I

ABSTRACT

The traditional methods of threshing millet are so tedious and drudgeous that they

discourage increased production of millet. It introduces impurities to the grain; causes grain

damage (visible and internal); and also reduces the grain quality. Therefore, a study of

millet properties becomes necessary to overcome the aforementioned problems. Physical

and mechanical properties of millet are necessary for the design of equipment to handle,

and process the crop. The physical and mechanical properties of two varieties of pearl

millet (SOSAT and EX-BORNO) have been determined as a function of grain moisture

content varying from 7.3% to 16.7%. In this moisture range, grain length, width, thickness,

geometric mean diameter, surface area, frontal area, volume, sphericity, porosity, thousand

kernel weight, solid density, angle of repose (wood and steel), bulk density and coefficient

of friction (wood and steel) were determined. T-test was used to analyze the data and the

results of the statistical analysis indicated that there was significant difference between the

means of values of some parameters investigated for the EX-BORNO and SOSAT, at 5%

level of significance. The dimensions and weight of the seeds can be used in the design of

seed separation and sieving mechanisms. The geometric mean diameter can be used in

determination of cylinder concave clearance of a thresher. Bulk and solid densities can be

used in separation mechanism also. Angle of repose can be used in the design of hopper.

Coefficient of friction can be used in estimating power requirement of a machine. Hardness

of the millet grains can be used to determine the type of materials to be used in selecting

cylinder beaters, and construction materials (metal type) of the thresher.

II

TABLE OF CONTENT

Title page - - - - - - - - - - I

Fly leaf- - - - - - - - - - II

Declaration - - - - - - - - - III

Certification - - - - - - - - - IV

Acknowledgement - - - - - - - - V

Abstract - - - - - - - - - VI

Table of content - - - - - - - - VII

List of table - - - - - - - - - VIII

List of figures - - - - - - - - VIII

List of appendices - - - - - - - - IX

CHAPTER ONE

1.0 Introduction - - - - - - - - 1

1.1 Statement of the problem - - - - - - 4

1.2 Objectives of the study - - - - - - - 5

1.3 Justification of the study - - - - - - - 5

1.4 Limitation of the study - - - - - - - 5

CHAPTER TWO

2.0 Literature review - - - - - - - - 6

2.1 Review of existing works on the topic - - - - - - 6

2.2 Deductions from the existing work on the topic - - - - 10

CHAPTER THREE

3.0 Materials and Methods - - - - - - - 12

3.1 Materials - - - - - - - - - 12

3.2 Methods (experimental procedures) - - - - - 12

3.2.1 Moisture content - - - - - - - - 12

3.2.2 Dimensions - - - - - - - - 13

3.2.3 Volume - - - - - - - - - 14

3.2.4 Bulk density - - - - - - - - 14

3.2.5 Angle of repose - - - - - - - - 15

3.2.6 A thousand kernel weight - - - - - - 15

3.2.7 Geometric mean diameter - - - - - - 15

3.2.8 Solid density - - - - - - - - 16

3.2.9 Porosity - - - - - - - - - 17

3.2.10 Sphericity - - - - - - - - 17

3.2.11 Frontal area - - - - - - - - 17

3.2.12 Hardness - - - - - - - - 18

3.2.13 Coefficient of friction - - - - - - - 18

3.2.14 Surface area - - - - - - - - 18

III

CHAPTER FOUR

4.0 Results and Discussion - - - - - - - 20

4.1 Results - - - - - - - - - 20

4.2 Discussion - - - - - - - - - 20

4.3 Significance of properties to the design of millet thresher - - - 28

4.3.1 Dimensions - - - - - - - - 28

4.3.2 Geometric mean diameter - - - - - - - 29

4.3.3 Bulk and solid densities - - - - - - - 29

4.3.4 Angle of repose - - - - - - - - 29

4.3.5 Coefficient of friction - - - - - - - 29

4.3.6 Porosity - - - - - - - - - 30

4.3.7 Weight - - - - - - - - - 30

4.3.8 Hardness - - - - - - - - - 30

CHAPTER FIVE

5.0 Summary, Conclusion, and Recommendations - - - - - 31

5.1 Summary - - - - - - - - - 31

5.2 Conclusion - - - - - - - - - 31

5.3 Recommendations - - - - - - - - 32

References - - - - - - - - - 34

Appendices - - - - - - - - - 36

LIST OF TABLES

Table 4.1: Variation in the physical and mechanical properties of EX-BORNO and SOSAT

varieties of millet at a moisture content of 7.3% - - - - - 20

Table 4.2: Variation in the physical and mechanical properties of EX-BORNO and SOSAT

varieties of millet at a moisture content of 16.7%- - - - - 21

Table 4.3: Comparison of selected physical and mechanical properties of two millet

varieties at a moisture content of 7.3%- - - - - - 23

Table 4.4: Comparison of selected physical and mechanical properties of two varieties of

millet at a moisture content of 16.7% - - - - - - 24

LIST OF FIGURES

Figure 4.1: Effect of moisture content on grain length for two varieties of millet at moisture

content of 7.3%- - - - - - - - - 25

IV

Figure 4.2: Effect of moisture content on grain width for two varieties of millet at a

moisture content of 7.3%- - - - - - - - 26

Figure 4.3: Effect of moisture content on grain thickness for two varieties of millet at a

moisture content of 7.3% - - - - - - - 26

Figure 4.4: Effect of moisture content on grain geometric mean diameter for two varieties

of millet at a moisture content of 7.3%- - - - - - 27

Figure 4.5: Effect of moisture content on grain volume for two varieties of millet at a

moisture content of 7.3% - - - - - - - 27

LIST OF APPENDICES

Appendix I - - - - - - - - - - 36

Appendix II - - - - - - - - - - 46

5

CHAPTER ONE

1.0 INTRODUCTION

Millets are in the family of cereals grown globally with differential importance across

continents and within regions of the world. They form a diverse group of small grains cultivated

in diverse and adverse environments, mostly in the dry, semi-arid to sub-humid drought-prone

agro ecosystems. Worldwide, there are nine species of millets with total production of 28.38

million tonnes, Among these, only four are produced significantly in Africa; including pearl

millet (76%), finger millet (19% area), tef (9%) and fonio (4%) (Obilana, 2003). Millet

production is distributed differentially among a large number of African countries; largest

producers being in West Africa led by Nigeria (41%), Niger (16%), Burkina Faso (7%), Mali

(6.4%), Senegal and Sudan (4.8% each). Finger millet is produced mainly in East and Southern

Africa. Out of which 11.36 million tons (40%) are produced in Africa

from six species (Obilana,

2003).

