(Structures & Environment)Department of Agricultural, Food

and Nutritional ScienceUniversity of AlbertaEdmonton, Alberta T6G 2P5

S.F. BARRINGTON(Waste Management)Department of Agricultural and

Biosystems EngineeringMacdonald College of McGill UniversitySte. Anne de Bellevue, Quebec H9X 3V9

H.STEPPUHN(Soil & Water)Semiarid Prairie Agricultural

Research CentreAgriculture and Agri-Food CanadaBox 1030Swift Current, Saskatchewan S9H 3X2

CSAE COUNCIL 1996-97

D.S.JAYAS(Food Engineering/Energy & Procesing)Department of Biosystems EngineeringUmversity of ManitobaWinnipeg, Manitoba R3T 5V6

L. GAUTHIER(Information & Computer Technologies)Departement des sols et de genie agroalimentaireUmversite LavalSainte-Foy, Quebec G IK 7P4

President DJ. NORUM SecretaryDepartment of Agricultural and

Bioresource EngineeringUniversity of SaskatchewanSaskatoon, Saskatchewan S7N 5A9

R. D. MacDONALD TreasurerAGVIRO Inc.14 Univeristy Ave. W.Guelph, Ontario NIG INI

J.J.R. FEDDES EditorDepartment of Agricultural, Food

and Nutritional ScienceUniversity of AlbertaEdmonton, Alberta T6G 2P5

REGIONAL DIRECTORS

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Fisheries and Food457 McCallum RoadAbbotsford, British Columbia V2S 8A I

JJ.LEONARDDepartment of Agricultural, Food

and Nutritional ScienceUniversity of AlbertaEdmonton, Alberta T6G 2P5

K.C. WATTS Past PresidentDepartment of Agricultural EngineeringTechnical University of Nova ScotiaHalifax, Nova Scotia B3J 2X4

S.F. BARRINGTON President-ElectDepartment of Agricultural and

Biosystems EngineeringMacdonald College of McGill UniversitySte. Anne de Bellevue, Quebec H9X 3V9

R.L. KUSHWAHA Vice-President (Technical)Department of Agricultural

and Bioresource EngineeringUniversity of Saskatchewan57 Campus DriveSaskatoon, Saskatchewan S7N 5A9

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Rural Development7000 - I 13th StreetEdmonton, Alberta T6H 5T6

Alberta

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and FoodBox 159Clinton. Ontario NOM ILO

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Estimation of hydraulic properties ofaggregated soils using a two-domain approach

B. WAGNER', V. R. TARNAWSKI2, G. WESSOLEK3 and R. PLAGGE3

I Geological Survey ofBavaria , He]3stra]3e 128,80797 Miinchen. Germany; 2Division ofEngineering, Saint Mary's University.Halifax, NS, Canada B3H 3C3; and 3Tecll1lica/ University ofBerlin, Institute ofEcology, Department ofSoil Science. Sa/zufer11-/2,10587 Berlin. Germany. Received 3 Novemherl995; accepted 25 September 1996.

Wagner, B., Tarnawski, V.R., Wessolek, G. and Plagge, R. 1996.Estimation of hydraulic properties of aggregated soils using atwo-domain approach. Can. Agric. Eng. 38:241-247. Hydraulicproperties of aggregated field soils estimated from limited data suchas grain size distribution and bulk density show large deviations fromexperimental results. This paper presents an extension of Campbell'smodel for the estimation of these properties. This was achieved byconsidering the geometric mean diameter and the average bulk den­sity of the aggregates. It is assumed that these soils are composed oftwo domains: the pore volume inside the aggregates and the porevolume between the aggregates (intra-and interaggregate porespaces). Water was assumed to flow primarily from the two domainsin sequence. This approach can be especially useful for mathematicalmodeling of solute movement during soil water drainage. The modelwas tested for three soil horizons with varying clay and humuscontents. The soil water retention curves and the unsaturated hydrau­lic conductivities of these horizons were determined experimentallytogether with the dry bulk density and geometric mean diameter ofthe aggregates. The model shows acceptable agreement with theexperimental data. Restrictions have to be made concerning theapplicability of the model in wetting cycles, in frozen soils, and inthe presence of transpiring vegetation.

Les proprietes hydrauliques des agregats de sol estimees apartirde donnees comme la grosseur des particules et la densitc apparentesont tres differentes des valeurs experimentales. Cet article presenteune extension du modele de Campbell pour la determination de cesproprietes. On a examine la moyenne geometrique des diamctres etla densite apparente moyenne des agregats. On suppose que ces solssont composes de deux entites: la porosite a I' interieur des agregatset la porosite entre les agregats (espace poreux intra- et inter­agregats). On a suppose que I'eau se depla~ait successivement entreles deux entites. Cette approche est particulierement interessantepour la modelisation du mouvement de I'eau de drainage du sol. Ona teste Ie modele sur trois horizons de sol dont les teneurs en argileet en matiere organique variaienl. Les courbes de retention d'eau etla conductivite hydraulique non-saturee ont ete mesurees pour cestrois horizons de meme que la densite apparente (base scche) et lamoyenne geometrique des diamctres des agregats. II y a une bonnecorrespondance entre les valeurs predites par Ie modele et Ics valeursmesurees. Cependant, il y a des restrictions quant a I'utilisation dumodele durant Ie cycle de mouillage des sols, avec des sols gclcs eten presence de vegetation qui transpire.

Therefore, several theoretical and semi-empirical models forpredicting the hydraulic properties of soils from more easilyavailable data have been developed (Brooks and Corey 1964;Campbell 1974, 1985; Bloemen 1980; van Genuchten 1980;Arya and Paris 1981). The majority of these models arederived from the earlier work of Childs and Collis-George(1950) and Marshall (1958) by applying the Hagen-Poiseullelaw and integrating with respect to pore size radii derivedfrom grain size distribution and bulk density or porosity.

In many applications these models produce satisfactoryresults and therefore have been frequently used in the com­puter simulation of water flow or heat and solute transfer insoils. One of the major drawbacks of these models is theinability to handle structured soils and associated effects likepreferential flow. These models have a tendency to underes­timate the vulnerability of structured soils to the leaching ofsolutes (Othmer et al. 1991). To accommodate these effects,Dumer (1991) developed a bimodal approach for the estima­tion of unsaturated hydraulic conductivity based on theMualem-model by applying the van Genuchten model todifferent sections of the soil-water-characteristic-curves.Gerke and van Genuchten (1993) developed a dynamicmodel that accounts for water flow in different soil domains.Chen et al. ( 1993) estimate the hydraulic properties of macro­porous soils during drainage.

Nevertheless, there is still a need for a model which willestimate hydraulic properties of structured soils based onfield observations and easily available measured data. Theobjective of this paper is to introduce a semi-empiricalmethod for estimating the hydraulic properties of aggregatedfield soils. It extends the two-parameter model for predictingsoil hydraulic properties (Brooks and Corey 1964; Campbell1974, 1985) into aggregated field soils.

CAMPBELL'S MODEL

According to Campbell (1974), the relationship between thesoil matric head and volumetric water content can be de­scribed by the power function:

INTRODUCTION

The in-situ measurements of hydraulic properties of fieldsoils usually requires laborious and time consuming experi­ments and ex-situ laboratory measurements often do notreflect field conditions (changes during soil sampling, differ­ent boundary conditions, different temperatures, etc.).

( )

-1>

'1/ ='l/e ~e.,.where:

'1/ =soil matric potential (kPa),'l/e =air entry potential (kPa),

(1)

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. Octobcr/November/Dcccmber 1996 24'

as =saturated volumetric water content (m3/m3),

a = unsaturated volumetric water content (m3/m3), andb =a parameter.

The parameter b was found by Campbell (1985) for twodata sets of British soils to be given by:

domain). Therefore, a two-domain concept for water move­ment within non-layered, aggregated soils, free of transpiringvegetation, is applied to the Campbell's model (Fig. 1). Forthe most part, water is assumed to move into and out of theintraaggregated pores via the interaggregate domain. Themathematical approach is based on the assumptions:

(5)

(6)

water flow In two domainsinteraggregate pore space

aggregates with Intraaggregatepore space

Fig. 1. Schematic representation of the aggregated soilmodel.

a) The intraaggregate domain is made up of capillarieswith smaller diameters than pore spaces between aggre­gates and conducts soil water slower than theinteraggregate domain.

b) During drainage, the interaggregate domain emptiesfirst followed by the intraaggregate pore space; theopposite order is assumed to occur when wetting takesplace; i.e., the intraaggregate pore space accumulatesand stores water first. Certainly, some restrictions haveto be made concerning this assumption; temporary stor­age and bypass flows have to be expected wheninfiltrated water enters the interaggregate system fasterthan the aggregates can take up water. This effect isneglected in the model presented here.

c) After saturation of the aggregates, total flow out of thesystem consists of water contributed from both the in­teraggregate and the intraaggregate domains; i.e., flowcontributions are additive (Chen et al. 1993).

In the following presentation, variables referring to prop­erties of the intraaggregate domain are denoted by thesubscript "ag"; those referring to the interaggregate domainare denoted by "ig" (Fig. 2). The porosity of the aggregatesis given by:

(2)

where:m "m2,m3 =mass fractions of clay, silt, and sand,

respectively,dj,d2,d3 =geometric mean particle diameters of clay,

silt, and sand (d, = 0.001 mm, d2 = 0.026 mm,d3 =1.025 mm).

The hydraulic conductivity of an unsaturated soil, KII

(mId), can be obtained from the relation provided by Camp­bell (1974):

2b+3

Ku=Ks(:s) (7)

where Ks (mId) =hydraulic conductivity of the water-satu­rated soil.

where:dg = geometric mean diameter of particles (mm), andO'g = geometric standard deviation of geometric mean

diameter (Gardner 1956).

The effect of soil bulk density on the moisture retentioncurve for the same British soils was given by the empiricalcorrection (Campbell 1985):

O.67b

lJfe = lJfes (i.~) (3)

where:Pb = dry bulk density of soil (Mg/m3), and'ties =air entry potential at the bulk density of 1.3 Mg/m3

(kPa), given by:

'tIes=-0.49dg-O•5 (4)

The geometric mean particle diameter dg and the geomet­ric standard deviation O'g are obtained from the relationsprovided by Shirazi and Boersma (1984) for soils having alog-normal function of particle size distribution:

dg=exp (I,:mj Ind;)

[2]~

Gg = exp I,:m; (In d;l2 - (I,: mj In d;) .

EXTENSION OF CAMPBELL'S MODEL FOR. AGGREGATED FIELD SOILS

Aggregated soils contain at least two different pore domains:the pore spaces between the aggregates (interaggregate do­main) and the pore spaces inside the aggregates (intraaggregate

242 WAGNER. TARNAWSKI. WESSOLEK and PLAGGE

(21)

(18)

(15)

(19)

(20)

Q;g = K u, ;g A i;g

Ku, rot = Kit, ig + Kit, ag (1 - 6;g)

while flows in the intraaggregate domain only take placethrough the area Aag filled by the aggregates:

(a )-b;g

'I' = 'l'e,;g as ; a= [aag .. as] (16)

Ku•ig = Ks•ig (:s )2b;, +3; B= [Bag" Bsl (17)

where Ks,;g is the saturated hydraulic conductivity of theinteraggregate pore domain and must be measured. Equation17 is basically identical to Eq. 7 and applies as long as therelative water content of the soil (a) is less than aag and thebulk of the soil water originates from, or enters, the intraag­gregate pores. At water contents where a is greater than aag,water flows in either domain at rates controlled by the inter­aggregate system. Flow between the two domains can occurat any time, but flux into or out of the soil usually occurs viathe interaggregate domain. These concepts give rise to theassumption of additive flows:

where:Qtot =total water flow (m3/d), andQag,Q;g = flows contributed from the intra- and

interaggregate pore domains (m3/d),respectively.

Water flows in the interaggregate pores are simulatedtaking place through an area, A, of the system, such that:

where i;g,iag =hydraulic gradients in the inter- andintraaggregate pore domains, respectively.

Assuming that there are no differences in the hydraulicgradients of the different pore systems, the total hydraulicconductivity KIt •ror of the aggregated soil follows from Eqs.18 - 20:

Interaggregate hydraulic properties in the range from aag to6s can then be obtained from:

For the interaggregate pore system, the air entry potential'Ve.ig is calculated from Eq. 4 with dga (mm) as the averagegeometric mean diameter of aggregate size (Gardner 1956):

'Ves. ;g = -0.49dga-O.5 (14)

Assuming Pb =1.3 Mglm3, 'Ve.;g = 'l'es.;g. The retention curveis assumed to be represented by a linear relation between'Ve.ag and 'Ve,;g on a logarithmic scale. To obtain this, big hasto be calculated as:

(8)

(13)

alr ontry po1entlals

'1'11

CampbeD model:

(e )_b

h ... 'I'., ­as

Interaggregate domain

. (8 )-biBh= "'dg 8

s

a -I _ Pagag-

Ps

8Q

,... e IlOl. water content eo afR S

Fig. 2. Denotations of variables for an aggregated soilsystem on a schematic soil water retention curve.

At moisture contents above 6ag, Klt,ag =Ks.ag . The saturatedhydraulic conductivity Ks•ag (mid) is calculated from the clay(cl) and silt (si) contents corrected for bulk density as de­scribed by Campbell (1985):

{ )

1.3b

- &s.Ks, ag - 3.3 1.3 exp ( - 6.88mcl- 3.63ms; - 0.025)

a;g = as - eag (9)

where 6s =saturated water content (m3/m3).

The hydraulic properties of the intraaggregate pore systemare calculated according to Eqs. 1 - 7 following the un-changed dg, (Jg' b, and 'l'es of the Campbell model, where:

-b

'lI ='lie. ag (B~g); B=[0 .. Bagl (10)

'lie. ag = 'lies(~ f67b (11)

Unsaturated hydraulic conductivity of the aggregates in therange from dryness to aag is calculated from:

2b+3

Ku•ag =K s•ag (B~g ) ; B=[0 .. Bagl (12)

The interaggregate pore space, a;g, may then be calculatedfrom total porosity:

wherePag =aggregate density (Mg/m3

),

Ps =soil particle density (Mg/m3), andOag = intraaggregate pore space (m3/m3).

CANADIAN AGRICULTURAL ENGINEERING Vol. 38, No.4, OctoberINovemberlDecember 1996 243

The accuracy of the extended model outlined above wastested by comparison with experimental data obtained fromthree different soil horizons.

MATERIALS AND METHODS

Two field sites in Gennany provided soil samples with vary­ing clay and humus contents for model testing (nomenclatureaccording to U.S. soil classification system): a clayey loam(vertic Cambisol) from Hordorf near Braunschweig and aloess soil (haplic Luvisol) from Ohlendorf near Hannover(Table I). A visual analysis of both soil profiles showed greatdifferences in structure and aggregation (Table II). Three soilhorizons were sampled. The Ap horizon of the loess is homo­geneous and has a fine structure with a weak tendency tofonn small crumbs. In contrast, the vertic Cambisol with aclay content between 30 and > 60% shows polyhedronicaggregates in the Ap horizon and prismatic lumps in the Swhorizon. In the wet and dry ranges, swelling and shrinkageoccur. The pH and cation exchange capacity (CEC) of thethree horizons are high (Table I).

The soil water retention curves and the saturated hydraulicconductivity were determined for the three horizons usinglaboratory-based, ceramic plates and a penneameter similarto that described by Hartge and Horn (1995). In addition,hydraulic conductivity near saturation (2-10 kPa) was deter­mined by a modified instantaneous profile approach (Plagge1991 ).

Measurements giving the density and geometric mean di­ameter of the aggregates were perfonned for all soils. Bulk

Table I: Physical properties of soil horizons

mean diameter of aggregates varied between 3.1 and 19.3mm. No significant differences in bulk density could befound for the different aggregate size fractions.

Figure 3 gives the measured and calculated water retentionand unsaturated hydraulic conductivity for the Hordorf Swhorizon. Using measured aggregate parameters in the ex~

tended Campbell prediction model, gives a good fit betweencalculated and measured retention data. Measured unsatu­rated hydraulic conductivity is not fully matched, but thedecline of hydraulic conductivity at lower suctions showsthat the predictions are closer to the measurements than theCampbell model. To test the sensitivity of the extendedmodel, geometric mean diameter and aggregate bulk densityof the Hordorf Sw horizon were varied within a broad rangeof aggregate properties with densities (1.6 - 2.0 Mg/m3) andgeometric mean diameters (0.2 - 40 mm)(Fig. 3, Table III).Aggregation of the soil should lead to lower water contentsat the same suctions depending on dry bulk density of theaggregates, while the air entry point is detennined by theaggregate sizes. Unsaturated hydraulic conductivity declinesat lower suctions, depending on aggregate sizes, while athigh suctions (above 1000 kPa) predicted values are nearlyindependent of aggregate dry bulk density.

Results of water retention functions produced by theCampbell model show significant deviation from experimen­tal data. This is due to the fact that Campbell's model wasoriginally developed for a homogeneous distribution of soilparticles and does not account for aggregated soil structure.

Figure 4 gives measured and calculated hydraulic proper-

1.44 0.421.50 0.431.42 0.48

pH Ks

(CaCI2) (mid)

7.5 0.0026.9 0.1686.3 0.350

Soil horizon

Hordorf SwHordorf ApOhlendorf Ap

Soil horizon

Hordorf SwHordorf ApOhlendorf Ap

Texture(kg/kg)

Clay Silt Sand

0.616 0.379 0.0050.348 0.430 0.2220.092 0.872 0.036

Texture Organic matter CEC(kg/kg) (cmole /kg)

Silty clay 0.006 24.7Clay loam 0.041 29.8Silt 0.014 11.2

Bulk density(Mg/m3)

Saturated volumetricwater content

Table II: Aggregation of investigated soil horizonsdensity was measured by dividing the aggregates of differentaggregate size fractions in water and weighing. Geometricmean diameter was detennined from two samples for eachsoil by drying and disintegrating the soil into the singleaggregates manually; aggregates were then sieved andweighed (sieve sizes: I, 2, 4, 10, 20 and 70 mm).

RESULTS AND DISCUSSIONS

Geometric mean diameters of aggregates and average aggre­gate densities are listed in Table III. The measured geometric

244

Soil horizon

HordorfSw

Hordorf Ap

Ohlendorf Ap

Aggregation (visual analysis)

prismatic lumps, slickensides, elasticdeformation

polyhedronic aggregates, coarse grained,swelling/shrinkage

fine texture, uniform small crumbs

WAGNER. TARNAWSKI. WESSOLEK and PLAGGE

Table III. Model parameters of investigated soil horizons

Soil horizon Density of h 'ill' dga 'IIe.ag

aggregates(Mg/m3) (kPa) (mm) (kPa)

--~~-

Hordorf Sw I 1.8 17.5 48 19.3 307(measured data)

Hordorf Sw 2 1.6 17.5 48 0.2 77(sensitivity analysis, lower range)

Hordorf Sw 3 2.0 17.5 48 40.0 1060(sensitivity analysis, upper range)

Hordorf Ap 1.8 9.9 8.8 4.3 28.2Ohlendorf Ap 1.52 7.4 5.5 3.1 8.8

(kPa)

29.2 0.12

72.3 1.14

17.6 0.08

16.2 0.2526.8 0.29

b = parameter from Campbell's model, 'ill' = air-entry potential in Campbell's model, dga = geometric mean diameter of aggregates,

'ile.ag =air-entry potential of aggregates in aggregated soil, hig = parameter in the extended model, 'IIc,ig =air-entry potential aggregated soil

::".-------------"~, "

~~ "·•..~2 "

o ..... ".......... "......,... ".... "

1 ..., ,------••.:a,..... "

"" ,,c measured- - - Campbell model- extended Campbell model 1... .. extended Campbell model 2+3

- 10.1

~ 10.2-~'S; 10-3;:;():::J

" 10-4C0()

10-5.2"3tU 10-6...-g.:t: 10.7

" 1\\... \\\ \\" '\\\ \\

\ \\\ \\. \\" '\

\ \\\ ........ \ \

3""\" ~ \ '.o ~ I

• ~ I" ~ I

\. \:\ 0 \l\"\ ~c measured

. - - Campbell model \- extended Campbell model 1 \..... extended Campbell model 2+3 \

\1+----r-----,---r---..,.-.o&---t0.0

105

104

-tU10 3a.

,:tJ:.-c0

~ 102

:::Jen

10

10 -8 +-"'-T"T'TT'I"Irr---r'T"'l'TTI".,...--,-r-rrTrnr---,I'"""T''T'T1nom-.,..,...,.,.'I1'ftt0.1 0.2 0.3 0.4 0.5 1 10 102 103 104 10 5

Water content (rn3/rn3) Suction (kPa)

Fig. 3. Measured and predicted (Campbell model and extended model) soil water characteristic curves of the HordorfSw. Results of the extended model are shown for measured aggregate parameters (model I) and the expected lowand high range of aggregate parameters (models 2 and 3) as given in Table III.

ties of the Hordorf Ap horizon. Water retention is well repre­sented by the extended model, but unsaturated hydraulicconductivity is overestimated. On the other hand, the estima­tion of the extended model clearly gives a better fit to themeasurements than the original Campbell model. This ap­plies especially at suctions below 2 kPa.

Figure 5 shows results of measurements and calculationsfor the Ohlendorf Ap horizon. The lower air entry point iswell met by the extended model, but at higher suctions watercontents are overestimated. Again, the model gives a betterfit to measured data than the original Campbell model and theimprovement is best at low suctions.

A possible reason for the deviations between the extendedmodel and measurements could be the influence of highhumus content on soil hydraulic properties, especially in theHordorf Ap horizon. One common characteristic seen in allfigures is that calculated hydraulic conductivity data are

approximated by two linear functions on the log-log scaleconnected by a non-linear one. This is explained by the factthat in the model the two different curves for unsaturatedhydraulic conductivity in the two domains of the aggregateflow model are overlain. After drainage of the interaggregatepore space, the air entry point of the aggregates has not yetbeen reached, so that unsaturated hydraulic conductivity re­mains relatively constant until drying of aggregates starts.This stepwise function is not reflected in the measurementsand likely due to the fact that sharp distinctions of drainagebetween intraaggregate and interaggregate pore space do notoccur. The transition tends to follow smoothly. Nevertheless,Figs. 3,4, and 5 show that the extended model allows a muchbetter prediction of unsaturated hydraulic conductivity thanthe Campbell model, especially at lower suctions.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. Octobcr/November/Dccembcr 1996 245

ooo

oD~

oD measured. - - Campbell model- extended Campbell model

1+---""T""----r---r-----r-........--I0.0

105 1\\\ - 10.1\0

104 , i,, - 10.2\~,- \ ">,

ca103

, =Q. ,, U 10-3~ , =- ,c " "t:J0

, c" 0 10~1i 102 " U

= D measured I .2Ien . - - Campbell model I '3 10-5I

- extended Campbell model I caI ..

10 I "t:JI >-I :::I: 10~II

-------------,,\

\\

\ ,,,,,,,,,\ ," \

\ ,\

",.\\ ,

10·7+--r-T"T'1rTT1'r--r-T"T'1I'"1'1"11rr--r-T"T"IrTT'IIrr--r-rrrTT'llrr-aor-r'i'TTmt0.1 0.2 0.3 0.4 0.5 1 10 10

210

3104 105

Water content (m3/m3 ) Suction (kPa)Fig. 4. Measured and predicted (Campbell model and extended model) soil water characteristic curves of the Hordorf Ap.

o measured

102 103

Suction (kPa)soil water characteristic curves of the

10

-----------..,\\\ • - - Campbell model\\ - extended Campbell model\\\\\\\\\

\\

\\\\\\

\\

\

1

10 -5+--r-rr""rr--.-,..,.T"I"I'IrTr"'~-r-r.",.nr-~-r-ip.",rTIr'--y---r"T"T'7mt

10.514---.........--..,....--"""T"--~-e---t

0.0 0.1 0.2 0.3 0.4

Water content (m3/m3)

Fig. S. Measured and predicted (Campbell model and extended model)Ohlendorf

CONCLUSIONS AND RECOMMENDATIONS

A semi-empirical approach to the estimation of hydraulicproperties of aggregated field soils from grain size distribu­tion, porosity, and bulk density data has been developed. Themodel extends the Campbell model by introducing two pa­rameters: density and geometric mean diameter of theaggregates. Measured values of these parameters gave im­proved predictions of the hydraulic parameters of theinvestigated soil horizons.

The following conclusions can be drawn about the newmodel:

1) it allows the adaption of the Campbell model to simu­late water movement, especially for drainage, throughaggregated soils by a parameter fitting procedure;

2) an adaption of the model to measured soil water charac­teristics will improve predictions of unsaturated

hydraulic conductivity;

3) a better prediction of hydraulic properties based ongrain size distribution may be achieved by integratingfield observations of aggregation into the model.

It is anticipated that the concepts outlined above in theextended Campbell model will greatly improve predictionsof water and solute transport in aggregated soils limited byinput data (e.g., only grain size analysis and bulk densitiesare necessary). This approach can be particularly useful formodelling leaching phenomena in aggregated soils inducedby macroporous flows. Water moving through the interag­gregate domain following high infiltration rates (e.g., afterheavy rains), and bypassing the aggregates, is not accountedfor in the model. Nor is the model applicable to soils withfrozen layers, nor those soils where vegetation is activelytranspiring.

Recommendations for further study include development

246 WAGNER. TARNAWSKI. WESSOLEK and PLAGGE

and testing of the extended model with a larger data set ofaggregate densities and geometric mean diameters.

REFERENCESArya, L.M. and J.F. Paris. 1981. A physicoempirical model

to predict the soil moisture characteristic fromparticle-size distribution and bulk density. Soil ScienceSociety ofAmerica J ourna/ 45: 1023-1030.

Bloemen, G. W. 1980. Calculation of hydraulicconductivities of soils from texture and organic mattercontent. Zeitschrift fur Pf/anzenerniihrung undBodenkunde 143:581-605.

Brooks, R.H. and A.T. Corey. 1964. Hydraulic properties ofporous media. Hydrology Papers, No.3. Colorado StateUniversity, Fort Collins, CO.

Campbell, G.S. 1974. A simple method for determiningunsaturated conductivity from moisture retention data.Soil Science 117:311-314.

Campbell, G.S. 1985. Soil Physics with Basic: TransportModels for Soil-Plant Systems. Amsterdam, TheNetherlands: Elsevier.

Chen, C., D.M. Thomas, R.E. Green and RJ. Wagenet. 1993.Two-domain estimation of hydraulic properties inmacropore soils. Soil Science Society ofAmerica Journal57:680-686.

Childs, E.C. and N. Collis-George. 1950. The permeability ofporous materials. Proceedings of the Royal Society ofLondon A 201:392-404.

Durner, W. 1991. Vorhersage der hydraulischenLeitfahigkeit strukturierter Boden. Ph.D. thesis,Lehrstuhl fUr Hydrologie, University of Bayreuth,Bayreuth, Germany.

Gardner, W.R. 1956. Representation of soil aggregate-sizedistribution by a logarithmic-normal distribution. SoilScience Society ofAmerica Proceedings 20: 151-153.

Gerke, H.H. and M.T. van Genuchten. 1993. A dual-porositymodel for simulating the preferential movement of waterand solutes in structured porous media. Water ResourcesResearch 29:305-319.

Hartge, K.H. and R. Horn. 1995. Die physikalischeUntersuchung von Boden. Enke, Stuttgart, Germany.

Marshall, TJ. 1958. A relation between permeability andsize distribution of pores. Journal ofSoil Science 9: 1-8.

Othmer, H., B. Diekkriiger and M. Kutilek. 1991. Bimodalporosity and unsaturated hydraulic conductivity. SoilScience 152:139-150.

Plagge, R. 1991. Bestimmung der ungesattigtenhydraulischen Leitfahigkeit im Boden.- Bodenokologieund Bodengenese 3, Technical University Berlin, Berlin,Germany.

Shirazi, M.A. and L. Boersma. 1984. A unifying quantitativeanalysis of soil particle size distribution. Soil ScienceSociety ofAmerica Journal 48: 142-147.

van Genuchten, M.Th. 1980. A closed form equation forpredicting the hydraulic conductivity of unsaturated soils.Soil Science Society ofAmerica Journa/44:892-898.

NOTATION

A area, (m2)

b constant in Campbell's equationbig constant in extended aggregate modeld 24 hrs period of timedg geometric mean particle diameter (mm)dga geometric mean diameter of aggregates (mm)di geometric mean diameter of soil separates (mm)i hydraulic gradient (m/m)mi mass fractions of soil separatesQ flux of water (m3/d)Ks saturated hydraulic conductivity (mId)Ku unsaturated hydraulic conductivity (mId)KU,101 total unsaturated hydraulic conductivity (mId)'" soil matric potential (kPa)"'es air entry potential (kPa)"'e air entry potential (corrected for bulk density) (kPa)

"'e,ig air entry potential of interaggregate pores (kPa)"'e,ag air entry potential of aggregates (kPa)O'g standard deviation of geometric mean particle

diameter8 volumetric moisture content8s saturated moisture content8ag porosity of aggregate domain8ig porosity of inter-aggregate domainAs density of solid particles (Mg/m3)Ab bulk density of dry soil (Mg/m3)Aag bulk density of aggregates (Mg/m3)

Subscripts

ag intraaggregate domainig interaggregate domain

CANADIAN AGRICULTURAL ENGINEERING Vol. 38, No.4, OClober/November/December 1996 247

Response functions for grain yield fromspring-sown wheats grown in saline rooting

mediaH. STEPPUHN, K. WALL, V. RASIAH and Y.W. JAME

Semiarid Prairie Agricultural Research Centre, Research Branch, Agriculture and Agri-Food Canada, P.O. Box 1030, SwiftCurrent, SK, Canada S9H 3X2. Received 30 November 1995; accepted 23 October /996.

Steppuhn, H., Wall, K., Rasiah, V. and lame, Y.W. 1996. Responsefunctions for grain yield from spring-sown wheats grown insaline rooting media. Can. Agric. Eng. 38:249-256. Farmers oftenrequest information about the salt tolerances of their crops. Field testsin saline soils can provide qualitative assessments; but because ofnatural variability, these tests cannot define the functional relation­ships required for modelling growth responses to root-zone salinity.These require tests under more controlled conditions. Two controltests were conducted in the Swift Current Salt Tolerance TestingLaboratory with five spring-sown Canadian wheat varieties(Katepwa, Neepawa, Biggar, Fielder, and Kyle). The first test fol­lowed the standard procedure (U.S. Salinity Laboratory) ofincreasing root-zone salinity gradually after plant emergence; thesecond treated root zones with full complements of salts beforeseeding. The plants were irrigated four times daily with hydroponicsolutions containing a range of salt concentrations between I and 14dS/m equivalent electrical conductivity for saturated soil paste ex­tracts (ECe). Responses were measured by the number of plantssurviving to harvest time, the grain yield, and the number of fertilespikes per plant. Three functions were evaluated for their suitabilityin desccibing grain yield response mathematically: (I) the conven­tionaltwo-piece linear model; (2) a sigmoid-shape response; and (3)an exponential non-linear function. The sigmoid function proved themost fitting in both tests and indicated that significant declines ingrain production began at ECe-values of I to 2 dS/m, which areconsiderably lower than that reported in the literature for wheats ingeneral (6 dS/m). The number of harvested plants was not signifi­cantly affected by salinity, but the number of fertile spikes per plant,in linear association with grain yield, decreased with increasing ECc.

Les agriculteurs s'informent souvent de la tolerance de leurscultures a la salinite. Des parcelles d'essais dans des sols salinspeuvent foumir une appreciation qualitative de la tolerance desplantes; cependant, acause de la variabilite naturelie, il n'est paspossible d'etablir des relations qui permellraient la modelisation deseffets de la salinite dans la zone des racines sur la croissance desplantes. Pour cela, il faut faire des tests dans des conditions con­trolees. Deux essais controles de 5 varietes canadiennes de ble deprintemps (Katepwa, Neepawa, Biggar, Fielder et Kyle) ont ete faitsau laboratoire de recherches sur la salinite de Swift Current. Lors dupremier essai, on a suivi la procedure standard (U.S. Salinity Labo­ratory) en augmentant progressivement la salinite dans la zone desracines apres la germination. Au second essai, la zone des racinesavait rec;ue des supplements de sel avant les semis. Les plantes ontete irriguees quatre fois par jour avec des solutions hydroponiquesdont les conductivites electri~ues des extraits de pate de sol saturevariaient entre I et 14 dS m- (ECe). La tolerance a ete evaluee apartir du nombre de plants vivants a la recolte, du rendement engrains et du nombrc d'epis fertiles par plant. On a examine trois typesde modeles mathematiqucs afin de decrire les impacts sur les rende-

ments: 1) un modele lineairc conventionnel; 2) une fonction sig­mo'ide; 3) une fonction exponentielle non lineaire. Pour les deuxessais, la fonction sigmo'ide s'ajustaitle mieux aux donnees experi­mentales et a montre que les rendements diminuaientsignificativement apartir d 'une conductivite electrique de 1 ou 2 dSm-I, ce qui est beaucoup plus faible que ce qui est rapporte pour Ieble dans la lillerature (6 dS m- I

). La salinite n'a pas eu d'impactssignificatifs sur Ie nombre de plants recoltes, alors que Ie nombred'epis fertiles qui varie lineairement avec Ie rendement en grainsdiminuait amesure que la conductivite electrique augmentait.

INTRODUCTION

Farmers in arid and semiarid climates often indicate thatspring wheat yields very poorly in saline soils. Field trialsverify wheat producers' observations (Marshall 1942; Bal­lantyne 1962; Holm 1983; McKenzie 1988). Researchers atthe United States Salinity Laboratory (1954) classify wheatas showing medium salt tolerance. They also suggest that theelectrical conductivity of water-saturated soil paste extractsprovides the best measure of salinity. .

Wheat plants exhibit different sensitivities to salinitywhile in different growth stages (Maas and Poss 1989; Fran­cois et at. 1994). Seeded wheat can usually germinate insaline media, but at a delayed rate (Torres et at. 1974;Aceves-N. et at. 1975). As wheat plants pass through vegeta­tive, reproductive, and maturation stages, they showincreasingly less sensitivity to salinity and less consequentloss in grain production (Maas and Poss 1989).

Neepawa, Katepwa, Biggar, Fielder, and Kyle are wheatvarieties sown in spring throughout the Canadian Prairies andare grown under either dryland or irrigation. Each variety hasbeen developed to produce a specific flour used in baking andrepresents four classes of products: Neepawa and Katepwa(Triticum aestivum L.) of the Canada Western Red SpringWheat Class for breads; Biggar (T. aestivum L.), a CanadaPrairie Spring wheat, for unleavened products; Fielder (T.aestivum L.) of the Soft White Spring Class for pastry; andKyle (T. turgidum L.), a Canada Western Amber Durum, forpasta. The diverse pedigrees of these varieties suggest thatthey also may differ in their inherent responses to salinity ingrowth and grain yield.

Maas and Hoffman (1977) summarized the responses inwheat yields obtained from controlled tests conducted inCalifornia and India (Hayward and Uhvits 1944; Ayers et at.1952; Asana and Kale 1965). They described the response to

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/November/December 1996 249

TESTING PROCEDURES

salinity using two linear lines, one a tolerance plateau with aslope of zero and the other a conductivity-:.dependent linewhose negative slope indicated the yield reduction per unitincrease in salinity. Besides this piecewise linear function,various non-linear models have been proposed to relate cropyield to salinity (Bresler et aI. 1982; van Genuchten andHoffman 1984).

van Genuchten (1983) presented three functions to ana­lyze and describe the inherent response in crop yields, Yp

relative to the maximum, Ym, where salinity has no influenceon yield:

and Yr = YIYm, with Y, the absolute yield, equal to thatproduced by the test crop when subjected to a rooting solu­tion whose salt concentration, or electrical conductivity, c, isconstant over the growing period. Equation 1 describes thepiecewise linear response function with c, denoting thethreshold salinity where the two lines meet and s representingthe slope of the decline in production when c> c, until C > Co

where crop yield equals zero. Equations 2 and 3 representnon-linear response functions (sigmoid and exponential)where p, oc, and ~ are empirical constants and Cso is thesalinity at which the yield is reduced by 50%.

The objective of this study is to compare and assess thesuitability of these functions for describing the inherent re­sponses in grain yield of selected, spring-sown, Canadianwheats to saline rooting media.

electrical conductivity ofeach solution was checked initially,biweekly, and at harvest.

