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NASA-CR-174636 19840023525
NASA Scientific and Technical Information Facility
FFNo 672 Aug 65
MAY 1 6 19&& LANGLEY MESEARCH CUHE~
lI'~AI!Y NASA HAMiYItlN, VIItGINIA
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https://ntrs.nasa.gov/search.jsp?R=19840023525 2020-06-24T05:27:36+00:00Z
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NASA Contractor Report 174636 3 1176 01324 3564 __ _
Analys1s and Test1ng of a New Method for Drop S1ze Measurement Us1ng Laser L1ght Scatter Interferometry
w. D. 6acha16 and M. J. Houser
Aerometr1cs, lric. Mounta1n V\ew. Ca11forn1a
(NASA-C~-174Lj6) dJAlY~lS AN~ I~Sll~G Uf A ~l:IO/ i1ETdlJ;:; FI.)l\ Li,Ll' S ... Z;': i'iLA;jr.;J.·L1";;~'I U511,G :'ASEH "Cid.'IEh 11 • .i:LHiEl-.C:1ETH £'llldl L;;port
----_.---
(lleroilli:.u:ics, LIC.) 6d p he 1\04/i11' Aul UIlel.l;;:
August 1984
Prepared for'
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION lew's Research Center
(~C~ 14c G3/35 20187
., Under Contract NAS3-23684
I" t 'rl
NOMENCLATURE ...
1.0 INTRODUCTIO;\;
Table of Contents
2.0 THEORETICAL DESCRIPTION
2.1 Light Scattering Theory ...... .
2.2 Phase/Doppler Spray Analyzer Technique
3.0 EXPERIMENT . . . . . . . . .
3.1 Description of tbe Apparatus .
3.2 Experimental Verification of the Theory
3.3 Signal Quality Effects ...... :.
4.0 St;MMARY A~D CO;'l;CLUSIOr-;S
REFERE~CES . . . . . . . . . . . . . . .
. iii
1
5
·5
13
16
16
20
24
28
30
This Page Intentionally Left Blank
NOMENCLATURE
C(m.O) proportionality constant
E elect ric field
lInt light b('am intensity
10 light beam intensity at the measurement station
L optical path length
S number of drops per unit volume
p pov.w
Qc:1 extinction coefficient
QUQI light scattering coefficient
S(o. m. OJ scattering amplitude functions
\' visibility
l'mill' \ 'm:n sign al \'olt agp levels
a drop radiu~
d drop diamt'tt'T
db Ia~er b('am diameter at transmittpr lens
d:;. beam waist diam('ter
J focallrngtb
11. I:! squares of tb(' moduli of the amplitudp runction~
j = V=-l imaginary number
m refractiH'indrx
n Ilumber of particles in size class
r polar coordinate
s b('am s('paration at the transrnitt('t It'ns
timt'
X,Y cartt'siall coordinates
iii
PRECEDING PACE BLANK NOT FILMED i)M'G: \ \JIIi'!"("I\'}'I"IJA1! \I ,' ... \.'~' ~-Ltw*-,~ n .... ij Vn 1..4.1 .lL.I-II<!,
o = i.e/I).. size parameter
') beam intersection angh'
b fringe spacing
'7 phase due to optical path length
(J scattering angJp
).. laser wavelength
r. 3.142
(1 combined phase due to focal lines, optical path, and reflection
., light ray incident angle to the surface tangent
.,., refracted ray
o phase shift of th(' Doppler signah;
tv
1.0 INTRODUCTION
ORIG!N,l\L P/\G;:: l~]
OF POOR QWHJn
A resea.rcb progra.m was conducted to eva.JuatE' an innovative concept for spray drop
siZl> and velocity cbaracterizat ion. This program was motivated by the increasing demands
on diagnostic techniques which have accelerated with the need to rorm spray drops having
controlled size distributions, spray patterns, and mass flow rates. The goa.l or this program
is to develop an instrument for fuel spray combustion applications. However, the required
capability oC efficiently and accurately characterizing sprays is associated with a much
larg('f rang!:' of technologies. These applications include coal-oil and coal-water slurry
combustion, nuclear reactor saCety, aircraft icing, a~icultural sprays, meteorology and a
variety of industrial processes.
Thl> development of advanced laoSer-based instrumentation remains of importance to
tbe progress of experiml'ntaJ research andpr{'dictive code development in fuel spray com
bustion .. Increa..<;ed Knowledge and undel"Standing of the fluid dyna.mics and combustion
chemistry are required in the development of aircraft engine combustors to enabll' con
tinuous and efficient burning of fuel at high rates ""it'ha, minimum of soot' and other'
pollutant formation. Prest'ntly thert' is considerable interest in obtaining measurem('nb
of thf' fuel ane! air motions within the spray dropl(·t combustors. It is known that tbe tur
bul('Ilt motions infiuenr(' th" rea('tions by increa.sing the oxygen supply to the burning fup!.