Pearl Millet (Pennisetum glaucum) is an important food for millions of people inhabiting

the semi-arid tropics and is a major source of calories and vital component of food security in the

semi arid areas in the developing world (FAO and ICRISAT, 1996). The crop is one of the

extensively cultivated cereals in the world, after rice, wheat, and sorghum, and particularly in

arid to semi arid regions. The most important characteristic of millets is their unique ability to

tolerate and survive under adverse condition of continuous or intermittent drought as compared

to most other cereals like maize and sorghum (Ojediran et al, 2010).

Nigeria being the largest producer of millet in Africa produces 41% which is nearly the

half of the millet grown in the whole of Africa (Obilana, 2003). It‘s also the second largest millet

6

producer in the whole world with 23% after India (Nambiar, 2011). The millet is mainly

cultivated in the Northern part of the country. The major types of recommended and local

varieties of millet in the Northern Nigeria namely, Ex-Borno with a yield potential of 2000 –

3000 kg/ha and the improved SOSAT variety with a potential yield of 2500- 3500 kg/ha

(Ojediran et al, 2010). Besides sorghum, millet is by far most important cereal crop in term of

kilogramme consumed per capita. It is cultivated on 5.10 million hectares with an output of 4.53

million tonnes (Obilana, 2003).

Most of the millet produced in Nigeria is consumed directly as food due to its protein and

lipids contents, and they are nutritionally equivalent or superior to most cereals; containing high

levels of methionine, cystine, and other vital amino acids for human health: 12% protein, 3%

crude fibre, and 4% fat (Ojediran et al, 2010). Only little of it serves as raw material for our

breweries for the production of beer. Millet crop residue and green plant also provide source of

animal feed, building material (fencing), and fuel for cooking.

Harvesting of many varieties of millet is done by removing the individual heads with

sickles or hand knives (Kajuna, 2001). This is sometimes preceded by breaking the stem

(Kajuna, 2001). The ears are cut with about 2 cm of stalk (Kajuna, 2001). The method of

harvesting millet in Nigeria is usually by hand-cutting with small knife or scythe (Vogel and

Graham, 1979). Usually the matured plants are cut and left in the field with head exposed to sun

to dry. The moisture content of 10-12% is aimed in sun drying (Vogel and Graham, 1979). When

dry, the heads are taken home in bundles, sacks, carts, etc to be stored. The size of the bundle

varies between 18 and 36kg (Vogel and Graham, 1979).

Threshing is the removal of grain from harvested plant head or plant part (Kajuna, 2001).

The prevailing methods of threshing millet in Nigeria are mostly traditional. Traditional methods

7

involves women and men, it entails either beating the heads with sticks on the ground or in sacks

repeatedly until almost all the grains are detached from the heads, or using a mortar and pestle.

The first step in both cases is to spread the heads on the ground, on mats, or on a special platform

to allow the grain to dry. This is followed by the actual threshing with the sticks or in the mortar

and pestle. In order to ease grain collection after beating, sometimes the heads of millet may be

stuffed in to bags, prior to beating (Kajuna, 2001). The time required to thresh the grain was

found in most cases to be related to three factors: the structure of the plant; the degree of dryness

of the heads; and the method of threshing used (beating being the fastest, the mortar and pestle

the slowest) (Vogel and Graham, 1979). Some labour-saving methods for threshing have also

been tried. For example, motorized threshers were experimented with but they were found to

produce more broken grains than the traditional methods. In this case, grain hardness, as related

to method, ease, and efficiency of threshing, becomes one of the criteria for cultivar acceptance

(Vogel and Graham, 1979).

The last step of threshing operation is winnowing. This is a process of millet cleaning

whereby approximately 2 to 3 kg of threshed millet grains are placed on a flat reed- or raffia-woven

basket and winnowed by up and down strokes. In this process, the basket is jerked up and down so

that the grains are thrown up in the air and allowed to fall back onto the basket. The sand and other

light contaminants are separated to the front of the basket from where they are thrown off by a jerky

motion, or are removed by hand. Often, the light contaminants are blown off by the mouth in a very

low scale situation. Women in both rural and urban areas are usually the experts. The process is

laborious, and time consuming, and may take up to 1 hr to clean 1 bag of 100 kg (Kajuna, 2001).

The straws that remain after threshing may be used as a source of fuel. It is also used as thatching

material for traditional houses or used as a mulch as well as animal feed.

8

The above mentioned threshing operations introduced impurities to the grain there by

rendering the grain unhygienic. The impurities comprise of vegetables such as foreign seeds,

kernel, chaff, stalk, empty grain etc, and mineral e.g. earths, stones, sand, metal particles. The

impurities adversely affect grain quality and subsequent storage and processing activities

(Usman, 2010). The energy expenditure is also high due to the number of men required for the

operation, resulting to high cost of threshing. Time consumption is another negative effect of the

traditional method of threshing. Other factors that discourage the use of the traditional methods

are the reduction in the quality of the grain and damaging of the grain. The grain damage can be

external or internal damage. The internal damage or injury hinders the grain from germinating

when used as seed. However, another major effect of traditional threshing is the drudgery which

makes the threshing exhausting, boring, and unpleasant to the workers. It also causes extreme

tiredness to the person performing the threshing operation. Therefore, the need for better

threshing method arises.

1.1 Statement of the Problem

The traditional methods of threshing are tedious practices and causes drudgery that

discourage increased production of millet (Vogel and Graham, 1979). The methods are also time

consuming and are uneconomical. Thus, to have larger output, huge labour is needed.

Other disadvantages of the traditional threshing are the introduction of impurities to the

grain; causes grain damage (external and internal); and also reduces the grain quality. Thus, the

study is aimed at eliminating the aforementioned problems or at least reducing them to the

bearest minimum.