Gradual concentration test

Twelve treatment solutions were prepared with target electri­cal conductivities equalling 2,3,4,5,6,8, 10, 12, 16,20,24and 28 dS/m. The relative variability in grain yield whichwould likely occur in association with each conductivity wasestimated from previous experiments. These estimates di­vided by an error tolerance squared and multiplied by anappropriate t-table value squared indicated the replicationwhich would increase the accuracy of the planned statisticalregressions. Consequently, the five treatments with the low­est salt concentrations were replicated twice (three times forthe 3 dS/m treatment) and the remaining treatments wereserved by one tank each. The tank arrangement followed arandomized block design with respect to cultivars, but wasmodified slightly to eliminate any bias caused by the tallerplants blocking solar radiation associated with low sun an­gles. Forty-five seeds per tank from three wheat varieties(Neepawa, Biggar, and Kyle) were sown 40 mm deep into thesand separated by 80 mm within rows spaced 150 mm apart.After emergence, the plant populations were thinned to 36plants per tank.

The procedure for adding salts to the irrigated solutions inthis test followed that practiced at the U.S. Salinity Labora­tory (Maas and Hoffman 1977). Salts were added graduallywith the first third on day 18 after seeding (plants showingtwo leaves), the second third on day 21 (plants showing threeleaves), and the final third on day 24 (3-4 leaves showing).Day lengths were adjusted during the growing period (Sep­tember - December) by 'using 475 W sodium lampspositioned 1.5 m above the sand surfaces to mimic a typicalfield seeding date of May 1 along the 50th parallel north.Setpoint temperatures equalled 24°C daytime and 20°Cnighttime. The maximum daily ambient air temperatureranged from 23 to 28°C and the minimum between 17 and21°C.

(1)

(3)

(2)

when 0::; C::; C,when c, < C::; Cowhen C~ Co

1Yr=-----

1+ (c/c50f

Yr =exp (occ - ~c2)

Two experiments were conducted using sand tanks housedwithin a greenhouse in the Salt Tolerance Testing Laboratoryat Swift Current, SK. This facility features control over irri­gation, fertility, root-zone salinity, and temperature under anelectronic, programmable logic controller (Steppuhn 1995).The plastic tanks (cylinders 0.85 m diameter x 1.0 m deep)contain washed silica sand (99.8% pure) having an averagebulk density of 1.65 Mg/m3. At saturation, the sand retains amean volumetric water content of 37.3%. In these tests, thetanks were flushed four times daily with a modified Ho­agland nutrient solution consisting of 2.0 mM Ca(N03h, 2.5mM KN03, 0.17 mM KH2P04, 1.0 mM MgS04, 0.05 mMchelated Fe, 0.5 mM NH4N03, 0.05 mM KCI, 0.023 mMH3B04, plus trace elements including Mn, Zn, Cu, Si, andMo. Solutions were salinized by adding NaCI and CaCl2 (1: 1by mass) resulting in pH values of 7.5-7.9 and nutrient solu­tion electrical conductivities of 2.0 dS/m. Each irrigationcontinued for five minutes until the sand was completelysaturated after which the solutions drained into 612-litrereservoirs for recycling the next irrigation. Water lost byevapotranspiration was replenished weekly or when neces­sary to maintain the concentrations of salts in solution. The

Instantaneous concentration test

Ten treatment solutions were prepared with target electricalconductivities equalling 2, 3, 4, 5, 6, 8, 10, 12, 14, and 18dS/m. As in the gradual concentration test, an estimate of theexpected grain-yield variability suggested the replicationleading to better accuracy: the 2, 3, and 4 dS/m treatmentswere replicated three times, the 5 dS/m tanks were repeatedtwice, and the remaining treatments consisted of one tankeach. In this test, full complements of salts were added to theirrigation water supplies prior to seeding. The tank arrange­ment followed. a randomized block design with respect tocultivars, but was modified slightly to eliminate any biascaused by the taller plants blocking solar radiation associatedwith low sun angles.

Fifty seeds per tank from one of three wheat varieties(Katepwa, Fielder, and Kyle) were sown 40 mm deep into thesand separated by 80 mm within rows spaced 125 mm apart.The resulting plants were not thinned in this test. The tankarrangement followed a randomized design modified slightlyto eliminate any bias in solar radiation. Day lengths wereadjusted during the growing period (February - June) by

250 STEPPUHN, WALL, RASIAH and JAME

using 475 W sodium lamps positioned 1.5 m above the sandsurfaces to mimic a typical field seeding date of May 3 atlatitude 50° north. Setpoint temperatures equalled 22°C day­time and 18°C nighttime resulting in maximum daily ambientair temperature ranging from 21 to 27°C and the minimumbetween 15 and 19°C.

Measurements and statistical analysesWithin each variety, the responses of the plants to the salinitytreatments were determined by measuring the number ofseed-bearing spikes, the oven-dried grain produced, and th~

number of plants remaining at harvest per tank. These meas­urements were averaged and related to electricalconductivities of water-saturated soil paste extracts, ECl' ,

derived from the electrical conductivities of the test solu­tions, ECs, using the conventional relationship followed bythe U.S. Salinity Laboratory (Maas 1990):

ECl' =0.5 ECs (4)

This equality assumes that the solutions fill the soil poresto field capacity and was substantiated for a southern Albertasoil saliniized in the laboratory by Janzen and Chang (1988)and for various Prairie soils in the field by Kohut and Dudas(1994).

To functionalize and generalize the production obtainedunder salinity and to compare possible responses betweentests and among varieties, grain yield had to be expressed ona relative basis. The usual procedure for converting absoluteyield to relative yield employs a scaling divisor based on theproduction where salinity has little or no influence on yield(Maas 1990). This normalizes the data set which for non­halophytes equals the maximum yield, Ym, associated withthe function.

Determining Ym for the three response functions (Eqs. I,2, and 3) for each wheat variety required inspection andanalysis. Inspection of the absolute grain yields initiated theselection of Ym for the piecewise linear response (Eq. I).Within each test and variety, a group of the EC,,-yield datapoints were identified which defined the horizontal segmentof the function. The average yield calculated from this groupdetermined Ym' Initially, the group consisted of the data pairshowing the greatest grain yield and any data resulting fromtesting at lower ECl'-values. Data pairs from the next highestsalinity level were only included if their grain yield exceeded90% of the average for the group.

Least-squares linear regressions for relative grain yieldcorrelated with ECl' generated the statistics which were usedto assess the suitability of the piecewise linear responsefunction. The regression statistics associated with the non­linear response functions were determined using themaximum neighborhood method of Marquardt (1963), whichis based on an optimum interpolation between the Taylorseries method and the method of steepest descent.

RESULTS AND DISCUSSIONS

Number of plants harvestedAt the salt concentrations tested, almost no plants died beforeproducing grain, although root-zone salinity visually reducedplant growth. The number of plants harvested in each tank at

the end of the gradual concentration test equalled 36, thenumber left following thinning. The number of harvestedplants in the instantaneous concentration test was not signifi­cantly reduced by salinity (Table I). This supports Maas andPoss's report (1989) that salinity has a minimal effect onwheat emergence and survival.

Table I: Average number of plants harvested from 50seeds sown per tank, sorted by wheat varietyand electrical conductivity of saturated soilpaste extract (ECe); instantaneousconcentration test.

ECe Katepwa Fielder Kyle(dS/mr l

1.0 46.5 49 451.5 47 46.7 44.32.0 49 47 45.52.5 48 47.5 433.0 49 49 434.0 48 49 455.0 44 50 416.0 48 48 477.0 47 50 439.0 46 48 47

Mean 47.2 48.4 44.4SO 1.15 1.16 1.91

SO Standard deviation

Absolute and relative grain yieldsThe quantity of grain produced during both tests generallydecreased with increasing root-zone salinity (Fig. 1). Scalingdivisors (Ym) to convert these absolute yields to relativevalues were determined appropriate to each response func­tion. For the piecewis.e linear function, inspection of theabsolute yields resulted in Ym values of 381, 334, and 561g/m2 from the gradual concentration test for Neepawa, Big­gar, and Kyle wheat varieties, respectively. Inspection of theinstantaneous concentration test data for Katepwa, Fielder,and Kyle gave rise to Ym-values equalling 768, 818, and 882g/m2

• The Ym-values associated with the non-linear responsefunctions (Eqs. 2 and 3) were determined from the regressionanalyses with these functions using the absolute test data.The Y-intercept identified a Ym for each variety and test.

RegressionsOnce relative grain yields (Yr) were obtained by normalizingwith Ym, least-squares fits of Eq. 1 for each variety in eachtest were possible. Figure 2 exemplifies the best-fit of thepiecewise linear function to the responses of Katepwa andKyle wheats to increasingly saline rooting environments inthe instantaneous test. These fits, which typify the Eq. Iresponse for the five wheat varieties tested, suggest thatnon-linear models may be more applicable for these data.The regressions using Eq. 2 (sigmoid-shape) for the sameKatepwa and Kyle responses show better fits (Fig. 3). Equation

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/November/December 1996 251

600 Gradual concentration test0

E c Biggar-~400• 0 0

o Kyle"C c ~ cQi c lJ. Neepawa.;;'

to gQc: 200 • c 0

.~ • e e c

" • 90

0 2 4 6 8 10 12 14

Salinity, EC. (dS/m)

Instantaneous concentration test

1.0.--.....

•

9

.6. Katepwa

• Kyle

•....

.•••.•. .......••

1

••

•

2345678

Salinity, EC. (dS/m)

· . .•...•............•..•.

••..•......••.•..••

...••.•.••.•..•.

.•••.

Two-piece linear response functions for relativegrain yield related to equivalent electricalconductivit), of saturated soil paste extracts(ECe ) of rooting media from Katepwa andKyle wheats; instantaneous concentration test.

0.0 '-----"_---'-_-'--_...L.._-'-_J.-----I~---"_~

o

0.8

0.2

Fig. 2.

"CQi.;;'

.!: 0.6~ClQ)

.~ 0.4IIIQia:

• Fielder

• Kyle

... Katepwa

••• •

• ••••• •

• •• ••• • ••

• • ••

800

1000

"E~600"CQi.;;'c: 400

~

" 200

1.0 •

•0.8 •

98

......... ..........•

•

•••••••• .6.

__ .6. Katepwa

..........• Kyle

·······..1

.................•....

2 3 4 5 6 7

Salinity, ECo (dSlm)

· \.

....

• ..

•

0.0 '---'_---"_-'-_-'--_-'-_-'-_'---'_-.Jo

0.2

Fig. 3. Sigmoid non-linear response functions for relativegrain yield relatcd to cquivalent clcctricalconductivit.y of saturated soil paste extracls(Eee ) of rooting media from Katep",a andK)'le wheats; instantaneous concentration tcsL

than the plants exposed to gradual incre;'lscs in salt concen­triltion. Based on the work of Francois et al. (1994). onemight expect eso 10 be significantly less for the instantaneouslest. Comparing c50-values within Tables II and III showedthis 10 be true.

The threshold (c/) and slope (s) parameters resulling from

"CQi.;;'c: 0.6.§ClQ)

~ 0.4IIIQia:

3 (exponenlial) also filS Ihe response data reasonably well asdemonstrated by Biggar and Kyle in the gradual concentra­tion lest (Fig. 4).

Tables II and III contain summaries of the regressionstatistics for all the functions and varieties within the twoteslS. The lowest residual slIlll-or-squares was obtained withthe sigmoid function for all varieties in both tests except forFielder in the inSlanlaneOus concel1lratioll test. A similartrend in the coefficients-or-variation and the chi-square­probabilities also favoured the sigmoid model. Theexponential function resulted in better fits than (he piecewise·model.

The sigmoid function could also be used to separate re­sponses by varieties or tests. Values of cso (conductivityproducing a 50% reduction in grain yield) backed by theirstandard errors (Tables II and III) relate to possible differ­ences among the wheat varieties and between tests. Theobjective in this report did not specifically focus on isolatingvarieties with these data; however. the sensitivity of cso toidentify differences was assessed for a range of independentmodel inputs (c-values) at a constant p (Fig. 5). From Ihissensitivity analysis. we concluded that eso could serve 10

compare the responses of wheat varieties 10 saline fOOlingmedia.

Wheal plan IS in the instanlaneous concentration lest weresubjecled 10 root-lone salinity earlier and for a longer period

252 STEPPUHN. WALL. RASIA II andJAME

Table II: Regression statistics from least-squares analyses using three response functions* applied to data f~om thegradual concentration test assessing the salt tolerance of three Canadian wheats (standard errors ID

parentheses)

Statistics for the piecewise linear function*

RSS')

X2Variety c, Slope r-

dS/m %(dS/m)-1 %2 prob.

Neepawa 1.0 (1.09) 8.8 (1.0) 10.0 0.775 0.810Bigar 2.0 (1.24) 8.8 (1.0) 17.0 0.692 0.770Kyle 1.0 (1.95) 9.4 (1.0) 18.0 0.598 0.670

Statistics for the sigmoid non-linear function*

RSS') x2

C50 p r-

dS/m %2 prob.

Neepawa 4.03 (0.26) 1.50 (0.16) 4.0 0.953 0.988Biggar 4.84 (0.37) 1.65 (0.21) 6.0 0.934 0.968Kyle 3.10 (0.29) 1.41 (0.21) 7.0 0.908 0.963

Statistics for the exponential non-linear function*

oc P RSS ,.2 X2

%2 prob.

Neepawa -0.162 (0.04) 0.0008+ 12.0 0.956 0.980Biggar -0.123 (0.09) 0.0014+ 26.0 0.912 0.954Kyle -0.184 (0.05) 0.0050+ 32.0 0.886 0.950

Functions:Piecewise linear: Y, = I-s(c-c,)

ISigmoid non-linear: Y,

I + (C/C50'l'

Exponential non-linear: Y, =exp(occ-plh+ Not significant

RSS Residual sum-of-squaresr2 Coefficient-of-determination

X2 Chi-square probability that random samples give no better fitsN Sample number aver:aged from available dataY, Relative grain yield; s = Slope; c = ECI!

c, Threshold ECe

C50 Value of Eel! where grain yield is reduced 50%

oc, P, p are regression constants.

N

121212

N

12

12

12

N

1212

12

the applications of the piecewise linear functions to twoCanadian wheat varieties equalled 1.0 dS/m and 15% (dS/mr)for Katepwa (bread), and 1.0 (dS/mr) and 16% (dS/mr) forKyle (durum) (Table III). The corresponding values reportedby Maas and Hoffman (1977) for wheat in general were 6.0dS/m for CI and 7.1 % (dS/mr' for .'I, indicating possibledifferences in salt tolerance among wheat varieties. TheCanadian wheats in our tests also appear considerably moresalt sensitive when compared to the results from later testingof an American bread wheat (e, = 8.6 dS/m and s = 3.0%

CdS/mr l and an American durum (cl =5.9 dS/m and s =3.8%(dS/mr) (Francois et a1. 1986).

Root-zone salinity affects the growth of wheat primarilyby reducing the number of fertile spikes per plant (Maas andGrieve 1990). This reduction occurs early in the plant's lifewhen the salt hinders the development of primordia whichdetermine the number of tillers produced by the plant (Grieveet a1. 1993). From this, one might infer that the averagenumber of spikes produced per plant should correlate linearlywith absolute grain yield. Correlations for the three varieties

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OctoberlNovemberlDecember 1996 253

Table III: Regression statistics from least-squares analyses using three response functions'" applied to data fromthe instantaneous concentration test assessing the salt tolerance of three Canadian wheats (standarderrors in parentheses).

Statistics for the piecewise linear function*

Variety c, Slope RSS 2 X2r(dS/m) %(dS/mr l %2 prob.

Katepwa 1.0 (0.96) 15.4 (2.0) 20.0 0.754 0.830Fielder 1.0 (0.84) 14.6 (2.0) 23.0 0.717 0.820Kyle 1.0 (0.91) 16.3 (2.0) 18.0 0.781 0.830

Statistics for the sigmoid non-linear function*

C50 p RSS 2 X2r(dS/m) %2 prob

Katepwa 2.90 (0.27) 2.21 (0.45) 10.0 0.890 0.945

Fielder 3.17 (0.53) 1.78 (0.58) 26.0 0.730 0.896

Kyle 2.67 (0.14) 2.57 (0.33) 4.0 0.965 0.985

Statistics for the exponential non-linear function*

~ RSS 2 X2oc r

%2 prob.

Katepwa - 0.116 (0.22) 0.034+ 15.0 0.883 0.920

Fielder - 0.143 (0.11) 0.016+ 34.0 0.753 0.898

Kyle - 0.064 (0.10) 0.061+ 7.0 0.946 0.970

* Please see Table II for footnotes.

N

10

1010

N

1010

10

N

10

1010

in the instantaneous concentration test support this inference(Fig. 6). The regression statistics in Table IV extend thevalidity of the linear correlation to the gradual concentrationtest results as well.

CONCLUSIONSTest results from spring-sown Canadian wheats grown insaline rooting media under controlled conditions led to thefollowing conclusions:

I. a sigmoid-shaped function described the responses inrelative grain yield of Neepawa, Katepwa, Biggar, andKyle wheat varieties better than either the two-piecelinear or the exponential response functions;

2. declines in grain yields from spring-sown Canadianwheats in both exposure tests occurred at relatively lowequivalent ECe-values of 2 dS/m or less;

3. subjecting the spring wheats to saline root zones fromseeding onward resulted in steeper (adverse) responsesin relative grain yield than gradually subjecting theroots to increasing salinity after plant emergence; com­parisons of the ECe-values where 50% yield reductionsoccurred also indicated that early exposure to salinitydecreases salt tolerances;

254

4. although the number of plants reaching harvest was notsignificantly affected by increasing salinity, the numberof seed-bearing spikes per plant, in linear associationwith grain yield, decreased with increasing equivalentECe•

A number of cautions accompany the extrapolation of theresults obtained in these tests to the field:

I. the greenhouse testing environment could not duplicateall the conditions encountered in the field;

2. the expression of root-zone test solution ECs values inECe equivalents rests on a general relationship for soilsat field capacity, which differs slightly for individualsoils, and varies widely within the normal ranges infield soil water contents;

3. these conclusions are based on the premise that osmoticeffects dominate the responses observed for the wheatvarieties at the salt concentrations tested.

ACKNOWLEDGEMENTSThe authors gratefully appreciate the assistance of K. Deo­bald, G. Winkleman, P. Taylor, D. Jenson, and B. Nybo inpreparing and conducting the experiment. Financial assis-

STEPPUHN. WALL. RASIAH and lAME

Table IV: Regression statistics from linear correlationsof the number of fertile spikes and grainyield of wheat grown in increasingly salinerooting media.

RMSE Root mean square errorr2 Coefficient of determination# Number of fertile spikes per plant

0.2

0.8

1.0

"as'>-.5 0.6l!I:n

~:; 0.4

"ia:

",.:::- ."..... '-, ,, ", .\ '.\ ...••... '\

\ '\

\ '\\ ..•.... '\" '\, ..... ,, ...•....... ", '. ," .....

""" ~.:.~.= :....:....=------------

0.0 L---L.-_..L.....----L._...L-.......L ~:::::r==::I=::::;;;;

0123456789

Salinity, ECe (dS/m)Fig. 5. Examples of non-linear sigmoid responses in

relative grain yield for root-zone salinities(ECe) from 0 through 9 ds/m using a constantp-parameter of 3.0 and values of 2, 3, 4 and5 dS/m for cso in Ym =1/[1 + (c/cso)P].

0.0094

0.0065

0.0047

0.01720.00910.0076

Slope.,#(g/m-)

0.980.99

0.98

0.970.900.98

Test andvariety

Instantaneous concentration testKatepwa 0.311

Fielder 0.226

Kyle 0.242

Gradual concentration testNeepawa 0.347Biggar 0.328Kyle 0.160

12001000

........... • Kyle

- . - • Fielder

200

10L..-__...l-__--L.__---1 .L....-__...L-__...J

o

2

7-fi 6Q.Gi 5Q.

en 4~Q.3en

400 600 800

Grain yield (glm2)

Fig. 6. Least-squares linear regressions for Katepwa,Fielder, and Kyle wheats relating the averagenumber of fertile spikes per plant to grain yield,instantaneous concentration test.

9

8

Ayers, A.D., l.W. Brown and C.H. Wadleigh. 1952. Salttolerance of barley and wheat in soil plots receivingseveral salinization regimes. Agronomy Journal44(6):307-310.

Ballantyne, A.K. 1962. Tolerance of cereal crops to salinesoils in Saskatchewan. Canadian Journal Soil Science42:61-67.

Bresler, E., B.L. McNeal and D.L. Carter. 1982. Saline andSodie Soils, Principles, Dynamics, Modeling. Berlin,Germany: Springer-Verlag.

Francois, L.E., C.M. Grieve, E.V. Maas and S.M. Lesch.

1412

[J

10

-- [J Biggar

·..··..·····0 Kyle

8642

\\..•.

o d-.

':'~""'" •••••••••"Q. 0

••••••••[J

............, ~ ~.---- ~0.0 L..-_--L__-'--__.1.-_---1__......L..__..1-_----l

o

0.8

0.2

1.0

"as.>-c 0.6.i!I:n

~;: 0.4as'ia:

tance from the National Soil Conservation Program and theWheatland Conservation Area, Inc. is also acknowledged.

REFERENCES

Aceves-N., E., L.H. Stolzy and G.R. Mehuys. 1975.Combined effects of low oxygen and salinity ongermination of a semi-dwarf Mexican wheat. AgronomyJourna/67:530-532.

Asana, R.D. and V.R. Kale. 1965. A study of salt toleranceof four varieties of wheat. Indian Journal PlumPhysiology 8( I):5-22.

Salinity, ECe (dS/m)Fig. 4. Exponential non-linear response functions for

relative grain yield related to equivalentelectrical conductivity of saturated soil pasteextracts (ECe) of rooting media from Biggarand Kyle wheats, gradual concentration test.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38, No.4. OClober/NovemberlDecember 1996 255

1994. Time of salt stress affects growth and yieldcomponents of irrigated wheat. Agronomy Journal86: 100-107.

Francois, L.E., E.V. Maas, TJ. Donovan and V.L. Youngs.1986. Effect of salinity on grain yield and quality,vegetative growth, and germination of semi-dwarf anddurum wheat. Agronomy Journal 78(6):1053-1058.

Grieve, C.M., S.M. Lesch, E.V. Maas and L.E. Francois.1993. Leaf and spikelet primordia initiation insalt-stressed wheat. Crop Science 33:1286-1292.

Hayward, H.E. and R. Uhvits. 1944. The salt tolerance ofwheat. In United States Salinity Laboratory Report ToCollaborators, 287-300. United States DepartmentAgriculture, Agricultural Research Service, Riverside,CA.

Holm, H.M. 1983. Soil salinity, a study in crop tolerancesand cropping practices. Publication 25M/3/83.Saskatchewan Agriculture, Plant Industries Branch,Regina, SK.

Janzen, H.H. and C. Chang. 1988. Cation concentration in thesaturation extract and soil solution extract of soilsalinized with various sulfate salts. Communications inSoil Science and Plant Analysis 19:405-430.

Kohut, C. K. and M.J. Dudas. 1994. Comparison ofimmiscibly displaced soil solutions and saturated pasteextracts form saline soils. Canadian Journal Soil Science74:409-419.

Maas, E.V. 1990. Crop salt tolerance. In Agricultural SalinityAssessment and Management, ed. K.K. Tanji, 262-304.American Society Civil Engineers, New York, NY.

Maas, E. V. and C.M. Grieve. 1990. Spike and leafdevelopment in salt-stressed wheat. Crop Science30: 1309-1313.

Maas, E. V. and G.1. Hoffman. 1977. Crop salttolerance-current assessment. Journal Irrigation andDrainage Division, American Society Civil Engineers103(IR2): 115-134.

256

Maas, E.V. and J.A. POSSe 1989. Salt sensitivity of wheat atvarious growth stages. Irrigation Science 10:29-40.

Marquardt, D.W. 1963. An algorithm for least-squaresestimation of non-linear parameters. Journal Society ofIndian Applied Mathematics II :431-441.

@REFERENCE =Marshall, J.B. 1942. Some observa­tions on the tolerance of salinity by cereal crops inSaskatchewan. Scientific Agriculture 22:492-502.McKenzie, R.C. 1988. Tolerance of plants to soil salinity.

Soil and Water Program, 1987. Alberta Special Crops andHorticultural Research Centre Pamphlet 88-10. AlbertaAgriculture, Brooks, AB.

Steppuhn, H. 1995. Swift Current Salt Tolerance TestingLaboratory. Report to Natural Science and EngineeringCouncil of Canada, Ottawa, ON.

Torres, B.C., F.T. Bingham 'and J. Oertli. 1974. Salt toleranceof Mexican wheat: II. Relation to variable sodiumchloride and length of growing season. Soil ScienceSociety ofAmerica Proceedings 38:777-780.

United States Salinity Laboratory Staff. 1954. Diagnosis andImprovement of Saline and Alkali Soils. AgricultureHandbook No. 60. Washington, DC: United StatesDepartment Agriculture.

van Genuchten, M.Th. 1983. Analyzing crop salt tolerancedata. U.S. Salinity Laboratory Research Report 120.Washington, DC: Agricultural Research Service, UnitedStates Department Agriculture.

van Genuchten, M.Th. and G.J. Hoffman. 1984. Analysis ofcrop salt tolerance data. In Soil Salinity UnderIrrigation-Process and Managemellt, eds. I. Shainbergand J. Shalhevet, 258-271. New York, NY:Springer-Verlag.

STEPPUHN. WALL. RASIAH and JAME

Round bale ensilage of intensivelyconditioned forage

P. SAVOIE1, D. TREMBLAy2, E. CHARMLEy3 and R. THERIAULT2

ISoils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, Sainte-Foy, QC, Canada G1V 2J3;2Departement des sols et de genie agroalimentaire, Universite Laval, Sainte-Foy, QC, Canada G1K 7P4; 3Research Farm,Agriculture and Agri-Food Canada, Nappan, NS, Canada BOL lCO. Contribution No. 538, SCRDC. Received 15 Januray1996; accepted 14 August 1996.

Savoie, P., Tremblay, D., Charmley, E. and Theriault, R. 1996.Round bale ensilage of intensively conditioned forage. Can.Agric. Eng. 38:257-263. A predominantly orchardgrass field wasmowed and intensively conditioned with an experimental 2.1 m widemower-macerator. The macerated forage consisted of long shreddedstems and smaller detached particles mixed in a windrow left to dryon the stubble. Macerated windrows and conventionally conditionedforage windrows were wilted in the field for 24 h and harvested witha round baler at two forward speeds (3.4 and 6.7 km/h). All baleswere wrapped with plastic film. Variables measured included fielddrying rate, mechanical losses after baling, bale density, and chemi­cal composition at mowing, at harvest, and after I, 4, 7, 14, and 70 dof fermentation. Macerated forage had a drying rate 39% higher over24 h than that of conventional windrows. Field losses were similarand averaged 3.4% after mowing, maceration or conditioning, andbaling. Bale density ranged between 122 and 147 kg DM/m3 withouta significant effect due to treatment. Bales of macerated forage had alower pH than conventionally conditioned bales for the first fourdays of fermentation. The more rapid decline of pH suggested anincreased rate of fermentation of macerated forage.

Un fourrage compose principalement de dactyle a cte fauche etsurconditionne au champ avec une faucheuse-surconditionneuse ex­perimentale de 2, I m de largeur. Les fourrages surconditionnesetaient constitues de longues tiges cisaillees en longueur et de pluspetites particules detachees, Ie tout etant dcpose en andain sur Iechaume au champ. Des andains de fourrages surconditionnes ouconditionnes de fa~on conventionnelle etaient secMs au champ pen­dant 24 h et recoltes avec une presse a balles mndes selon deux vitessesd'avancement (3,4 et 6,7 kmIh); toutes les balles etaient enrobees avecun film plastique etirable. Les variables mesurees incluaient Ie taux desechage au champ, les penes mecaniques du fourrage apres Ie pressage,la masse volumique des balles, et la composition chimique ala fauche,ala recolte et apres 1,4, 7, 14et 70 jours de fermentation. Les fourragessurconditionnes ont eu un taux de sechage 39% plus eleve, sur uneperiode de 24 h, que les fourrages conditionnes conventionnelle­ment. Les pertes au champ ont ete a peu pres egales et representaienten moyenne 3,4% apres la fauche, Ie conditionnement ou surcondi­tionnement, et Ie pressage. La masse volumique des balles a varieentre 122 et 147 kg MS/m3 sans effet significatif par rapport autraitement. Les balles de fourrage sur~onditionne avaient un plusfaible pH que les balles de fourrage conditionne conventionnelle­ment durant les quatre premiers jours de fermentation. La diminutionplus rapide du pH suggerait une augmentation du taux de fermenta­tion des fourrages surconditionnes.

INTRODUCTION

Over the last 15 years, there has been increased interest inintensive forage conditioning, sometimes referred to as mac-

eration, superconditioning, or mat making. Krutz et at.( 1979) originally proposed a mower that included maceratingrolls and a compression system to deposit a thin mat on thestubble. Koegel et a1. (1988) built a small-scale field proto­type that was successful in producing dry hay within 6 to 8 hinstead of 2 to 3 d typically required in Wisconsin. Muck etal. (1989) showed that maceration also improved fermenta­tion characteristics of finely chopped silage because lacticacid bacteria (LAB) multiplied more rapidly on the laceratedsurface of the forage and soluble sugars were released fasterfrom the ruptured cells. Koegel et al. (1992) reported thatmacerated forage also improved the digestibility of foragefiber fed to ruminants. Savoie et al. (l993b) observed thatrespiration loss was less and that more soluble sugars wereretained in macerated forage than in conventionally condi­tioned forage that was not subjected to rainfall. There hasbeen industrial interest in developing commercial mower­macerators (Deutz-Fahr 1993; Krone 1993) and researchwork to develop larger experimental prototypes (Shinners etal. 1992; Savoie et al. 1993a).

Over the same period, round balers became the preferredmachine to harvest large quantities of unchopped forage inNorth America. Round balers were originally developed tohandle large quantities of field-dried hay (Renoll et al. 1978).With increasing interest in handling high moisture roundbales (Harrison 1985; Tremblay et al. 1993), manufacturershave developed more robust round balers. To make goodquality round bale silage, it has been suggested to harvest ata moisture content below 72% (Haigh 1990) and to ensuregood wrapping and sealing (Vough and Glick 1993). How­ever, round bale silage is considered not as good as finelychopped silage at the same moisture content especially forhigh producing lactating dairy cows (Genest et al. 1990) andfor steers fed for rapid growth (Nicholson et al. 1992).

Maceration has the potential of improving round bale silagefor at least four reasons: (1) it increases the natural drying ratewhich allows faster removal from the field and reduces weatherrisks; (2) it makes soluble sugars readily available for use byLAB; (3) it provides a greater surface area for LAB to multiplyon and to produce anaerobic conditions more rapidly; and (4) itfacilitates forage compaction, thereby increasing bale density.The sequential combination of mowing-maceration and roundbaling could therefore bring an economically improved harvestoption to livestock farmers.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OClober/November/December 1996 257

METHODOLOGY

OBJECTIVE

Fig. 1. Schematic view of experimental mower-maceratorequipped with a 2.1 m wide cutterbar and eightstaggered macerating rolls 1.5 m wide by 0.20 mdiameter.

ing fingers. It formed a windrow about 1.2 m wide by adjust­ing the rear deflectors. Such a narrow windrow was made tofacilitate baler pickup and formation of a 1.2 m wide roundbale. The actual operating parameters for the two mowers aregiven in Table I.

A round baler (New Holland, Model 640, New Holland,PA) was used to harvest the wilted windrows. The baler hada variable geometry chamber composed of belts and rollswhich formed a controlled density core and a relatively uni­form density bale. The baler windrow pickup width was 1.75m, chamber width was 1.18 m, and bale release diameter wasset at 1.22 m.

Within one or two hours after baling, the round bales werewrapped with a continuous, overlapping plastic film. Thewrapper (Kvemeland Model 7510, Kerteminde, Denmark)was set up to rotate the bale four times with 50% fibnoverlap. The plastic film (Mobilwrap, Mobil Canada Ltd,Belleville, ON) was white, had a tacky side set against thebale, and had a thickness of 25 Jlm.

Table I: Average mowing parameters

Mower Working Mowing Windrow Widthspeed width width ratio(km/h) (m) (m)

Mower-macerator 5.00 2.11 1.01 0.48

Mower-conditioner 7.17 2.76 1.17 0.42

Experimental design

Forage mowed and harvested as round bale silage was amixed crop based on orchardgrass (about 80% of the drymatter) and white clover from fields at the Nappan ResearchFarm, Nappan, NS. Fields were subdivided into 16 experi­mental units (E.U.) of approximately 200 m long by 8 m wide(three or four mowing widths). Forage was mowed between0900 and 1100 h at two dates during the first growth cycle.Half of the E.U. was mowed on June 17 (block 1) and theother half on June 20 (block 2) in 1993. On each mowingdate, four E.U. were mowed with the mower-macerator; theother four E.U. were mowed with the commercial mower­conditioner. Experimental units were assigned randomly toeach mower. After 24 h (± 2 h) of wilting, two E.U. from eachconditioner treatment were baled. One E.U. for each condi­tioner treatment was baled at a slow forward speed (3.4 km/h)and one was baled at a faster forward speed (6.7 km/h). Acomparison of two baling speeds was intended to assess theimpact of speed on losses. At least two round bales (about175 kg OM and 700 kg wet mass for each bale) were ensiledfrom each harvested E.U. The four unbaled E.U. of eachblock were left in the field to measure drying rate duringprolonged wilting. It was intended to harvest these windrowsas round bale hay but rainfall prevented adequate drying ofboth blocks.

For field drying measurements, the experimental designwas a randomized block design with a total of 16 E.U.: two

\

\

Auger -

_ Macerating unit (spring forceagainst the upper rolls)

Feeding rolls -- - 2740~ 3130 N3920N

4700N

-1. _

Machine description

Two machines were used to mow and condition forage: anexperimental mower-macerator developed by Savoie et al.(1993a) and a commercial mower-conditioner (Kuhn ModelFC300G, Saveme, France).

Figure 1 illustrates the main components of the mower­macerator which included a 2.1 m wide cutterbar and eightmacerating steel rolls of 0.2 m diameter and 1.5 m width. Therolls were knurled lengthwise with grooves 1 mm deep and 2mm apart (pitch). The four upper rolls turned at 1000 rpmwhile the bottom rolls turned at 670 rpm; the 1.5: 1 differen­tial speed between the rolls created a shredding or maceratingeffect on the forage as it flowed through the machine. Theupper rolls were spring loaded with increasing total force perroll as indicated in Fig. 1. Minimum distance between theupper rolls and lower rolls was 1.5 mm. The maceratedforage was ejected on the stubble out of the last two macer­ating rolls and formed a windrow about 1.0 m wide. Althoughthe macerator could form a 1.5 m wide windrow, a narrowerwindrow was selected, by adjusting the feeding auger flight,so the ratio of windrow width to mowing width would besimilar (0.4 to 0.5) to the ratio of the commercial mower-con­ditioner.

The commercial mower-conditioner (Kuhn FC300G) wasa 3.0 m wide disk mower with steel intermeshing condition-

The objective of the research project was to assess the advan­tage, if any, of forage maceration on round bale silagequality. Differences between conventional round bale silageand macerated round bale silage were assessed on the basisof drying rates and losses in the field and of chemical com­position and fermentation characteristics during storage.

258 SAVOlE. TREMBLAY. CHARMLEY and THERIAULT

Table II: Weather conditions recorded at the Nappan experimental farm

blocks, two conditioning treatments, and four replicationswithin each block. For measurements related to round baling,the experimental design was a two-factor factorial random­ized block with a total of eight E.U.: two blocks, twoconditioning treatments, and two forward baling speeds.There were at least two samples within each E.U. (see be­low).

Measurements in the fieldImmediately after mowing, sections of windrows were liftedand laid on three wire mesh trays (1.2 m by 0.9 m) placedrandomly within each E.U. There were 24 trays in the fieldduring each mowing date. Trays were weighed at mowing(0900-1100 h), after about 4 h of drying (1300-1500 h), afterabout 10 h of daytime drying (1900-2100 h) and after about24 h of wilting (0900-1100 h on day after mowing). In block1, weather permitted continued field drying so an additionalweighing was taken about 29 h after mowing (1400 h on theday after mowing). Drying rate was estimated from the expo­nential model used by Rotz and Chen (1985). A dryingcoefficient was estimated for each drying interval as:

Relative humidity Sunshine Average Rain Evaporation(%) wind

a.m. p.m. (hId) (km/h) (mm/d) (mm/d)

94.7 55.5 11.0 8.3 0.0 6.284.5 73.8 1.7 7.3 0.8 3.885.8 82.0 2.5 4.1 0.5 3.594.7 42.1 13.7 6.9 0.0 6.370.7 90.2 3.5 10.7 13.4 3.4

the commercial mower) were selected randomly within eachE.U. that was harvested after baling. All forage particlesremaining on the ground after baling ("lost particles") werehand lifted, collected in a bag and oven dried.