The rela.t i\'e velor it i('S between t he gas pbase and liquid droplets not only provid('s oxygPli
to tb(· burning droplet but also serves to remove tbe products of ('ombustion and bell(,(',
affects tbe evaporation and burning ratt'S and the poilutant formation. Thus, tt\:' drop!!'!
size distribution and velocity are importa.nt data to be obtained when characterizing the
combust ion process.
Basic r('Searcb ha.s also been conduded on two-pha.<-e turbulent j€'ts1.:!.3,4 to furni~h
a ba..<;is for the development of predirtin codes tbat may ultimately describ(' the' fluid
dyna.mics of spray rombustioD. This work has revealed that the turbulence structure of tll(·
continuous pha.se is altered by the presence of tbe dispersed phase. As may be exppcled.
the dispersed pha.<;e reduces the turbulense spectral intensity. in particular tlH' hibhl'r
frt'quencies. siure the dispersed pbase droplets do not tra~k the turbulent eddy fluctuatioIlS
and thus, increase th!:' dissipation of turbulent kim .. tic en (;rf:,,)·. Experimental in"esligati0n~
1
)
" /
._~ _..: ... : .. I. ::::{
uHICNi~,L. 'Pj':.~~.,: ','J
OF po on QU;\:...iC\/
<> ........ ~.~~" •• ,'- \--':"
have been carried out to measure the turbulence chara.cteristics with solid monodispersed
particulate. The need to obtain a complete data base using monodisperse and poly disperse
liquid droplets requires a. reliable means for drop size and velocity.measurement and (or
the separation of the gas pbase and liquid droplet velocity measurements.
The need ror simultaneous size and velocitv ~ea.suremeDts bas been recognized even
for the general characterization of sprays. This is especially true when studying nozzles
that generate droplets that a.re moving at a. relatively high velocity and subsequently relax
to the ambient Bow speed in accord witb their initiai momentum. The differing flux of the
various size classes can affect the measured size distributions depending on the metbod of
measurement.
In general, droplet sizing imposes unique constraints upon the techniques that may be
utilized. Droplets are deformable, break up under aerodynamic forces and collisions with
probes, contaminate surfaces, and are often present at high Dumber densities. Sampling
and otb!;'r material probe methods are therefol'e less desirable for implementation in spray
measurements. Optical methods consisting of im?-ging and laser light scatter detection
have been applied with varying degrees of success. The relative success of a method is
largely dependent upon the measurement environment, droplet size and number density,
type of matE.'rial forming the droplets, and othE.'r physical constraints of th,e test apparatus.
Instrument limitations are dependent upon the physical concepts incorporated Gto the
measurement de\'ice and how these cODcepts are affected by mteraction with the surround
ing spray, aerodynamic and temperature fields. Techniques that have proven reliable in
ODe measurement situation bave produced erroneous results in others.
Because of the high droplet Du:nber densities in\'olved, most light scattering method~
classified as single particle counter systems will not function properly in spray environ
ments. Basic methods utilizing absolute light scattering intensity measurements will ex
perience significa.nt errors due to partial extinction of the laser beam and scattered light.
For these rE.'asons, the small angle scatter detection methods developed by Dobbins et
a\.5 and Swithellbank et a1.6 bave been favorably received. tJnfortunately, instrumC'nts
based on these concepts can only measure the Sauter mean diamet<.>r (S~ID) dirl'ctly.
Furthermore, these measurements are made_o~er' the entiret'xposed path of tb(' laser beam
2
,~/
k: __ . ':' .. : .... \., \ •.• -,:t I -:'~'
OflIGINN •• f),e.c.': ,j OF POOR QUj:~L1TY
which resul1s in poor spatial resolution. The methods cannot produce inCormation on th(·
droplet number density or the velocity.
Simultaneous measurement of the droplet size and velocity bas led to the combinat ion
oC the laser Doppler velocimeter (LDV) witb particle sizing methods. Particle sizing
interferometry developed by Farmer7 was a significant attempt in achieving this' goal. The
method utilized a standard LDV optical arrangement with on-axis light scatter detection.
Signal visibility was processed to obtain information relatable to the particle diametE't. The
method was however. limited to very low number density particle or droplet environmenb.
YulE'. et al8 attE'mpted to make simultaneous size and velocity measurements using an LDV
with small off-axis angle scatter detection. The droplet size inrormation was obtained from
th(' amplitude of the s('attered light intensity. The difficulties involved with the Gaussian
beam intensity distribution notwithstanding, the measurements were also affected by the
partial extinction of the laser beams and the scattered light.
Bachalo9 described a method that eliminated many of the aforementioned diflieulti('s
by producing a rigorous an:;dysis of the dual beam laser light scatter for large off-axic;
r('ceiYE'T angles. By using large angle light scatter detection, the measurement region couid
be reduced by as much as two orders of magnitude compared with the on-axis approach
This contribution suggested that the measurement of the size and velocity oC individual
droplet~ might be possible in dense sprays. Cse of the light scattered by reflection and
refraction allowed the measurement of dropl~ts as large as several millimeters in diame'ter.