1.2 Objectives of the Study

9

The broad objective of this project is to determine some physical and mechanical

properties of two varieties of pearl millet. Based on the properties that will be determined, the

significance of each property in the design of pearl millet thresher will be highlighted.

The specific objectives of the study are:

i) To review the existing pearl millet threshing methods.

ii) To determine some physical and mechanical properties of pearl millet.

iii) To state the significance of each property determined in the design of small scaled

low cost pearl millet thresher using local materials.

1.3 Justification of the Study

When this project is completed, the physical and mechanical properties determined will

help immensely in the design and production of small scaled low cost pearl millet thresher that

can be used by small and medium scale millet processors. This will definitely increase the millet

processing, improving its grain quality, reduces drudgery, saves time, and maintain physical and

hygienic properties of the grain.

1.4 Limitation of the Study

The entire study will be limited to two varieties of pearl millet only viz: EX-BORNO

and SOSAT. This is because; they are the recommended, improved and local varieties that are

cultivated in the Northern Nigeria (Ojediran et al, 2010).

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 Review of existing work on the topic

10

Ojediran et al (2010). Determined some physical properties of pearl millet (Pennisetum

glaucum) seed as they relate to moisture content. They obtained two varieties of Pearl millet

seeds (Pennisetum glaucum) (Ex-Borno and SOSAT C88) from the Lake Chad Research

Institute, Maiduguri-Nigeria and reconditioned to moisture contents ranging from 10% - 20%

wet basis. The reconditioned seeds were then evaluated for dimensions, sphericity, bulk density,

solid density, porosity, thousand seed mass, angle of repose, and static coefficient of friction on

five structural surfaces. Within the range of moistures analyzed, physical properties of millet

seeds are related to the moisture content by polynomial equations. SOSAT C88 and Ex-Borno

increased their width by 15.7% and 15.6%; similarly, their length increased by 15.3% and

19.8%, and their thickness increased by 22.4% and 7.8% respectively with increase in moisture

content. Seeds from Ex-Borno were the smallest. Sphericity changed with the increase in

moisture content with SOSAT C88 coming closer to a spherical form. The solid and bulk

densities of the seeds for different moisture levels decreased with the increase in moisture

content. The porosity started at 17% and 15.2 % and increased to 26.6% and 32.6% for SOSAT

C88 and Ex-Borno varieties respectively. The thousand seed mass and angle of repose also

increased with increasing moisture levels for both varieties. Both varieties showed a comparable

behaviour in relation to the static coefficient of friction, this variable increased with moisture

content on two structural surfaces namely concrete and plastic, but decreased with increasing

moisture levels on glass, steel and aluminium. Regression equations that could be used to

adequately express the relationship existing between the above properties and seed moisture

were established.

Swami et al (2010). Determined the physical properties of finger millet (Eleusine coracana)

and evaluated as a function of grain moisture content varying from 13 to 48% (db). In this

11

moisture range, true density increased from 1120 to 1130 kg/m3; the bulk density increased from

709 to 775 kg/m3. The porosity of the finger millet grain was found to increase from 13.00 to

41.72%. The geometric mean diameter increased linearly 1.608 to 1.822 mm. The sphericity of

the finger millet grains were in the range of 0.960 to 0.987 for the grain moisture content varying

from 13 to 48% (db). The surface area and the surface volume were in the range of 9.00 to 10.2

mm2 and the surface volume was 2.8 to 3.2 mm2 and found to increase with the increase in

moisture content of the grains.

Singh et al (2010). Determined Moisture-dependent properties of barnyard millet grain and

kernel. The geometric mean diameter, sphericity, grain surface area, 1000 grain mass, true

density (toluene displacement method), terminal velocity, dynamic angle of repose, coefficient of

internal friction, coefficient of static friction at different surfaces (sun mica, canvas and mild

steel surfaces), specific deformation and rupture energy of the grain were found to increase

12.21%, 4.79%, 30.47%, 30.75%, 6.74%, 32.99%, 127.05%, 60%, 18.57%, 34–67%, 69.2% and

88.87% respectively at increase of moisture content from 0.065 to 0.265 kg kg-1

dry matter.

However, true density (proximate composition method), bulk density, interstices and rupture

force of grain was found to be decrease 8.64%, 20.1%, 86.49% and 21.17% respectively at

increase of moisture content. Similar trend was observed for barnyard kernel also. True density

(toluene displacement method) was found lower as compared to true density (proximate

composition method) at all experimental moisture range indicated that the presence of void space

inside the grain and kernel.

12

Shirsat et al (2008). Studied the physical and mechanical properties of local varieties of

Kodo millet (Pasplum scrobiculatum L.) were conducted in the moisture range of 13.47 to

50.60% (dB) to generate information as an aid for design, development and modification of

handling, processing, equipments/machine and storage system. It was found that the thousand

grain mass increased from 5.55 to 7.32 g, sphericity varied from 0.75 to 0.81, length-breadth

ratio varied from 1.30 to 1.18 and the equivalent diameter varied from 2.15 to 2.31 mm with

increase in moisture content. It was further observed that the bulk density decreased from 760 to

640 kg/m3 while true density increased from 1200 to 1240 kg/m3. The angle of repose and

porosity increased linearly from 250 34‘ to 330 47‘ and 37.7 to 48.39%, respectively. The result

indicated that the moisture content of the grains significantly affects some of the physical and

engineering properties of Kodo millet.

Ndirika et al (2006). Determined some selected physical properties and their relationship

with moisture content for pearl millet (Pennisetum glaucum) was conducted as part of

Agricultural Mechanisation Research Project of the IAR that was aimed at the establishment of

relationship between the existing properties that will aid in the design and improvement of post-

harvest systems. Selected physical properties of pearl millet (Pennisetum glaucum) such as

kernel volume, length, width, thickness, geometric mean diameter, surface area, sphericity,

roundness, angle of repose, thousand kernel weight (TWK), specific gravity, bulk density, and

porosity were determined as a function of moisture content. Kernel volume and other dimensions

such as length, width, thickness, and geometric mean diameter vary linearly and directly

proportional with the grain moisture content (ranging between 7.5%-21.2% wet basis). A

comparative evaluation of the two varieties of millet (Ex-Borno and Zango) for the above

13

properties revealed that only the difference in the means of surface area, specific gravity, and

grain density were not statistically significant at 5% level of significance, while the difference

with the other properties such as length, width, thickness, geometric mean diameter, volume,

sphericity, roundness, angle of repose, thousand kernel weight, bulk density, and porosity were

statistically significant at the 5% level. Correlation coefficient between 76% and 95% were

obtained with the relationship between moisture content and grain length, width, geometric mean

diameter, and grain volume for both varieties of millet.