Measurements at the storage siteRound bales were weighed just before wrapping with a flatplate scale (Weigh-Tronix, Model DSL363602, capacity1000 kg, precision ± 0.2 kg). Two 500-g core samples weretaken. from each round bale at ensiling and after 1, 4, 7, 14,and 70 d of storage, with a highly adhesive patch resealingafter sampling. There was a total of 16 round bales sampled:two bales per harvested E.U., four E.U. harvested per block,two blocks. One of the 500-g core samples was oven dried at50°C for 72 h, the other was frozen. The oven dried samplewas analyzed for OM after further drying at 105°C for 24 h,for ash-free neutral detergent fibre (NOF), and for acid deter­gent fibre (AOF) (Van Soest et al. 1991). Ash wasdetermined as residual mass after burning at 550°C. Thefrozen sample was analyzed for volatile fatty acids and alco­hols by gas chromatography, lactic acid (Barker andSummerson 1941), total N (procedures 7.033-7.037, AOAC1984) and pH. Crude protein (CP) was estimated as 6.25times total N. Oven dried fresh samples at mowing and lostparticles after baling were also analyzed for CP, AOF, NDF,ash, and moisture content. Statistical analysis of forage com­position and fermentation products was done by the leastsquare mean difference procedure (SAS 1985).

RESULTS AND DISCUSSION

Weather conditions during the field drying experiment areshown in Table II. The two mowing days (June 17 and 20)had generally favourable drying conditions with more than11 hours of sunshine and a pan evaporation above 6 mm forthe day, although morning relative humidity was high (over90%). The day following mowing was overcast in both casesand rainfall occurred shortly after bales were harvested. OnJune 18, it was possible to take an additional measurement ofdrying at about 1400-1500h before rain. On June 21, how­ever, rain fell soon after baling (l100h) so no additionaldrying observation was taken of windrows left in the field.

Crop characteristics were fairly homogenous betweenblocks (Table III). Yield averaged 4.2 t DM/ha. It was com­posed of 80% grass (mainly orchardgrass), 13% legume(clover), and 7% other crop species. The initial moisture wasrelatively high at 84.5%.

p.m.

23.519.018.523.016.0

(I)

Temperature

tC)

13.514.017.013.515.0

a.m.

Date

93-06-1793-06-1893-06-1993-06-20

93-06-21

k =-lin (.M..-)t Mo

where:k = drying coefficient (h-1

),

t = time interval between weighings (h),M =moisture content (dry basis) at the end of the

drying interval (kg water!kg OM), andMo =moisture content (dry basis) at the beginning of

the interval (kg water!kg OM).

Twenty four 500-g samples of freshly mowed forage weretaken in each mowing block next to each of the 24 trays.These samples were oven dried at 50°C for 72 h (ASAE1993) to measure initial moisture content. The initial mois­ture content measurement and the initial fresh forage mass intrays were used to estimate dry matter in each tray for dryingcoefficient calculations. Dry matter yield of the fresh cropwas estimated from dry matter on each tray and the mowedarea corresponding to the forage on the tray (a strip of 0.9 malong the windrow and the actual mower width). Actualmowing width and windrow width were measured at 50, 100,and 150 m along each 200 m long windrow. There were threeor four windrows per E.U.

A composite sample of 2 kg from each E.U. was taken tomeasure botanical composition.Forage was separated in threeclasses: grass, clover, and otherplants ("weeds"). Average mow­ing and baling speeds were esti­mated by measuring time to cover50 m over several windrowlengths.

Mechanical losses were meas­ured after windrows were pickedup and baled. Two strips of 0.5 mwidth by the actual mowing width(approximately 2.1 m for themower-macerator and 3.0 m for

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/NovemberlDecember 1996 259

Table III: Crop characteristics at mowing in drying time between 10 and 30% to reach atarget moisture of 40%, wet basis, when the

Date Yield Botanical composition (%, w.m.) Inital moisture ratio was 0.60 rather than 0.38 in early maturitycontent grass. Ratios between 0.44 and 0.71 had little

(t DM/ha) legume grass weed (%) effect on drying rate of more mature grass. Inthe present study, possibly 10% out of 39% of

93-06-17 the drying rate increase for macerated wind-

(block I) 4.28 13.8 72.2 14.0 84.6 rows could be attributed to the greater width

93-06-20ratio.

(block II) 4.15 12.3 86.8 0.9 84.3 The 39% increase of the drying coefficientdue to maceration (and possibly windrow

Average 4.22 13.1 79.5 7.5 84.5width) was less than increases reported fortimothy and alfalfa which averaged 99% in the

Table IV: Drying rate, mechanical field losses and bale density

Block Unit Mower Baler Drying rate (h-I) Field Balespeed losses density

kt k2 k3 k4 (%, DM) (kg DM/m3)

6 M.-c 0.1082 0.1071 0.0421 0.04952 M.-c Slow 0.0503 0.0786 0.0351 2.9 145.71 M.-c 0.0526 0.0991 0.0451 0.05037 M.-c Fast 0.1152 0.1113 0.0426 1.9 132.75 Mac. 0.1411 0.1522 0.0603 0.06914 Mac. Slow 0.1410 0.1499 0.0591 2.7 129.93 Mac. 0.0915 0.1296 0.0572 0.06828 Mac. Fast -* -* -* 3.3 127.4

6 M.-c 0.1480 0.1147 0.04423 M.-c Slow 0.1284 0.1062 0.0428 3.8 146.54 M.-c 0.1259 0.1064 0.0418

2 2 M.-c Fast 0.1197 0.1023 0.0429 3.9 122.18 Mac. 0.1891 0.1329 0.04727 Mac. Slow 0.1740 0.1307 0.0486 5.0 131.25 Mac. 0.1779 0.1411 0.0520I Mac. Fast 0.1772 0.1697 0.0662 3.3 135.7

Average Mower-cond 0.1060 0.1032 0.0421 0.0499 3.1 136.8Macerator 0.1560 0.1437 0.0558 0.0687 3.6 131.1

* Mowing unit #8 (block 1) was delayed because running belts broke

Field measurements are reported in Table IV. Statisticalanalysis was not done on drying coefficients, losses, or baledensity because of the small number of data; the discussionsimply indicates trends. Drying rate coefficients (k1, k2, k3.and 14) corresponded to four time intervals after mowingdescribed in the methodology (0-4 h, 4-10 h, 10-24 h, 24-29h approximately). Macerated forage dried more rapidly thanconditioned forage in all time intervals. Drying coefficientsof macerated forage were between 33 and 47% higher thanthe drying rate coefficients of conditioned forage (an averageincrease of 39%). Part of the drying rate increase could beattributed to a difference in the ratio of windrow width tomowing width (0.48 for macerated, 0.42 for conditioned,Table I). It is known that wide windrows dry faster thannarrow windrows. Savoie et at. (1984) estimated a decrease

260

field (Savoie et at. 1993a) and 111 % in the laboratory (Savoieet at. 1993b) under favourable weather conditions. However,it was similar to a drying rate increase of 31 % observed in thelaboratory under a shaded environment without rain (Savoieet al. 1993b). The current experiment confirms that macera­tion generally increases the drying rate of forage comparedto conventional conditioning but to a more moderate degree(30-40%) in a high relative humidity, overcast, or otherwiseless favourable drying environment than large increases(100-110%) that have been reported under a very favourabledrying environment.

Total mechanical losses due to mowing, conditioning, andpickup with a round baler ranged from 1.9 to 5.0% of DMyield (Table IV). Overall differences due to maceration orbaler speed were small (0.5% or less). Total average loss due

SAVOlE, TREMBLAY, CHARMLEY and THERIAULT

Table V: Chemical composition of forage in freshly mowed forage, at baling and in lost forage particles

Fresh forage Baling Lost particles

macerated mow-condo macerated mow-condo macerated mow-condo

13.5 13.8 14.9 14.9 19.3 18.2

38.6 37.3 36.9 35.8 30.4 31.1

66.7 63.6 61.5a 58.4b 42.9 46.4

9.5 9.5 5.7 5.6 12.9 11.9

84.2 85.2 76.0 74.5 50.8 54.7

CP(%, OM)ADF(%, OM)NOF(%, OM)Ash (%, OM)Mositure content

(%, wet basis)

Parameter

a Values with different letters in the same row and for the same operation are significantly different for a probability level of 5%.

TableVI: Chemical composition of round bales during fermentation

Parameter Treatment Days of fennentation

0* 4 7 14 70

CP(%, OM) mow-condo 14.9 15.1 15.3b 15.1 15.1 15.3

macerated 14.9 14.3 14.4a 14.8 15.1 15.1ADF(%, OM) mow-condo 35.8 35.1 35.1 37.5b 35.73 36.33

macerated 36.9 36.3 36.5 36.63 37.3b 37.4b

NOF(%, OM) mow-condo 58.43 57.03 55.8a 56.63 55.63 55.43

macerated 61.5b 59.8b 58.7b 59.4b 59.1b 57.6b

Ash (%, OM) mow-condo 5.6 5.5 5.5 6.0 6.0 5.5

macerated 5.7 5.5 5.4 6.2 6.3 5.5Moisture content mow-condo 74.5 77.4 76.8 76.4 74.1 73.8

(%, OM) macerated 76.0 77.1 75.8 75.8 75.6 75.1

* These values are the same as those of Table V for baling.3 Values with different letter in the same column and for the same parameter are significantly different for a probability level of 5%.

to mowing, conditioning or maceration, and baling was 3.4%.Bale dry matter density averaged 134 kg DM/m3. This was

a relatively low density compared to other round bale silagedensities reported in the range of 150 to 190 kg DM/m3

(Tremblay et al. 1993). However, it is within the wide rangeof 100 to 200 kg DM/m3 observed by Genest et al. (1990).Maceration did not result in higher density bales. Actually,bales of macerated forage were less dense (131 kg/m3) thanbales made of conditioned forage (137 kg/m3). Operating thebaler at a fast speed resulted in a lower density (130 kg/m3)

compared to operating the baler at a slow speed (138 kg/m3).

This was expected because a slow speed provides more time(and more energy) for belts and rolls to apply pressure to thebale.

There was generally no significant difference in chemicalcomposition of forage either macerated or conditioned with acommercial (regular) conditioner (Table V). The only excep­tion was neutral detergent fiber of macerated forage at baling(61.5%) which was higher than NDF of regular forage atbaling (58.4%). Maceration caused slightly more loss (0.5%of DM) than conventional conditioning; lost macerated parti­cles had a lower NDF (43%) than the average NDF in the

windrow (67%) or lost conventionally conditioned particles(46%). Since leaves have a higher nutritive quality thanstems (Savoie 1988), losses due to maceration would tend tobe composed of lea~es in a larger proportion than losses dueto conventional conditioning. However, even if all maceratedlosses were leaves and all conditioned losses were stems, thiswould explain only a one percentage unit difference in NDF.A three percentage unit difference must be partially due tospatial variability in the field and experimental error.

Moisture content was not significantly different at the timeof baling between samples of the macerated forage and theconventionally conditioned forage. Half the samples of mac­erated forage were drier than conventionally conditionedforage and half were wetter when considering bales sampledafter different fermentation periods (Table VI). The dryingrates measured in the field always indicated faster waterremoval rate (by an average of 39%) from macerated foragecompared to conventionally conditioned forage. However,this was not reflected in final moisture content of the bales.One explanation is the fact that mowing and baling of experi­mental plots were done in a random sequence. The totaldrying interval could vary between 22 to 26 h so some

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. Octobcr/November/December 1996 261

Table VII: Fermentation products of round bale silage

Parameter Treatment Oays of fermentation

0* 4 7 14 70

pH mow-condo 5.65b 5.19 4.73b 4.65 4.51 4.28macerated 5.00u 5.10 4.51 u 4.68 4.39 4.30

Lactic acid (g/kg OM) mow condo 0.00 24.3 62.3 69.7 89.0 95.7macerated 0.00 25.0 64.6 76.8 85.9 107.4

Acetic acid (g/kg OM) mow-condo 6.88 10.9 13.4 10.2a 12.7 20.5macerated 6.88 12.8 14.5 12.7b 12.2 20.0

Butyric acid (g/kg OM) mow-condo 0.79 0.14 0.11 0.20 0.86 1.60macerated 0.48 0.04 0.03 0.39 0.38 1.03

Total acids (g/kg OM) mow-cond. 11.9 41.0 80.9 82.8 109 128macerated 12.4 44.7 86.1 95.8 105 136

Methanol (g/kg OM) mow-condo 2.06 2.59 2.56 2.16 2.48 2.40macerated 2.31 2.23 2.16 2.33 2.35 2.61

Ethanol (g/kg OM) mow-condo 0.67 12.2 15.2 13.2 16.2 17.0macerated 1.26 11.0 13.1 10.9 15.3 15.1

* These values are the same as those of Table V for baling.a Values with different letter in the same column and for the same parameter are significantly different for a probability level of 5%.

conventional treatments that dried slower may have had theopportunity to dry longer and reach a similar moisture con­tent to macerated treatments. A heavy dew was observed inthe morning of the second drying day for both blocks. Al­though the effect of dew was not measured, absorption islikely to be more important in macerated forage than unmac­erated forage as in the case of rainfall (Savoie et al. 1993b).On average for both conditioning treatments, the high rela­tive humidity, dew, and the short wilting time resulted in anoverall high final moisture content in bales (75.7%).

Sampling of bales between days I and 70 revealed aconsistently higher NDF of macerated forage (59.4%) com­pared to conventionally conditioned forage (56.5%, TableVI). As indicated above, this difference in NDF was in partdue to increased loss of the leaf portion after maceration.

The pH was significantly lower in macerated forage thanin conventionally conditioned forage in two instances (day 0and day 4 after baling, Table VII). This is in accordance withobservations made by Muck et al. (1989) who noted a fasterdecline of pH in chopped macerated alfalfa silage. Fermenta­tion products were not significantly different betweenmacerated round bale silage and conventionally conditionedround bale silage, except for acetic acid after seven days offermentation. Lactic acid increased similarly to about 100g/kg DM in both silages although the final level in maceratedbales was higher and significant at the 10% level (p =0.099).Butyric acid tended to be lower in macerated silage but thiswas not statistically significant· because of large variationsbetween individual observations and a high standard error.Other acids and alcohols were of similar final concentrationsin both treatments.

The chemical and physical characteristics of maceratedforage harvested and stored as round bale silage did notindicate important differences with conventional round bale

262

silage. However, feeding trial data showed a marked increasein dry matter intake (+10%) and in body weight gain (+25%)of growing steers fed macerated round bale silage comparedto conventional round bale silage (Charmley and Savoie1996). Although maceration did not show a marked differ­ence in quality measures reported here, there seems to be astructural alteration of the plant that significantly improvesits feeding value. This is in agreement with other feedingstudies with intensively conditioned or macerated forage(Hong et al. 1988; Koegel et al. 1992; Petit et al. 1994).

Conserving macerated forage in the form of round balesilage was certainly feasible without a significant increase indry matter loss and with the potential of a lower moisturecontent. Chemical and physical characteristics of maceratedforage did not indicate any improvement compared to con­ventionally conditioned forage, except for a slightly fasterdecline of pH and greater lactic acid production. New meas­ures such as a physical structure index or a ruptured surfaceratio may be useful in assessing the degree of conditioning.Such measures would be helpful in better understanding theeffect of intensive forage' conditioning on livestock response.

CONCLUSIONS

1. Maceration applied at mowing with an experimentalprototype increased the field drying rate of an orchardgrass-white clover mixture by 39% on average. This didnot have a significant impact on moisture content ofround bale silage that was harvested after a short 24-hwilting period under relatively humid conditions.

2. Maceration did not cause significantly more mechanicalloss (3.6%) than conventional conditioning (3.1 %) aftermowing and baling.

3. The chemical composition of round bale silage after

SAVOlE. TREMBLAY. CHARMLEY and THERIAULT

fermentation was generally not much different betweenmacerated forage and conventionally conditioned for­age. The pH decline was slightly faster and lactic acidproduction was slightly h'igher for macerated forage.Maceration did not increase round bale dry matter den­sity.

ACKNOWLEDGEMENTS

The authors thank the Conseil de recherche en peche et enagro-alimentaire du Quebec (CORPAQ) and the Canada­Nova Scotia Agri-Food Development Agreement forfinancial support to carry out this project. They also acknow­ledge the technical help of the staff at the Nappan ResearchFarm of Agriculture and Agri-Food Canada.

REFERENCES

AOAC. 1984. Official Methods of Analysis. 14th ed.Washington. DC: Association of Official AnalyticalChemists.

ASAE. 1993. ASAE S358.2. Moisture measurement-forages.In ASAE Standards 1993. 451. St. Joseph. MI: ASAE.

Barker, S.B. and W.H. Summerson. 1941. The colorimetricdetermination of lactic acid in biological material.Journal ofBiological Chemistry 137:535-554.

Charmley, E. and P. Savoie. 1996. Effect of maceration atharvest on silage composition and performance of steersfed round-bale or precision-chop silage. CanadianJournal ofAnimal Science 75 (in press. abstract).

Deutz-Fahr. 1993. GrasLiner MSS 1.40Matten-System-Selbstfahrer. Kodelstasse I, 0.:8882Lauingen, Germany.

Genest, J., A. Amyot, R. Caron, J.N. Couture, S. Poussier. M.Quevillon, D.O. Rony, P. Savoie and J. Lachance. 1990.L 'ensilage de balles rondes. Publication 90-0036.Ministere de I 'agriculture, des pecheries et deI'alimentation, Quebec, QC.

Haigh, P.M. 1990. The effect of dry matter content on thepreservation of big bale round silages made during theautumn on commercial farms in South Wales 1983-87.Grass and Forage Science 45(1):29-34.

Harrison, H.P. 1985. Preservation of large round bales at highmoisture. Transactions of the ASAE 28(3):675-679.686.

Hong, B.1., G.A. Broderick, R.G. Koegel, K.1. Shinners andR.J. Straub. 1988. Effect of shredding alfalfa oncellulolytic activity, digestibility, rate of passage andmilk production. Journal of Dairy Science71 (6): 1546-1555.

Koegel, R.G., K.J. Shinners. F.J. Fronczak and R.J. Straub.1988. Prototype for production of fast drying forage mats.Applied Engineering in Agriculture 4(2): 126-129.

Koegel, R.G., R.1. Straub, K.1. Shinners, G.A. Broderick andD.R. Mertens. 1992. An overview of physical treatmentsof lucerne performed at Madison, Wisconsin. forimproving properties. Journal of AgriculturalEngineering Research 52: 183-191.

Krone. 1993. Das Intensive-Conditioner-System ICS I.Postfach 1163, D-48478 Spelle, Germany.

Krutz. G.W., D.A. Holt and D. Miller. 1979. For fast fielddrying of forage crops. Agricultural Engineering8:16-17.

Muck, R.E., R.G. Koegel, K.1. Shinners and RJ. Straub.1989. Ensilability of mat-processed alfalfa. InProceedings of the CIGR Conference. Dublin, eds. V.A.Dodd and P.M. Grace, 2055-2061. Rotterdam, TheNetherlands: A.A. Balkema.

Nicholson, J.W.G., E. Charmley and R.S. Bush. 1992. Effectof moisture level on ensiling characteristics of alfalfa inbig bales or chopped and compacted in plastic tubes.Canadian Journal ofAnimal Science 72:347-357.

Petit, H.V., P. Savoie, D. Tremblay, G.T. Dos Santos and G.Butler. 1994. Intake, digestibility and ruminaldegradability of shredded hay. Journal of Dairy Science77:3043-3050.

Renoll, E., L.A. Smith, J.L. Stallings and D.L. Hess. 1978.Machine systems for handling and feeding round bales. InProceedings of the International Grain and ForageHan'esting Conference, 296-299, St. Joseph, MI: ASAE.

Rotz, C.A. and Y. Chen. 1985. Alfalfa drying model for thefield environment. Transactions of th'e ASAE28(5): 1686-1690.

SAS. 1985. SAS User's Guide: Statistics. Version 5.Statistical Analysis System Institute Inc., Cary, NC.

Savoie, P. 1988. Hay tedding losses. Canadian AgriculturalEngineering 30(1):39-42.

Savoie, P., M. Binet, G. Choiniere, D. Tremblay, A. Amyotand R. Theriault. 1993a. Development and evaluation ofa large-scale forage mat maker. Transactions ofthe ASAE36(2):285-291.

Savoie. P., R. Chabot and D. Tremblay. 1993b. Loss anddrying characteristics of forage mats after rainfall.Transactions of the ASAE 36(6): 1533-1539.

Savoie. P.• E. Pattey and G. Dupuis. 1984. Interactionsbetween grass maturity and swath width during haydrying. Transactions of the ASAE 27(6):1679-1683.

Shinners, K.1., TJ. Kraus, R.G. Koegel and RJ. Straub.1992. A crushing-impact macerator, beltless press foragemat formation machine. Paper No. 9201 16. AgriculturalEngineering 1992 Conference, Uppsala, Sweden.

Tremblay, D., P. Savoie and Q. LePhat. 1993. A comparisonof fixed and variable chamber round balers. ASAE PaperNo 93-1584. St. Joseph, MI: ASAE.

Van Soest, P.J., J.B. Robertson and B.A. Lewis. 1991.Methods for dietary fiber, neutral detergent fiber, andnon-starch polysaccharides in relation to animalnutrition. Journal ofDairy Science 74:3583-3597.

Vought L.R. and I. Glick. 1993. Round bale silage. In SilageProduction: From seed to animal. NRAES Publication67: 117-123. Cooperative Extension, Riley-Robb Hall,Ithaca. NY.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/November/December 1996 263

Modeling airflow inside and around hoodsused for pneumatic control of pest insects.

Part I: Development of a finite element modelM. KHELIFI I, J.-L. ROBERT2 and C. LAGUE1

lSoil Science and Agri-Food Engineering Department and 2Civil Engineering Department, Universite Laval, Quebec, QC,Canada G1K 7P4. Contribution No. CRH-/58 from the Centre de recherche en horticulture. Received 3 November /995;accepted 3 October 1996.

Khelifi, M., Robert, J.-L. and Lague, C. 1996. Modeling airflowinside and around hoods used for pneumatic control of pestinsects. Part I: Development ofa finite element model. Can. Agric.Eng. 38:265-271. A two-dimensional finite element model to simu­late airflow inside and around hoods used for pneumatic control ofpest insects is presented. The model is based on the 2-D Navier­Stokes equations. The Stream Upwind Petrov-Galerkin method(SUPG) is used to improve the modeling of the highly convectivezones. The contour element concept allows a more accurate simula­tion of the effects of the boundary layer in the immediate proximityof the walls. Three different elements are used to discretize themodelled surfaces and domains: a nine-node quadrilateral, a six-nodetriangle, and a three-node linear. These elements have three degreesof freedom per summit node (ll, v, p), the two components of the airvelocity vector and the static pressure respectively, and two degreesof freedom per middle node (ll, v). The numerical scheme of resolu­tion relies on the use of the Newton-Raphson method. Preliminarytests show the potential of the model for simulating airflow underdifferent conditions. Keywords: modeling, airflow, finite element.pest insects, pneumatic control.

Un modele numerique bidimensionnel faisant appel ala methodedes elements finis a ete developpe pour simuler I'ecoulement de I'airdans et aux environs de buses utilisees ades fins de controle pneu­matique des insectes nuisibles. Le modele est base sur les equationsde Navier-Stokes en deux dimensions. La methode de decentrageamont dans Ie sens de l'ecoulement de Petrov-Galerkin (SUPG) a etcutilisee pour ameliorer la modelisation des zones hautement convec­tives. Le concept d'element de contour a egalement etc utilise poursimuler avec plus de precision les effets des couches limites aproxi­mite des parois. Trois elements differents ont servi ala discretisationdes surfaces et domaines de modelisation: un quadrilatere a9 noeuds,un triangle a6 noeuds et un element lineaire a3 noeuds, tous troiscomportant trois degres de liberte par noeud de sommet (II, \', p), lesdeux composantes du vecteur vitesse de l'air et la pression statiquerespectivement, et deux degres de liberte par noeud intermediaire (II,v). La methode de Newton-Raphson a ete utilisee pour resoudre numcri­quement Ie systeme d'equations non-Iineaires. Des tests preliminairesont demontre Ie potentiel du modele asimuler l'ecoulement de l'air sousdifferentes conditions. Mots clefs: modelisation, ecoulement de l'air,elements fmis, insectes nuisibles, controle pneumatique.

INTRODUCTION

The use of pesticides against Colorado Potato Beetles (CPBs)started in the 1860s (Weisz et al. 1994). During the 1940s,CPBs were first noted to develop resistance to availablepesticides. To date, there is no registered chemical capable ofeffectively managing this significant agricultural pest. This

has prompted researchers to seek other effective strategiesagainst CPBs, such as mechanical control. In particular, theuse of pneumatic systems to remove CPBs from potato plantsappears to be promising.

No pneumatic system previously designed and tested inpotato fields has been reported to be effective against CPBs(Boiteau et al. 1991; Duchesne and Boiteau 1992; Puttre1992). This is mostly attributed to the inadequate design ofthe operating units as no relevant scientific data are availablein the literature (Khelifi et al. 1992, 1995). Suitable andreliable predictions of the airflow inside and around theoperating units arranged in different geometries ranging fromsimple (air suction or blowing) to more complicated (simul­taneous air suction and blowing) configurations constitute animportant part of the design process of such units.

One alternative for solving this complex fluid mechanicsproblem is to use the finite element method (FEM), The FEMis a powerful numerical procedure for solving partial differ­ential equations. It is often used in situations where thegoverning equations are known, but complicated geometryand/or boundary conditions render analytical solutions diffi­cult or impossible to obtain. The FEM has been successfullyused for a long time to solve most practically encounteredengineering problems: steady-state and time-dependent; lin­ear and nonlinear; defined in any geometric domain in one,two or three dimensions. In addition, this method is welladapted to a heterogenous medium. According to Dhatt andTouzot (1981), the FEM is widely used in industry, particu­larly in aeronautical, aerospace, naval, and nuclearapplications. However, it is still in a developing stage forfluid mechanics applications (Donea and Laval 1988), Manystudies show the potential of the FEM for solving manyproblems related to different domains in agriculture (Lagueand Jenkins 1991; Chi et al. 1993). Agricultural fluid me­chanics problems could be solved as well.

The objective of this study was therefore to develop afinite element model to predict the airflow inside and aroundhoods arranged in simple geometries (air suction or blowing,and in more complicated ones (combinations of two to threehoods). This allows the simulation of many working unitsand the selection of the most appropriate one for pneumaticcontrol of pest insects without the need of extensive proto­typing and testing.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4, October/November/December 1996 265

DEVELOPMENT OF THE FINITE ELEMENTMODEL Equations 1a, 1b, and 1c can be written in matrix form as:

(la)

(I b)

Taking into consideration that either u =v =0 on the boundary

(5b)

(3)

(5a)

(2)

=temporal variation of the velocity vector,=gradient operator,= velocity vector, and= external forces vector.

+H:J(a'Vl' dV + d'Vl' aV)dVp v ax ax dy ayJl I dV--:r 'Vl'- dS = 0P s an

w= J{'V( j[Ll lui +Ivl dV = 0v

J (dV dV 1 dp )

'Ill' u-a +v-a +--a+Iy dVv x y p y

where:{u}[L l{u}Ifl'}

lui +[Ll lui +ltvl = 0

Integrating Eqs. 4a and 4b by parts using Green's Theoremgives:

J (au au 1 ap )

v'Vu u dX +V ay +p dX +f'( dV

+H:J (a'Vu au + d'Vu aU)dVp v ax dX ay ayJl I au

- - 'J 'Vu - dS = 0P s an

When the flow is steady, as in this problem, {it} becomesnegligible.

Integral formulation

To numerically solve Eq. 2, it must be transformed into anintegral form using the weighted residual method:

where {'V} =a weighting function vector.

Weak integral formulationTo reduce the differentiation order of the test functions andto clarify the flux boundary conditions, the strong integralformulation (Eq. 3) is transformed into a weak form by theintegrating by parts of Eq. 3. Selecting the weighting func­tion from the same test function set, we get the Galerkinintegral form:

J'Vu [J!!- +~+.!. dp - H: (a2u + d

2U)+ IX] dV = 0

v ax dy p ax p d.\2 ay2

(4a)

J. [av dV 1 ap Jl (d2V a2v) ]

v 'Ill' ua; +vay +Pay -P ax2 +al +I y ~ = 0

(4b)

(lc)

u,v =mean components of the velocity vector in x and ydirections, respectively (m/s),

p =static pressure (Pa),t = time (s),Ixly =forces applied per mass unit (N/kg),Jl = air dynamic viscosity (kgem-1es-1), andp = air density (kg/m3).

Similarly, the application of the principle of mass conser­vation for an incompressible fluid leads to the continuityequation:

- the flowing medium is continuous,

- the fluid is homogeneous and incompressible (subsonicflow), .

- the fluid is viscous and Newtonian (Ryhming 1985),

- the variations of all fluid properties under the effect oftemperature are negligible according to Tritton (1988),i.e., the temperature changes are negligible and have noeffect on the flow itself (isothermal flow), and

- the flow analysis is carried out in two dimensions (x, y).

Fluid propertiesThe problem studied involves the flow of air at temperaturesand pressures that approximate normal ambient values, 20°Cand 101.3 kPa respectively. In this case, the two necessaryfluid properties, namely the kinematic viscosity, v, and thedensity, p, have the magnitudes (Giles 1984): v = 1.4888 x10-5 m2/s and p =1.2047 kg/m3.

Variables or degrees of freedomThe dependent variables for this particular problem are thestatic pressure, p, and the two components (u, v) of the airvelocity vector along the two directions of an orthonormalCartesian reference plane (x, y).

Mathematical model

Taking into consideration the assumptions established above,the development of the momentum equation results in a setof partial differential equations known as the 2-D Navier­Stokes reference equations:

au au au 1 ap Jl (a2u d2U)a;-+~+vay+p ax -p ax2 +ay2 +lx=O

dV av dV 1 ap Jl (a2v a2v)at +ua;+vay +PdY - P ax2 +dy2 +Ix = 0

where:

Assumptions

The equations of continuity (conservation of mass) and ofmomentum (Newton's second law) govern this particularfluid mechanics problem. For simplification purposes, thefollowing assumptions are made:

266 KHELIFI, ROBERTand LAGUE

(6)

(9)

(8)

(10)

where O<y<h

=-0.4 where n is the normal outside thedomain on rigid walls,

= 0 on open limits, and= 0 at the walls.

aLlanL

where:aLlan

This is in fact the behavior equation of a membrane underflexure. It was solved using a triangular element on the samemesh used to calculate the flow. This allows a two-dimen­sional distribution of the eddy viscosity that takes intoconsideration the geometry of the domain by the wall effects(mixing length) and the characteristic of the flow by thevelocity gradient modulus.

Numerical viscosity To improve the modeling of the highlyconvective zones, the Streamline Upwind Petrov-Galerkinmethod (SUPG) was used (Donea 1991). This method con­sists of adding a numerical viscosity defined by the tensor:

a4 L-=0ay4

with the following boundary conditions at the walls:aLlay = 0.4 at y = 0,aLlay =-0.4 at y =h, andL =0 at y =0 and y =h.

The exact solution of Eq. 9 is the profile (8).

Generalizing Eq. 9 to two dimensions results in:

L:KY(I-f,)where h = the distance between the walls.

In this case, geometries are complex and the principle ofdistribution could not be applied integrally. Therefore, aninterpolation technique was defined in order to satisfy thewall conditions on a two-dimensional domain in a manner toget the previous profile when the geometry is simplified toparallel walls. This technique can be represented by:

or that null flux boundary conditions are used, the contourintegral terms vanish.

Viscosities of the fluid

Fundamentally, the viscosity of a fluid is a measure of itsresistance to mechanical deformations. However, if themodel calculates only the mean components of the velocityvector without explicitly calculating its turbulent fluctuation,an additional virtual viscosity due to the fluctuations must beintroduced. This concept, introduced for the first time byReynolds, is called the eddy viscosity.

In addition, the numerical schemes that result from thediscretization of the Galerkin integral form by the finiteelement method are centered, Le. the discrete equation writ­ten on one node gives to the neighboring nodes the sameimportance whatever their position. When the problem con­tains some high convection zones, such as spatialaccelerations due to contractions, this discretization does notyield good results (Brooks and Hugues 1982). This is not thecase when using an uncentered upwind scheme. It can bedemonstrated that such schemes can be obtained from theGalerkin formulation by modifying the weighting function.This results in adding a viscosity term called numerical vis­cosity (Donea and Laval 1988).

Fluid viscosity This term gains more importance when thefluid is highly viscous, Le. it is close to the eddy viscosity.Nevertheless, if the eddy viscosity model allows for an ad­justment according to the flow intensity, this term should bewell defined in order to correctly represent the laminar re­gions.

Eddy viscosity In general, the simplest way to consider thisparameter is as a constant. The major drawback of this as­sumption is that the viscosity is considered a property of thefluid rather than the flow. The direct consequence of this canbe observed on the velocity profiles that consequently remainlaminar.

To remedy this drawback, Prandtl introduced the mixinglength concept (Schlichting 1979) which appears in the defi­nition of eddy viscosity as:

2 duv =L I-I

t dy

where:v t =eddy viscosity, andL = mixing length.

The main constraint to compute Vt consists of determiningempirically the distribution of "L" knowing that it is negli­gible at the walls and increases proportionally with thenormal distance (y) to them:

L=Ky (7)

where:v

Ui,Uj

(11 )

= a purely numeric artificial viscosity that isproportional to the characteristic dimension ofthe element "h\" and the intensity of the velocitypassing through it, and

=the components of the flow velocity "U" in the xand y directions, respectively.

=diameter of the circle inscribed in the triangle,and

= a free parameter. B= I corresponds to a full

where K = 0.4, the von Karman constant.

Some one-dimensional flow studies on the mixing lengthdistribution (Robert and Ouellet 1987) led to the determina­tion of accurate turbulent profiles. For example, the value ofL between two walls can be represented by:

-v

where:hI

B

with 0::;; J3::;;1 (12)

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4, Octobcr/November/December 1996 267

simulation of the effects of the boundary layer at the wallwithout the need of modeling the details (Khelifi et al. 1996).

Contour element and shear forces

During the partial integration of the integral form of themomentum equations (Eqs. 4a and 4b), some contour termsinvolving a velocity gradient normal to the wall appear.Practically, a one-dimensional element, L3-2, can be easilydefined to numerically proceed with this integration alongthe relevant contours (or walls) (Fig. I). These terms can bewritten using Newton's law of viscosity as:

(15)

(14)

(13)J: [u au*] ! ['txn]] 'VII· -- ds=:r 'V,,. - dsspan ... P

! [u av*] ! ['t\'n]:r 'V,," - -a ds =:r 'V,," ~ dss p n s P

where:txn = shear stress component in the x-direction

(N/m2),

tyn =shear stress component in the y-direction(N/m2), and

u* and v* =velocity components at the wall in the x andy directions, respectively (m/s).

The shear stress components are proportional to the squareof the velocity:

t xn =7 p ,,* ~ u*2 + v*2

o u. v. p

• u. v

T6-3

upwinding of the Petrov-Galerkin method where­as B=0 leads to the standard formulation ofGalerkin.

The major drawback of the SUPG method is the use of thefree parameter B to adjust the magnitude of the added viscos­ity (Donea 1992). Indeed, there is no standard method for theselection of this parameter.

Elements used to discretize the modeled surfaces anddomains

Three different elements were principally used to mesh themodeling surfaces and domains: a nine-node quadrilateral(Q9-4), a six-node triangle (T6-3), and a three-node linear(L3-2). These three elements, along with the degrees of free­dom associated to each node, are presented in Fig. 1. u and vwere quadratically interpolated on the elements, whereas pwas interpolated linearly because it was proven by Dhatt andHubert (1986) that the quadratical interpolation of p leads tonumerical stability problems.

Boundary flow conditionsAt this point, the numerical modeling of airflow was basedon the hypothesis of perfect adhesion of the fluid to the walls(i.e. u = v = 0 on all fixed solid surfaces). This conditionallows more realistic velocity distributions than those ob­tained with a perfect slip condition (Le. u free and v = 0).However, to improve the modeling of airflow in the neighbor­hood of the walls, a more detailed study was conducted for twospecific hood configurations that seemed more appropriate forremoving CPB from potato plants, namely the simple horizontalair blowing and the shielded simultaneous oblique ascending airsuction and blowing (Khelifi et al. 1994, 1995). An intermediatecondition was considered for this purpose: v was kept null onthe walls and an adhesion law expressed as a tangent con­straint was used for u. This condition allowed a more accurate

The adjustment of the veloci!}' profile has then to be made inrelation to this local value, r, and the selection of the eddyviscosity model.

which represents the ratio between shear and inertial forces.In this case, the global concept of the adhesion factor couldnot be directly applied because the model calculates a profileof speed over the wall. If this profile is defined from a localspeed v* in the immediate neighborhood of the wall, a Darcy­Weisbach type local factor known as the Fanning frictionfactor (Janna 1993) can be defined as:

(18)

(17)

(16)

f=_t_s _

1 y*2IP

tf=­

I V2IP

t yn =7 p v* ~ u*2 + v*2

wherer =a local adhesion coefficient.