Ndirika (1994). During his project on the development and performance evaluation of a

millet thresher, it was necessary for him to determine some physical and mechanical properties

of two varieties of pearl millet (Ex-Borno and Maiwa). The average grain length, grain diameter,

grain weight, grain hardness, angle of repose, earhead weight, earhead length, length of grain

portion, earhead diameter(top), earhead diameter(middle), earhead diameter(bottom), and

moisture content of the Ex-Borno and Maiwa seeds are 4.00 mm and 3.90 mm; 2.00 mm and

2.48 mm; 0.017g and 0.038, 2.00 kg and 2.05 kg; 789.00 kg/m3 and 870.00 kg/m

3; 13.95

0 and

14.000; 44.73 g and 58.10 g; 35.20 cm and 44.30 cm; 31.61 cm and 43.49 cm; 1.80 cm and 1.85

cm, 2.22 cm and 2.08 cm; 2.12 cm and 2.00 cm; 29.22 g and 40.89 g; 10% and 9.10%

respectively.

2.2 Deductions from the existing works on the topic

Ojediran et al (2010). This study is in-line with the project in the sense that the same

varieties of pearl millet were used and the physical properties determined were also part of the

project. But, this study is only limited to the determination of some physical properties of pearl

14

millet (Pennisetum glaucum) as a function of moisture content. This implies that the study does

not include relating the significance of the properties determined to the design of post harvest

systems such as thresher and SOSAT C88 was used in the study instead of SOSAT.

Swami et al (2010). The study is in total agreement with the research topic. The only

problem with the study is the variety of millet used. In the Northern Nigeria, where this research

is intended for, finger millet (Eleusine coracana) is not common. Therefore, replacing the millet

variety is necessary in order to make the research useful.

Singh et al (2010). The study compliance also with the objectives of this project except in

the variety of millet used, and does not relate the properties determined with the design of a

millet thresher. Therefore, this project is intended to address the aforementioned deficiency in

the study.

Shirsat et al (2008). This study is same as above. Though, the millet variety has to be

changed from Kodo millet (Pasplum scrobiculatum L.) to pearl millet (Pennisetum glaucum)

also.

Ndirika et al (2006). This study is also in total agreement with the research topic. But,

there is slight difference in one of the variety of the pearl millets used in the study. Ex-Borno and

Zango were used instead of Ex-Borno and SOSAT as it‘s in the research topic.

Ndirika (1994). This is also another study that tally with the research topic. The only

hindrance here is the use of different variety from the one intended in the research project. Thus,

15

the replacement of Maiwa with SOSAT variety is necessary for the attainment of the objectives

of this project research.

CHAPTER THREE

3.0 MATERIALS AND METHODS

3.1 Materials

Pearl millet seeds (Pennisetum glaucum) varieties locally recognised as Ex-Borno and

SOSAT obtained from the Institute of Agricultural Research (IAR), Zaria were used for the

16

study. Their selection was based on their yield potential as compared to others. They are also

chosen because they are improved variety developed by the Institute of Agricultural Research

(IAR). The seeds were thoroughly cleaned (manually by winnowing and hand sorting) to remove

foreign materials such as dirt, stones, dust, and unremoved chaffs, then divided into lots and

thereafter conditioned to obtain six different levels of moisture content ranging from 7.3%, 9.3%,

10%, 11.3%, 14.7%, and 16.7% w. b by adding pre-determined quantities of distilled water

through spraying and thoroughly mixing. The prepared samples were sealed in hermetic

polyethylene bags and then stored at room temperature of 250C, to allow uniformity of mixture

samples distribution.

3.2 Methods (experimental procedures)

3.2.1 Moisture content

In order to obtain the desired moisture content, the samples were conditioned by spraying

them with required quantity of water and mixing thoroughly and then sealing them in a

polyethylene bags for some hours to allow the moisture to distribute uniformly throughout the

sample. All of the physical properties of the grain were assessed at a moisture level of 7.3%,

9.3%, 10%, 11.3%, 14.7%, and 16.7% dry basis. For attaining equilibrium, the samples were

placed in air tight plastic container until further use (Ndirika et al, 2006).

The moisture content of the whole grain was determined by oven method according to

Agrawal (2005). Small quantity of the sample slightly greater than the required for the test was

grinded. Great care was taken to avoid loss of grain or moisture in the sample before grinding,

during the grinding and before weighing. For pearl millet, fine grinding is necessary. At least 50

percent of the ground material must pass through a wire mesh sieve of 0.5 mm and not more than

17

10 percent remain on a wire sieve with meshes of 1.00 mm. The oven used was UNISCOPE

SM9023 Laboratory oven, manufactured by SURGIFRIEND MEDICALS. This was done by

putting 10-15 g of the millet grain for each variety into a container and then weighed using an

electronic weighing balance of 0.01 g calibration, it was then oven dried at a temperature of

130oC for 1 hour. The average moisture content of the two samples was calculated to obtain the

moisture content of the samples using the relationship below:

%100xW

WWMc

w

dwwb

- - - - - 1

(Agrawal, 2005)

Where:

Mc wb = Moisture content wet basis (%)

wW Weight of wet samples (g).

dW Weight of dried samples (g).

3.2.2 Dimension

The grain dimensions such as length, width, and thickness were determined using a

Vernier Caliper. The Vernier Caliper is having a least resolution of 0.01 cm. The experiment was

replicated 10 times.

3.2.3 Volume

The volume of the grain was determined by taking the dimensions of the two varieties of

the grains in three axes of length, width, and thickness in 10 replications and then the volume

was estimated using the following relationship as described by Mohsenin (1986):

6

LwhV

- - - - - - - 2

(Mohsenin, 1986)

18

Where:

V = Volume of kernel (mm3.)

L = Length of kernel (mm).

w = Width of kernel (mm).

h = Thickness of kernel (mm).

= Constant 7

22

3.2.4 Bulk density

Bulk density of the grain was determined by weighing the grain packed in a container of

known volume. The grains were densely packed by gently tapping the container to allow the

settling of grains in the container (Ndirika et al, 2006). The volume of the container was

estimated by taking the dimensions of the container and then the volume is then computed and

recorded. The experiment was replicated 10 times, and the following expression was used in

determining the bulk density of the two varieties of the millet.

meKnown volu

packed material ofWeight densityBulk - - - 3

(Ndirika et al, 2006)

3.2.5 Angle of repose

In determining the angle of repose of the grains, the set up for the determination of

coefficient of friction was used. It is made up of wooden board with holes for the fixing of the

platform at a required position. The platform has a protractor with a thread attached to it for

obtaining the corresponding angle the platform made with the horizontal axis as it is being tilted.

The seeds were placed on the platform, and then the platform was tilted until the grains began to

slide (flow) freely, the angle the platform makes at the time of free flow was taken as the angle

of repose of the grain. This experiment was repeated for the two varieties of the grain and

19

replicated 10 times at different moisture contents as to ascertain the mean angle of repose of the

material.

3.2.6 A thousand kernel weight (TKW)

In determining the weight of the grains, one thousand (1000) whole kernels of the two

varieties of millet grain were weighed using the electronic weighing balance of 0.01 g sensitivity.

The experiment was replicated 10 times.

3.2.7 Geometric mean diameter (Dg)

The geometric mean diameter, Dg of the grain was calculated using the following

relationship by Singh et al (2010):

3

1

LWTDg - - - - - - - 4

(Singh et al, 2010)

Where: L, W, and T are the length, width, and thickness of the kernel respectively. Dimensions

are in mm. Samples of 10 randomly selected whole kernels of the two varieties were used to

determine the grain dimensions and the experiment was replicated 10 times.

3.2.8 Solid density

Solid density is another way of describing density and was determined by using a specific

gravity. This was carried out by first weighing the empty density bottle, followed by filling the

bottle one-third of grain full and then weighed again. The bottle was then filled with water and

the mixture of the grain was also weighed. The bottle was filled with water only and weighed.

20

The experiment was replicated 10 times, and the solid density of the material was determined

using the expression described by Okeke and Anyakoha (1987):

Solid density = Density of water x specific gravity of the grain (Gsp)

)( 2314

12

MMMM

MMGm

- - - - - - 5

(Okeke and Anyakoha, 1987)

Where:

Gsp = Specific gravity of the grains.

M1 = Weight of empty density bottle (g).

M2 = Weight of empty density bottle about one-third full of grain (g).

M3 = Weight of density bottle filled with grain and water (g).

M4 = weight of density bottle filled with water only (g).

3.2.9 Porosity

Porosity or bulk porosity was determined using the bulk and solid densities parameters as

described by Mohsenin (1986).

Porosity = 1001

tysoliddensi

yBulkdensit - - - - - 6

(Mohsenin, 1986)

3.2.10 Sphericity

Sphericity of the seeds was determined using the relationship described by Mohsenin

(1986) and the experiment was replicated 10 times:

21

L

DSphericity

g - - - - - - - - 7

(Baryerh and Mangope, 2003)

Where;

Dg = Geometric mean diameter (mm).

L = Length (mm).

3.2.11 Frontal area

The frontal area was determined using the relationship below as described by Mohsenin

(1986), and the experiment was replicated 10 times:

Frontal area = 4

21LL - - - - - - 8

(Mohsenin, 1986)

Where:

L1 = Length of the seed (mm).

L2 = Width of the seed (mm).

= Constant 7

22 .

3.2.12 Hardness

Grain hardness testing machine was used to measure the hardness of the seeds. The

samples were placed and held on the top of the seed placing area; weight was then applied to the

indenter through turning a screw which in turn presses the sample until the samples breaks. This

experiment was repeated for the two varieties of the grain and replicated at different moisture

contents as to ascertain the mean hardness of the material and the experiment was replicated 10

times.

3.2.13 Coefficient of friction

22

In the determination of the coefficient of friction of the two varieties of the pearl millet,

the set up used in the determination of angle of repose was also used here. The only difference is

that, here the seeds were piled on the surface of the platform instead of placing them in a box.

The tangent of the angle made by the tilted platform was obtained. The experiment was repeated

and replicated 10 times each for both varieties.

3.2.14 Surface area (S)

The surface area ‗S‘ of the millet grain was assessed by analogy with a sphere of same

Dg, using equation below by Singh et al (2010), and the experiment was replicated 10 times:

- - - - - - - - 9

(Singh et al, 2010)

Where:

S = Surface area of the millet grain (mm2).

= Geometric mean diameter (mm).

π = Constant.

23

CHAPTER FOUR

4.0 RESULTS AND DISCUSSION

4.1 Results

The data obtained during the experiments were analysed using MSTAT-C software,

which was developed by Prof. Russell D. Freed of the Crop and Soil Science Department,

Michigan State University. The software is a microcomputer program for design, management,

and analysis of Agronomic Research Experiments (Bricker, 1993).

4.2 Discussion

The data obtained during the experiments are summarized in tables 4.1, 4.2, 4.3,

and 4.4. The results are also indicated graphically in figures 4.1, 4.2, 4.3, 4.4, and 4.5.

Table 4.1: Variation in the physical and mechanical properties of EX-BORNO and

SOSAT varieties of millet at a moisture content of 7.3%.

Parameters

No of sample

measured (n)

Mean Value S. D

EX-

BORNO

SOSAT

EX-

BORNO

SOSAT

Length, L (mm) 10 3.760 3.780 0.257 0.278

Width, W (mm) 10 2.160 2.500 0.207 0.333

24

S

D:

Standard

deviatio

n

Table

4.1

shows

the

compari

son of the selected physical and mechanical properties of the two varieties of pearl millet (EX-

BORNO and SOSAT) at a moisture content of 7.3%. The table shows that there were deviations

in all of the measured parameters but the most significant deviation was found with surface area

of both EX-BORNO and SOSAT varieties with standard deviation of 2.889 mm2

and 4.148 mm2

respectively. The least significant parameter was the coefficient of friction on wood surface

having 0.0008 and 0.0014 for EX-BORNO and SOSAT varieties respectively.