Determination of the adhesion coefficientIf the shear force is evaluated from a mean estimation of theflow velocity over a fixed wall, the adhesion coefficient cangenerally be defined as:

oo •

REFINEMENT OF THE MODEL

Q9-4 13-2

Fig. 1. Schematic representation of the triangular(T6·3), quadrilateral (Q9-4), and linear (L3-2)elements used to mesh the modeling domains,surfaces, and contours.

268 KHELIFI. ROBERTand LAGUE

Numerical method of resolutionAfter discretizing the partial differential equations, it is nec­essary to use an adequate numerical method to solve thesystem of algebraic equations obtained as:

MODEL TESTING

To test the performance of the model, airflow inside a round0.4 in long x 0.15 m radius duct was simulated. Because theproblem is axisymmetric, the study was carried out on onlyhalf of the domain and null airflow flux conditions wereimposed at the axis of symmetry (Fig. 2). Static pressures of380 and 200 Pa were imposed at the inlet and outlet of theduct, respectively. The quadrilateral (Q9-4) element wasused to mesh the modeling domain (Fig. 2). Four situationswere tested: (I) perfect adhesion of the fluid at the wall (Le.u = v = 0) with constant viscosity, (2) perfect adhesionassociated with the mixing length concept, (3) use of thecontour element concept with constant viscosity, and (4) useof both the contour element and the mixing length concepts.The resolution of the system of equations was achieved by

30

30

25

(b)

(a)

20 25

15 20

u (ntis)

15

u (m/s)

10

10

5

5

-e- f* ;e 0; L = 0 (CASE 3)___ f* ;eO; L;eO(CASE4)

-e- f* =0; L=O(CASE 1)___ f* = 0; L;e 0 (CASE 2)

O~!.....-_..I.-__..L-__..L-__...I...-__...I...-_-----l

o

1 ;0­

j

0.6

0.4

0.8 ~

0.2

0.8

0.6

~....0.4

0.2

00

the MEFL3D code (Robert 1994) and the pre- and post-treat­ment by the interactive code MOSAIC, developed at theUniversity of Compiegne, Compiegne, France.

RESULTS AND DISCUSSION

The output of the model for the four cases studied is pre­sented in Fig. 3. The use of a perfect adhesion condition ofthe fluid at the wall level (j* =0) with a constant viscosity(L =0) yields a parabolic velocity profile with null airspeedsat the wall. This profile becomes slightly logarithmic with theintroduction of the mixing length concept (L :I; 0) because theflow is less restricted in the vicinity of the duct wall (Fig. 3a).The presence of airspeeds different from zero on the wallfollowing the introduction of the contour element concept<I' :I; 0) gives to the velocity profile a logarithmic appearance(Fig. 3b) which is more realistic than that obtained with aperfect adhesion condition on the wall. Results show that the

(19)

i : ! I

I I P =200 Pa

I I i II"I I I I _\----j

-l I I I I~ -j, I I I I

[K (U)] ju I=jF I

p= 380Pa

where:[K(U)] = global stiffness matrix characterizing the

system,{U} =global vector of all nodal variables of the

problem, and{F} = global vector of body forces.

The presence of nonlinear terms in the Navier-Stokesequations (Eqs. I a and Ib) and in the friction factor (Eq. 18)as convective (velocity times the gradient of velocity) andvelocity squared terms, respectively implies that the matrix[K] is a function of vector solutions {U}; which means thatthe problem is nonlinear. For this kind of fluid mechanicsproblem, one of the most efficient techniques for the conver­gence of the matrix system to the intended solution consistsof using the Newton-Raphson method (Dhatt and Touzot(981).

Fig. 2. Duct modeling domain and the related finiteelement mesh: 861 nodes, 200 elements (more20 L3-2 elements on the wall when using thecontour element concept).

Fig. 3. Simulation results: (a) perfect adhesion conditionof the fluid on the wall with a constant viscosityand with the introduction of the mixing lengthconcept (L::t: 0); (b) use of the contour elementconcept <f:l; 0) with a constant viscosity and withthe introduction of the mixing length concept.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OClobcr/November/Decembcr 1996 269

combination of the contour element and mixing length con­cepts <f ::F- 0; L::F- 0) leads to a better simulation of a turbulentflow (Yalin 1977). This is translated by the logarithmic ve­locity profile of Fig. 3b.

The model handled adequately the four cases studied andshowed its potential in dealing with different techniques.However. even though these tests are satisfactory, the per­formance of the model was evaluated in a more complicatedsituation, the simulation of airflow inside and around hoodsof different geometries used to remove Colorado potato bee­tles from potato plants (Khelifi et al. 1996).

SUMMARY AND CONCLUSIONS

1. A two-dimensional finite element model was developedto simulate airflow inside and around hoods arranged indifferent geometries. Based on the 2-D Navier-Stokesequations, the model uses the Stream Upwind Petrov­Galerkin method (SUPG) to improve the modeling ofthe highly convective zones.

2. A contour element concept was used to simulate moreaccurately the effects of the boundary layer in theneighborhood of the walls.

3. Preliminary results show the potential of the.model forsimulating airflow under different conditions. The pre­diction of airflow patterns is highly valuable indesigning and selecting the most adequate configura­tions allowing for a better removal of CPBs from potatoplants.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the financial support ofthe Natural Science and Engineering Research Council ofCanada, Premier Tech Ltd.• Provigo Inc., and the Conseil derecherche en peche et en agro-alimentaire du Quebec. Spe;.cial thanks are extended to Philippe Savoie. research scientistat Agriculture and Agri-Food Canada, Sainte-Foy ResearchStation, and adjunct professor at Departement des sols et degenie agro-alimentaire, Universite Laval. for revising themanuscript.

REFERENCES

Boiteau, G.L., G.C. Misener, R.P. Singh and G. Bernard.1991. Evaluation of a vacuum collector for insect pestcontrol in potato. American Potato Journal 69: 157-166.

Brooks, A.N. and T.J.R. Hugues. 1982. Streamlineupwind/petrov-galerkin formulations for convectiondominated flows with particular emphasis on theincompressible Navier-Stokes equations. ComputerMethods in Applied Mechanics and Engineering32: 199-259.

Chi, L., S. Tessier and C. Lague. 1993. Finite elementmodeling of soil compaction by liquid manure spreaders.Transactions of the ASAE 36(3):637-644.

Dhatt, G. and G. Hubert. 1986. A study of penalty elementsfor incompressible laminar flows. International Journalfor Numerical Methods in Fluids 6: 1-19.

Dhatt, G. and G. Touzot. 1981. Une presentation de la

270

methode des elements finis. Paris, France: Maloine andQuebec, QC: Les Presses de I'Universite Laval.

Donea, J. 1991. Generalized Galerkin methods forconvection dominated transport phenomena. AppliedMechani.cs Review 44(5):205-214.

Donea, J. 1992. Application de la methode des elements finisaux problemes de convection-diffusion. Notes written onthe occasion of the summer school of Cargese, CommonResearch Center, European Communities Commission,21020 Ispra, Italy.

Donea, J. and H. Laval. 1988. Application de la methode deselements finis en dynamique des fluides. In Aspectstheoriques et numeriques de la dynamiqlle des structures,eds. J. Donea. H. Laval. Y. Bamberger, R.P. Shaw and J.Planchard, 1-55. Paris, France: Eyrolles.

Duchesne, R.-M. and G. Boiteau. 1992. Outlook onmechanical, physical, and cultural control strategiesagainst the Colorado potato beetle. In Proceedings ofthe38th Annual Meeting of the Canadian Pest ManagementSociety/J99J, 33-54. Fredericton, NB.

Giles, R.V. 1984. Mecanique des fluides et hydraulique,serie Schallmm. New York, NY: McGraw-Hill.

Janna, W.S. 1993. Introduction to Fluid Mechanics, 3rd ed.Boston. MA: PWS-Kent Publishing Company.

Khelifi, M., C. Lague and B. Lacasse. 1992. Test bench forthe pneumatical control of pest insects. ASAE Paper No.92-1599. St. Joseph. MI: ASAE.

Khelifi, M., C. Lague and B. Lacasse. 1995. Resistance ofadult Colorado potato beetles to removal under differentairflow velocities and configurations. CanadianAgricultural Enginnering 37(2):85-89.

Khelifi, M.• C. Lague and J-L. Robert. 1996. Modelingairflow inside and around hoods used for pneumaticcontrol of pest insects. Part II: Application and validationof the model. Canadian Agricultural Engineering38:273-281.

Khelifi, M.• C. Lague, J.-L. Robert and C. St-Pierre. 1994.Numerical modelling of airflow inside and around hoodsarranged in different geometries. CSAE-paper No.94-409. Saskatoon, SK: CSAE.

Lague, C. and B.M. Jenkins. 1991. Modeling pre-harveststress-craking of rice kernels: Part I: Development of afinite element model. Transactions of the ASAE34(3):1797-1811.

Puttre, M. 1992. Bug-busting alternative to pesticides.Mechanical Engineering 114(12): 108.

Robert, J .-L. 1994. MEFL3D manuel de reference.Departement de genie civil, Faculte des sciences et degenie, Universite Laval, Quebec, QC.

Robert, J.-L. and Y. Ouellet. 1987. A three-dimensionalfinite element model for the study of steady andnon-steady natural flows. In Three Dimensional ModelsofMarin and Estuarine Dynamics, eds. J.C.J. Nihoul andB. Jamart. 359-372. Elsevier.

Ryhming, I.L. 1985. Dynamique des fluides. Lausanne,Suisse: Presses polytechniques romandes.

KHELIA. ROBERTand LAGUE

Schlichting~ H. 1979. Boundary Layer Theory. New York,NY: McGraw-Hill.

Tritton, D.1. 1988. Physical Fluid Dynamics~ 2nd ed. NewYork, NY: Oxford University Press.

Weisz~ R., M. Saunders, Z. Smilowitz, H. Huang and B.Christ. 1994. Knowledge-based reasoning in integrated

resistance management: The Colorado Potato Beetle(Coleoptel:a: Chrysomelidae). Journal of EconomicEntomology 87(6): 1384-1399.

Yalin, M.S. 1977. Mechanics ofSediment Tral1sport~ 3rd ed.London, England: McGraw Hill.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38, No.4, October/November/December 1996 271

Modeling airflow inside and around hoodsused for pneumatic control of pest insects.

Part II: Application and validation of themodel

M. KHELIFI 1, C. LAGUE 1 and J.-L. ROBERT2

lSoil Science and Agri-Food Engineering Department alld 2Civil Engineering Departmellt, Universite Laval, Quebec, QC,Canada G1K 7P4. Colltribution No. CRH-/59 from the Celltre de recherche en horticulture. Received 3 November 1995;accepted 3 October 1996.

Khelifi, M., Robert, J.-L. and Lague, C. 1996. Modeling airflowinside and around hoods used for pneumatic control of pestinsects. Part II: Application and validation of the model. Can.Agric. Eng. 38:273-281. To optimize the design of pest controlmachines, the airflow inside and around blowing and suction hoodsof different configurations for the specific case of pneumatic controlof Colorado Potato Beetles (CPBs) was numerically modeled. Suchpredictions of airflow patterns can help in locating the optimal zonesfor CPB removal for a given configuration. Preliminary results showthat two particular hood configurations (horizontal blowing andsimultaneous oblique blowing and suction) that generate differentairflows across the potato plant foliage are the most promising.Airflow inside and around these two configurations was furtherinvestigated using the contour element concept. This allowed airflowmodeling at the wall level. Evaluation of the numerical model per­formance proved its validity and capability in adequately predictingairspeeds. Results are sufficiently accurate and detailed to serve asthe first stage of the design process. Keywords: modeling, airflow,finite element, design, pneumatics, pest control, potato.

Pour optimiser la conception de machines destinees acontroler lesinsectes nuisibles, I'ecoulement de l'air a l'interieur et autour desbuses de soufflement et d'aspiration placees selon differentes con­figurations a ete numeriquement modelisc (it des fins de controle dudoryphore de la pomme de terre (DPT». La prediction du patrond'ecoulement de l'air pourrait aider it localiser les zones propices al'elimination du DPT pour une configuration donnee. Les resultatspreliminaires montrent que deux configurations, soil Ie simple souf­flement horizontal, soit Ie soufflement et I'aspiration obliquessimultanes, sont prometteuses. L'ecoulement de l'air it I'interieur etautour de ces deux configurations a ete examine en detail en intro­duisantla notion d'element de contour pour modeliser I'ecoulementde l'air au niveau des parois. L'evaluation des performances dumodele numerique prouve sa validite et son aptitude it predireadequatement les vitesses de l'air. Les resultats sont suffisammentprecis et detailles pour' servir a la conception prcliminaire de cesmachines. Mots des: modelisation, ccoulement de I'air, elementsfinis, conception, pneumatiques, controles des insectes nuisibles,pomme de terre.

INTRODUCTION

For a long time, the use of chemicals in agriculture hascontributed to the increase of crop yields. However, someinsects such as the Colorado Potato Beetle (CPB) have be­come resistant to many insecticides, including those that

were very effective at one time (Forgash 1981; Boiteau et at.1987). In some areas, these applications have contaminatedthe environment and created public health problems.

For the past few years, many attempts have been made atinvestigating alternatives to insecticide application. The useof pneumatic systems to remove the CPB from potato plantshas attracted the attention of many growers. Some machineswere designed and tested in potato fields; however, none ofthese machines currently provides complete satisfaction(Boiteau et at. 1991; Duchesne and Boiteau 1992; Puttre1992). This is mostly attributed to the inadequate design ofthe operating units. Khelifi et at. (1992) also reported a lackof scientific data on pneumatic control of insect pests. In­deed, only very few studies have been done on this particularsubject (deVries 1987; Misener and Boiteau 1991, 1992).

Pneumatic control of the CPB is a complex process. Itsefficiency depends on many factors including: the variabilityin the gripping ability of the insects at different growingstages, the potato plant geometry, and the resistance of cropfoliage to airflow. The success of this technique appears todepend upon an appropriate design of the control units, Le.the hoods. The main factors that have to be taken into consid­eration are the geometry or the shape of the hoods, whichgreatly affects the airflow pattern at the plant foliage level,the dimensions of the hoods, their position relative to theplants, and obviously the airflow rate that the hoods candeliver.

The selection of the optimal hood geometry also dependson many factors such as the growing stage of the plants andthe mode of action planned, Le. total or partial coverage ofthe plants by suction, blowing, or a combination of both.

Experimentally, Dalla Valle in 1930 (Burgess et at. 1989)was the first researcher to investigate the capture velocity infront of hoods of different shapes. Dalla Valle derived for thispurpose some empirical formulas. However, according toFlynn and Ellenbecker (1986), the capture velocity is not anadequate design parameter capable of providing the neces­sary information.about the performance of hoods. Recently,many researchers like Flynn and Ellenbecker (1986, 1987),Ellenbecker et al. (1983), and Conroy et at. (1988) investi-

CANADIAN AGRICULTURAL ENGINEERING Vol. 3X. No.4. October/November/December 1996 273

gated the performance of hoods in the presence of an airflowperpendicular to the air suction direction. They used a moreappropriate index, the capture efficiency. It was simply de­fined as the proportion of particles captured among thosereleased by the process to be controlled. According to Bur­gess et at. (1989), the use of the notion of capture efficiencyas a design tool is very limited. Indeed, the research at thislevel is still at a preliminary stage and has only dealt with lowair velocity, i.e. the terminal velocity of dust particles whichis not appropriate for pneumatic control of pest insects.

The objective of this study was therefore to numericallymodel, by the finite element method, the airflow inside andaround hoods arranged in si~ple geometries (air suction orblowing) and in more complicated ones (combinations of twoto three hoods). This presents the advantage of predictingairflow patterns which allows for the detection of the mostpropitious zones for a better removal of CPB. The best com­bination, and consequently the most adequate geometryensuring an efficient control of CPB, could therefore beselected as the working unit for subsequent field testing. Thenumerical model used for these simulations was developedby Khelifi et at. (1996). The performance of this model waspreliminarily tested in a simple case, the simulation of air­flow inside a round 0.4 m long x 0.15 m radius duct.

PROBLEM DESCRIPTION

Airflow combinationsIn this study, the following combinations of airflow wereinvestigated: a simple air suction from the top, a simultane-

sas

t

ous horizontal air suction and blowing through the plantfoliage, a simultaneous oblique ascending air blowing andsuction, two horizontal air jets blowing across the plant andair suction provided at the top, and two oblique ascending airjets blowing and air suction at the top. All these airflowcombinations are illustrated in Fig. I.

Hood geometriesThe different configurations required to ensure the necessaryairflows for this study were obtained from some combina­tions of hoods already tested in the laboratory. The staticpressure measured at the inlet and the outlet of these hoodswas taken into consideration. Figure 2 presents the modelingdomain of a hood in a suction position. The boundaries of thedomain were selected sufficiently away from the vacuumingarea in order to obtain the maximum information about theairflow fields and to avoid any possible interference with theexpected results. All modeling domains for the other con­figurations were selected on the same basis. In axisymmetricsituations like that of Fig. 2, the study was carried out on onlyhalf of the domain and null airflow flux conditions wereimposed at the axis of symmetry.

Fluid propertiesThis study involves the flow of air at ambient temperature(20°C) and atmospheric pressure (101.3 kPa). In this case, thetwo necessary fluid properties, namely the kinematic viscos­ity, v, and the density, p, have the magnitudes (Giles 1984):v = 1.4888 x 10-5 m2/s and p = 1.2047 kg/m3.

Simple air suction Simple horizontal air blowing

lobs

t

Simultaneous air suction and blowing

las

t

,/'asb

,/'las

Two oblique air suction Two opposite air blowing andand blowing an air suction from the lop

Fig. 1. Different combinations of airflow studied by the finite element method.

274

Two oblique ascending air blowingand an air sucUon from lhe lop

KHELIFI. LAGUE and ROBERT

2.3 m ------------

Fig. 2. Schematic representation of a suction hood modeling domain.

MODEL VALIDATION

To validate the numerical model, twoof the tested configurations (horizon­tal blowing, and simultaneous obliqueblowing and suction) were carefullyreproduced in the laboratory using thesame hoods simulated by the finite

achieved by the MEFL3D code(Robert 1994) and the pre-and post­treatment by the MOSAIC software(Compiegne Science Industrie, Com­piegne, France). Three differentelements were principally used tomesh the modeling surfaces and do­mains: a nine-node quadrilateral(Q9-4), a six-node triangle (T6-3),and a three-node linear (L3-2).

InRuence domain

r- - - - - _- -- -- ----- - -- -- - - +-----------------1_- --M suclion

O.04m fll0.15 m

II

I0.055 m

Variables or degrees of freedom

The dependent variables for this particular problem are thepressure, p, and the two components (u, v) of the air velocityvector along the two directions of an orthononnal Cartesianreference plane (x, y).

Boundary conditions

All boundary conditions were imposed on 1.1, v, and p over theboundaries such as those presented in Fig. 3 for the simulta­neous air suction and blowing configuration. The boundaryconditions of the other configurations were imposed on thesame basis. When only p was imposed without specifyingany value for 1.1 or v, the nonnal velocity gradient was set tozero.

Airspeed measuringaxis

Marking

SucUon

Fig. 4. Marking of different points to measure airspeedsalong the longitudinal central axis of the hoods.

element method. The semicircular shield of the combinedconfiguration was made from 0.4 x 0.8 m sheet metal. All thetests were carried out on the test bench described by Khelifi

et al. (1992). Airspeed was measuredat the inlet (suction) and outlet (blow­ing) of the hoods using a 2% precisiontelescopic anemometer (Multi-pur­pose Solomat Instrument, SolomatInstrumentation Division, Norwalk,CT) and a Prandtl tube along with apressure anemometer. However, be-fore taking the speed measurements, amarking of the measuring points cor­responding to the simulation nodeswas perfonned as described in Fig. 4.This allowed a sweep of the cross sec­tion of the hoods (inlet/outlet) witheither the anemometer or the Prandtltube to record the necessary measure­ments at specific points located on thelongitudinal central axis.

For each configuration, measuredand predicted airspeeds were plotted

C3 -.

CI

C2

Blcnring

CI: u .. 0, Y .. 0, p free.C2: u free. ., free. p .. O.C3: u free. v free. p II -380 Pe.C4: u free, ., free. p .. 380 PII.

Fig. 3. Example of the domains and frontiers for the simultaneous air suctionand blowing configuration.

Modeling of the hoods

The numerical part of this study was completed at the Nu­merical Analysis and Computing Research Center of theDepartment of Civil Engineering of Universite Laval. Themodel developed by Khelifi et al. (1996) was used for thispurpose. The resolution of the system of equations was

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/Novcmber/Decembcr 1996 275

(I)

Fig. 5. Example ora finite clemen I mesh for lhe simple airsuction configuration: 3029 nodes, 995 clemenls.

on the same graph in order to obtain an idea about thevelocity profiles. Thereafter. they werc plaited against eachother in order to determine the degree of agrecment betweenthem to check qualitatively how well the model prcdicted themeasured values. Also. lO have a beller idea about the nu­merical approach. the error made over measured values wasestimated. Finally, the modcl pcrformance was fUrlhcrcvalu­ated using one of the criteria suggested by Fox (1981) andWillmot (1982). the mean absolute error (MAE):

N

MAE=N- t I IP;-O;I

i = I

where:N :;;; number of cases.Pi :;;; predicted value. andOi :;;; observed or measured valuc.

The MAE gives a general idca aboul the mean differencebetween measured and predictcd valucs. hcnce, of the accu­racy of the model.

Fig. 6. Example of a deformation for the simple airsuclion configura lion.

276

IOemt------<

Fig. 7. Simulation results for the simple air suctionconfiguration (air 'Ieloeities are in m/s).

9C1l1

t------<

Fig. 8. Simulation rcsulls for Ihe simple air blowingconfiguralion (air velocilies are in m/s).

RES L1'S AND DISC SSIO!

To get the most accurale approximation of (he solution,especially inside and around the hoods. fine elements wereused to mcsh thesc areas. The elcments were gradu<.l1ly in­creased in size toward the boundaries of the modclleddomains. An examplc of one such finite element mesh for asuction hood is illustrated in Fig. 5. This figure shows onlyhalf of the domain of modelisation. thus half of the hoodbecause it is an axisymmetric casco

As men(ioned by Khelifi el al. (1996). the mixing lenglh"L" concept was used 10 ensure turbulent velocity profiles.For (his purpose, "L" was calculated at each node for everyconfiguration before solving the model. An example of theresults. visualized as a vertical displacement. is presented onFig.6 for the same configuration as Fig. 5.

Figure 7 shows the approximatcd velocity field for thesimple suction configuration. The presence or the Ilangesconfirms the results reported by McDermott (1977). Indeed,it secms that they can effectively enlarge the now pallern.However. we note that the velocity magnitude decreasesdrastically from inside the hood toward the ground. Thisshows Ih<lt the air suction efficiency is limited to a zonc closeto the hood inlet. This configuration. alone. could not there­fore be used (0 rcmovc efficiently CPB because of theircapability to grasp to potato foliage.

111 Fig. 8 (the simple air blowing configuration), the air-

KHELIFI. LAGUE alld ROBERT

9cm~

Fig. 9. Simulation results for the simultaneous air suctionand blowing configuration (air velocities arein m/s).

15cmI--i

Fig. 10. Simulation results for the shielded simultaneousoblique air suction and blowing configuration(air velocities are in m/s).

13 emI--i

Fig. 11. Simulation results for the shielded simultaneousoblique air suction and blowing with deflectorconfiguration (air velocities are in m/s).

flow maintains a considerable velocity even very far from thehood outlet. It is also wide enough to cover a large part of theplant. The air blowing efficiency appears to be far better thanthat of suction because the air can penetrate more in distancefor improved dislodging and removing of CPB.

Fig. 12. Simulation results for the two opposite airblowing across the plant foliage and an airsuction from the top configuration (airvelocities are in m/s).

Figure 9 presents the results of a combination of the twoprevious configurations, i.e. a simultaneous air suction andblowing across the plant foliage. One of the advantages ofthis configuration is to keep the plant close to the suctionhood under the effect of blown air. In this case, the efficiencyof the suction can be kept at a high level. We can, however,note that there is some airflow escaping away between thetwo hoods. It would then be practical to provide a shield toprevent this air from escaping.

The configuration presented in Fig. 10 includes a semicir­cular shield having a DAD m radius centered at theintersection point of the y and horizontal hood axes. In addi­tion, hoods were tilted upward 200 from their horizontal axis.This directs the airflow more toward the upper part of theplant where the CPB tend to feed first. Results show that theprevious airflow loss is remarkably reduced. However, theperfect semicircular shape of the shield has to be slightlymodified to keep airflow in contact with it and consequentlyprevent any eventual possible recirculation of air.

The configuration of Fig. 1I is similar to that of Fig. 10except for the addition of a deflector inside the blowing hood.

Fig. 13. Simulation results for the two oblique ascendingair blowing and an air suction from the topconfiguration (air velocities are in m/s).

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. Octobcr/Novcmbcr/Dccember 1996 277

This was expected to enlarge the airflow pattern in the vicin­ity of the hoods resulting in more air covering the plants.However, results show that this deflector badly affected theairflow as an important zone of air recirculation is generatedat the upper left side of the shield (not shown on the figure).This is mainly due to the boundary conditions of the deflec­tor. Furthermore, the air velocity distribution is not improvedby the introduction of the deflector although the airflow lossfrom the bottom can be totally eliminated.

The main idea behind the use of the configuration pre­sented in Fig. 12 was to dislodge the CPB by two opposite airstreams blowing across the plant foliage and to suck them outfrom the top. Unfortunately, the analysis of the simulationresults show the presence of a stagnation point slightly underthe blowing hood axis. This appears to be a result of theconvergence of the two air streams blowing in oppositedirections. The immediate consequence of this is the loss ofa considerable amount of air velocity at the ground level.

To remedy this problem, the two blowing hoods wererotated 200 from their horizontal axis (Fig. 13). In this case,the air loss due to the interference of the two air streams is

greatly reduced. Again, the simulation results show that astagnation point is still present. In addition, a large amount ofair is escaping through the space between the suction andblowing hoods as well as from underneath. This may consid­erably reduce the efficiency of this configuration.

One way to solve this problem consisted of sealing the spacebetween the suction and blowing hoods (Fig. 14). As a result,the airflow loss at the upper part could be totally eliminated.However, a stagnation point was again present. In this case,either the blowing hoods have to be rotated more than 200 or theair suction power has to be increased which is costly.

Results of the numerical modeling using the contour ele­ment concept are presented in Figs. 15 and 16. In contrast tothe previous results for the simple horizontal air blowing andshielded simultaneous oblique air suction and blowing con­figurations, airspeeds appear different from zero at the walllevel (especially for the suction hood).

Figure 17 shows that predicted airspeeds for the simplehorizontal air blowing configuration are very close to thosemeasured in the laboratory. However, the difference betweenpredicted and measured airspeeds seems more pronounced inFigs. 18 and 19. This is mainly due to the slight inclinationof the hood flanges which did not allow for an accuratepositioning of the anemometer at the measuring points level.

15cmI---i

Fig. 14. Simulation results for the two oblique ascendingair blowing and an air suction from the topconfiguration with sealed spaces betweensuction and blowing hoods (air velocities are inm/s).

Fig. 16. Simulation results for the shielded simultaneousoblique air suction and blowing with deflectorconfiguration using the contour element concept.

4035

-- PredIcted airspeedo Measured airspeed

30252015

HOod axis

101 4r==:::....-r----r-___,r---,...--..,--...,..-~-___,

o

28

31

co 25'::~8. 22

~ 19'Ci 18

a 13

."~ 10C.l:

=<

12cmI---l

Fig. 15. Simulation results for the simple air blowingconfiguration using the contour elementconcept.

Airspeed (m/s)

Fig. 17. Predicted and measured simple air blowingspeed profiles at the outlet of the hood.

278 KHELIA. LAGUE and ROBERT

40

Airspeed (m1s)

Fig. 19. Predicted and measured combined air blowingspeed profiles at the outlet of the hood.

30252015105o

21

19C Predicted airspeed~ 17 0

'w;0 MeastJn!d airspeed

Cl 15 0CI.

co 13'i::lIII=~e

"CS~~ 7CI.III...:(

However, the model overestimates the measured combinedair suction and blowing speeds (Figs. 21 and 22). This ismostly due to the complexity of this configuration (simulta­neous shielded oblique air suction and blowing) which madeinaccessible, as stated earlier, the use of the Prandtl tube tomeasure airspeeds. In addition, measuring points are locatedin a very sensitive area, the diffusion zone (Fig. 4). Any shiftaway from the measuring axis generally influences the re­sults; which is the case for this particular configuration.Measured airspeeds were consistently lower than the realvalues that should be obtained at the exact measuring points.

Relative errors made over measured values were estimatedat 2.5%. This reflects the capabilities of the numerical ap­proach in predicting measured values. MAE calculated fromEq. I are 1.59 mls for the simple air blowing, 1.37 mls for thecombined air suction, and 3.00 mls for the combined airblowing. These results show that the model predicts com­bined air suction speeds more accurately than simple andcombined air blowing speeds.

Airspeeds were then measured on a backward shifted axis(to~ards the .outlet of the hood) in contrast to that initiallydesIgnated. AIrspeeds presented in Fig. 18 were measured witha Prandtl tube because of the simplicity of the configuration.

Figures 17 to 19 show that airspeed profiles are far fromthe classical turbulent profiles although the Reynolds numberis greater than 2.1 x 103, the transition threshold betweenlaminar and turbulent regimes. This could be explained bythe fact that the ducts are very smooth and not subjected tomany vibrations (Bird et a1. 1963).

In Figure 18, a slight discrepancy between measured andpredicted airspeeds at the central node levels appears. Theminimum airspeed measured at those nodes was 12 mlsagainst a simulated airspeed of about 14 m/s. To investigatethis disagreement, the model was subjected to many tests. Auniform airflow in a duct was used for this purpose. Themodel responded satisfactorily because the adjustment. ofairspeed profiles was easily made by only varying the frictioncoefficient. In our case, the airflow is both highly non-uni­form due to the inclination of the hood walls (24°) and morecomplicated by the presence of a simultaneous blowing andsuction process. These two phenomena could explain thedifference between predicted and measured airspeeds at thecentral node levels for the suction hood. This discrepancywas not observed in the simple and combined air blowingcases.

On the other hand, the model adequately predicts air­speeds at the extreme nodes situated on the walls at the outletand inlet of blowing and suction hoods, respectively. For theblowing hoods, airspeeds are high enough in the expansionzone that the airflow could not remain in contact with theinternal walls of the diffuser. It lifts before leaving the hoodswhich gives null airspeeds at the extreme nodes (Figs. 16 and19). Predicted and measured airspeeds near the wall at theinlet of the suction hood are higher (about 5 m/s). This ismainly attributable to the effect of the airflow jet comingfrom the blowing hood. Practically, an airspeed as high as 5mls in these locations greatly contributes to the suction ofmore CPBs.

Figure 20 shows that the model predicts adequately meas­ured speeds for the simple air blowing configuration.

4030

Unity line

20

••

•

10O~-----r------r------r--------..

o

~ 30-

16

Predicted airspeedMeaIDred airspeedo

12

oo

oo

Hood axis 0••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -0- •••••••

oo

oo

1+-----,--......::c~_.~---...,....---__.

o

21

19c:~ 17iii8. 15

~ 13'C; 11

~E 9

1 7~

c.rl 5

:(

Airspeed (m/s) Measured airspeed (m1s)

Fig. 18. Predicted and measured combined air suctionspeed profiles at the inlet of the hood.

Fig. 20. Predicted vs. measured simple air blowingspeeds.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/November/December 1996 279

Measured airspeed (m/s)

Fig. 21. Predicted vs. measured combined air suctionspeeds.

formance are satisfactory and prove the validity and thecapability of the model to adequately predict measuredairspeeds.

6. A future improvement to the model would require t~e

introduction of a potato plant in the airflow dom~m.This could be accomplished by empirically introducmga friction zone equivalent to a plant.

REFERENCES

ACKNOWLEDGMENTS

The authors gratefully acknowledge the financial suppo~t ofthe Natural Science and Engineering Research CouncIl ofCanada, Premier Tech Ltd., Provigo Inc., and the Conseil derecherche en peche et en agro-alimentaire du Quebec: SP.e­cial thanks are extended to Philippe Savoie, research SCIentistat Agriculture and Agri-Food Canada, Sainte-Foy ResearchStation, and adjunct professor at Departement des sols et degenie agroalimentaire, Universite Laval, for revising themanuscript.

1412

• -1'••••

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10

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•

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•

16

14-~!

12'C~~

Q.

~ 10.;'C~ 8Col

:a~..=- 6

44

CONCLUSIONS AND RECOMMENDATIONS

I. Numerical modeling can be used to investigate theairflow patterns for pneumatic control of CPB withoutthe need of designing and building costly prototypes.

2. Among the eight configurations studied, two appearedpromising: the horizontal air blowing and the shieldedsimultaneous oblique ascending air suction and blow­ing across the plant foliage.

3. The horizontal air jet could be efficiently used providedan adequate catching system is set to catch the CPBsblown out by the air.

4. The shielded simultaneous oblique ascending air suc­tion and blowing configuration does not require acatching system because the suction hood ensures thistask. However, the shield has to be improved to avoidany eventual possible air recirculation.

5. Results of the evaluation of the numerical model per-

30

Measured airspeed (m1s)

Fig. 22. Predicted vs. measured combined air blowingspeeds.

Bird, R.B., E.S. Warren and N.L. Edwin. 1963. TransportPhenomena, 3rd ed. New York, NY: John Wiley & Sons,Inc.

Boiteau, G.L., G.C. Misener, R.P. Singh and G. Bernard.1991. Evaluation of a vacuum collector for insect pestcontrol in potato. American Potato Journal 69:157-166.

Boiteau, G., R.H. Parry and C.R. Harris. 1987. Insecticideresistance in New Brunswick populations of the ColoradoPotato Beetle (Coleoptera: Chrysomelidae). CanadianEntomology 119:459-463.

Burgess, W.A., MJ. Ellenbecker and R.D. Treitman. 1989.Ventilation for Control of the Work Environment. NewYork,·NY: John Wiley & Sons, Inc.

Conroy, L.M., MJ. Ellenbecker and M.R. Flynn. 1988.Prediction and measurement of velocity into flanged slothoods. American Industrial Hygiene Association Journal49(5):226-234.

deVries, R.H. 1987. An Investigation Into a Non-ChemicalMethod for Controlling the Colorado Potato Beetle.Unpublished M.Sc. Thesis. Graduate School, CornellUniversity, Ithaca, NY.

Duchesne, R.-M. and G. Boiteau. 1992. Outlook onmechanical, physical, and cultural control strategiesagainst the Colorado Potato Beetle. In Proceedings ofthe38th Annual Meeting of the Canadian Pest ManagementSocietyl1991, 33-54. Fredericton, NB.

Ellenbecker, M., R. Gembel and W. Burgess. 1983. Captureefficiency of local exhaust ventilation systems. AmericanIndustrial Hygiene Association Journal 44( 10):752-755.

Flynn, M.R. and M.J. Ellenbecker. 1986. Capture efficiencyof flanged circular local exhaust hoods. Annals ofOccupational Hygiene 30(4):497-513.

Flynn, M.R and M.J. Ellenbecker. 1987. Empirical validationof theoretical velocity fields into flanged circular hoods.American Industrial Hygiene Associatioll Journal48(4):380-389.

Forgash, A. J. 1981. Insecticide resistance of the Colorado

302520

Unity line

••

15

•

10

•:

5

- 25

i-"0 20

Q,JQ,JQ"fI).. 15.;

"0Q,J- 10CJ

:0Q,J..~

5

00

280 KHELIFI. LAGUE and ROBERT

Potato Beetle, Leptinotarsa decemlineata (Say). InAdvances in Potato Pest Management, eds. J.H. Lashomband R. Casagrande, 34-46. Stoudsburg, PA: HutchinsonRoss Publishing Co.

Fox, D. G. 1981. Judging air quality model performance: Asummary of the AMS workshop on dispersion modelperformance. Bulletin American Meteorological Society62:599-609.

Giles, R. V. 1984. Mecanique des fluides et hydraulique,serie Schaumm. New York, NY: McGraw-Hill.

Khelifi, M., C. Lague and B. Lacasse. 1992. Test bench forthe pneumatical control of pest insects. ASAE Paper No.92-1599. St. Joseph, MI: ASAE.

Khelifi, M., J.-L. Robert and C. Lague. 1996. Modelingairflow inside and around hoods used for pneumaticcontrol of pest insects. Part I: Development of a finiteelement model. Canadian Agricultural Engineering38:265-271.