Table 4.2: Variation in the physical and mechanical properties of EX-BORNO and

SOSAT varieties of millet at a moisture content of 16.7%.

Parameters

No of sample

measured (n)

Mean Value S. D

EX-

BORNO

SOSAT

EX-

BORNO

SOSAT

Length, L (mm) 10 4.100 4.170 0.403 0.330

Width, W (mm) 10 2.360 2.730 0.207 0.374

Thickness, T (mm) 10 2.270 2.460 0.316 0.291

Geometric mean diameter, Dg (mm) 10 2.789 3.029 0.188 0.269

Volume, v (mm3) 10 11.512 14.881 2.274 4.034

Sphericity 10 0.687 0.728 0.078 0.064

Frontal area (mm2) 10 7.582 8.966 0.844 1.596

Surface area (mm2) 10 24.555 29.043 3.271 5.197

Thousand kernel weight (g) 10 11.140 9.010 0.206 0.110

Angle of repose (grain on wood) (0) 10 28.720 34.050 0.244 3.128

Thickness, T (mm) 10 2.080 2.220 0.294 0.266

Geometric mean diameter, Dg (mm) 10 2.557 2.751 0.181 0.237

Volume, v (mm3) 10 8.686 11.127 1.847 2.921

Sphericity 10 0.686 0.730 0.079 0.067

Frontal area (mm2) 10 6.363 7.434 0.733 1.233

Surface area (mm2) 10 20.625 23.942 2.889 4.148

Thousand kernel weight (g) 10 9.80 8.04 0.067 0.117

Angle of repose (grain on wood) (0) 10 26.36 31.43 0.414 0.386

Angle of repose (grain on steel) (0) 10 22.49 27.26 0.22 0.28

Coefficient of friction on wood 10 0.3375 0.3111 0.0008 0.0014

Coefficient of friction on steel 10 0.4303 0.4159 0.0029 0.0016

Hardness (kg) 10 2.690 3.760 0.623 1.103

Bulk density (kg/m3) 10 840.49 806.68 0.53 1.99

Solid density (kg/m3) 10 1342.54 1333.47 1.54 0.44

Porosity (%) 10 39.914 37.261 0.184 0.925

25

Angle of repose (grain on steel) (0) 10 26.55 29.96 0.34 0.50

Coefficient of friction on wood 10 0.3102 0.2923 0.0008 0.0009

Coefficient of friction on steel 10 0.3911 0.3785 0.0066 0.0043

Hardness (kg) 10 1.700 1.890 0.618 0.448

Bulk density (kg/m3) 10 781.65 802.47 1.43 0.41

Solid density (kg/m3) 10 1316.55 1327.66 0.37 0.45

Porosity (%) 10 39.048 41.126 0.029 0.118

SD: Standard deviation

Table 4.2 shows the comparison of the two varieties of pearl millet at a moisture content of

16.7%. The comparison shows that there were deviations in all the measured physical and

mechanical properties of the two varieties of pearl millet. It shows that the grain surface area has

the highest standard error of 5.197 mm3

and 3.271 mm3

for the EX-BORNO and SOSAT

varieties respectively. This means that, the measurement error was higher at a moisture content

of 16.7% than that of 7.3%.

26

Table 4.3: Comparison of selected physical and mechanical properties of two millet varieties at a

moisture content of 7.3%

Parameters Mean values S. D Calculated

‗t‘ value

Table

‗t‘

value

Signific

ance

EX-BORNO

SOSAT

EX-BORNO

SOSAT

27

SD: Standard deviation

NS: Non-significant at 5% level

S: Significant at 5% level

Table 4.3 shows the comparison between the differences in the mean of the physical and

mechanical properties of the two millet varieties at a moisture level of 7.3% using the student t-

test. From the table, it was revealed that only length, thickness, and sphericity were not

statistically significant at the 5% level. The SOSAT variety has the highest length (3.780 mm),

width (2.500 mm), thickness (2.220 mm), geometric mean diameter (2.751 mm), volume (11.127

mm3

), sphericity (0.730), frontal area (7.434 mm2), surface area (23.942 mm

2 ), angle of repose

(31.430 on wood surface and 27.26

0 on steel surface), hardness (3.760 kg), and bulk density

(806.68 kg/m3

). But having lower thousand kernel weight (8.04 g), coefficient of friction

Length, L (mm) 3.760 3.780 0.257 0.278 0.1393 2.262 NS

Width, W (mm) 2.160 2.500 0.207 0.333 3.1568 2.262 S

Thickness, T (mm) 2.080 2.220 0.294 0.266 1.2641 2.262 NS

Geometric mean diameter,

Dg (mm)

2.557 2.751 0.181 0.237 2.5110 2.262 S

Volume, v (mm3) 8.686 11.127 1.847 2.921 2.5271 2.262 S

Sphericity 0.686 0.730 0.079 0.067 1.3055 2.262 NS

Frontal area (mm2) 6.363 7.434 0.733 1.233 3.4813 2.262 S

Surface area (mm2) 20.625 23.942 2.889 4.148 2.5447 2.262 S

Thousand kernel weight (g) 9.80 8.04 0.067 0.117 -57.6095 2.262 S

Angle of repose (grain on

wood) (0)

26.36 31.43 0.414 0.386 26.3143 2.262 S

Angle of repose (grain on

steel) (0)

22.49 27.26 0.22 0.28 46.8630 2.262 S

Coefficient of friction on

wood

0.3375 0.3111 0.0008 0.0014 -48.7443 2.262 S

Coefficient of friction on

steel

0.4303 0.4159 0.0029 0.0016 -15.4286 2.262 S

Hardness (kg) 2.690 3.760 0.623 1.103 2.3793 2.262 S

Bulk density (kg/m3) 840.49 806.68 0.53 1.99 -60.7371 2.262 S

Solid density (kg/m3) 1342.54 1333.47 1.54 0.44 17.6745 2.262 S

Porosity (%) 39.914 37.261 0.184 0.925 8.8641 2.262 S

28

(0.3111 on wood surface and 0.4159 on steel surface), solid density (1333.47 kg/m3), and

porosity (37.261%) compared to EX-BORNO variety.

Table 4.4: Comparison of selected physical and mechanical properties of two varieties of millet

at a moisture content of 16.7%

Parameters Mean values S. D Calculated

‗t‘ value

Table

‗t‘

value

Signifi

cance

EX-BORNO

SOSAT

EX-BORNO

SOSAT

Length, L (mm) 4.100 4.170 0.403 0.330 0.4304 2.262 NS

Width, W (mm) 2.360 2.730 0.207 0.374 3.1258 2.262 S

Thickness, T (mm) 2.270 2.460 0.316 0.291 1.5404 2.262 NS

Geometric mean diameter,

Dg (mm)

2.789 3.029 0.188 0.269 2.7599 2.262 S

Volume, v (mm3) 11.512 14.881 2.274 4.034 2.7472 2.262 S

Sphericity 0.687 0.728 0.078 0.064 1.2091 2.262 NS

Frontal area (mm2) 7.582 8.966 0.844 1.596 3.5078 2.262 S

Surface area (mm2) 24.555 29.043 3.271 5.197 2.7662 2.262 S

Thousand kernel weight (g) 11.140 9.010 0.206 0.110 -26.5219 2.262 S

Angle of repose (grain on

wood) (0)

28.720 34.050 0.244 3.128 5.2070 2.262 S

Angle of repose (grain on

steel) (0)

26.55 29.96 0.34 0.50 17.0287 2.262 S

Coefficient of friction on

wood

0.3102 0.2923 0.0008 0.0009 -41.3077 2.262 S

Coefficient of friction on

steel

0.3911 0.3785 0.0066 0.0043 -4.5493 2.262 S

Hardness (kg) 1.700 1.890 0.618 0.448 0.9515 2.262 NS

Bulk density (kg/m3) 781.65 802.47 1.43 0.41 39.8427 2.262 S

Solid density (kg/m3) 1316.55 1327.66 0.37 0.45 62.2264 2.262 S

Porosity (%) 39.048 41.126 0.029 0.118 48.8043 2.262 S

SD: Standard deviation

NS: Non-significant at 5% level

S: Significant at 5% level

Table 4.4 shows the comparison between the difference in the mean of physical and mechanical

properties of the two varieties of pearl millet at a moisture level of 16.7% using student t-test.

From the table, it was revealed that only length, thickness, sphericity, and hardness were not

statistically significant at 5% level. The SOSAT variety has the highest length (4.170 mm), width

(2.730 mm), thickness (2.460 mm), geometric mean diameter (3.029 mm), volume (14.881 mm3

29

), sphericity (0.728), frontal area ( 8.966 mm2

), surface area (29.043 mm2

), angle of repose

(34.0500

on wood surface, and 29.960

), hardness (1.890 kg), bulk density (802.47 kg/m3

), solid

density (1327.66 kg/m3

), and porosity (41.126%). Except for the thousand kernel weight (9.010

g), and coefficient of friction (0.2923 on wood surface and 0.3785 on steel surface). This implies

that EX-BORNO variety is heavier than SOSAT variety. This means that separation mechanism

of the two varieties should be different.

Fig 4.1: Effect of Moisture Content on Grain Length for Two Varieties of Millet at a

moisture content of 7.3%.

y = 0.0403x + 3.4896

R2 = 0.9937

y = 0.0336x + 3.5422

R2 = 0.9227

3.7

3.75

3.8

3.85

3.9

3.95

4

4.05

4.1

4.15

4.2

0 2 4 6 8 10 12 14 16 18

Moisture content (%)

Avera

ge g

rain

len

gth

(m

m)

SOSAT

EX-BORNO

30

Fig 4.2: Effect of Moisture Content on Grain Width for Two Varieties of Millet at a

moisture content of 7.3%.

Fig 4.3: Effect of Moisture Content on Grain Thickness for Two Varieties of Millet at a

moisture content of 7.3%.

y = 0.0295x + 2.5495

R2 = 0.9664

y = 0.0242x + 2.3917

R2 = 0.988

2.5

2.6

2.7

2.8

2.9

3

3.1

0 5 10 15 20

Moisture content (%)

avera

ge g

rain

wid

th (

mm

)

SOSAT

EX-BORNO

y = 0.0246x + 2.3398

R2 = 0.8874

y = 0.0215x + 2.0101

R2 = 0.9592

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20

Moisture content (%)

Avera

ge g

rain

th

ickn

ess (

mm

)

SOSAT

EX-BORNO

31

Fig 4.4: Effect of Moisture Content on Grain Geometric Mean Diameter for Two

Varieties of Millet at a moisture content of 7.3%.

Fig 4.5: Effect of Moisture Content on Grain Volume for Two Varieties of Millet at a

moisture content of 7.3%.

From the above figures, it shows that the R2 value or the coefficient of determination

(correlation) of the two variables for the five properties above are approximately equals to one

y = 0.0211x + 1.928

R2 = 0.9236

y = 0.0258x + 2.0491

R2 = 0.9456

2.05

2.1

2.15

2.2

2.25

2.3

2.35

2.4

2.45

2.5

0 5 10 15 20

Moisture content (%)

Avera

ge g

rain

geo

metr

ic m

ean

dia

mete

r (m

m)

SOSAT

EX-BORNO

y = 0.2825x + 6.8752

R2 = 0.991

y = 0.3973x + 8.3797

R2 = 0.9793

0

2

4

6

8

10

12

14

16

0 5 10 15 20

Moisture content (%)

Avera

ge g

rain

vo

lum

e (

mm

3)

SOSAT

EX-BORNO

32

(1). This means that the two variables are related to each other for the five properties at a

moisture content level of 7.3%.

4.3 Significance of properties determined to the design of a millet thresher

The study of physical and mechanical characteristics of agricultural materials such as

dimension, volume, surface area, density, porosity, and hardness is important in many problems

associated with design of a specific machine or analysis of the behaviour of the product in

handling of the material (Mohsenin, 1986). The theoretical performance of machines and

mechanisms used in mechanical handling and processing of materials cannot be fully appreciated

without knowledge of the physical properties of the material (Mohsenin, 1986).