McDermott, H.J. 1977. Handbook of Ventilation forContaminant Control. Michigan, MI: Ann Arbor SciencePublishers, Inc.

Misener, G. C. and G. Boiteau. 1991. Force required toremove Colorado Potato Beetle from a potato leaf. CSAEPaper No. 91-404. Saskatoon, SK: CSAE.

Misener, G. C. and G. Boiteau. 1992. Determination of InsectParameters to Improve the Beetle Vacuum Machine.Report B3009-2, Canada/N.B. Cooperation Agreementon Agri-Food Development (CAAFD). AgricultureCanada Research Station, Fredericton, NB.

Puttre, M. 1992. Bug-busting alternative to pesticides.Mechanical E?1gineering 114(12): 108.

Robert, J.-L. 1994. MEFL3D manuel de reference. Dept. degenie civil, Universite Laval, Quebec, QC.

Willmot, C.J. 1982. Some comments on the evaluation ofmodel performance. Bulletin American MeteorologicalSociety 63:1309-1313.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/November/December 1996 281

Wind tunnel for spray drift studiesM. FAROOQ, D. WULFSOHN and RJ. FORD

Department of Agricultural and Bioresource Engineering, University of Saskatchewan, Saskatoon, SK, Canada S7N 5A9.Received 13 February 1996; accepted 11 September 1996.

Farooq, M., Wulfsohn, D. and Ford, R.J. 1996. Wind tunnel forspray drift studies. Can. Agric. Eng. 38:283-289. An instrumentedwind tunnel was developed to study the drift from sprayer nozzlesunder controlled and repeatable environmental and spraying condi­tions. The wind tunnel has a 1 m2 cross section and a 4 m long testsection. Wind speed and wind direction (by rotating the nozzle),nozzle operating pressure, flow rate, and height can be controlled andmeasured while relative humidity and temperature are recorded. Animage of the spray sheet captured against a black matt background isobtained using a series of electronic flashes and a 35-mm SLRcamera set to an f:stop of 5.6 with black and white ISO 400 film. Aflat fan nozzle was tested at wind speeds of 0, 1.4, 2.8, and 4.2 mlsand operating pressures of 205, 275, and 345 kPa with 3 replicates.Analysis of the images of the spray sheet revealed that the systemresponded in a meaningful way to changes in environmental andspray par.uneters. It was confirmed that the wind tunnel was able toproduce repeatable conditions. Keywords: spray drift, wind tunnel,visualization, instrumentation

Un tunnel aerodynamique a ete developpe pour I'etude de laderive des buses des pulverisateurs fonctionnant sous un environne­ment contr61e ainsi que sous un environnement OU les variablesd'atomisation peuvent etre reglees. Le tunnel aerodynamique utiliseavait pour aire de coupe transversale 1 m 2, et avait 4 metres delongueur. II nous etait possible de regler ainsi que de mesurer lavitesse et la direction du vent, la pression de la buse, la vitessed'ecoulement, ainsi que I'elevation de la buse. Par contre, l'humiditeet la temperature ne pouvaient qu'etre notees. Une image d'une lamede jet a pu etre obtenue en photographient cette demiere (appareil35-mm SLR, f:stop 5.6, film en noir-et-blanc ISO 400) pendantqu'une eserie de flashes electroniques l'iIluminait. Pour obtenir uneimage, I' interieur du tunnel a ete peint en noir. La buse it jet plat a etcteste ades vitesse de vent de 0, 1.4, 2.8 et 4.2 mIs, et ades pressionsde 205, 275 et 345 kPa. Chaque essai a ete repete trois fois. Lesresultats des analyses des images de lame de jet eeont demontre queces demieres etaient sensible au reglage des parametres. Par cesanalyses, nous avons egalement pu confirmer Ie fait que les condi­tions choisies pouvaient etre reproduites dans Ie tunnelaerodynamique.

INTRODUCTION AND BACKGROUND

There is still a need to minimize spray drift from agriculturalsprayers. New sprayer systems, designed to fulfill this need,frequently arrive on the market with unverified claims aboutreduction in drift (Wolf 1992). These claims are generallyover-optimistic, based more on a belief in what 'ought' towork rather than on sound testing and evaluation (Ford1975). SACAM (1994) recommended that commercial cropsprayers be assessed for their potential loss of agriculturalchemicals through large drop drip-off and drift losses.

During the last few years, the number of field and labstudies related to drift have increased tremendously, e.g.,Bouse (1994); Fox et a1. (I 993a); Franz et a1. (1993); Howard(1993); Khdair et a1. (1994); Kirk et al. (1992); Reichard et

at. (1992); Salyani and Cromwell (1992); Wang et at. (1993);Womac et at. (1993). In many field studies, the samplinglayouts arranged on the downwind· side of the spray swathwere spread over wide areas (Nordby and Skuterud 1975;Fox et at. 1993a). The advantage of field studies is the naturalspray and environmental conditions. However, results offield studies have generally not been consistent (Salyani andCromwell 1992; Bouse et at. 1992; Picot et al. 1993).

In most field and laboratory studies, samplers are used tocollect and measure the amount of spray drift. These haveincluded cylindrical collectors (e.g., Bouse et at. 1992), paper(e.g., Franz et at. 1993), mylar sheets (e.g., Salyani andCromwell 1992), plant leaves (e.g., Howard 1993), and oth­ers (Miller 1993). These collectors are quite inconsistent inproviding information on the drift. Deposits from collectorsat the same location have been reported to differ by 100%(Fox et at. 1993b).

The study of drift in a wind tunnel has the advantage ofcontrolling and repeating the spraying and atmospheric con­ditions (Miller 1993; Khdair et at. 1994; Reichard et al.1992). Flow visualization (Sagi and Derksen 1991), a tech­nique of making invisible flows visible, combined with windtunnel and image processing, provides an opportunity tostudy spray droplets under controlled conditions, just afterthey are produced.

OBJECTIVES

The objective of this study was to develop an instrumentedwind tunnel for estimation of spray drift under varying envi­ronmental and sprayer operating conditions.

The scope of the instrumented wind tunnel was limited toproviding the following capabilities: (1) visualization ofwind flow pattern inside the wind tunnel; (2) measurement ofenvironmental factors; (3) control and measurement ofspraying parameters; and (4) acquisition of a digital image ofthe spray pattern for analysis using image processing.

WIND TUNNEL DESIGN

FeaturesAn instrumented wind tunnel was developed with the follow­ing features: (a) provision for altering the sprayingconditions, i.e., wind speed, wind direction in reference toorientation of nozzle, height above the crop, operating pres­sure, and flow rate; (b) provision to monitor and recordenvironmental variations, i.e., wind speed profile, tempera­ture and relative humidity; (c) capability to acquire a frozenimage of the spray sheet; and (d) provision for using a varietyof spray nozzle types and sizes.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38, No.4. Octobcr/Novcmber/Decembcr 1996 283

Fig. 2. Average calibration curve for velocity sensors.

where:VII' = wind speed (m/s). andT = resistor temperature (oC).

The calibration has an average error of ± 3.32%. Thedirection of the sensor relative to the wind direction alteredthe wind speed measurement up to 20%. Although the resis­tors selected were all of the same sizc, construction errors

8x

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~2

"-x....x0

-x.-x_x x

00 00 100 120 140 100 ISOResistoclc~ ("0

Measurement of environmental conditions

A grid of 24 air velocity sensors was installed across thecross-section ortlle tunnel upstream or the nozzle. The veloc­ity sensors arc simplc resistors with constant currcnt passingthrough. Temperature of cilch resistor is measured with aT-typc thermocouplc allached to the surface of the resistorwith epoxy and is related to \vind speed. The resistors usedarc a precision, thick film chip, surface mount type rated at10 Q and 0.125 W (model SMR8E. Cardinal Eleclronies.Saskatoon. SK). To obtain higher sensitivity. especially athigh wind speeds, the resistors werc subjected to 225 mAcurrent with a power dissipation of 0.5 Wjresistor.

Three sample sensors were calibrated in a bench-typewind tunnel for wind speeds of 0.15 to 7.5 m/s. Regressionanalysis resulted in Eq. I, with coefficient of determinationR2 = 0.99. and calibration curvc as shown in Fig. 2.

(I)In 1/". ; 7.056 - 0.0737" + 0.0001167"2

The wind tunnel consists of a basic tunnel structure. asuction fan. flow straightcners, spray control system. flowvisualizalion unit, imllge acquisition unit, and wind speedsensor grld (Fig. I). The entire set-up is 6.5 m long. I m wideand 2 In high. The tunnel is mounted on a frame supported onfour wheels. The frame also has four screw-type legs tosupport the load when the tunnel is in operation.

Tunnel structure

Thc wind tunnel (Fig. I) is an open circuit type and has a 4m long test section. The see-through front wall of the tunnel.madc of plexiglass. permits recording images of spray and airflow patterns. The other three sides of the tunnel are made ofplywood. The cross section of the tunnel increases from 0.91m x 0.91 111 at the entrance to I 111 X I 111 at the exit with a slope01'0.5°. This helps to reduce the friction orthe walls to air. tominimize the effect of boundmy layer, and to maintain un i­fonn wind speed through out the section (Pope and Harper1966). The tunnel contains entrance and exit ducts made ofgalvanizcd steel sheet shaped to smooth air flow at both endsof the tunnel. The cntrance duct can be opencd as an entranceto the tunnel. The exit duct is 0.38 m long and holds thesuction fan. A transition ducl. 1.62 mlong. is placed betweenthe main tunnel and exit duct to get a diversion angle of 6° toair flow. within the 5-70 recommended for smooth transitionfrom a rectangular to a circular cross section (Pope andHarper 1966). Two acrylic windows have been provided inthc top panel of the tunnel, through which the spray patternis illuminated.

Two flow straighteners have becn used to control the airflow pattern inside the lest section. one at the inlet and theother at the exit of the section to eliminate disturbancc due tothe converging of air from around the tunnel edges and theeffect of swirling action of the fan. respectively. Reynoldsnumber (Re) for the holes in the flow straighteners wascalculated to be from 5000 10 27000 for wind speeds of 1.510 8.0 m/s as opposed 10 vailles on Ihe order of 105 for a I xI 111 cross seclion. The propeller-type suclion fan is poweredby <I 2.2 k\V motor and has a maximum discharge of 9.441113/s. which produces a wind speed of 10 m/s in the windtunnel. The suction fan speed is cOlltrolled through a variablefrequency AC invertcr. This arrangement allows averagewind speeds inside the tunnel ranging from 0.8 to 10 m/s.

Fig. l. Structure of the wind tunnel.

[xlt duet

Suclion'00 flo ... slrclghlen&r

Trcnsilion duet

[nlronee due!

caused vari<llion in the response of lhe sensors.To eliminate this variation, three-point calibra­tion of all the sensors was performed using thesame type of model. In higher relativc humidity(RI-I) conditions. the sensors indicatc higherwind speeds. The effect of air temperature to theresponse of sensor is opposite 10 the effect ofRH. To correct for the effect of relative humidilyand air tempcrature. all wind speeds are adjustedby the same percent as the difference betweenthe nominal speed and the average speed from allsensors.

The outplltS from all the sensors are connectcdto a data logger (model 8028A. Scicmetric In­strumcnts. Manotick. ON) which is connectcd toa 80286-based com pUler. A BASIC program

28.J FAROOQ. WULFSOHN .1Ild FORD

converts the voltages from the data logger corresponding tothe 24 sensors to temperature and then to wind speed usingregression equations developed for each sensor. The programalso calculates the average wind speed for each row andcolumn and total average, and displays the results on a moni­tor along with speeds recorded by individual sensors. Theprogram updates the wind speeds every 4 s on the screen andwrites data to a diskette.

A humidity sensor (model RH-5, General Eastern,Woburn, MA) is used to record the relative humidity near thetunnel entrance. A T-type thermocouple is located inside thetunnel close to the nozzle to record the temperature inside thetunnel. The output of the thermocouple and humidity sensoris recorded by the data logger.

Spray control unit

The spraying control unit is meant for developing spray andcontrolling and measuring spray variables, i.e., operatingpressure and flow rate. The liquid first passes through adamping tank that eliminates the pressure fluctuation in thedownstream flow line. The liquid is then passed to the nozzlewhich is fixed to a brass bushing at the end of a copper tube.The copper tube passes from the top of the tunnel through aplastic bushing in such a way that the tube can be moved upor down or can be rotated by simply loosening a nut. Thebrass bushing can accommodate commonly used nozzle bod­ies. The plastic bushing can be removed from the tunnelalong with the copper tube and nozzie when needed tochange the nozzle. On the top of the tunnel, a pointer indi­cates the height of the nozzle from the floor of the windtunnel. Liquid flow rate is measured using a variable areaflowmeter (Cat. no. H-03286-22, Cole-Parmer InstrumentCo., Niles, IL). The pressure downstream of the pressure tankis measured with an analogue pressure gauge (Wika Instru­ment Corp., Hauppauge, NY).

Visualization and image acquisition

The visualization unit makes the air flow inside the tunnelvisible and was used to confirm laminarity of the air flowalong the length of the tunnel. Uniformity of the flow throughthe cross section is checked with the wind speed sensor grid.Grey smoke is generated by exploding a smoke bomb into aheavy-duty plastic barrel. The smoke is injected into thetunnel from four, equally-spaced pipes along the vertical axisthrough the flow straightener at the entrance. The smoke inthe container remains at atmospheric pressure and is drawninto the tunnel by the fan. Both air and smoke being atatmospheric pressure, the air and smoke in the tunnel main­tain the same speed. The rate of smoke injected into thetunnel and thus the density of smoke produced, is controlledby a valve.

To find a suitable setup for image acquisition, differentlight sources and their positions, film speeds, apertures, andshutter speeds were tested in a series of experiments. Theselected image acquisition system is comprised of four, 100­W Britek master/slave flashes having a flash duration of1/850 s for lighting, and a 35 mm SLR camera with black andwhite ISO 400 film. The bulbs are placed on top of the windtunnel, to the rear of the nozzle and are plugged into socketshaving multi-directional movement. Three flash bulbs are

placed on the downstream side of the nozzle and one on theupstream side. The bulbs can be moved up and down to adjustthe light intensity and area covered. Every flash bulb ispaired with a 60 W incandescent bulb to illuminate the windtunnel interior for camera adjustment. The two flash unitsclose to the nozzle are tilted towards the nozzle. All the flashbulbs are also tilted towards the front of the wind tunnel. Thebulbs are shielded with black cards in such a way that lightfalls neither on the background nor on the plexiglass. This isto avoid reflections in the tunnel which reduce spray/back­ground contrast. The flash units are triggered by a set ofsynchronization cables attached to the camera. The shutterspeed of the camera is set at 1/60 s but due to the shortduration of the flash illumination, the image is effectivelyfrozen on the film.

The top, bottom and back inner panels of the wind tunnelare painted flat black to eliminate the effect of any lightreflection other than the deflection by spray particles duringimage acquisition. A black cloth was placed between cameraand wind tunnel and the camera pointed through a hole in thecloth. This helped in controlling any reflection to the imagefrom behind the camera.

WIND TUNNEL TESTING

Tests were conducted to verify (1) that the air flow through­out the cross section of the wind tunnel is uniform and notturbulent, (2) that the setup alters spray pattern with changesin testing conditions, and (3) that the setup is capable ofproviding information for quantification of drift. In bothtests, images of flow were recorded using image acquisition.

For wind flow pattern, the camera was placed 2.7 m awayfrom the tunnel and an image captured of the entire length ofthe testing section. For the spray pattern, the camera wasplaced 1.0 m away from the wind tunnel to cover an area fromthe nozzle to the bottom of the wind tunnel, extending 0.75m downwind from the nozzle. All the images were taken incomplete darkness with the spray illuminated by the flashbulbs.

Wind flow pattern experiment

For wind flow pattern visualization, smoke flow in the windtunnel was photographed at wind speed settings of 1.4, 2.8,4.2,5.6,7.0, and 8.4 m/s. Wind speed was also measured withthe velocity sensor grid. The relative humidity and tempera­ture inside the tunnel ranged from 55.4 to 58.5% and 20.80 to21.4 °c, respectively, during these tests.

Results and discussion Figure 3 is an image of smoke flowinside the wind tunnel at wind speed of 5.6 m/s. This, andother images, indicated that the flow from the lower outletsis quite laminar throughout the testing section while the flowfrom the upper outlet rises upward over the last half of thetesting section. The turbulent eddies were more evident atspeeds of 1.4 and 2.8 m/s than at other speeds. This may bethe effect of the nozzle just protruding into the top surface ofthe tunnel. These images may also have been taken soonerafter release of the smoke compared to the times in otherspeeds. There is also glare near the top of some images dueto light reflection from the plexiglass in the tunnel ceilingwhich exaggerates the turbulent eddies in the upper portion

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OClobcr/November/Decembcr 1996 285

Table I: \Vind sl>ceds measured by velocity sensors at different nominal speeds

Fig. 3. Image of smoke 110w in the testing section at wind speed of 5.6 m/s.

(2)

not common under field condi­tions. The fact Ihat thc orienta­tion of the sensor changes themeasurement by up to 20% ofthe reading suggests Ihat rigidholders for thc sensors arenecded.

8.4

1.110.13

5.52

8.48­10.19

7.0

7.14­8.974.581.030.14

The size of thc droplets can then be estimatcd using Eq. 3whel1the particle Re is up to 2 (Mohsenin 1986). In this study

Spra~v pattern experiment

Model The assumption is madethat the spatial distribution ofparticles in a spray sheet is re­lated to panicle size. Smallparticles in thc spray were alsoassumed to reach their terminalvclocity before exiting the areain the image and thai same sizedparticles in Ihe spray sheetwould be following the samcpathlines, referred 10 as "iso­sized" pathlines. Straightiso-sized pathlines would indi­cate thai particles forming theselines are at terminal velocity andthe vertical velocity of the parti­cles is not decreasing.

As defined in Fig. 4, 80 is thcangle that the spray sheet makeswith the horizontal with no wind.This angle increases to 811' whenthere is wind in the given direc­tion (i.,e. 80 = 8\1' when \III' = 0).The spray angle (8j) changeswith pressure change (Teejct1993) but may not change withwind speed within the range ofwind speeds allowed for spray­ing. The sheet defleclion angle(Od) is defined as Ihe differencebet ween 80 and 8\1" The angle 8/is the slope of the iso-sized path-lines on the image. At higher

wind speeds and thus greater drifl distances. the slope ofthese lines will decrease. The angles 80, 811" and 8, can bemcasured directly from thc image using drawing tools avail­able with most image analysis programs. The average windvelocity (\Ill') was calculated for each test. The initial sprayvelocily (IIi), i.e., Ihe veloeily of Ihe parlicles as Ihey exitfrom the nozzle, depends upon liquid flow rate through thenozzle.

The water droplets at terminal velocity arc assumed tomove at the same speed as the wind in the horizontal direc­tion. Knowing \1\1' and 8/ for droplets at tenninal velocity(downwind of thc nozzle). terminal velocity (\I,) of the pani­cles can be determincd from:

5.6

5.88­7.403.880.790.13

Nominal wind speed (Ill/S)

2.8 4.2

2.79* 4.25*

4.04 5.171.96 2.860046 0.540.17 0.13

104

1.42*

1.95

1.040.22

0.16

Paramctcr

* The means arc not significantly different from nominal speeds'\I 95% level.

Mean

Maximum

Minimum

Standard deviation

Coefficient of variation

of the tunnel. The triangular dead zone in the upper left sideof the image is because of the dark zonc created by thelighting coming from both sides of the nozzle. Reynold'snumber for the tunnel cross scction was calculated to be inthe range of 105. but the turbulcncc is suppressed by the twoflow straightencrs. ThaI is. flow straightcners divide the tun­nel cross-section into small subsections or the size ofopenings in the flow straighteners reducing the calculated Reto values in the order of 103.

The wind speeds measured with the velocity sensors hadsome spatial vari~lIion but the measurements from all sensorsat all set speeds were not significantly different at 95%probability level. The mean. maximum. and minimum windspeeds from all the sensors 1.11 different sci speeds wilh stand­ard deviation and coefficient of variation are presenled inTable I. There is a considerable difference between minimumand maximum speeds. but the coefficient of variation wasacceptable for our purposes since uniform wind patterns are

286 FAROOQ. WULFSOIIN and FORD

Fig. 4. Angles and velocities in spray wind interaction.

where:d" = Droplet diameter (11m),

1'" = Density of droplet (I 000 k~/m\PI = Density of air (1.206 kg/m ).~ = Viscosity of air (1.78 x 10-5 Pa.s, andg = Acceleration due to gravity (9.81 m/52).

Experimental procedure A flat fan nozzle (FII0/06/3. De­lavan, Lexington, TX) was tested under various sprayoperating pressures and wind speeds. The experiment wasdesigned as a two factor factorial with 4 wind speeds (5 I = 0m/s; S2 = 1.4 m/s; S3 = 2.8 m/5; and S4 = 4.2 m/s), 3operating pressures, (PI = 205 kPa; P2 = 275 kPa; and P3 =345 kPa) and 3 replicates (R) for a total of 36 tests. The

experimental design was completely randomized with thctcsts randomized over time.

For each test. operating pl.·essure was set and recorded.5ufficicnI time was given for the pressure, each time it waschanged, 10 stabilize before starting the test. Liquid flow ratefor each test was recorded using the flow meter. The windspeed was sci by adjusting the input frequency 10 the f<.ln.Average wind speed, tunnel temperature, and rclative humid­ity were recorded by the data logger.

The prints of the images were digitized using a CCTVcamera (model JE3462RGB, Javelin, Japan) and a poblicdomain image analysis program NIH Image 1.55 (U.S. Na­lional Institute of Health, Bethesda. MD). Using drawinglools available with this program, iso-sized lines were drawnmanually at three locations on the images as shown in Fig. 5.Location I was selected as the top edge of the image on thedownwind side while locations 2 and 3 were selected wherethe straight lines were visible. Thc slopes of thcse lines weredetermined by the program. From the slopes of these lines.the falling velocity or the water droplets was determinedusing Eq. 2. while the diameter of the droplet was detennincdusing Eq. 3.

The data obtained for slope, terminal velocity, and dropletdiameter were analyzed lIsing the one-way analysis of vari­ance (ANOVA) module in SPSS stalistical software (SSPSInc.. Chic<lgo, IL) to determine the significance of the effectof wind speed, pressure, and replicate on the slope, terminalvelocity. and droplet size and to compare the means of theseparameters. The same procedure was lIsed to test the relation­ships of pressure ancl wincl speed with spray sheet denectionangle. The 0.05 probability level was used as the criterion fortests of significance throughollt the data analysis.

(3 )

9,

Panicles assumed at Icmlin:Jlvelocity V,

-.J 18rJII,g(pp - PI)

particle Re ranged from 0.2 to IA.

-v.

Fig. 5. Establishment of iso·sized pathlincs on an image.

CANADIAN AGR[CULTURAL ENGINEER[NG Vol. 38. No.4. OClolx:r/No\'cmocr/Dcccmbcr [996 287

Table II: Average slope, terminal velocity, and droplet size averaged over pressureat three locations on the image for three wind speeds

Wind speed (m/s) Slope of iso-sized Tenninal velocity of Droplet diameterline (degrees) the droplet (m/s) (Jlm)*

Location 1

1.4 22.5 (1.8) a 0.58 (0.05) a 137 (6.25) a2.8 13.2 (1.6) b 0.66 (0.08) ab 146 (9.12) ab4.2 8.3 (1.1) c 0.61 (0.08) b 141 (9.42) b

Location 2

1.4 33.9 (3.9) a 0.94 (0.14) a 175 (12.9) a2.8 21.5 (4.3) b 1.10 (0.24) ab 188 (21.7) ab4.2 17.3 (3.0) c 1.30 (0.24) b 205 (19.0) b

Locationn 31.4 45.5 (5.4) a 1.44 (0.30) a 216 (21.4) a2.8 31.3.(3.1) b 1.70 (0.20) b '235 (14.5) b4.2 24.8 (3.0) c 1.93 (0.27) b 251 (17.3) b

- Values in parenthesis are standard deviations.

- Means with similar letters in each column (separate comparisons for each location)

are not significantly different from each ot~er at the 0.05 probability level.* Droplet diameter calculated using Eq. 3.

edge of the image unless the areaof interest is marked on the imagefield before an image is captured.There is a need to develop a pro­gram to estimate the drift potentialof the particles on the rest of theimage. There is also a need tocompare the drift data from thetunnel with other techniques andto calibrate the system to find therelationship between intensity ofthe image and number of particles.

Results and discussion The effect of replicate on all thespray sheet characteristics was not significant at the 0.05probability level, showing that the tunnel can be used toconduct repeatable experiments.

The analysis of variance indicated that the slope of theiso-sized lines, terminal velocity, and calculated droplet sizewere not affected by the operating pressure at locations I and2 on the images but were affected at location 3. These pa­rameters were averaged over pressure for each wind speedand the statistics determined for the averaged parameters(Table II). As expected, the slope of iso-sized lines (9/ )decreased with increasing wind speed, indicating a largerdrift distance. The wind speed did not significantly affectterminal velocity and droplet size at locations I and 2, but didat location 3. The average droplet size at locations I, 2, and3 was calculated as 141, 189, and 234 J,lm, respectively.

The sheet deflection angle (9d) increased from 2.7° (±1.0°)to 4.6° (±1.6°) as wind speed increased from 1.4 to 4.2 m/s.This was due to increase in angle 9w with increasing windspeed. The sheet deflection angle increased from 2.6° (±1.10)to 4.4° (±1.9°) as operating pressure increased from 205 to345 kPa. This was due to decrease in angle 90 with increasedpressure. The ANOVA indicated that these changes in sheetdeflection angle were statistically significant.

The above results indicate that the responses of the spraysheet characteristics to spray control parameters were similarat locations 1 and 2 but different at location 3. There wassome bias in manually selecting a line at locations 2 and 3since, unlike location 1, the position of these lines, beingsubject to human judgement, is difficult to locate in a consis­tent manner. The analysis used is helpful only for estimatingthe drift potential of the particles on the downwind upper

288

CONCLUSIONS

The results of the testing of the instrumented wind tunnelhave led to the following conclusions.

1. The flow inside the test section of the wind tunnel isessentially laminar in the lower 75% of the tunnel cross­section. This is the portion of the cross-section which ismost important for the study of nozzles. Although thereis variation in measurements of wind speeds among thesensors, the spatial variation across the cross-section isinsignificant and random. The presence of the nozzleitself causes some downstream turbulence.

2. The system responds in a meaningful way to changes inenvironmental and spray parameters such as wind speedand operating pressure.

3. The wind tunnel provides similar conditions for re­peated tests.

4. The image acquisition successfully captures the infor­mation about spray sheet and spray drift. It was possibleto identify and trace relevant information from the im­age.

RECOMMENDATIONS

I. The flow along the tunnel cross-section does not simu­late the wind speed pattern over the crop canopy as auniform sized grid was used for the flow straighteners.It would be useful to further study the role of flowstraighteners, i.e., variable resistance flow straighten­ers, or the use of baffles, to simulate a wind velocityprofile over a crop canopy.

2. It is recommended that an alternate rigid mount for the

FAROOQ. WULFSOHN and FORD

velocity sensors inside the tunnel be designed and im­plemented.

3. There is still a need to develop an image analysisprogram that automates the analysis process and trans­forms information in the image about the number ofparticles, particle velocities, and the size of particles tothe potential drift of particles.

4. The system should be calibrated for particle sizes andvelocities using mono-sized droplet generators and la­ser velocimeters.

ACKNOWLEDGMENT

This project was made possible by funds from Natural Sci­ences and Engineering Research Council. Funding for thestudies by the first author was provided by the CanadianCommonwealth Scholarship and Fellowship Program, Min­istry of Foreign Affairs and Trade, Government Canada, andis also duly acknowledged.

REFERENCES

Bouse, L.F. 1994. Effect of nozzle type and operation onspray droplet size. Transactions of the ASAE37: 1389-1400.

Bouse, L.F., S.G. Whisenant and J.B. Carlton. 1992. Aerialspray deposition on mesquite. Transactions of the ASAE35:51-59.

Ford, RJ. 1975. A method for the comparative evaluation ofdrift abatement techniques for ground sprayers. CanadianAgricultural Engineering 18:21-22.

Fox, R.D., F.R. Hall, D.L. Reichard, R.D. Brazee and H.R.Krueger. 1993a. Pesticide tracers for measuring orchardspray drift. Transactions of the ASAE 36:50 I-50S.

Fox, R.D., D.L. Reichard, R.D. Brazee, C.R. Krause and F.R.Hall. 1993b. Downwind residues from spraying asemi-dwarf apple orchard. Transactions of the ASAE36:333-340.

Franz, E., L.F. Bouse, J.B. Carlton, I.W. Kirk and M.A.Lateef. 1993. Aerial spray deposit relations with plantcanopy and weather parameters. ASAE Paper No.93-1061. St. Joseph, MI: ASAE.

Howard, K.D. 1993. Use of mechanical shields for increaseddeposition. ASAE Paper No. 93-1545. St. Joseph, MI:ASAE.

Khdair, A.I., T.G. Carpenter, and D.L. Reichard. 1994.Effects of air jets on deposition of charged spray in plantcanopies. Transactions of the ASAE 37:1423-1429.

Kirk, I.W., L.F. Bouse, J.B. Carlton, E.Franz and R.A.Stermer. 1992. Aerial spray deposition in cotton.Transactions of the ASAE 35: 1393-1399.

Miller, P.C.H. 1993. Spray drift and its measurement. InApplication Technology for Crop Protection, eds. G.A.Matthews and E.C. Hislop, 101-122. Wallingford,England: CAB International.

Mohsenin, N.N. 1986. Physical Properties of Plant andAnimal Materials, 2nd revised edition. New York, NY:Gordon and Breach Science Publishers.

Nordby, A. and R. ·Skuterud. 1975. The effect of boomheight, working pressure and wind speed on spray drift.Weeds Research 14:385-395.

Picot, J.J.C., D.O. Kristmanson, R.E. Mickle, R.B.B.Dickison, C.M. Riley and C.J. Wiesner. 1993.Measurement of folial and ground deposits in forestryaerial spraying. Transactions of the ASAE 36: 1013-1024.

Pope, A. and J.J. Harper. 1966. Low Speed Wind TunnelTesting. New York, NY: John Wiley and Sons.

Reichard, D.L., H. Zhu, R.D. Fox and R.D. Brazee. 1992.Computer simulation of variables that influence spraydrift. Transactions of the ASAE 35:1401-1407.

SACAM. 1994. Study on Commercial Crop Sprayers:Recommendations. Saskatchewan Advisory Committeeon Agricultural Meteorology, Saskatchewan AdvisoryCouncil for Agriculture, Saskatchewan Agriculture andFood, Regina, SK.

Sagi, Z. and R.C. Derksen. 1991. Detecting spray droplets onleaves with machine vision. ASAE paper No. 91-3050.St. Joseph MI: ASAE.

Salyani, M. and R.P. Cromwell. 1992. Spray drift fromground and aerial applications. Transactions ofthe ASAE35:1113-1120.

Teejet. 1993. Agricultural spray products. Catalog 43A.Wheaton, IL: Spraying Systems Co.

Wang, L., N. Zhang, G.E. Thierstein and O.K. Kuhlman.1993. Experimental analysis of spray pattern distributionuniformity for agricultural nozzles. ASAE paper No.93-1546. St. Joseph MI: ASAE.

Wolf, T.M. 1992. Novel approaches to spray delivery. InProceedings of APPLI-TECH '92 conference:Agricultural Chemical Application Technology in the'90s. Regina, SK.

Womac, A.R., J.E. Mulrooney and L.F. Bouse. 1993. Spraydrift from high velocity aircraft. Transactions of theASAE 36:341-347.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. Octobcr/Novembcr/Dcccmber 1996 289

Method to evaluate the average temperatureat the surface of a horticultural crop

B. GOYETTE 1.2 C. VIGNEAULTI.2 B. PANNETON 1and G.S.V. RAGHAVAN2

/Horrintllural Research (/ud De\'e!opmell1 Cl'wre. Agrintllure and Agri-Food Canada. 50il11·)eall-sur-Ricl1elicu. QC. CanadaJ3B 3£6: and 2Deparfmem oj AgriculTf/ral ond Biosy.wems Engineering, McGill VI/il'ers;ty. Saime-AlIne-de·8ellevue. QC.Cal/ada '-19X 3V9. Agriculture Canada COll1riblllioll No. 335/96.01.05R. Recch'cd 5 JI/Ile /995: accepted 23 Sepfember /996.

Goyclte. B.. Vigneault. c.. Panncloll. B. and Raghavan. G.S. V. 1996.Method (0 evaluate the 3vcrage temperature al lhe surfucc of ahorticultural crop. Cm. Agric. Engr. 38:291-295. Precooling sys­tems must decrease Ihe temperature of freshly harvested honiculturalcrops as fast as feasible. A good system provid~s a unifonn finalIcmperaturc throughoul thc mass of produce iml1lcdiatcly followingtreatment Thereforc. the evaluation of precooling systems shouldinclude me,lsurcmcnls of both thc cooling rate and the uniformity ofthe tcmperature within the cooled produce. Cooling rale measurcs.'iuch as (he half-cooling time. have been used (0 evaluatc pnxoolingsystcms but npply only with a known homogeneous cooling mediumtemperature. This paper describes an extension of these methods bywhich the me,lI1tempcraturc ofthc medium surrounding the produceis calculated using the same sel of data required 10 evaluate cooling.r:lles. The theoretical basis for (he method is prcscllted and a labora­tory experimenl demonstrates the tcchnique and its accuracy.Keywords: vegetable. postharvest. precooling. icing. cooling ratecoefficient. half-cooling lime

Les systcmes de prcrefroidissement des produits horticolesfraichelllent recohes doivcnt abaisscr la temperature de ces produilsaussi rnpidement que possible. Un systcllle cfficace produira unetemperature finale unifonne il travers la masse de produits immcdi­;ltemenl apres Ie traitel1lent Une methode d'evaluation des systcmesde prerefroidisselllent doit ainsi inclure ;'1 la fois une mcsun.: du tauxdc refroidissement et de runifonnitc de la temperature ;1 travers lamasse de produits lmiles. Dcs mcthodes dc rnesurc du laux den:froidissernent. tel Ie temps dll demi-rcfroidisscrnel1l. sont actuelle­ment utilisees pour cvailier les syslCIllCS de prerdroidisselllcilt maisils s'appliqucllt seulelllent lorsque la tcmpCr;Hurc dll milieu cl1viron­nant est hOlllogcnc. Cc documcnt decrit une mcthodc dccoulant dcsmethodes exislames ct qui peflnel de calculer la temperature1110ycnne du milieu entour:ml Ics produits. Celie melhade utilise lesmemcs donnces qui scrvent it cvaluer Ic taux de rcfroidissemcllt dcsproduits. La Ihcoric et 1:1 Illclhodologic sont presentccs. Des essais Cll

laboratoirc dcmontrent la precision de c.:ellc methode.

ture of the cooling medium is uniform around thc produce.Furthermore. the CC and HCT depend on the size of theproduce being tested. In the particular case of evaluating theuniformity of ice distribution for broccoli precooled using anicc-water mixture. these t\\'o factors become vcry important.Broccoli stalks are asymmetric and their diameter is difficult10 mcasure. Because ice distribution is mrely unifOlm insidea box of produce. there is a non-uniform temperature distri­bution arnund the produce (Prussia and Shewfelt 1984).Although the amount of ice retained in boxes ensured suffi­cient cooling capacity. Prussia and Shewfelt (198..n did notobwill uniform temperaturc throughout the mass of produceover a 36 h period.

A method is required 10 evaluate ice distribution insideboxes or produce. Based on prcliminary experimel1ls. meas­uring ice distribution using only visual observarion \Vas notprecise enough. Ice fell into empty spaces as broccolis werercmoved from the package.

The objective of this study was to improve and extend themethods currcl1l1 y uscd to measure the efficiency of a cooling:-,yslcm by estimating tempcrature uniformity throughout theproduce during the precooling process. This extendedmcthod has been developcd espccially to evaluatc the effectof ice 10 w::ller ratio and icc particle size on the performanceof a liquid ice syslem developed by Vigneault et "I. (1995).

THEORY

The heat-transfer process can be divided into three c1asscsdepcnding on the Biot number (Mohsenin 1980). The Biotnumber is defined as the ratio of the extcrnal resistance 10 thcintcrnal resistance to heat transfer:

\Vhen Bi > 10. II is high comp;,tred 10 k and the thermalconductivity of the produci bccomes the limiting factor tohcat transfer. On the other hand. when Hi < 0.2. k is highcompared to IISo. In such a casc, thc tcmperature is cOllsid-

INTRODUCTION

Good cooling and temperature managemcnt practiccs arecritical to prcvel1l thc physiological deterioration of fruits andvcgetables (Ryall and Lipton 1972). High respiration ratesmust be slowed down by prompt, rapid, and uniform coolingimmediatcly after harvcst. Such cooling proccsses are calledrapid cooling (Fraser 1991) or precooling (ASH RAE 1986).

Cooling rate coefficient. CC. and half-cooling time. /lCT.methods havc been used for comparing precooling tech­niques (Hackert el al. 1987: Gariepy el al. 1987: Baird el al.1988: Fraser and Otten 1992) and wcre presentcd in dctail byGuillou (1958). These IwO methods apply where the temper,,-

where:BiIISok

( 1)

= Biot number.

= convective heaHransfer coefficicl1I (W.m-2.K- 1).

= ch.\raclcristic length or the body (m). and= Ihermal conductivity of the product (W e m-2.K- 1).

CANADIAN AGRICULTURAL ENGINEERING Vol. 31t No. 4. OClOhcr/Novl:l11l~r/Decl:llll~1' 1996 291

where.lo and.l[ = Bessel functions of the first kind. Coeffi­cient C" C<.In be determined from:

(6)

(7)In (0.5)

I-ICT=-­CC

MATERIALS AND METHODS

Based on Eqs. 3, 6. and 7, both CC and I·ICT depend verymuch on the radius of the body being cooled. Furthermore,the coefficient Ab is a function of Bi CEq. 4) which varies withthe radius of the produce. In practice, CC and '-ICT vary withproduce subjected to the same cooling conditions, mainlybecause all conditions are not tightly controlled. For exam­ple, the diameter of a broccoli stalk is a physical parameterrelatively difficult to measure (the stalk being particularlymisshapen). Hackert et al. (1987) installed thermocouples inthe center of broccoli stalks to read their internal tempera­tures and measure the '-ICT. Their results were fairly constantunder laboratory conditions but were imprecise uncler fieldconditions.

The temperature at any position insidc a product attemptsto reach equilibrium with the temperature of the coolingmedium at the surface ot"the product, Too, through heat trans­fer (Holman 1986). It was hypothesized that, over a specificperiod of time during the precooling process, Too can bedetermined by recording the temperature of a product atregular time intervals. The recording periodmllst correspondto a period where CC is constant and it can be determined

I'rom the Q ratio (Eq. 3) in which values of 0.2 for aotl r02 ,2.4 for A" and 1.6 for C" (I-Iolman 1986) have been subSli­tuted. These values at" Ah and Ch imply a very large Binumber which should accommodate all possible conditionsfound in precooling horticultural crops. Under these condi­

tions, Q:5 0.5 and is linearly related 10 lime.

Too is the unknown to be dctcrmined. Since Q also needs tobe determined, Too is initially assumed to be the initial tem­perature of the cooling medium. For example, if broccoli isharvested at a temperature of" 24°C (7) and it is proccssedwith liquid ice at OoC (assumed Too), Q = 0.5 is rcached whenh = 12°C 10.5 = (T" - 0) I (24 - O)J. The temperalure 01' pro­duce is recorded from T/) = 12°C and until Th reaches atemperature equivalent 10 Q = 0.125. Then. Too is iterativelyadjusted 10 get the greatest linear correlation coelTicicnt byplotting In (Q) against cooling lime. The Too finally obtainedis considered as the mcan temperature at the surface of theproduct during the precooling process.

ASI-IRAE (1986) defined the NCT as the lime required toreach a temperature ratio of 0.5. that is:

(3)

(2)

(4)8iA"./t (A,,)

./0 (A,,)

Holman (1986) gives general solutions in terms ofinf1niteseries for transient heal' transfer applicable for differentshapes. These shapes arc: infinite plate, infinite cylinder, andsphere. Broccoli stalk can be approximated as an infinitecylinder. Holman (1986) shows that for Fo > 0.2. the infiniteseries solution for the center temperature of a body. initiallyat a uniform temperature, can be approximated within 1%error llsing a single term:

where:Q = temperature ratio,

8 = h -T~ (OC).

8; =T;-T~ (0C),T/) = temperature of the body (OC).T = temperature of the surface of the body (OC),T j = initial temperature inside the body (OC),C II = constant, a function of Bi and the shape of the

body, andAh = constant, a function of Bi and the shape of the body.

Equation 3 holds for a cylinder having a constant anduniform thermal conductivity and So = ro, the radius of thecylinder. Coefficient Ah can be determined from

creel unifoml throughout thc whole volume of the productand II is considered as the limiting factor to heat transfer. Bydefinition, such a condition does not occur with solid foodwhen performing the precooling process because k of solidfoad -is reJ<uiveJy small compared to h. Between a Bi of 0.2and 10, there is a finite internal and extemal resistance to heattransfer (Mohsenin 1980). Precooling processes for horticul­!llral crops are considered to be within this range.

Another useful non-dimensional parameter in the study ofthe transient heat transfer proccss is the Fourier number, Fo,the square of the ratio of the temperature-wave penetration

depth,(uot) 1/2, at time' to the characteristic dimcnsion of the

body, So'

From Eq. 3, the logmithm of the tcmperature ratio. In (8/0 j ),

plolted against timc should give. after a certain lag time, astraight line where CC is the slope of the linc (ASH RAE1986) and denotes the change in produce temperature perunit time (Gariepy el al. 1987). Guillou (1958) presented CCas a function of the temperature ratios at two times. 'I and (2:

Evaluation of the hypothesis concerning the feasibility ofcalculating Too for a horticultural crop during precooling wasperformed on broccoli stalks. Tests were performcd underlaboratory conditions. Since a broccoli stalk has the smallestsurface-to-volume ratio among olher parts of a broccoli he'ld.it is assulllcd to be the critical part during the precoolingprocess (Jiang et al. 1987). Two sets of five broccoli stalkswere used. The diameter of the stalks ranged from 0.022 to

292 GOYETTE. VIGNEAULT.I>ANNETON and RAGHAVAN

CC =-0.035 and R2=0.9919. By assliming this incorrect T~.the linearity of In(Q) vs lime is lower. as shown by the curvedline results (Too = aOC). Although the correlation coefficients..Ire fairly close together. thcse results dcmonslralc thc impor­tance of choosing the right value of Too. CC is greatly affectcdby an incorrect choicc of the value of Too (changing rrom-0.053 to -0.035 minot).

These results also demonstrate that the linearily of In CQ)vs time begins at a value of Q even greater than 0.5. This waspredictable since the limiting value of Q = O.S was calculatedby using conservativc values ror Hi. This conservative valuepermits the extension of the results to the precooling processof any size and shape of horticultural produce.

The relative efreci of underestimaling to ovcrestimatingthe Too on the 1?1 was calculated (Fig. 2). For a particular Too.there is much less variation in R2 when Too is underestimatedthan when it is overestimated. For values of Teo ranging from3°e to 3.25°C. the same R1of 0.9998 was obtained whenusing four decimal precision. A fifth decimal precision hadto be used to determine Teo at ± 0.1 DC.

0.037 m and the length was 0.125 m. A tcmperature probewas inserted into the center of the stalk. The initial tempera­lUre of the stalks was approxim"llely 24°C. To insure uniformcooling conditions. the t1rst set of broccoli sialks was placcdin a 10 L reservoir filled wilh ice and waler. \Vater wascirculated around the broccoli stalk using a pump. Icc wasadded to mainlain Ihe tempcralure of lhe walcr al 0.1 °e. Thetemperatures of the icc-water mixture and iH the center of lhebroccoli stalk were recorded every minute unlil the tcmpera­turc at the center of the broccoli reached about 3°C. Thesecond set of broccoli stalks was used to tcst the methodunder non-uniform cooling conditions. The broccoli stalkswere lying on an ice bed with about half of the surfacecxposed to ice. The ice bed and broccoli stalks were placedin a cold room at 6°C. The ice surface to air was insulatcdusing a thin styrofoam board to reduce the tempcrature gra­dicnt bClwecn the ambient air and the ice bed. A fan was usedto create air movement abovc the ice bed surface. With thisset up. one side of the broccoli stalks was exposed to O.loC(water-ice mixture) and the other side to 6DC (air). Thetemperature at the center of the broccoli stalk was rccordedevery minute unlil Ihe temperature al lhe cenrer of the broc­coli was stable. Temperature sensors were calibrated with afreezing water bank to obtain a 0.1 °C accuracy. Both Teo andCC wcre calculalCd using a macro developed on MicrosoflExcel VT:'oI. This macro was documenrcd to be uscr friendlyand is available upon request.

1.000

0.996

underestimate Tm overestimate T m

4

RESULTS AND DISCUSSION

Figure I shows Ihe efrect of roo on the relationship betweenIn(Q) and cooling time. 1. The Too obwincd while cooling abroccoli stalk on the ice bed and 6°C rorced air was 3.16°Cwith a CC = -0.053 and R2 = 0.9998. IfT~ is assumed at DoC.as it is assumed while using the liquid ice systcm. wc obtain

0.988

-2.5 +--~--~-~--~---.---

o 20 ~ 60Time (min)

Fig. I. Effed of the choice of the Too on (he linearity of'In(Q) "Inllcd as a funetinn of timc.

5

(8)

4o 2 3

T=<"C)

Fig. 2. Effect of overestimating or underestimating Teo·

Thc Too of Ihe broccoli stalk was also calculated when thetemperature was 110t homogeneous around the stalks. Table II

0.984 +-----,-------r---,.-----r---,

Figure 3 shows the results obtained by plolling In (Q)against time during the hydrocooling of broccoli stalks offive different diametcrs. The time zero of these data is takenal the installt when Q reached a.s. as established by Eq. 3.The temper'lture of Ihe ice-water mixture showed a variationof a.loC throughoul the whole cooling process; this impliesthat the ice melting heat sink compensated very well for theheat lost from the broccoli. The Too of the broccoli stalksvaried betwcen O.I3°C and a.20D C for the five broccoli di­ameters ICsted (Tablc I). The R1 or each best fit regressionline was 0.9982 and higher. This result showed Ihat the linearrcgression method allows the calculation of Too inde­pendently from the size of the produce. Figure -t shows theimportance of the relalion between CC (min· I) and D (m)during the hydrocooling process CEq.S).

T..,=OOC .,cc = -0.035 minR

2=0.9919

T..,=3.16°C .,cc = -0.053 mInR

2= 0.9998

-2.0

-1.5

-1.0

In(0.5)

-0.5

CANADIAN AGRICULTURt\L ENGINEERING Vol. :\8. No.4. October/Novelll1.Jcr/DecemOCr I\)96 2\)3

Table II: Temperature at the surface calculated usingthe surface temperature method and R 2 of thebest fit straight line for broccoli of difl'erentdiameters under liquid ice I forced airh)tbrid cooling process.

o

-0.5

In(0.5)

-1.0

~ -1.5

-2.0

-2.5

diameter (m)

o 0.037

+ 0.034

o 0.032

'" 0.027X 0.022

Diamctcr

(m)

0.0270.0280.0300.0360.037

-0.1

Tcmpcralurc al the surface Too(0C)

3.583.503.623,45

3.2-l

0.99990.99980.99990.99990.9999

x-3.0 +---,------r----,----,----,

o 2 3 4 5

Time (min)Fig. 3. In(Q) as a function of time for broccoli stalks of

different diamelers during the h)'drocoolingIlrocess starting from Q = 0_5_

Table I: Temperature at the surface calculated usingthe surface tcmrerature method refers to theequation and R- of the besl fit straight line 1'01'

broccoli of different diameters underhydrocooling process refers to the equation.

""g~ -0.2

'u=(I)

olJ

~co~ ·0.3

-=ooo

o

o

CC = ·1.7 X10-4 0 .2

R2 = 0.996

c:c. = 0.05

CONCLUSION

A method 10 calculale the avcmge temperature al the surface ofproduce being cooled has becn developed and tested on a broccolistalk. II can be used under both homogcneous and heterogeneousprecooling conditions_ 1l1e method is indcpendent on thc size ofthe producc. It was developed for the panicularcase of a liquid iceprecooling. where the ice might not be unifonnly distributedthroughoutthc mass of produce. 1l1C unifollnity of ice distribution

shows the results obtained for Too varying between 3.24°C 10

3.62°C 1'01' Ihe five broccoli S1alks leSied. The R1 of eachlinear regression is 0.9998 and higher. The broccoli stalkswere supposed (0 be in an environment with an averagetemperature of 3°C. A small variation may have occurredbecause of the difficuliy to expose exactly half of the surfaceof the stalks to each cooling mcdium_ However. it demon·strales that thc dcvelopcd mcthod can be used 10 calculate Tooundcr non-uniform prccooling conclilions.

Diameter

(m)

0.0220.0270.0320.0340.037

Temperature at the surfncc Too(0C)

0.130.200.180.140.17

0.99850.99820.99980.99920.9992

-0.4 +---------,---------,0.02 0.03 0.04

Broccoli stalk diameter (m)Fig.4 Cooling rate coefficient as a function of the

diameter for broccoli stalks during thehydrocooling process.

depends on the size of icc pal1icles and the ice to water ri.llio.Thus. the cooling uniformity has been evaluated by calculal­ing the mean temperature at the surface of produce aldiffereI1l locations inside a box during the precooling proc­esses.

REFERENCES

ASH RAE. 1986. Melhods of precooling froilS. vegetables.and ornamentals. In Refrigeration Sy.'-tem.\- andApp/icariolls Hand/wok. Chapler II. Allanta. GA:Amcrican Socicty of Heating, Refrigerating andAir-Conditioning Engineers. Inc.

Baird. CO., J.J. Gaffney and M.T. Talbo!. 1988. Designcritcria for cfficient and cost cffcctive forccd air coolingsyslCl11s for fruits and vegelables. ASf-Il?AE Transactions94( I): 1434-1454.

Fraser. H. W. 1991. Forced-air rapid cooling oJJresh Ollfario[mil.\' alld \·egetable.\'. AGDEX 202-736. Ministry ofAgriculturc and Food. Toronto. ON.

294 GOYErrE. VIGNEAULT. PANNETON and RAGIIAVAN

Fraser, H.W. and L. Otten. 1992. Predicting 7/8 cooling timesfor peaches by comparing heat transfer modelling andfield measurement methods. ASAE Paper No 92-60 16. St.Joseph. MI: ASAE.

Guillou. R. 1958. Some engineering aspects of cooling fruitsand vegetables. Transactions aflhe ASAE 1(I): 38-39.42.

Gariepy. Y.. G.S.Y. Raghavan and R. Theriault. 1987.Cooling characteristics of cabbage. Canadia"AgriclIllIlral Engineering 29( I):45-50.

Hackert. J.M .. R.Y. Morey and D.R. Tompson. 1987.Precooling of fresh market broccoli. Transactions of till'ASAE 24(4): 1073-1076.

I-Iolman. J.P. 1986. fleat Trall.\!er. Toronto. DN:McGraw-Hili Book Company.

Jiang. 1-1 .• D.R. Thompson and R.Y. Morey. 1987. Finite.elemcnt model of temperature distribution on broccolistalks during forced·air precooling. Tra1lsactioll.\- of theASAE30(5): 1473-1477.

Mohsenin. N.N. 1980. Thermal Properties of Foods andAgriclIllIIra/ Materials. New York. Y: Gordon amiBreach.

Prussia, S.E. and R.L. Shewfelt. 198-1. Icc distribution forimproved quality of leafy greens. ASAE Paper No.84-6014. St. Joseph. MI: ASAE.

Ryall. A.L. and W.J. Lipton. 1972. /-/andling.Transportatio/l.and Storage of Frllits and Vegetahles. Vo/ullle I:Vegetahles and Me/ons. \Vestp0rl. CT: The AVIPublishing Company.

Vigneau I!. C.B. Goyette and G.S.V. Raghavan. 1995.Continuous flow liquid-ice system tested on broccoli.Canadian AgriclIIlIlral Engineering 37:225-230.

NOMENCLATURE

A" ;;;; constant. a function of Bi and the shape of the bodyBi = Biot numberC" = constant. a function of Bi and the shape of the bodyCC = cooling rate cocfficient (min-I)D ; diameter of lhe broccoli stalk (01)Fo = Fourier numberIi = convective hcat transfer coefficicnl (W_m-1_K-1)I-ICT = half cooling time (min).10. .1 I = Bcssel functions of the lirst kind/.: = thennal conductivity of the solid (\V_m-t_K- I)Q = temperature ratior = radial coordinate (m)1'0 = radius for the cylinder (m)R1 = correlation coefficiclllSo = characteristic Icngth of thc body (m)Tt, ; lemperature of the body (DC)T; = initial tempenHure inside the body (OC)Too ;;;; avemge temperature at the surface of a body (OC)t ; time (s)tl . t1 ;;;; time at the installt 1 and 2 (min)0. = statistical level of significance0.0 = thermal diffusivity (m1/s)8 ; Tt, - T_ (DC)8i ; Ti - T_(DC)

C,\NADIAN AGRICULTURAL ENGINEERING Vol. ]X. No.4. OClolX=I/Novcmlll.:r/Dcccmbcr 1996 295

Recirculation of filtered air in pig barnsA.K. LAU '. A.T. VIZCARRA '. K.V. LO' and J. LUYMES2

IDeparlmem of Bio~Reso/{rceEngiHeeting, UIIiversify of I3ril ish Ca/llmbia. Vancouver, Be, Canada \l6T 124: and 2ReSOf/rccManagement Brancll. B.C. Mini.Hry of Agriculfure. Fisheries and Food, Ahhor,I'ford. Be. Callada V3G 2M3. Receil'ecl 6Seprcmher/995: accepled II Scplemher /996.

Lau, A.K., Vizcarra. A.T.. La. K.V. and LllYlllCS. J. 1996. Recircu­lation of filtered air in pig barns. Can. Agric. Eng. 3S:297-30-LRecirculating air filtration systems were tested to reduce e1l1SI andbacteria levels inside the feeder barns of a hog farm in the FraserValley of British Columbia. Design of lhe air riltration systems had10 be reconciled with the existing structures and ventilation systcmin the barns. Multiple fabric filters and a high-voltage. plate-typeelectrostalic precipitator were selecled as dllst collection dt.::viccs furthe grower and finisher barns. respectively. Each barn Wi'S parti­tioned into two halves with one serving as the experimental L1nitequipped wilh Ihc air filtration system and the other as the controlunit. Recirculalion air now rate was set at 20 air changes per hourwhich lies between the summer and winter ventilation rates. Moni­tored parameters included air quality indices (respirable andinhalable dust levels. bacteria counts. and ammonia level), environ­mental and operating parameters (temperature. relative hUlllidity,filter pressure drop, and air now rate), and animal performance(average growth rate, carcass grading. and necropsies), Visits to tht.::farm were conducted regularly once a week during the first 9 monthsand subsequently once every two weeks during the rest of the IR­month period of the study. The air filtration systems effectivelyreduced dust levels and aerial bacteria cOllnts inside the pig barnsalthough their efficiency was dependenl upon air recirculation rIowrate. location, size, and number of inlets and outlets. and humidity.Although the effect on indoor ammonia level was indetenninalc. airfiltration resulted in reduced prevalence of enzootic pneumonia andatrophic rhinilis among the pigs. It also accelerated ;Ulimal growth asevidenced by an increase in average daily mass gain which lranslated10 a shorter number of days 10 market. Air fillration showed nosignificant effecl on the temperature and humidity inside the banl.The eleclroslatic precipilillOr exhibited higher dust removal cffi­ciency during winter and spring timc and WilS nlmost as effeclive asthe fabric filtcr during the other seasons of the year. In terms ofbacteria reduction, the electrostatic precipitator was consistentlymore effective than the fabric filters.

Des systcmes de filtration de l'nir par recirculation Olll etC tcstesafin de reduirc les taux de poussicres el de bacteries :1 rintcricllr desbiltiments (I'cngraisselllent (I'une fennc porcine de la vallee du Fraseren Colombie Brilannique. Le design du systcme de filtration de I'airdevait lenir compte des structures el du systcme de ventilation exis­tants. On a selectionne el instal Ie dans des bfltiments s~parCs deuxsyslcmcs de filtration pour enlevcr la poussiere: tin fi It re cornprcnalllplusicurs epaisseurs de tissu et un prccipitatcllr :\ plaques il haUlvoltage. On avait divise les bflliments en deux: line llloitic expcri­mCI1I;llc avec 1c systcme de filtration a l't:ssai. ct !'autre moitic quiscrvait de temoin. Le taux de recirculation de l'air avait etc fix~ i\ 20changemcnts par heurc, ce qui correspond ;1 un taux de ventilationqui sc sillle cntre ceux d'ctc et d'hiver. Les indices de quaJit~ de rail'(taux de poussicres respirables. nombre de bacteries et concelltrationd';Llllllloniac), les paramelres environneillentallx et Opcf;llionncls(temperature, humiditc relative, baissc de pression il traver!" Ie filtreet debit d'air) ct Ie cornportcment des animaux (taux de croissanct.::moyen, c1asscmcnl des carcasses et autopsies) am ete sllivis. On it

visite les bfltimcnts une fois par semaine lors des 9 prcmicrs mois et

;\ 101IIes les deux semaines dumnt Ie reste de la periode de 18 mois deI'~tllde, Le~ syslcmes de filtration ;\ l'essai ont rCllssi a rcdllire lapoussierc etle nombre de bacteries;1 l'interieur des b:itimenls. L'cr­ficacite dcs systcmes dcpendait du taux de recirculation de l'air. dela localisation, la grosseur el Ie nombre d'cntrces ct de sorties d'airet de I'hurnidite. Bien que Ics impacts sur les concentrations (l'alll­maniac i, I'intcrieur soit indctermincs. les systcllles de filtration ontperm is une diminution des cas de pncumonie enzootique el de rhiniteatrophique t:hez les pores. On a aussi observe une augmentalion dugain de poids moyen joumalier des porcs ce qui se traduit par unraccourcisscmem de la periodc d'engraissemenL Le systeme de fil­tration de rail' n'a pas ell d·impacts significatifs sur la tcrnpcrawrc elrhllmiditc ;1 l'interieur des bfltimellts. Le precipitatellr clectrosta­tique a etc plus efficace que Ie fillre dans I' enlcvcment de la poussiereen hiver ct au printemps et prcsqu'aussi cfficace durant les :lUtressaisons. En tcnnc de reduction des bacleries. Ie prccipitateur eleclro­statique a toujours etc pillS efficacc que Ie filtrc en tisSlJ,

INTRODUCTION

Dust control is an important aspcct of environmental man­agement in swine confinement buildings. Animal health andproductivity as well as human health and comfort arc subject

to harm with contaminatcd cnvironmcnts. Dust Can aCI as anirritant On the respiratory tract and as a carrier of pathogens

that cause cnzootic pneumonia (Mycoplasma Pneumonia)and atrophic rhinitis. the two most common respiratory dis­

eases found in swine herds. Ammonia absorbed intoinhalablc e1ust particles can be carried deep into the lungs.Thesc problems call become especially severe in the wintcrwhen, in an effort to conserve energy, vcntilation ratcs arekcpt at a minimull1 lcvel where dilution of aerial contami­

nants is insufficient.In pig barns. dust is largely organic in nature and origi­

nates from rced. faeccs, animal hair, and skin. It is usually

contaminated with microorganisms - bacteria, fungi. and

viruses, Most bacteria arc of a size < 2~1l1, however, a large

proportion <Ire attached to e1ust panicles of a size> 5 ~m

(Carpenter and Fryer 1990), Viruses and mycoplasma are in

the respirable panicle size range of 0.05 to 0,5 ,um.

Dust particles have been classified according to their abil­ity to penetrate the respiratory systcm (Andersen 1958:;vlercer 197R: Carpenler 1986), Parlicles > Ia ~lm are depos­

ited in the nasal passages. 5-10 ~11l in the upper respiratory

tract and < 5 ~1l11 (respirable particles) in the lungs, About 70to 95% of the tolal number of' dust panicles has been classi­fied as respirable dust (Bundy and Hazen 1975: Honey andMcQuitty 1979). In terms or mass. however. respirable dustpanicles have been reported to constitute only from 3.7 to7.5o/c of the total mass of dust (Barber et al. 1991 b: Phillips

CANADIAN AGRICULTURAL ENGINEERING Vol. 3H. No.~. Ocloocr/Non:lIlhcr/l.>ccclllocr IlJl)6 297

and Thompson 1989~ Heber et al. 1988~ Meyer and Manbeck1986).

The recommended threshold limit values (TLV) for totaldust and respirable dust concentrations are 2.4 mg/m3 and0.23 mg/m3, respectively (Donham et al. 1989), while thesuggested TLV for ammonia is 7 ppm.

In measuring concentrations of airborne bacterial-colony­fonning-particles (BCFP) using an Andersen viable samplerand tryptose agar, Curtis et aI. (1975) found that the averageconcentration of BCFP in swine finisher barns was about5.52 ± 0.08 x 105 cfu/m3. At the same time, total dust levelsas measured by a Staplex high-volume air sampler averaged7.9 ± 1.0 mg/m3.

Feddes et aI. (1983) studied the influence of managementpractices on air quality in swine housing. A forward lightscattering particle counter was used to measure concentrationof dust particles in two size ranges. Dust concentrations(particle size greater than and less than 5 J..lm alike) weresignificantly higher under a lower temperature regime of21.9°C versus 24.8°C; significant differences were alsofound with two feeding methods, dust levels being higherwith floor-feeding due to more vigorous pig movements anddrier pen floors.

In a project involving some 50 fanns in Saskatchewan,total dust level measurements never exceeded 10 mg/m3

(Barber et aI. 1991 b). These measurements are in line withthose of Heber et aI. (1988) who reported an average level of8.1 mg/m3 of dust in mechanically ventilated swine finisherbarns in Kansas. In the Kansas study though, 13 out of 88farm visits resulted in dust level readings in excess of15 mg/m3. Barber et aI. (l99Ia) further measured airbornedust at 16 locations in a partially slatted floor, grower-fin­isher piggery at Silsoe, UK. The mean dust concentration was2.2 mg/m3 and ranged from 1.60 to 2.74 mg/m3.

Several methods can be used for controlling dust withinthe airspace (Mody and lakhete 1990). Reducing the fonna­tion and release rate of dust should be considered beforeother attempts are made; better manure management prac­tices would be helpful here. Ventilation with frequentreplacement of contaminated air by fresh air is anothermethod~ however, this is not economically feasible duringwinter. Morrison and Ogilvie (1990) suggested that the lowwinter ventilation rates of 2 to 8 air changes per hour wereineffective for dust control largely because of pig activity; inthe summer, though, respirable dust levels were reduced by50% from 0.74 to 0.37 m'g/m3 as ventilation rate increasedfrom 12 to 60 air changes per hour.

More recently, Welford et al. (1992) reported the use of anaerodynamic particle sizer system for determining inhalablemass concentration (IMC) of airborne dust in a swine feederroom with a totally slatted floor. IMC was found to be 4.7 ±2.3 mg/m3 based on 18 one-week trials.

The third alternative of dust control methods is to removeairborne dust particles using air cleaning devices. Wet scrub­bing, electrostatic precipitation, and dry fi Itration are thethree principal methods of air cleaning in livestock buildings.Wet scrubbers have high operating costs and require largeareas for the equipment. Dry filtration includes facilities suchas centrifugal/cyclone separators, baghouses, and dry par-

298

ticulate filters. Cyclone separators are only suitable for parti­cles > 10 J..lm and are too costly for livestock ventilationpurposes. Baghouses have high collection efficiencies forrespirable dust but they are not suitable for the humid airconditions typical of fann operations.

The overall goal of the study was to investigate the effectsof recirculating air filtration systems in swine confinementbuildings. Similar work in confinement production units hasbeen reported. For instance, Carpenter and Fryer ( 1990) con­cluded that air filtration using dry filters was a feasiblemethod for reducing dust mass concentration and the numberof bacteria colony-fonning particles by 50-60% in smallrooms for early weaners. A ventilation and recirculationsystem with mechanical filters as designed and studied byHillman et aI. (1992) was deemed effective in reducing theparticle count of airborne respirable aerosols (dust and bac­teria particles down to 0.5 J..lm) in calf nurseries.

The specific objectives of this study were to design, in­stall, and evaluate the performance of electrostaticprecipitator and fabric filter air-cleaning systems in terms ofdust and bacteria removal efficiency and to compare animalgrowth rate and health with and without them.

MATERIALS AND METHODS

The study was conducted at a hog fann in Chilliwack, BritishColumbia over a period of 18 months during 1990-1992.Annual production of the farm was about 3000 feeder pigs.The grower barns were stocked from farrowing operations onthe same farm. The pigs were kept in the grower barn for sixweeks and in the finisher barn for another six weeks prior tomarketing. All throughout, the pigs were self-fed from feed­ers which were located near the fronts of the pens andautomatically, replenished at designated times. Water wasprovided from nipple drinkers in the dunging area. Bothbarns had a north-south orientation and were mechanicallyventilated with exhaust fans.

Previous research work conducted by Donham et aI.(1989) and Barber et al. (1991 b) established that respirable­to-total dust ratio was higher in weanling rooms than infinishing buildings; nevertheless, reducing dust levels infeeder barns was considered more beneficial to producers ineconomic terms. The air filtration systems were thereforeinstalled in the feeder barns. The layout of the building andfiltration systems is shown in Fig. I.

The grower barn was partitioned into two sections. Eachcompartment was 12.2 m long, 10.7 m wide, and 2.4 m high.There were 12 partially slotted-floor pens in each compart­ment, 6 pens to a row on both sides of the central alley. Openpen dividers were 1.0 m high and were made from solid steelrods mounted on concrete (Fig. 2). Each compartment hadfour exhaust (negative pressure) fans which could be stagedto provide for the desired summer ventilation rate (310m3/min maximum) or winter ventilation rate (14 m3/minminimum). Fresh air came in from the attic through 12discontinuous baffle inlets, one for every pen. One compart­ment was kept as the control (unfiltered, abbreviated asCTRL) room, that is, no changes to its existing ventilationsystem were instituted. The other compartment served as theexperimental room (filtered, abbreviated EXPT) where the

LAU. VIZCARRA. LO and LUYMES

IO.67m

IO.67m

3.66m

Experimental Room

airintakc rIretumair

Control Room (unfiltered)

concretelplywoodpartition

conc:retc/plywoodpartition

IO.67m

Grower Bam

l.83m

cipitator. Applied voltage and current levels were found tohave a significant effect on the dust collection efficiency ofan electrostatic precipitator (St. George and Feddes 1995)which increased from 18.5% at 10.3 kVDC (0. I I rnA) to96.4% at 12.1 kVDC (3.0 rnA). As air passes through thepassages between the plates, the dust particles are electricallycharged and adhere to the collection plates. In accordancewith ASHRAE Standard 52-76 (ASHRAE 1985), up to 95%of all the dust at 3 /lm diameter particle size are collected andheld until they can be washed away by a built-in automaticwashing system. To protect the electrostatic filter from beingoverloaded, the dust-laden air from the bam is initially fil­tered by a roll filter (Trion Model 2R65, Trion Co., Sanford,

air intake

Control Room

6.tOm

retumair

Experimental Room (filtered)

trusses 1.22m ole

...- ""e=.;.....-------- \_~~-- .......-------

roll prefilter~electrostaticprecipitator

fan

I2.29mI. ~.~ _~ ~ self-feeder

,.. I U'I!,lii'II.~RH///Tl.L .UJjJ-LW_~ 1_ I I..1.- '- ~ .:..... ___J

L---------.- ~--~.-.- --.

Alley

fabric filtration sys- NorthFinisher Bam South

tern was installed. r---r------------...::.;".:..:.::.:.----------~=::._--._The filtration systemconsisted of primary,secondary, and terti-ary filters. Theprimary and secon-dary filters weremade of 3-ply multi-graduated syntheticfibers (Pacific AirFilters Ltd., Vancou-ver, BC underlicence from theTridim Filter Corp.,).Their respective fil-tration efficiencywas spec-ified as 30-35% and 45-50%.The tertiary filterswere HEPA (high ef­ficiency particulateair) filters that canremove dust with acollection rating of99.9% at 0.3 /lmparticulate size(Whatman Prod-ucts, Allendale, NJ). Fig. 1. Schematic filtration system arrangements.Both the primaryand secondary filters require regular vacuum cleaning beforefinal disposal. The blower installed for the system was aDayton non-overloading blower Model No. 3C073 coupledto a 1.1 kW electric motor. At 1850 rpm and 32 mm staticpressure, the blower was rated to deliver 100 m3/min of airwhich is equivalent to 20 air changes per hour inside theroom. The blower drew dust-laden air through a single 1.20m x 0.30 m opening on the ceiling at about the center of theroom and the filtered air was recirculated back to the roomthrough five sets ofevenly distributed, spring-controlled 0.60 mx 0.30 m baffle inlets. The positions of these baffles relativeto the fresh air inlet baffles can also be seen in Fig. 2.

The finisher bam had the same dimensions and internallayout as the grower bam. It toowas divided into two with oneserving as the experimental unitand the other as the control unit.Each compartment also had 12pens. Construction of the duct­work and air openings in theexperimental room was similarto that in the grower barn ex­peri mental room. The onlydifference was in the air filtra­tion system installed. The mainfilter was an electrostatic pre­cipitator (Trion Model 80, TrionCo., Sanford, NC) which is atwo-stage, high voltage (13kVDC, 1.9 rnA), plate-type pre- Fig. 2. Cross section view of the feeder barn.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OClobcr/Novembcr/Dccember 1996 299

NC) that was automatically advanced by a fixed length oncea day until exhaustion and may be regenerated by automaticwashing. This filtration system 'was serviced by a Daytonnon-overloading blower Model No. 4C333 driven by a 1.5kW motor. At an rpm of 2075, the blower is rated to deliver92 m3/min of air against a static pressure of 19 mm.

The design recirculation air flow rate for both experimen­tal rooms was 95 m3/min equivalent to 20 air changes perhour or 15.4 Ls- Iem-2 of floor area. This rate was selected onthe basis of clean space concept as applied to hospitals or thelike. The quantity of air moved is 7 times the minimumwinter ventilation rate and is about one third of the maximumsummer ventilation rate (Turnbull and Huffman 1987).

Parameters regularly monitored included air quality indi­ces (respirable dust concentration, bacteria counts, andammonia level), environmental and operating parameters(temperature, relative humidity, filter pressure drop, and airflow rate), and animal performance (average daily mass gain,number of days to market, and animal health via slaughterchecks or necropsies). Background air quality data were alsomeasured prior to the installation of the recirculating filtra­tion systems.

A light scattering particle counter "MiniRAM" (miniaturereal-time aerosol monitor) was used for measuring inhalabledust (MIE Inc., Model PDM-3, Bedford, MA). A personalsampler adapter (MIE Inc., Model PDM-2Fs) and air samplerpump (SPECTREX Corp. PAS-3000, Model II) were fittedto the MiniRAM to measure the concentration of respirabledust particles. The adapter had a 10 mm nylon cyclone forpreselecting respirable dust, with a 50% cut off point at 3.5~m when the air pump is operated at 2 L/min. To measure thedust level in any compartment, the MiniRAM was placed atthe center of the room at animal level. The instrument wasleft inside the room for two intervals of 20 minutes each anda time-weighted average over the period was taken alongwith the standard deviation of the readings.

For bacteria sampling, an RCS centrifugal air sampler(Biotest AG, Frankfurt, Germany) was used. Air sampleswere drawn from locations near the center of the room alongthe service alley about one meter from the floor and awayfrom the vicinity of any exhaust fan in operation. Air parti­cles were imparted onto Trypticase Soy Agar strip for totalbacteria counts and onto MacConkey Agar strip for coliformbacteria counts. The bacteria-laden agar strips were incu­bated in a gravity convection dry type bacteriologicalincubator (Blue M Electric Co.) with the temperature main­tained between 30 and 35°C for 48 hours prior to counting.A Darkfield Quebec colony counter (American OpticalModel 3325) was used for counting bacterial colonies.

Ammonia (NH3) concentration in the air was directlymeasured by means of a portable NH3 Gas Detector (CEAInstruments Inc., Emerson, NJ, Model TG-2400KA). A tem­perature sensor and a Jenway HPI humidity probe (accuracyto within 5%) alternately attached to a Fluke Multimeterwere used to monitor indoor and outdoor temperature andrelative humidity.

Inclined vertical manometers (Model No. 25 and No. 40-1 ,Dwyer Instruments Inc., Michigan City, IN) with a range of25 to 75 mm of water column were permanently installed

300

across the fabric filters. Requirements for filter cleaning andreplacement were indicated by the pressure drop across thefilter media. Filter cleaning is done by means of an in-linevacuum system and the dust collected was weighed once aweek. An inclined vertical manometer (Model No. 40-1) wasalso used to measure the pressure drop across the roll filter ofthe electrostatic precipitator.

The barns were visited once a week. Measurements wereusually taken between IOOOh and 1500h at which time theoperator was finished with the morning chores and the pigshad already attained normal daytime activity level. Thenumber of pigs and the extent of ventilation (number of fansin operation) in every room were noted at the time of everydata collection. Farm visits were reduced to once every twoweeks during the last 8 months of the project. As ventilationrate was reduced in winter, more frequent cleaning of up tothree times a week was needed for the primary filters. Thisoperation was sustained after a testing of washable filters wasfound to be unsatisfactory. Even so, the prefilters had to bereplaced every three weeks during the winter months. TheHEPA filters were replaced after one year.