4.3.1 Dimension

What shape is to be assumed for the material and which dimension is to be employed in

calculation are two first questions which one must answer before understanding the problems of

separation of seeds and grains from undesirable materials (Mohsenin, 1986). Therefore, the

dimensions of the millet grain can be used to choose the appropriate fan that can separate the

millet grain from the undesirable material. Besides the fan selection, the efficiency of sieving

and, hence, the removal of chaff, is affected by the seed parameters (size, shape) of each seed

(Datta, 2003). However, sieve parameters—size, shape, and spacing of perforations can also be

determined using the dimensions of the millet grain (Datta, 2003).

4.3.2 Geometric mean diameter

33

One of the important design parameter in conveying of solid materials by air is the

accurate determination of the geometric mean diameter of the material. The geometric mean

diameter is essential in the determination of terminal velocity and drag coefficient (Mohsenin,

1986). The knowledge of the geometric mean diameter can also be used in the determination of

cylinder concave clearance of the threshing unit (thresher).

4.3.3 Bulk and solid density

The knowledge of density of agricultural products is needed in separating the product

from undesirable materials, thus the design of fan (Mohsenin, 1986). It is also used in the

determination of purity of the agricultural products (Mohsenin, 1986).

4.3.4 Angle of repose

The angle of repose of agricultural material (millet) is used in the determination of the

angle at which the hopper of the thresher will be slanted so as to have free flow of the millet

grains in the hopper.

4.3.5 Coefficient of friction

The knowledge of coefficient of friction of the food grains on various structural surfaces

is necessary in analysis and design of post-harvest grain handling, processing and storage

equipment such as grain bins, silos, conveyors, flow of food grain from bins by gravity or loaded

auger and other machines. A machine can only be started or stopped if forces of static friction or

dynamic friction are overcome by the power source. Therefore, information on both static and

dynamic coefficient of friction is vital in estimating the power requirement of machines

34

(Nwakonobi and Onwualu, 2009). The static and sliding coefficient of friction of grains and some

other farm products on metal, wood, and other materials are needed by design engineers for rational

design and predicting motion of the material in harvesting and handling equipment (Mohsenin,

1986). Frictional properties of granular materials such as seeds and grains are important in

design of equipment for solid flow and structures (Mohsenin, 1986).

4.3.6 Porosity

The percent of voids of an unconsolidated mass of materials such as grains and other

porous materials is often needed in the design of air flow mechanisms (Mohsenin, 1986).

4.3.7 Weight

The weight of the millet grain can be used to determine the type of fan and sieve that can

be used to separate the millet grains from the undesirable materials (Datta, 2003).

4.3.8 Hardness

Mechanical properties such as cracking force, hardness, and compressive strength are

important and in some cases necessary engineering data in studying size reduction of cereals

grains as well as seed resistance to cracking under harvesting and handling conditions

(Mohsenin, 1986). Therefore, the hardness of the millet grains can be used to determine the type

of materials to be used in selecting cylinder beaters, and construction materials (metal type) of

the thresher.

CHAPTER FIVE

5.0 SUMMARY, CONCLUSION, AND RECOMMENDATION

5.1 Summary

35

The physical and mechanical properties of two varieties of pearl millet (Pennisetum

glaucum) namely EX-BORNO and SOSAT have been determined and compared as a function of

grain moisture content varying from 7.3% to 16.7% (db). In this moisture range, grain length,

width, thickness and geometric diameter increased from 3.780 to 4.170mm; 3.760 to 4.100mm,

2.500 to 2.730mm; 2.160 to 2.360mm, 2.220 to 2.460mm; 2.080 to 2.270mm, and 2.751 to 3.029

mm; 2.557 to 2.789 mm, respectively; the grain surface area, frontal area, volume, sphericity,

and porosity increased from 23.942 to 29.043mm2; 20.625 to 24.555mm

2, 7.434 to 8.966mm

2;

6.363 to 7.582mm2, 11.127 to 14.881mm

3; 8.868 to 11.512mm

3, 0.730 to 0.728; 0.686 to 7.582 ,

37.261 to 41.176 %; 39.914 to 39.048% respectively; the 1000 seed mass, solid density, angle of

repose (wood and steel) and increased from 8.04 to 9.010g; 9.80 to 11.140g, 1333.47 to

1327.47kg/m3; 1342.54 to 1316.55kg/m

3, 31.43 to 34.050

0; 26.36 to 28.720

0 for wood; 27.26 to

29.960; 22.49 to 26.55

0 for steel respectively. Bulk density and coefficient of friction decreased

from 806.68 to 802.47kg/m3; 840.49 to 781.65kg/m

3 and 0.3111 to 0.2923; 0.3325 to 0.3102 on

wood, 0.4159 to 0.3785; 0.4303 to 0.3911 on steel respectively.

5.2 Conclusion

Some physical and mechanical properties of two varieties of millet namely SOSAT and

EX-BORNO which were obtained from the Institute for Agricultural Research (IAR), Zaria,

were determined in relation to grain moisture content. The properties determined are length,

width, thickness, geometric mean diameter, thousand kernel weight, volume, surface area, frontal

area, sphericity, angle of repose on wood and steel, coefficient of friction on wood and steel,

hardness, bulk density, solid density, and porosity. Length, thickness, sphericity, and hardness

36

were the only properties that are not statistically different at 5% significance level. Thus, the

remaining properties were found to have significant different at 5% significance level.

Despite the effort been made on the search of available literature on the significance of the

properties determined to the design of millet thresher, hands were laid on few available

literatures on the significance of the properties determined to the design of millet thresher.

5.3 Recommendation

1. The physical and mechanical properties of the two varieties of millet (EX-BORNO and

SOSAT) determined in this project can be used in the design of post-harvest machines

and equipments such as a small scale low cost millet thresher using local materials for

our local and small scale farmers.

2. The study was limited to EX-BORNO and SOSAT and at moisture content levels of

7.3%, 9.3%, 10%, 11.3%, 14.7%, and 16.7%. Therefore, further investigation can be

conducted on different varieties and different moisture content levels which vary from

one region or area to another.

3. The study has been done on some of physical and mechanical properties of two varieties

of pearl millet. Thus, some properties were omitted especially the cracking force. The

cracking force was unable to be determine due lack of equipments in our laboratory.

Though the equipment was available at ABU, where an attempt was made to use it. It was

not possible due to lack of electricity. Thus, the cracking force and other important

properties can further be determined.

37

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