Harvest records of animal live and carcass masses anddays to market (sum of the days the pigs spent in the farrow­ing room, grower and finisher barns) were obtained weeklyfrom the farmer. Two indices were used to evaluate theperformance of the filtration systems in terms of animalhealth (BCMAF 1989). Data arising from necropsies (slaugh­ter checks) were used to determine percent lung scores (theindex for the extent of Enzootic pneumonia) as well as snoutscores (the index for the extent of atrophic Rhinitis). Theextent of lung lesions was examined in each pig and theaverage lung score equals the sum of the percent lung lesionsdivided by the total number of pigs. Snout scores were derivedfrom an examination of nasal turbinates, whereby the totalamount of space on both sides of the nose was given a graderanging from 0-1 (negative) to 5 (severe atrophy).

RESULTS AND DISCUSSION

In the course of the study, outdoor temperature ranged froma low of 2.5°C to a high of 26°C. The temperatures inside thebarns varied from 14 to 30°C, the grower barn being severaldegrees higher than the finisher barn (Figs. 3a and 3b). Therewas no significant difference between the control and experi­mental compartments. The operator varied the setpointtemperature for ventilation between 25 and 30°C. Supple­mental heat was available, but as both barns were normallyunheated, temperature fluctuations inside followed the out­side temperature pattern quite closely. These occasionalspot-check data indicated that the buildings were operated attemperatures above the lower critical temperature for theanimals.

The outdoor relative humidity ranged from 40 to 85%whereas indoor readings were mostly within 60 to 80%; highindoor humidities of 90% were only experienced in July.Relative humidity was generally higher in the grower barnthan in the finisher barn (Figs. 4a and 4b). Again, there wereno significant differences in this environmental factor be­tween the control and experimental rooms. Lemay et al.(1994) cited advice by Nicks and Dechamps (1986) for re­ducing the possibility of infection; besides the management

LAU. VIZCARRA, LO and LUYMES

40 100

-Outdoor-Experimental--Control

_ 30

e!::J10 20...8­E~

10

0+-:--:-...............--+--.--...----+--+-.-_...-.......-4NoY-90 Jan-91 Mar May Jul Sep Noy Jan-92 Mar

MonthFig. 3a. Indoor and outdoor temperatures - grower barn.

-Outdoor- Experimental--Control

20~-:+"':'-+-~---4~_...--+---+_~+--+-........-+-.-..........-tNoY-90 Jan-91 Mar May Jul 8ep Noy Jan-92 Mar

MonthFig. 4a. Indoor and outdoor relative humidity levels­

grower barn.

40100

-Outdoor--Experimental--Control

20 .......-t--+~~+- .....--+-.....--+---+---+-......-t--+~~+- ....Noy-go Jan-91 Mar May Jul Sep Nov Jan-92 Mar

Month

Fig. 4b. Indoor and outdoor relative humidity levels ­finisher barn.

~:a'E::J 60J:

~1iiGi 40a:

tion using the fabric filters ranged from 18 to 64% while thereduction using the electrostatic precipitator ranged from 20to 66%. Dust levels inside the barns were below the thresh­old limit value of 0.23 mg/m3 (Donham et. al. 1989) in thespring and summer but were over the TLV in the fall andwinter. Continuous data (every 30 min recording over a 24 hperiod) were obtained using the MiniRAM on two occasionsin April; similar dust levels were observed and no particulartrends were exhibited with regard to diurnal variation oranimal feeding times.

Total bacteria counts in the experimental units were sig­nificantly lower (p < 0.05) than in their matching controlunits in both grower and finisher barns (Fig. 6). In the growerbam, the filtered room had bacteria total counts that rangedfrom 1.1 x 105 to 2.7 x 105 cfu/m3 while the control room hadbacteria counts ranging from 1.3 x 105 to 5.2 x 105 cfu/m3.

Most of the time, the bacteria level in the finisher barnexperimental compartment was the least with a range of0.8 x 105 to 3.2 x 105 cfu/m3. The corresponding levels in thecontrol compartment ranged from 1.4 x 105 to 4.5 x 105 cfu/m3.These data are lower than the reported average value of 5.52± 0.08 x 105 cfu/m3 (Curtis et al. 1975) and values rangingfrom 6.9 x 105 to 44 x 105 cfu/m3 in pig farms (Personal

-Outdoor- Experimental--Control

10

30

cE!::J! 20Q)CoE~

O~:+":"-+:......--:-:"_~_...-_--+_-.--+-...............--+---lNoy-go Jan-91 Mar May Jul Sep Noy Jan-92 Mar

Month

Fig. 3b. Indoor and outdoor temperatures - finisher barn.

practice of all in-all out, smaller animal density and properventilation, relative humidity is recommended to vary be­tween 60% and 80%.

Over the entire study period, there were more pigs residingin the grower bam than in the finisher bam. The number ofpigs in the grower experimental unit averaged 170 ± 10compared to 125 ± 15 in the finisher experimental unit.However, there were no significant differences betweenCTRL and EXPT units in both barns in terms of the numberof resident pigs.

On a monthly basis, inhalable and respirable dust levels inthe experimental compartment of the grower bam rangedfrom (0.5 to 1.5 mg/m3) and (0.11 to 0.30 mg/m3) respec­tively; the corresponding values in the control room were(0.7 to 2.8 mg/m3) and (0.17 to 0.57 mg/m3). In the finisherbam, the experimental unit had inhalable dust levels rangingfrom 0.4 to 1.7 mg/m3 whereas the control unit had levelsfrom 0.6 to 3.6 mg/m3 (Fig 5). As for respirable dust, thesevalues were (0.09 to 0.31 mg/m3) and (0.13 to 0.84 mg/m3)

respectively. Therefore, on average, respirable dust levelconstituted 15 to 23% of inhalable dust. Statistical analysisby paired t-test showed that dust levels in the experimentalrooms were significantly lower than those in the controlrooms (p < 0.05). These observed values compare well withpublished values. The reduction in inhalable dust concentra-

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/November/December 1996 301

100

_ 0.60- Grower System "C

~ 80 - Finisher System ~ 0.55e.... -~ c 0.50() 'cui 60 C)

'u ~ 0.45

== 'cu 0.40CD"C(;i4OCD> C) 0.350 me ...CD 0.30! 20 ><

0.25May-91 Jul

0MarNoy-90 Mar Jul Noy

Month

Sep Noy

Month

-Control (unfiltered)- Expt (filtered)

Jan-92

Fig. S. Room dust removal efficiency - grower andfinisher barns.

600

Fig. 7a. Records of average daily gains after thefiltration systems were installed.

0.60

OI.J-.....--+-.....--+--+o--f-+--.....--+-.....-......-+o--f-+---4Dec-go Feb Apr Jun Aug Oct Dec Feb

Month

Fig. 6a. Bacterial levels in the grower barn.

. Ol.l--........~I---t---fo-+-- ........~I---t---fo-+--......~~Feb-91 Apr Jun Aug Oct Dec Feb

Month

Fig. 6b. Bacterial levels in the finisher barn.

communication: E.M. Barber, Professor, Agricultural andBioresource Engineering, University of Saskatchewan,Saskatoon, SK). Room bacteria removal efficiencies werecalculated to be 10 to 50% for the fabric filters in thegrower barn and 20 to 52% for the electrostatic filter in the

_ 500C')eC')-~ 400

!!c6 300()

coi: 200S()com 100

600

_ 500C')eC')-~ 400

-~6 300()

coi: 200S()com 100

-Grower~rimental- GroweroCOntrol

-Finisher~rimental- FlnisheroCOntrol

~ 0.55

~~ 0.50'ien 0.45~

~ 0.40CDen 0.35l!! 0.30

0.25.1-,.,. .........., 'T"'I"T ~

Jan-SO Mar May Jul 5ep Noy Jan-91 Mar

Month

Fig. 7b. Records of average daily gains before thefiltration systems were installed.

finisherbarn.Average ammonia level in the grower barn experimental

room was 22.2 ppm in the winter months which dropped to13.5 ppm in the spring. The corresponding readings in thecontrol room were 22.8 ppm and dropped to 9.5 ppm in thespring. The ammonia levels in the finisher barn compart­ments were slightly lower. Winter level was 15 ppm in theexperimental room versus 17 ppm in the control room, whilespring level was reduced to 10 ppm in the experimental roomand to 11 ppm in the control room. All of the ammoniaconcentrations measured exceeded the TLV of 7 ppm asspecified by Donham et al. (1989), though they meet ACGIHStandards (ACGIH 1986).

Animal performance in terms of average daily gain overthe entire growing cycle was assessed from carcass gradingrecords and records of the number of days to market. Withreference to Fig. 7a, between May and October 1991, theaverage daily mass gain was found to have increased by 0.04kg/d. In other words, the number of days to market wasshortened by about 10 days by using recirculating air filtra­tion. Less increase in daily mass gain was detected insubsequent months. Table I further summarizes the seasonalmass gain data for the growers and the finishers separately.In the winter, finishers in the experimental unit had a signifi-

302 LAU, VIZCARRA, LO and LUYMES

Average lung score (percent lung affected)

Table I: Comparison of animal performance· mass gain[kg/d]

Grower Finisher.----~ -- ------

EXPT CTRL EXPT CTRL~------

Winter 0.68 0.66 0.87 0.78Spring 0.61 0.63 0.79 0.76Summer 0.68 0.61 0.90 0.84Fall 0.55 0.59 0.86 0.90Average 0.63 0.62 0.86 OJQ

- ------------

cantly higher mass gain compared to their counterparts in thecontrol unit, whereas in the summer, mass gains were signifi­cantly higher for both the growers and finishers residing inthe experimental units. On average, pigs spending theirgrowing and finishing cycles in filtered rooms gained 0.02kg/d more in mass than those coming from unfiltered rooms.This difference in mass gain is predominantly attributed tothe finisher barn air filtration system (for a gain of 0.04 kg/d)rather than the marginal gain of 0.01 kg/d in the filteredgrower barn. A comparison of records obtained after thefiltration systems were installed (Fig. 7a) with past records(Fig. 7b) revealed an obvious increase in average daily massgain. An examination of the index-to-mass ratio indicated ahigher value for pigs in filtered rooms, though the differenceis not pronounced.

Animal health was found to improve with filtered air in thebam, as evidenced by the reduction in percent lung scores aswell as snout scores. Necropsies (slaughter checks) weredone quarterly coinciding with the seasons. Results are pre­sented in Table II. In most of these tests, the percent lungscores and snout scores for pigs reared in the filtered roomswere lower (better) than those in the unfiltered rooms andimprovements are seen with reference to slaughter .checksperformed before the filtration systems were in place. espe­cially for the lung scores. The summer slaughter checks had

Table II: Results of quarterly necropsies

both scores better for the unfiltered rooms versus the filteredrooms; in December, the lung score was also better withoutfiltration. Overall, the necropsies results are compatible withthe animal performance as illustrated previously in Table Iand Fig. 7a; poorer slaughter check indices are attained fol­lowing an extended period of comparatively less daily massgain in filtered rooms.

CONCLUSIONS

Subject to the conditions of this study, the following conclu­sions can be made.

The air filtration systems effectively reduced dust levelsinside the pig barns. Room dust removal efficiency rangedfrom 18 to 64% for the grower system (fabric filters) andfrom 20 to 66% for the finisher system (electrostatic precipi­tator). In the fall and winter, dust levels were not suppressedto below the threshold limit value of 0.23 mg/m3. The elec­trostatic precipitator only exhibited higher dust removalefficiency in the winter and spring time and was almost aseffective as the fabric filter during the other seasons of theyear. The air filtration systems have also significantly re­duced the concentration of aerial bacteria inside the barns.Room bacteria removal efficiency was 10 to 50% for thegrower system and 20 to 52% for the finisher system. Theelectrostatic precipitator was more effective than the fabricfilters in aerial bacteria reduction throughout the year. Theair filtration systems contributed no significant changes tothe temperature and humidity regimes inside the bam andtheir effect on indoor ammonia levels was indeterminate.

Air filtration lessened the prevalence of enzootic pneumo­nia and atrophic rhinitis among the pigs, especially during thefall and winter. Average lung scores were 35-40% lower(better) for filtered rooms compared to unfiltered rooms.whereas average snout scores were 25-40% lower. Animalgrowth was accelerated; the increase in the average massgain of 0.04 kg/d meant that the number of days to marketcould be shortened by 10 days.

The fabric filters system requires intensive labor for clean­ing and induces higher recurring operating cost uponfr;quent filter replacement, thus offsetting its advantage in alower initial capital cost. Based on the test results, the elec­trostatic precipitator is considered a more cost effectivesystem. However. further tests are needed to determine aproper benefit-to-cost ratio.O<.:t 91 Dec 91Jul91Apr 91Dec 90

Unfiltered 16.08(40)* 15.52(25) 8.21(24) 8.80(15) 9.15(26)Filtered N/A 8.92(25) 11.30(27) 5.69(16) 9.86(29)

*Numbers in brackets denotc thc numbcr of animals that ea<.:hscore represented

------- -_.-

Average snout score

ACKNOWLEDGMENTS

The authors extend their special thanks to the J.W. Hog Farmfor their collaboration in the project and to Mr. Neil Jacksonand Mr. Juergen Pehlke, technicians in the Bio-ResourceEngineering Department. University of British Columbia forinstalling the filtration systems. Thanks are also due to therersonn~1 of the Resource Management Branch and theHealth Management Veterinarians of the B.C. Ministry ofAgriculture, Fisheries and Food for their advice. The finan­ci711 support of the Canada-B.C. Agri-Food RegionalDevelopment Subsidiary Agreement (ARDSA) is gratefullyacknowledged.

0<.:191 De<.: 91Jul91

1.09(23) 1.50(14) 0.72(28)1.63(27) 1.39(14) 0.55(9)

Apr91

1.04(24)0.60(26)

1.09(39)

N/A

Dec 90

UnfilteredFiltered

CANADIAN AGRICULTURAL ENGINEERING' Vol. 3X. No.4. OClobcr/Novcmbcr/Dcccmbcr 1l)lJ6 303

REFERENCES

ACGIH. 1986. Threshold Limit Values for ChemicalSubstances in Work Air. Cincinnati, OH: AmericanConference of Governmental and Industrial Hygienists.

Andersen, A.A. 1958. New sampler for the collection, sizingand enumeration of viable airborne particles. Journal ofBacteriology 76:471-484.

ASHRAE. 1985. Methods of Testing Air Cleaning DevicesUsed in General Ventilation for Removing ParticulateMatter. ASHRAE Standard 52-76. Atlanta, GA:American Society of Heating, Refrigerating andAir-Conditioning Engineers.

Barber, E.M., J.R. Dawson, V.A. Battams and R.A.C. Nicol.1991 a. Spatial variability of airborne and settled dust in apiggery. Journal of Agricultural Engineering Research50:107-127.

Barber, E.M., C.S. Rhodes and J.A. Dosman. 1991b. Asurvey of air quality in Saskatchewan pig buildings.CSAE Paper No. 91-216. Saskatoon, SK: CSAE.

BCMAF. 1989. British Columbia swine health program.Extension notes: November issue. British ColumbiaMinistry of Agriculture and Fisheries, Vancouver, BC.

Bundy, D.S. and T.E. Hazen. 1975. Dust levels in swineconfinement systems associated with different feedingmethods. Transactions of the ASAE 18: 138-144.

Carpenter, G.A. 1986. Dust in livestock buildings - review ofsome aspects. Journal of Agricultural EngineeringResearch 33(4): 227-241.

Carpenter, G.A. and J.T. Fryer. 1990. Air filtration in apiggery: filter design and dust mass balance. Journal ofAgricultural Engineering Research 46: 171-186.

Curtis, S.E., J.D. Drummond, K.W. Kelley, OJ. Grunloh,V.J. Meares, H.W. Norton and A.H. Jensen. 1'975.Diurnal and annual fluctuations of aerial bacterial anddust levels in enclosed swine houses. Journal of AnimalScience 41 (5): 1502-1511.

Donham, J.K., P. Haglind, Y. Peterson, R. Rylander and L.Belin. 1989. Environmental and health studies of workersin Swedish swine confinement buildings. British Journalof Industrial Medicine 40:31-37.

Feddes, JJ.R., J.J. Leonard and J.B. McQuitty. 1983. Theinfluence of selected management practices on heat,moisture and air quality in swine housing. CanadianAgricultural Engineering 25(2): 175-179.

Heber, AJ., M. Stroik, J.M. Faubion and L.H. Willard. 1988.Size distribution and identification of aerial dust particlesin swine finishing buildings. Transactions of the ASAE31 (3):882-887.

304

Hillman, P., K. Gebremedhin and R. Warner. 1992.Ventilation system to minimize airborne bacteria, dust,humidity, and ammonia in calf nurseries. Journal ofDairy Science 75:1305-1312.

Honey, L.F. and J.B. McQuitty. 1979. Some physical factorsaffecting dust concentrations in a pig facility. CanadianAgricultural Engineering 21(1):9-14.

Lemay, S.P., A. Marquis and S. D'Allaire. 1994.Environmental conditions in a grower-finishing swinebuilding ventilated with and without earth tube heatexchanger. Canadian Agricultural Engineering36(4):263-272.

Mercer, T.T. 1978. Respirable fraction of airborne dust:quantitative descriptions, formal definitions andperformance characteristics of samplers matched to them.Journal ofTesting and Evaluation 6(1):9-19.

Meyer, D.J. and H.B. Manbeck. 1986. Dust levels inmechanically ventilated swine barns. ASAE Paper No.86-4042. S1. Joseph, MI: ASAE.

Mody, V. and R. Jakhete. 1990. Dust Control Handbook.New Jersey: Moyes Data Corporation.

Morrison, W.O. and J.R. Ogilvie. 1990. Dust control inanimal facilities for human and animal health. CanadianSociety of Animal Science Annual Meeting, Chilliwack,BC.

Nicks, B.. and P. Dechamps. 1986. Relations entre lesconditions d'habitat et la pathologie infectieuse. AnnalsofVeterinary Medicine 130:485-496.

Phillips, P.A. and B.K. Thompson. 1989. Respirable dust infan and naturally ventilated hog barns. Transactions ofASAE 32(5):1807-1810.

S1. George, S.D. and J.J.R. Feddes. 1995. Removal ofairborne swine dust by electrostatic precipitation.Canadian Agricultural Engineering 37(2): 103-107.

Turnbull J.E. and H.E. Huffman. 1987. Fan ventilationprinciples and rates. Canada Plan Service, M9700.Agiculture Canada, Ottawa, ON.

Weifo!d '. R.A., ~.J.R. Feddes and E.M. Barber. 1992. Pigbulldmg dustmess as affected by canola oil in the feed.Canadian Agricultural Engineering 34(4):365-374.

LAU. VIZCARRA. LO and LUYMES

Dynamics of drying bentonite in superheatedsteam and air as a model food system

S. CENKOWSKI, N.R. BULLEY and C.M FONTAINE

Department ofBiosystems Engineering, 438 Engineering Building, University ofManitoba, Winnipeg, MB, Canada R3T 5V6.Received 18 March 1996; accepted 21 October /996.

Cenkowski, S., Bulley, N.R. and Fontaine, C.M. 1996. Dynamics ofdrying bentonite in superheated steam and air as a model foodsystem. Can. Agric. Eng. 38:305-310. The objective of this researchwas to compare temperature patterns, drying rates, and diffusivitiesof bentonite as a food model with a high concentration of solids driedin hot air and superheated steam at 160°C. In our preliminary inves­tigations on the drying of liquid food droplets in hot air andsuperheated steam, spherical samples of 13.5 mm in diameter wereprepared from chemically stable bentonite paste. In superheatedsteam drying, bentonite samples reached the saturation temperaturefor steam (100°C) after the first minute of drying. During this periodthe samples gained approximately 0.1 kglkg dry basis (db) of mois­ture, due to condensation of water on the surface of the sample. In airdrying at 160°C, the temperature of a similar sized sample graduallyincreased to a wet bulb temperature of 80°C over a 10 min period.The drying rate in the superheated steam was higher by 8 to 10% thanin the 160°C air in the initial stage of drying. However, this situationreversed when samples reached the falling rate-of-drying stage. Forthis period and below moisture content of 0.10 kglkg db, the overalldiffusion coefficient was 50 to 80% higher for samples dried in the160°C air than in superheated steam of the same temperature.

L'objectif de cette recherche etait de comparer Ie comportementdes temperatures, les taux de sechage et les diffusivites de la ben­tonite utilisee pour simuler un aliment it haute teneur en solides quiest secM avec de ('air chaud et de la vapeur surehauffce a 160°C.Lors de nos travaux preliminaires sur Ie seehage de gouttelettesd'aliments liquides avec de I'air ehaud et de la vapeur surehauffee,des eehantillons spMriques de 13.5 mm de diametre ont ete preparesit partir d 'une pate de bentonite chimiquement stable. Pendant Ieseehage it la vapeur surehauffee, les spheres de bentonite ont atteintla temperature de saturation (100°C) apres une minute. Durant cetteperiode, Ie gain de poids des eehantillons a ete de 0.1 kg/kg baseseehe, it cause de la condensation de ('eau it la surface des spheres.Lorsque Ie sechage se faisait it ('air it 160°C. la temperature d'uneehantillon de meme dimension augmentait graduellement jUSqU'ilune temperature humide de 80°C en 10 minutes. Lors de la premierephase de sechage, Ie taux de sechage it la vapeur surchauffce a etc de8 it 10 % superieur it celui du sechage it l'air. Cependant, la situations'est inversce lorsque les cehantillons ont atteint la phase ou Ie tauxde scchage decroit. Lors de eette periode et pour des taux d 'humiditcinferieurs it 0.10 kglkg base seehe, Ie coefficient de diffusion globaldes echantillons seeMs it I'air it 160°C ctait de 50 it 80% superieur itcelui des eehantillons seehcs it la vapeur surehauffee it la memetemperature:

INTRODUCTION

The potential of superheated vapour as a drying medium hasbeen recognized by researchers and by the chemical industry(Wenzel and White 1951; Chu et at. 1953; Lane and Stern1956; Trommelen and Crosby 1970; Faber et at. 1986; Zhang

and Wang 1992). Drying solids by direct contact with super­heated steam has been recommended and determined to bemore efficient than hot air convective drying, providing thatthe dried solids are not temperature sensitive (Sheik­holeslami and Watkinson 1992; Wenzel and White 1951).

Spray drying is a widely used dehydration technique forliquid products containing dissolved solids. Researchershave studied the evaporation from a single drop of liquidwhich was suspended in a controlled environment by meas­uring the change in weight of individual drops during drying(Charlesworth and Marshall 1960; Trommelen and Crosby1970). To pennit the weighing of a droplet evaporating in aflowing drying medium, deflection shields were used at thetime a weight reading was taken. To avoid frequently inter­rupting the flow, several researchers measured the changes inweight over time of gelled spheres of skim milk of 10 mm indiameter, which were placed on a perforated tray in a dryingchamber (Ferrari et at. 1989). The obtained data were used todetennine the drying rates of single droplets. This fundamen­tal information on the rate of water loss in individual dropsduring drying is essential to the design of modem spraydrying units (Ondrey 1995).

Application of heat to food products usually induceschemical changes in the product. This complicates the mathe­matical analysis of the drying process. Bentonite pastes havebeen widely used as model food systems in the study ofthennal processing (Tong and Lentz 1993). The pastes arehomogenous, as well as thermally and chemically stable,making their use advantageous in thennal process investiga­tions. This allows verification of the results of mathematicalheat and mass transfer models of the drying process.

In our preliminary investigations on the drying of liquidfood droplets in hot air and superheated steam and reportedhere, samples were prepared from ~entonite paste. Becauseof its chemical stability, high moisture bentonite paste wasused to simulate the final stage of drying liquid food droplets.The objective of this research was to compare temperaturepatterns, drying rates, and diffusivities of bentonite as a foodmodel with a high concentration of solids dried in hot air andsuperheated steam environment.

APPARATUS

The drying experiments were carried out in a drying chamberdeveloped in the Department of Biosystems Engineering atthe University of Manitoba. The apparatus consists of a steamgenerator, drying chamber, auxiliary equipment to control

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OClober/November/December 1996 305

based on the AACC (1995) procedure and ranged from 1.7 to2.7 kg H20/kg dry basis (kg/kg db).

PROCEDUREMoisture and temperature changes during the drying processwere measured in two separate series of experiments. In oneseries of tests, the mass of the sample was recorded as itdried, and in the other series of tests the temperature at thecentre of the sample was recorded during the course ofdrying. Both types of tests were performed in superheatedsteam and then in hot air at a temperature of 160 ± 2°C. Thisspecific temperature was selected as it is a typical tempera­ture range used in industrial spray drying of liquid egg. Thesamples were dried for 35 min in either superheated steam at0.6 mls or hot air at 1.0 m/s.

Mass change measurements

A spherical sample of bentonite was weighed and then placedin a holder of known mass made of tin wire (Fig. 2). It wasthen hung from a string attached to the scale in the dryingchamber. The mass of the sample in the chamber was moni­tored continuou'sly using a balance connected to a dataacquisition system. The chamber temperatures (TI, T2 andT4, Fig. I) were recorded every 5 s. After the drying wascomplete, the sample was oven dried to obtain the dry massrequired for detennination of the exact initial moisture of thesample and its moisture changes during the course of drying.Calculation of the initial moisture content of the samplebased on its mass detennined before the drying test usuallyled to erroneous results as the sample kept losing its moistureduring handling for several seconds in the chamber whichwas preheated to 160°C.

Temperature measurements

A second sample was prepared from the same mixture as inthe previous test. A thermocouple tip (T3, Fig. 1) was in­serted at the centre of the spherical sample. The sample wasdried in the chamber using the same conditions, however, thechanges of mass were not recorded this time. Because of thelight mass of the sample (1.2 to 1.8 g), the sample wassuitably supported by the thennocouple. The sample wasagain dried in either superheated steam or hot air, and thetemperature at its centre (T3), as well as the temperature inthe chamber at T I and T2 were recorded while the sampledried for 35 min.

chamber

¢ Hot air

T1

~ <:=I Hot air

Scale

Cooling air ~8FanSuperheated steam r- String

Hofrair <lIzTI

T3

T2

t T4Superheated steam

or Hot air

Fig.l. Drying chamber.

Hot air at a temperature of 160 ± 2°C (Fig. 1, T4) wasforced through the air jacket during the entire experiment.This was to ensure adiabatic conditions for the inner chamberwhere the sample was placed. Two thennocouples placed oneither side of the sample, above (Tl) and below (T2), wereused to monitor the temperature in the chamber. The averagetemperature of the two thennocouples was used to control thetemperature in the inner (drying) chamber. An electronicbalance connected to a computer allowed for continuousweighing of the sample. To avoid overheating of the balance,a cooling fan was installed between the chamber and thescale to prevent any rise in temperature due to hot air orsuperheated steam leaking from an opening in the innerchamber. The operating conditions in the drying chamberwere controlled by a computer connected to a data acquisi­tion system. A computer program handled the collection ofall data and regulated the appropriate components to main­tain the pre-determined conditions in the chamber, inresponse to feedback from sensors in the chamber.

and measure flow parameters of steam or hot air, and a dataacquisition system. The drying chamber itself consists ofan inner rectangular chamber and a surrounding air jacket.A simplified diagram of the drying chamber is shown inFig. I.

MATERIALSodium bentonite mined in Wyoming was obtained fromBentonite Corporation in Denver, CO. A mixture of ben­tonite and water was prepared by adding distilled water topure bentonite and thoroughly mixing in a crucible. Theresulting paste was then manually rolled by hand using acircular motion to produce spheres of approximately 12 to 14mm in diameter. Since these samples were not perfectlyspherical, three measurements of their diameter were takenand averaged. The average diameter of individual samples isindicated in the figures. The initial moisture content wasmeasured for each sample using the oven drying method

Wire holder

SampleFig. 2. A sample placed in the wire holder.

306 CENKOWSKI. BULLEY and FONTAINE

where:M(8) = average moisture content of a sphere at any time

(kg/kg db),8 = drying time (s),Mo =initial moisture content (kg/kg db),Me =equilibrium moisture content (kg/kg db),Il = index of summation, andFOm = Fourier number for mass transfer.

The Fourier number for mass transfer was defined as:

where:R = radius of a sphere (m), andDm = mass diffusion coefficient (m2/s).

Since the variables on the left hand side of Eq. I weredetermined experimentally, the mass diffusion coefficientwas calculated after incorporating Eq. 2 into Eq. I and rear­ranging. To simplify the calculations, only the first series wasused. Because of the high temperature of the drying media(160°C) the equilibrium moisture content of the bentonitesamples was zero in our experiments. Thus, after rearrange­ment, Eq. 1 can be written in a symbolic form as:

Dm = R2rl (M(8)] (3)

e Mo

In the analysis of the data, the shrinkage of the spherical

Data analysis

The flow of the drying medium moving upward past thesample creates a "lifting force". To compensate for this ap­parent loss in mass, a series of tests were performed on 10 to15 mm wooden beads instead of the bentonite spheres. Toprevent any changes in mass during testing, the woodenbeads were oven dried prior to being tested in the chamber.

The mass of the wooden bead placed inside the chamberand exposed to superheated steam or hot air was comparedwith the actual mass of the bead for both superheated steamand hot air. The compensation factors were obtained usinglinear regression on the data from the beads. Linear regres­sion was also used to establish that there was no significantdifference, in terms of resistance to flow, between thewooden spheres and the bentonite spheres. It was also deter­mined that spheres of different diameters behaved similarlyin the chamber over the range of tested diameters.

Researchers generally agree that the velocity of the dryingmedium has no or little effect on drying rate for the fallingrate-of-drying period (Jayas et al. 1991). Therefore, the cal­culation of the mass diffusion coefficient for samples driedwith two different media was done for this period. The criti­cal moisture for the falling rate-of-drying period wasdetermined based on the experimental drying curves. Anaverage moisture content of a sphere can be calculated froma series solution of a mass diffusion equation (Crank 1956):

samples was neglected. laros et al. (1992) determined thatthe maximum error in calculation of the diffusion coefficientfor wheat was up to ±3% when compared with the calculationat the constant radius of a kernel.

RESULTS AND DISCUSSION

Figures 3 and 4 show the drying characteristic, temperaturechanges, and drying rates of samples dried in the superheatedsteam and hot air, respectively. The numbers associated witheach curve indicate the run number and the arrows attachedto curves show the corresponding axis.

In the first minute of drying in the superheated steam thesamples gained approximately 0.1 kg/kg db of moisture (Fig.3b, plots I to 4). This was due to condensation of water onthe surface of the sample while it warmed up to the saturationpoint (100°C). The two selected plots of the temperaturehistory (plot No.5 and 6) at the centre of the bentonite sampledrying in superheated steam confirm this. A very sharp risein temperature is seen during the first minute followed by aperiod of fairly stable temperature beginning at 100°C (thesaturation temperature of steam). In the first 18 min of dry­ing, the temperature of a centre of the sample slowlyincreased from 100°C to approximately 110°C. This upwarddrift in sample's temperature was probably caused by thehigh velocity of the superheated steam. In case of drying inthe conditions of the natural convection, temperature of asample remains constant until the end of the constant-dryingperiod (Pabis 1982). Also, our preliminary experiments con­ducted with single water drops dried in the same conditionsshowed that the possible heat conduction through a thermo­couple could be excluded as the droplet temperatureremained constant at the saturation point throughout the en­tire drying period.

The four drying curves obtained in the superheated steamenvironment have approximately the same slope. A graphicaldifferentiation of these curves allowed for determination ofdrying rates. The results of the differentiation are shown inFig. 3a. In the first several minutes of drying the drying ratewas in the range between -0.1 I to -0.13 min- I which corre­sponded to a moisture content range between 2.5 and 1.5kg/kg db. When the moisture of a sample fell below approxi­mately 1.5 kg/kg db, a constant decrease in the drying ratewas observed, although (based on the temperature history ofthe sample) this was still the 1st drying period. It is difficultto determine precisely when the constant rate-of-drying pe­riod (1 st drying period) ends and the falling rate-of-drying(2nd drying period) begins. However, taking under consid­eration the temperature history, shape of dryingcharacteristics, and drying rate, it was concluded that thefalling rate-of-drying period definitely began when the mois­ture content was approximately 0.4 to 0.5 kg/kg db. Thismoisture is also known as the critical moisture (me>.

The drying characteristics of four samples dried in hot air(Fig 4b, plots 7 to 10) have more linear shapes than the dryingcharacteristics measured in the superheated steam environ­ment. Also, no initial gain in moisture was observed. Figure4a shows the results of the graphical differentiation of thefour drying curves (plots 7 to 10). The maximum drying ratewas obtained within the first 4 min of drying and was in therange between -0.10 to -0.12 min-I. In spite of the air having

(I)

(2)Dm 8

FOm =--2­R

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. October/November/December 1996 307

1

1.5

1.0

0.00.0

EC..,;c:Q)

'0IEQ)

8 0.5c:o'enE(5

-UJN'-E

'9o,....-

0.1 0.2

Moisture content, M (kg/kg db)

Fig. 5. The overall diffusion coefficient of sphericalsamples of bentonite dried in 160°C superheatedsteam. The numbers associated with each curvecorrespond to runs I to 4 in Fig. 3b.

by an additional 1 to 3°C in the next several minutes. Basedon the temperature history, it was concluded that the fallingrate-of-drying began at the point where the temperature afterreaching the plateau (between 80 to 83°C), suddenly in­creased sharply. This point occurred between the 12th and16th min of drying. This corresponds to the critical moisturecontent (me> of approximately 0.4 to 0.6 kg/kg db.

The drying rate (Fig. 4a) kept decreasing as the samplemoisture decreased, however, this decrease was slower thanthat for the sample dried in the superheated steam. For exam­ple, at 0.4 kg/kg db moisture for drying in the superheatedsteam and hot air, the drying rates were in the range from-0.04 to -0.06 minot and from -0.06 to -0.08 min-I, respec­tively. In summary, the drying rate in the superheated steamwas higher than in air during the initial stages of drying,however, the situation was reversed in the final stage - in thefalling rate-of-drying period. This could probably explain thedisagreement with respect to the evaporation rates in thesetwo different drying environments (Trommelen and Crosby1970; Wenzel and White 1951). Trommelen and Crosby(1970) reported that evaporation of water from a droplet wasfound to take place more slowly in superheated steam than inair. However, they also indicated the need to take into ac­count the characteristics of the material dried. This laststatement supports the results obtained by Wenzel and White(1951) which indicated that higher drying rates and thermalefficiencies are possible when drying with superheated steamrather than air.

The falling rate-of-drying periods of samples dried in su­perheated steam and hot air were compared by analyzing theoverall diffusion coefficients. Only the portions of the dryingcharacteristics below the critical moisture point (me) wereused in the calculations. The critical moisture range has been

140

40

40

60

80

160

6120 ::-

~100 ~

8­80 E

~

140

2!!"'"--~160

10 20 30

Drying time, 9 (min)

10 20 30

Drying time, 0 (min)

b)

b)

1-02- •3-04- •

00. 0

0 0 ..°$ 0°

d'

~ 0.0 0

$0

..o •o·

"0. 0

e. 0

0°..,

-0.10 -0.05 0

Drying rate, d(M)/dO (min-1)

a)

a)2.0 r-------- 2.0 -y-------------, 180

2.5

0.5

1)'tJ 1.5

I~

li 1.0

~e~ 0.5:=:

Fig. 4. Drying characteristics in the hot air environmentof 160°C (plots 7 to 10), temperature patternsof the geometric centre of three spherical samples(plots 11 to 13), and drying rates correspondingto runs 7 to 10. The average diameter of the samples(Dia) and corresponding initial moisture contents(M0) are indicated in the graph.

3.0 r---------3.0.....------------,180

:=:oJ~ 1.5

§~ 1.0iii15:=:

a higher velocity than the superheated steam, the drying ratein the air was lower by 8 to 10%. This was probably causedby a much slower build up in the temperature of the geomet­ric point of a sample.

Also, Fig. 4b shows three plots of temperature changes(plots 11 to 13) of the geometric centre of the sample. Thesamples were initially at the 1.8 to 2.5 kgjkg db moisturecontent. The temperature of the geometric centre graduallyincreased to approximately 80°C over a 10 min period andthen, due to high velocity of the drying air, slowly increased

Fig. 3. Drying characteristics in the superheated steamenvironment of 160°C (plots 1 to 4), temperaturepatterns of the geometric centre of two samples(plots 5 and 6), and drying rates correspondingto runs 1 to 4. The average diameters of sphericalsamples (Dia) and corresponding initial moisturecontents (Mo) are indicated in the graph.

308 CENKOWSKI, BULLEY and FONTAINE

The relationships in Eq. 4 were obtained for ME (0.050,

Experiment RegressionAirdrying _

SS drying 0

0.1 0.2

Moisture content, M (kg/kg db)The comparison of overall diffusion coefficientsfor spherical samples of bentonite dried at 160°Cin the superheated steam and hot air environment.The symbols are the averages of the experimentaldata and the lines are the best fit lines to theexperimental data.

0.00.0

ECl

2.0

.,;

5i 1.0'0!EQ)

8§ 0.5'en~CS

~E

Ojlo 1.5T""-

Fig. 7.

CONCLUSIONS

For superheated steam drying, the temperature in the centreof approximately 13.5 mm diameter bentonite samplesreached the saturation point for steam (100°C) after the firstminute of drying and then slowly increased by 10°C duringthe first rate-of-drying period. For air drying at 160°C, thetemperature in the centre of a similar sized sample graduallyincreased to 80°C over a 10 min period and then, due to highair velocity, slowly increased, reaching 81 to 83°C at the endof the Ist period of drying.

In the first minute of drying in superheated steam thesamples gained approximately 0.1 kg/kg db of moisture. Thiswas due to condensation of water on the surface of the samplewhile it warmed up to the saturation point (100°C).

The beginning of the falling rate-of-drying stage, duringdrying in both media, was marked by a sharp increase in thetemperature of the geometric centre of a sample. This corre­sponded to a critical moisture content ranging between 0.4and 0.6 kg/kg db.

The drying rate in the superheated steam was higher by 8to 10% than in the 160°C air in the initial stage of drying.However, the situation was reversed when samples reachedthe falling rate-of-drying. For this period the overall diffu­sion coefficient increased more rapidly with moisture

0.225 kg/kg db) and the drying media temperature of 160°C.Based on Fig. 7, it was concluded that, in the final stage

of drying for samples dried in the hot air, the overall diffu­sion coefficieIit increased more rapidly with moisturedecrease than in the superheated steam and was 50 to 80%higher for samples being at moisture content below 0.10kg/kg db.

0.20.1o.0 L..-.--'-----'-_L--'-----'-----''---..L-~____l_..J.__'__.L_

0.0

.,;c:Q)

'0!EQ)

8 1.0c:o'en~o

~E

bT""

- 2.0E

Cl

Moisture content, M (kg/kg db)Fig. 6. The overall diffusion coefficient of spherical

samples of bentonite dried in 160°C hot air.The numbers associated with each curve correspondto runs 7 to lOin Fig. 4b.

3.0

already discussed, and the me of 0.4 kg/kg db was used in ourcalculations. Figures 5 and 6 show the overall diffusioncoefficient as a function of moisture content as calculated forsamples dried in the superheated steam and hot air environ­ments, respectively. The numbers associated with each curvecorrespond to drying characteristics in Figs. 3b and 4b. Thecharacteristics follow a trend reported in the literature (Jaroset al. 1991; Fortes et al. 1981; Keey 1972). The overalldiffusivity increased with a decrease in moisture up to ap­proximately 0.02 or 0.04 kg/kg db for the samples dried in thehot air or superheated steam, respectively, and then droppedsharply. Fortes et al. (1981) analyzed liquid diffusivity inwheat kernels and concluded that the vapour-phase diffusiv­ity falls with increasing moisture in wheat in the rangebetween 0.05 to 0.25 kg/kg db. This explanation follows thetrend observed in our experiments, however, no attempt wasmade to separate the liquid from vapour diffusion.

Based on the characteristics shown in Figs. 5 and 6, theaverage overall diffusivities were calculated for the samplesdried in the two environments. The calculations were con­ducted for the 0.05 to 0.025 kg/kg db moisture range. Theresults are shown in Fig. 7. The symbols are the averageoverall diffusivities and the vertical bars indicate the 95%confidence intervals. The solid line and the dashed line arethe best fit lines describing the overall diffusion coefficientas a function of moisture content:

Air drying: Dm =-8.21 x 10-8 M + 2.04 x 10-8; m2/s

Superheated steam drying:Dm = -4.50 x 10-8 M + 1.20 x 10-8; m2/s

(4)

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OClober/November/Dccember 1996 309

decrease for samples dried in the 160°C air than in super­heated steam at the same temperature and was 50 to 80%higher for moisture contents below 0.10 kg/kg db.

ACKNOWLEDGEMENT

The authors acknowledge the Natural Sciences and Engi­neering Research Council of Canada for providing funds tosupport this research.

REFERENCES

AACC. 1995. Method: 44-15A. Moisture - air-oven method.,In Approved Methods of the American Association ofCereal Chemists. St. Paul, MN: American Association ofCereal Chemists.

Charlesworth, D.H. and W.R. Marshall, Jr. 1960.Evaporation from drops containing dissolved solids.AIChE Journal 6:9-23.

Chu, C., J.A.M. Lane and D. Conklin. 1953. Evaporation ofliquids into their superheated vapours. Industrial andEngineering Chemistry 45: 158"6-1591.

Crank, J. 1956. The Mathematics of Diffusion. London,England: Oxford University Press Amen House.

Faber. E.F. , M.D. Heydenrych, R.U.!. Seppa and R.E.Hicks. 1986. A techno-economic comparison of air andsteam drying. In Drying '86, ed. A.S. Mujumdar,VoI.2:588-594. New York, NY: Hemisphere PublishingCorporation.

Ferrari, G., G. Meerdink and P. Walstra. 1989. Dryingkinetics for a single droplet of skim-milk. Journal ofFood Engineering 10:215-230.

Fortes, M., M.R. Okos and J.R. Barret, Jr. 1981. Heat andmass transfer analysis of intra-kernel wheat drying andrewetting. Journal ofAgricultural Engineering Research26: 109-125.

310

Jaros M, S. Cenkowski, D.S. Jayas and S. Pabis. 1992. Amethod of determination of the diffusion coefficientbased on kernel moisture content and its temperature.Drying Technology 10:213-221.

Jayas, D.S., S. Cenkowski, S. Pabis and W.E. Muir. 1991.Review of thin-layer drying and wetting equations.Drying Technology 9:551-588.

Keey, R.B. 1972. Drying: Principles and Practice. Toronto,ON: Pergamon Press.

Lane, A.M. and S. Stern. 1956. Application ofsuperheated-vapor atmospheres to drying. MechanicalEngineering 78:423-426.

Ondrey, G. 1995. Models demistify spray drying. ChemicalEngineering 102:30-31.

Pabis, S. 1982. Theory of the Convective Drying ofAgricultural Products. Warsaw, Poland: PWRiL.

Sheikholeslami, R. and A.P. Watkinson. 1992. Convectivedrying of wood-waste in air and superheated steam. TheCanadian Journal ofChemical Engineering 70:470-482.

Tong, C.H. and R.R. Lentz. 1993. Dielectric properties ofbentonite pastes as a function of temperature. Journal ofFood Processing and Preservation 17:139-145.

Trommelen, A.M. and E.J. Crosby. 1970. Evaporation anddrying of drops in superheated vapours. AIChE Journal16:857-867.

Wenzel, L. and R.R. White. 1951. Drying granular solids insuperheated steam. Industrial and EngineeringChemistry 43:1829-1837.

Zhang, G.S. and H.T. Wang. 1992. Energy analysis ofsuper-heated steam Yankee dryer. In Drying' 92, ed. A.S.Mujumdar, 1108-1114. New York, NY: Elsevier SciencePublishers B.V.

CENKOWSKI, BULLEY and FONTAINE

TECHNICAL NOTE

A belt-roller mechanism for soil clodreduction on a potato harvester

a.c. MISENER and L.P. McMILLAN

Agriculture and Agri-Food Canada Research Centre, P.O. Box 20280, Fredericton, NB, Canada E3B 427. Received 21 May1996; accepted 2I October 1996.

Misener, G.c. and McMillan, L.P. 1996. A belt-roller mechanismfor soil clod reduction on a potato harvester. Can. Agric. Eng.38:311-314. A clod crusher-elevator was developed to operate at theend of the primary conveyor of a potato harvester. The mechanismwas designed to accelerate the material leaving the primary bed whileexerting pressure on the mixture in order that soil clods would bebroken into smaller sizes that would fall through the slots of thesucceeding conveyors. During the process, the potatoes were ele­vated an additional 1.7 m by the first prototype and 1.0 m by thesecond prototype when compared to the conventional system. Themechanism successfully reduced the amount of clods by 79.9% ascompared to a conventional primary and cross conveyor arrange­ment. The amount of soil that was recovered with the potatoes wasalso reduced (48.6%) when the clod crusher-elevator was utilized.However, the level of mechanical injury imparted to the potatoesincreased by 69.8% when the mechanism was used.

On a mis au point un systeme combine emotteuse-elevateur tixe itla fin du transporteur principal d'une arracheuse de pommes de terre.Le mecanisme est con~u pour accelerer Ie passage des materiaux quiquittent Ie premier tablier tout en excr~ant une pression sur Iemelange de fa~on it briser les mottes en plus petits fragments pourqu'elles passent a travers les ouvertures des transporteurs suivants.Au cours du processus, Ie premier prototype eleve les pommcs detcrre 1,7 m plus haut que Ie systeme classique et Ie deuxieme proto­type, 1,0 m plus haut. Le mecanisme permet de reduire la quantite demottes de 79,9%, comparativement a un systeme classique trans­porteur principal-transporteur transversal. La quantite de sol laissccdans les pommes de terre est egalement reduite (48,6%) lorsque Iesysteme emotteuse-elevateur est utilise, mais les dommages d'orig­ine mecanique infligees aux pommes de terre augmentent dc 69,8%.

INTRODUCTION

The formation of soil clods during potato production is gen­erally caused by the smearing and compacting during theridging operation (McRae 1980). These operations are oftenconducted under adverse conditions in eastern Canada whichfurther aggravate the problem. At harvest, the separation ofclods from potatoes is difficult and the mechanisms em­ployed for separation can severely injure the potatoes(Campbell 1980). Some clod removal is obtained by meansof agitation on the primary bed where the weaker clods arefrequently broken into smaller pieces. However, the effi­ciency with which loose soil is sieved between the bars of theprimary bed of a harvester is inevitably reduced by the pres­ence of clods as they reduce the effective web area openings(Campbell 1980).

McPhee (1994) investigated the use of a series of rotatingparallel rollers to achieve separation of clods from potatoes.The mechanism consisted of alternating plain and spiral rub­ber rollers and worked on the principle that friction betweenthe clods and the rollers forces the clods through the smallgap (10 mm) between the rollers while the potatoes roll overthe top and off the end. The slope and speed of the rollerswere adjustable. The results from the study indicated that therollers removed 60-80% of the clods. Sturenburg (1959)investigated the use of air-inflated rollers for crushing clods.The study suggested that the efficiency of the method andlevel of mechanical injury caused to the potatoes dependedon the hardness of the clods.

Sorokin and Maksimov (1979) evaluated a clod crusher­elevator for both crushing clods and elevating potatoes. Themethod employed rollers running on a conveyor belt whichmoved at a speed" of 2-3 m/s. The device appeared to havedisintegrated clods while elevating potatoes to a height of900-1800 mm. Damage to the potatoes was reduced in com­parison with the roller type clod crushers.

The objectives of the study reported in this technical notewere to develop and evaluate a clod separation devicemounted on a harvester and to further investigate the possi­bility of elevating potatoes by the method of Sorokin andMaksimov (1979). Both the efficiency of separation andlevel of mechanical injury of potatoes were determined.

MATERIALS AND METHODS

Machine description

The two row test machine consisted of a share and full widthprimary bed approximately 2 m in length. At the rear of theprimary bed, a cross conveyor was positioned similar to theconfiguration on a conventional windrower but without asecondary conveyor or deviner. The clod crusher-elevatorwas mounted to receive the material from one of the two rowsof potatoes. Positioned at 45° to the horizontal, it deliveredthe product to a second cross conveyor similar to the devicedescribed by Sorokin and Maksimov (1979). This arrange­ment allowed one row of potatoes to be sampled at the end ofthe cross conveyor similar to a conventional windrower andthe adjacent row to be sampled after the clod crusher-eleva­tor.

CANADIAN AGRICULTURAL ENGINEERING Vol. 38, No.4, October/November/Deccmbcr 1996 311

Speed (m/s)

Table I. Machine operational parameters

height from the conventional arrangement that the pOlatoeswere elevatcd was 1.0 m.

The tcst machine was operated with the same operationalparameters in both ycars with the exception of the speed orthe inclined belt (Table I). The primary conveyor operated at0.91 m/s and the cross conveyors at 0.75 m/s. In year one. theclod crusher-elevator belt was operated at 4.0 m/s. This wasreduced 10 2.7 m/s in year two. The draper chain conveyoradded in year 2 was operated at 1.2 m/s. The three forwardspecds of the harvester during the tcsts were 0.45. 0.90, and1.35 m/s. Each test was replicated rour times.

Ycar Year 2

0.45 0.450.90 0.901.35 1.35

0.91 0.914.00 2.70N/A 1.200.75 0.75

Forward specd

EXllcrimcntal IH·occdure

For both years or the two-year study. processing potatoes (cv.Russet Burbank) were grown at the Fredericton RcsearchCentre following standard crop managemcnt practiccs. Avinc killing trcatmcnt was applied in mid-September. Thechemical desiccant diquat was applied at 0.75 kg/h ..\. Pota­lacs were grown in solid blocks for harvest with the testmachine. Plots were organized on a completely random basisalong the potato rows. A canvas sheet W<lS placed on theground to collect allmatcrial from the lower cross conveyor.A plastic containcr was held on a sliding bracket to collectmaterial I"rom the upper cross conveyor. As thc machinetravelled across the field. two rows of potatoes were dug andthe material was deposited back to the groLlnd. When thesample plot W<lS approached. material was deposited on theground sheet and into the plastic container. respectively.This procedure was repeated for each forward speed and eachreplicalion.

The field operations were performed in Fundy clay soil.which is compact clay in the upper horizons with anunderly­ing clay subsoil starting at 400 mm depth (Rees and Fahmy1984).

The samples were tagged and sorted into component parts(soil. clods, stones. tubers, and vines). To determine the makeup of each sample collected, a sicve was constructed rrom a42- mm-pitch draper chain. The chain rods were J I mmdiametcr with an opening of 31 111m between the rods. Thesamples were gently placed on the sievc and clods and tuberswcre collcclcd while allowing soil to drop through the open­ings to a collection tray. The potatoes wcre stored at roomtcmpcraturc for an additional two weeks before they wereevaluated for mechanical injury.

Primary conveyorClod crusher-elevator belt2nd draper conveyorRear cross conveyors

Machine paramctcr

During the second year of testing the length or the 45°sloped belt was reduced to 1000 111m. The lower foam rollerremained in its original position. The distance between thetwo roam rollers was reduced to 500 mm. leaving the beltextended past the top roller 500 mill. A 750- mm-wide,42-mJ11-pitch rubber covered draper chain. 1000 mm long.was added at ,111 angle or 15° to the horizontal to receive thetubers from the rubber belt and continucd to move the prod­uct 10 the rear cross conveyor. The same cross conveyor usedin the previous year was repositioned to receive the materialfrom this draper chain. With this arrangement. the additional

Fig. I. Schematic diagram of clod reducing device.

The clod crusher-clevator consisted of a flal rubber belt600 mm wide over which two rubber covered foam rollersrotated at the same surface velocity as the belt. The elevatorwas inclined at I S° for the first 400 mm portion where il wasin contact with the first foam roller. Aftcr contact with thefirst roller, the belt was inclined at an angle of 45°. A sccondfoam roller was placed on the belt a further 1200 111m up thcslopc from the first roller. The rubber belted conveyor cx­tended beyond the second roller 1200 mm. By adjusling thespeed of the belt and the foam rollers, the pOlato. clod, andsoil mixture could be accelerated such that the mixture wouldconvey up the slope of 45°. The vertical velocity componentof the produci approached zero at the top of the conveyor.Thc potatoes were elevatcd an additional 1.7 m when com­pared to the conventional arrangemenL A schemal ic view ofIhe assembly is presented in Fig. I.

The rollers wcre construcled from foam rubber rings 330mm in outside diameter and 150 mrn thick. Several rings ofthe foam rubber wcre placed on a 76 mm diameter tube. Theends of the roller were capped with 19-ml11-thick plywood(330 mm diameter) 10 provide a surface for the roller to rideon the belting without compressing the foam. The assemblywas covered by a natural rubber tube and sealed againstmoisture infiltration.

312 MISENER and McMILLAN

For mechanical injury assessment, the method ofThornton(1969) was employed. Tuber damage was determined byusing a potato peeler to remove a slice of approximately 3mm thickness. Damage was classified as: (a) undamaged, (b)scuffed or skinned - skin only broken, (c) slightly or peeler- flesh damage removed by a 3-mm-deep stroke of the peeler,(d) severely damaged - damage to flesh which was not re­moved with one peeler stroke, and (e) black spot. A damageindex was calculated based on the percentage of tubers ineach category multiplied by 0, I, 3, 7, and 5, respectively.The values were then added to give a total damage index(Robertson 1970; McGechan 1980).

The pressure that the foam exerted on a tuber as it passedbetween the foam roller and belting was measured in thelaboratory. Tubers of various sizes were pressed into thefoam and the compressive force measured. A foam roller waspositioned on the base of a Universal Testing Machine,model MC3000 (Nene Instruments Inc., Wellingborough,England). A flat piece of rubber belting with a metal backingwas attached to a 1 kN load cell on the movable head of thetesting machine. The belting was covered with a non-dryinglayout dye, 35v Prussion blue (Permatex Limited,Orangeville, ON). A tuber was positioned on the foam rollerand covered with a soft paper towel. The movable head waslowered at a fixed speed of 500 mm per minute until the tuberwas compressed into the foam roller a distance equal to itsdiameter as would be the case on the clod crusher. Theresulting compression force was recorded on a computerusing software provided with the testing machine. The papertowel was removed after raising the movable head. The dyeon the belting resulted in a stain on the paper towel equal to

Table II. Summary of performance data

the contact area between the tuber and the belting. This areawas measured by tracing the stained area with a digitizerpad, model GraphicMaster 11 (Numonics Corp.,Montgomeryville, PA) connected to a personal computerusing AutoCAD, Ver. 13 software (Auto desk, Sausalito,CA). Twenty tubers were selected with an average mass of233.6 ± 69.8 g.

RESULTS AND DISCUSSION

The performance of the clod elimination apparatus in fieldconditions was monitored over the two year study. In general,the clod crusher-elevator functioned well and adjusted tovarying soil conditions. It was observed that the mixture ofpotatoes, clods, and soil leaving the primary bed flowedevenly into the roller-belting device and moved without hesi­tation up the inclined belt conveyor. Material was depositedon the adjacent conveyor in an efficient manner. Vines werealso effectively pulled in by the roller-belting device andmoved up the inclined conveyor. Sufficient pressure wasdeveloped between the rollers and potatoes to achieve accel­eration of the soil, clods, and potatoes.

The effectiveness of the clod crusher-elevator at reducingthe percentage of clods is given in Table II. In all tests, therewas a reduction in the percentage of clods and the amount ofsoil collected when compared with the standard harvesterarrangement. The higher moisture content (20.2%) of the soilin the third test in the first year resulted in less soil removedas compared to the other tests. Clods were totally eliminatedat the slow forward speed (0.45 m/s) during the second yearof the study; whereas, only 33.2% were eliminated at aforward speed of 0.45 mls during the first year. The lower soil

Year I

Year 2

Forward speed Soil moisture Mechanical injury (damage index) 1 Clod reduction2 Soil reduction2

content(m/s) (%, db) Standard Clod crusher (%) (%)

0.45 19.1 220.3ab 319.6abc 90.7ab 63.6ab0.90 19.1 146.8b 293.0abc 83.6ab 43.2ab1.35 19.1 143.9ab 303.3abc 85.2ab 49.0ab

0.45 10.5 139.2b 308.2abc 33.2c 48.4ab0.90 10.5 123.lb 299.2abc 61.6abc 62.5ab1.35 10.5 120.0b 355.5bc 48.4bc 39.7ab

0.45 20.2 190.0ab 309.0abc 97.9a 16.2ab0.90 20.2 209.5ab 243.2c 91.7ab 6.0b1.35 20.2 212.3ab 249.4bc 93.4ab 32.7ab

0.45 19.1 203.9ab 364.4a 100.0a 76.3a0.90 19.1 264.9a 339.lab 89.2ab 77.1a1.35 19.1 109.8b 286.9abc 87.1ab 69.0ab

--------

1 Means with the same letter are not significantly different at the P=0.05 level according to Duncan's Multiple Range Test2 Clod or soil reduction was determined by wt of clods (standard) - wt of clods (clod crusher)

x 100wt of clods (standard)

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OctoberlNovembcrlDccember 1996 313

moisture content during the second set of tests of the firstyear of the study suggests that the clods had a higher strengththan at the higher moisture content. Decreasing the distancebetween the two rollers did not appear to have any effect onthe performance of the device in eliminating clods.

One disadvantage with the device appears to be the in­crease in the level of mechanical injury of the potatoes. Onaverage, mechanical injury increased by 69.8% over thestandard arrangement. However, the level of mechanical in­jury was lower than that found on commercial harvesters.Misener et al. (1989) found that the average injury index was368.6 for commercial harvesters operating in eastern Canada.The average index for the clod reducing device was 297.3.Reducing the distance between the rollers did not affect thelevel of mechanical injury (Table II).

Mohsenin (1965) found that a mean normal pressure rangeof 241 - 326 kPa was required before skinning was initiatedby potatoes rubbing against each other. Average pressurebetween the rollers and potatoes was measured as 181 kPa ±55 kPa which was less than the normal pressures required forskinning. The amount of stones mixed with the potatoes(mean 11.4%) may have contributed to the injury of potatoesas they passed between the rollers and belting as well as atthe transition points between conveyors. .

CONCLUSIONS

The clod crusher-elevator device performed well under fieldconditions for reducing both the number of clods and theamount of soil on the test harvester. The key components ofthe device were a pair of foam rollers which operated on abelted conveyor to facilitate acceleration of the material andthe breaking of soil clods. The amount of soil clods wasreduced by 79.9% when compared to the standard harvester.Similarily, the amount of soil reaching the final cross con­veyor was reduced by 48.6%. During the process, thepotatoes were elevated an additional 1.7 m and 1.0 m by thefirst and second prototype units, respectively, when com­pared to the conventional arrangement. However,mechanical injury increased by 69.8%. Work needs to bedirected towards reducing the level of mechanical injurycaused to potatoes by the clod reducing device.

314

REFERENCES

Campbell, DJ. 1980. The clod problem in potato production.Technical report. Scottish Institute of AgriculturalEngineering, Penicuik, Scotland.

McGechan, M.B. 1980. An investigation into the damagesustained by different varieties of potatoes duringriddling to remove soil. Journal of AgriculturalEngineering Research 25:345-353.

McPhee, J. 1994. A different approach to clod separation forsingle row harvesters. Potato Australia 5:34-35.

McRae, D.C. 1980. Potatoes 2, Advances in Mechanization.SPAN 23(2):68-70.

Misener, G.C., C.D. McLeod, J.R. Walsh and C.F. Everett.1989. Effect of potato harvesting injury on post-storagemarketability. Canadian Agricultural Engineering31:7-10.

Mohsenin, N.N. 1965. Friction force and pressure causing"skinning" of potatoes. American Potato Journal42(3):83-88.

Rees, H. And S. Fahmy. 1984. Soils of the AgricultureCanada Research Station, Fredericton, NB. AgricultureCanada Land Resource and Research Institute,Fredericton, NB.

Robertson, I.M. 1970. Assessment of damage in potatotubers. Dept. Note SIN/60. Scottish Institute ofAgricultural Engineering, Penicuik, Scotland.

Sorokin, A.A. and B.I. Maksimov. 1979. The design of anelevator clod crusher for a potato harvester.Mekhanizatsiya i elektrifikatsiya sotsialisticheskogo.'IeI'skogo khozyaistva 37(9): 14-15.

Sturenburg, P. 1959. Investigations on air-inflated rollers forthe breaking of clods in potato harvesters. Journal of .Agricultural Engineering Research 4(1):88-90.

Thornton, R.E. 1969. Problems and solutions on bruising ofpotatoes in harvesting and handling. Paper presented atthe 1969 Annual Meeting of the Pacific NorthwestSection. St. Joseph, MI: ASAE.

MISENER and McMILLAN

CANADIAN AGRICULTURAL ENGINEERING1996

Volume 38INDEX

Soil and Water

Modeling soil water content and pressure head with SWACROP in potato fields- M.H. Mahdian and J. Gallichand

Modelling cool season soil water erosion on a fine sandy loam soil in Prince Edward Island- l.R. Burney and Linnell M. Edwards

Estimation of hydraulic properties of aggregated soils using a two-domain approach- B. Wagner, V.R. Tarnawski, G. Wessolek and R. Plagge

Response functions for grain yield from spring-sown wheats grown in saline rooting media- H. Steppuhn, K. Wall, V. Rasiah and Y.W. Jame

Power and Machinery

Dynamic analysis of a swather/windrower header- T.G. Crowe and G.E. Laliberte

Quantification of mechanical forage conditioning by compressibility- P. Savoie, M. Roberge and D. Tremblay

A test bench for vacuuming insects from plants- R. Chagnon and C. Vincent

Application of unsaturated soil mechanics for agricultural conditions- D. Wulfsohn, B.A. Adams and D.G. Fredlund

Round bale ensilage of intensively conditioned forage- P. Savoie, D. Tremblay, E. Charmley and R. Theriault

Modeling airflow inside and ar.ound hoods used for pneumatic control of pest insects.Part I: Development of a finite element model

- M. Khelifi, J.-L. Robert and C. Lague

Modeling airflow inside and around hoods used for pneumatic control of pest insects.Part II: Application and validation of the model

- M. Khelifi, J.-L. Robert and C. Lague

Wind tunnel for spray drift studies- M. Farooq, D. Wulfsohn and R.I. Ford

Energy and Processing

Breakage susceptibility studies on alfalfa and animal feed pellets- T.B. Larsen, S. Sokhansanj, R.T. PatH and W.I. Crerar

Effect of fines on storage and handling properties of alfalfa pellets- 0.0. Fasina and S. Sokhansanj

Bulk and handling properties of hulless barley- M. Rameshbabu, D.S. Jayas, W.E. Muir, N.D.G. White and J.T. Mills

Heat of respiration of Cryptolestes Ferrugineus (Stephens) adults and larvae in stored wheat- R. Cofie-Agblor, W.E. Muir, Q. Zhang and R.N. Sinha

Apparent flow coefficient of carbon dioxide through wheat bulks- K. Alagusundaram, D.S. Jayas, W.E. Muir, N.D.G. White and R.N. Sinha

149

241

249

13

157

167

173

257

265

273

283

21

25

31

37

69

CANADIAN AGRICULTURAL ENGINEERING Vol. 38. No.4. OClobcr/November/Decembcr 1996 315

Finite element model of three-dimensional movement of carbon dioxide in grain bins- K. Alagusundaram, D.S. Jayas. W.E. Muir, N.D.G. White and R.N. Sinha

Distribution of introduced carbon dioxide through stored wheat bulks ~ a pilot scale study- K. Alagusundaram, D.S. Jayas, W.E. Muir, N.D.G. White and R.N. Sinha

Average convectlvc--pore velocity of carbon dioxide gas through grain bulks- c.L. Bundus, D.S. Jayas, W.E. Muir, N.D.G. White and D. Ruth

Comparison and sensitivity analyses of models for simulating aeration of stored wheat- R. Sinicio and W.E. Muir

Compression characteristics of alfalfa cubes- R.T. Patil, S. Sokhansanj, M.H. Khostaghaza and L.G. Tabil, JI'.

Size and shape related characteristics of alfalfa grind- W. Yang. S. Sokhansanj, W.J. Crerar and S. Rohani

Method to evaluate the average temperature at the surface of a horticultural crop~ B. Goyclle, e. Vigneault, B. Panneton and G.S.V. Raghavan

Structures and Envirol/ment

Structural design of liquid manure tanks- J. Jorriet, Y. Zhang, J.W. Johnson and N.Bird

Ice pressures in liquid manure tanks- J. Jorriet, Y. Zhang. S. Goodman and E. Skolseg

Ef1'ects of chopped sinusoidal voltages on the behavior and perl'ormance of laying hens- G. Vidali, F.G. Silversides, R. Boily, P. Villeneuve and R. Joncas

Design and implementation of a system for automatic milking and feeding- S. Devir, H. Hogeveen, P.H. Hogewerf, A.H. Ipema, c.e. Ketelaar-de Lauwere, W. Rossing,

A.C. Smits and J. Stefanowska

Composting paper mill deinking sludge with forced aeration- M. Brouillette, L. Trepanier, J. Gallichand and C. Beauchamp

The effect of timing of noor-application of mineral oil on dust concentrations in a swine farrowing unit- S.L. Perkins and J.J.R. Feddes

Evaluation of methods to measure the performance of perforated ventilation duds- K. EI Moueddeb, S.F. Barrington and B.G. Newman

Respirable dust control in a scale;model horse stable using filtration and mechanical ventilation- A.P. Dunlea and V.A. Dodd

Recirculation of filtered air in pig barns~ A.K. Lau, A.T. Vizcarra. K.V. Lo and J. Luymcs

Food Engineering

Measurement of glucose concentrations of potato extract using a blood glucose lest strip- G.c. Misener, W.A. Gerber, G.c.c. Tai and E.J. Embleton

Food processing waste dewatering by electro-osmosis~ V. Orsat, V.G.S. Raghavan and E.R. Norris

Dynamics of drying bentonite in superheated steam and air as a model food system- S. Cenkowski, N.R. Bullcy and C.M Fontaine

3t6

75

83

91

183

195

201

291

45

53

99

107

115

123

207

215

297

59

63

305

INDEX

Information and Computer Technologies

Use of a multitasking operating system as a setting for the simulation of an enclosed agro-ecosystemunder cognitive control

- R. Lacroix, R. Kok and O.G. Clark

Classification of various grains using optical properties- S. Majumdar, D.S. Jayas, J.L. Hehn and N.R. Bulley

Technical Notes

A small plot potato planter- W.J. Arsenault, H.W. Platt, E. Pippy and A. Cannon

Response of Colorado potato beetles on potato leaves to mechanical vibrations- G. Boileau and G.C. Misener

A belt-roller mechanism for soil clod reduction on a potato harvester- G.C. Misener and L.P. McMillan

129

. 139

145

223

315

CANADIAN AGRlCULTURAL ENGINEERING Vol. 38. No.4. October/November/Decembcr 1996 317

NOTES TO CONTRIBUTORSThe Editorial Board witl assess suitability and esselltial detail ofpapers submitted for publicntion in Cal/adian Agricllllltral Engineer­ing. One or more reviewers will be llsed. Their COllllllents andsuggestions will be compiled and SUblllillccllO Ihe author. The reviewwill ensure that:

1. A research paper presents a piece of research carried to awell-defined stage of advancement and Ihe conclusions are adequatelysllpp0rled by the cxpcrimcmal resulls.

2. A (echll;co/ paper prescms a clear. concise, and factual outlineand interpretation of the development. design. ICSt. or analysis underconsideration and that it is a corllribution ill one or the fields ofagricultural. biosystcms. or food engineering.

3. A g('lleral paper all education. research. or extension is pertincntto major changes in curriculum. research. or cxtension or to forward­looking developments in these areas.

4. A fecIJnicalllofe on equipment development. tcchnique of meas­uremcnt. or mcthod of analysis will have an application for otherworkers in the ficlds of agricultural. biosystClllS. or food enginecring.

MANUSCRIPTThe manuscript should be typcd doublc.sp"lccd on papcr 216 x 279111m (8.5" x II ") with margins not less than 30 lllm. The first pagcshould contain only the title. authors' namcs. addresses (includingpostal codcs), and contribution number wherc applicable. The tele­phonc number, FAX number. and E·mail address (if available) of thecorresponding author should also be included. Tablcs and captions forillustrations should bc on separate pages. placed aftcr thc text. Manu­script paper with numbercdlincs is preferred. Six copies arc required.After a paper has been acceptcd for publicmion. the author will beexpccted to provide a copy of the paper on floppy disk in a formatcompatiblc with MS·DOS or MacinlOsh systems.

Thc title of the paper should give an accmate desl..Tiption of thearticle. using key words that can be uscd for computer-indexing.

ORGANIZATIONThc paper should be organized 10 conform with present Journal prac­tice. See Norulll and Jayas (1995). All papers must include a shortabstruct section of about 200 words. Authors arc encouraged to submitthe abstract in both English and French. There will be a charge fortranslation services that must be provided by the Journal.

Major headings - Center on the page with all words in capitililelters.Subheadings - Start at left-hand margin. capitalize first ICller.Sub-subheadings - Samc as subheadings but underline.

Technical and detailed information should be includcd only in theform of description. table. graph. chart or photograph. In general.follow the style givcll in Norum and Jayas (1995).

References

List references alphabetically by authors at the end. Follow the formatset by Narum and Jayas (1995). Material in press, with the Ilame of thejournal. m,ly be used ..is a reference. Privatc cOTllmunications andunpublished reports should be referred 10 in parentheses in the text.Privale communications should include the person's title and address.Avoid the use of footnotes. Use the author-date systeTll in thc manu+script when referring 10 anicles in the Reference section.

Tables

Designate tables at the 101' by table number (Roman numerals) andtitle, in upper and lower case letters. All headings and other infonlla­tion in tables arc to be in lower case except first letter of first word.Keep the wble compact and place it across the page wherever possible.00 not lise vertical lines.

Measurements

Only metric system (51) llllits arc to be lIsed.

Equations

Equations and formulas must be set up clearly. Use capitals for SYI11+boIs as llluch as possible and lower case for superscripts andsubscripts. Greek and othcr characters should be identified clearly.Equations should be numbered on the right-hand margin and in linewith the center of the equation.

Abbreviations

Abbreviate units of mcasure only when used with llumerals. Usecorrect SI unit abbrcviations. Do not Lise abbreviations in thc title.

ILLUSTRATIONSEither original drawings or glossy pholOgraphs are acceptable forillustrations. An illustration should be planned to fit. after reduction.into a space 90 mm wide (one column) or 183 wide (two columns). Theori!!inal should be not more than three times the size of the final fi!!ure.Fo~ identification. the figure number and author's name shoul~1 bewritten on the lower left corner with soft pencil.

Line drawings should be machine produced on white drawing paperor tracing paper. Authors are encouraged to produce drawings usingonc of the commonly used computer packages. Leiters. numcrals.labels and axis captions should have only the first word capitalized.Axis captions should be followed by a comllla. the symbol in iW1ics.and the units in parentheses [i.e. Acceleration of particle. Ap (m/s-) I. Ifa symbol is not lIsed. omit the comllla. Letters and numcrals must beat least 1.5 mill high and preferably 2 mm high in final fonn. Curveson graphs must be 0.3 mm wide after reduction. Axes and grid linesshould be clearly visible but inconspicuous; a width of 0.2 111m afterreduction is suggested. Figure numbers and captions should be typedon a separate page, not on the original illustrations. When a paper issubmitted for publication. the original illustrations need not be pro+vided so long as the copies are of such quality that reviewers canunderstand them. Original drawings must be provided when the paperis accepted for publication. If a drawing has been produced by acomputer packagc. a copy of the file should be submincd on disk at thetime that the manuscript is submitted on disk.

DISCUSSIONSDiscussions may be submitled on any paper or technical note publish~

ed in the Joumal for a period of not more than four months followingpublication. Discussion of a paper or technical note is open to anyonewho has significant COllllllents or questions about the contcnt of thepaper/tech[~cal note. A discussion will not be accepted for publicationif it contains material readily found elscwhere. is purely speculative.illlroduces personalitics. or otherwise falls below the standards of atechnical paper in a professional joumal. Authors will be given anopportunity to reply to discussions.

The format for discussions differs 1'1'0111 those of papers in thatfigures are to be identified by capital leiters 10 avoid confusion withthe original paper. The discusser should refer to him/herself as "thewriter" or "I" and to the author of thc original paper as "thc author."The first page shows the title or the original paper with a footnote toidentify the author. volullle. page. and date. Name and address of thewriter of the discussion follow the title.

Discussions will be reviewed by the Editorial Board and possiblythe reviewers of the original paper. The length of a discussion isrestricted to one journal page. Lengthy discussions will be returned forshortening. or the writer may be encouraged to submit a paper ortcchnical note.

REFERENCENorulll. 0.1. and D.S. Jayas. 1995. Instructions for preparing a paperfor Calladian Agr;cl/lmral ElIg;IIl'erillg. Calladian Agricl/lfllral ElIgi­I/aring 37(3):239-243.

Technical Note

A BELT-ROLLER MECHANISM FOR SOIL CLOD REDUCTION ON A POTATO HARVESTERG.C. Misener and L.P. McMillan 311

INDEX - Volume 38 (1996) 315