The Droplet Sizing Interferometer based on the technique proved t.o be successful
in producing droplet size and velocity and size-velocity corrE'lations measurements under
limited spray conditibns. However, because of the signal processing methods used. th(·
system had some serious limitations. These included the need Cor extremely cardul
alignment, a size rangr sensitivity of a decade or less witb reduced size sensitivity at thl'
small size end of the range, a narrow Doppler frequency response range and sensitivity to
laser beam quality and relative intensity of the two beams.
Because of the significant potential advantage's of the light scattering interferometry
method, a new means fur processing the interference information was derived. This ~~
f!
innovation promised to increase the dynamic range of the syst~m while reducing the
possibility of measurement error resulting from imperfect alignment or beam intensity
differences at the probe volume. The concept resulted in a linear response to the drop size
with a r.elath·ely uniform sensitivity over the entire measurement range. A measurement
range of o\"('r a fa~tor of 30 can be attained while a factor of 100 may be possible without
optical adjustment but with only a ~haDge in photodetector gain.
In the following sections, a theoretical description of the concept is presented and the
experimental setup of the device is described. The test procedures used to evaluate the
method are outlined and test results are presented.
4
"\
.. ) -.
2.0 THEORETICAL DESCRIPTION
2.1 Light Scattering Theory
The scatt.ering of light by homogeneous dielectric spberes of arbitrary size is described
exactly by the well-known Loren~-Mie theory. However, even with large computers, the
computation time rE:'quired to calculate the scattering coefficients for a range or drop sizes
can bE:' prohibitive. The number of terms needed to be computed in the series solution is
proportional to the size parameter 0 = lid/A. Fortunately, for drop sizes greater than
thE:' light wavE:'length A, simpler asymptotic theories may be used. For spherical scatterers
that can be regarded as small spherical lenses or mirrors, the geometrical optics methods
produce accurate results.
van de Hulst 10 showed that for spheres much larger than the light wavelength and
with refractive index sufficiently different from the surroundings, the amplitude functions
derived from the geometrical optics approa('h were, in the asymptotic limit, equal to the
~1ie ampJit ude ru))('tions. Comparisons have been made to the exact Mie theory by a , ' . " 'I ~
number of research~r~ll:l:! to demonstrate the accuracy of the geometrical optics methods.
Yery good agreement was dE:'monstratedby Glantschnig and Chen12 for drops as small a::;
5 micrometers ..... an de Hulst demonstrated that for 0 > 10, the scattering of light can be
separated into the simplified theories of diffraction, refraction, and reflection.
Sca.ttered Intensity
Light scattered by diffraction which is described by the following expression
S. (0,8) -:- 02
A[J1(OSin 8)] d,!! 47r 0 ~in e (1)
where Jl is the Bessel's {unction and 0 is the scattering aUble is concentrated in a lobe
centered about the transmitted beam. This forward scattered light becom(:s more intense
by the diameter squared and smaller in angular distribution with increasing drop size.
Hodkinson and Greenleaver11 have shown that. for 0 > 15, diffraction becomes insignificant
at scattering angles greater than 10°. For spheres of refractive index m - 1.5 and
diameters as stnall as 2 micrometers, diffractive scatter is less than 10% of the total light
scattered at 45°. Thus, the light s('attered by diffraction canbe avoided when desired, by
proper placement of the r(>cciver.
5
;J '.<
l
" '"' .
ORIGINt\L rf{f:~:': ;", OF POOR QUt\!_:',
Light sC'aHered by refi('rtion and refraction is best described in terms of rays and the
use of tht' simple laws of refiedion and refraction, When a ray impinges on the surface of
a transparent sphere it produces a reflected and refracted uy, figure 1. The direction of
the refracted ray follows from Snell's law:
cos T = m cos r' (2)
whNe T and.T' are the angles between the surface tangent and the incident and refracted
rays. respectively. The partitioningof the energy into the two rays follows from the Fresnel
The emerging rays are characterized by two parameters, tbe angle T of the incident
ra\" and the integer p o( the interface, from which it emerges, That is, p = 0 (or the first . ,
surfacr reflection. p = 1 for the transmitted ray and p = 2 for the ray emerging after
one internal reflection, The energy in the remaining re~t'ctions is insignificant. The angl~""
betw('en thp incident ray and tbe pth emergent ray is given by
8 = 2(pi' - i) (3)
The fra("~ion of the incident intensity contained in tbe emergent rays can be obtained from
the Frbnrl coefficients. The details of derivation of the closed form 8-dependent intensity
functions are given in GJantschnig and Chen and only the results will be quoted herE',
In thr- notation of van de Hulst, the scattered light is described in terms or two
amplitude functions, SI(O', m, 0) and S2(0', m, 8) for the perpendicular (to the scattering
plane) and parallel incident polarizations, respectively. van de Hulst demonstrated that a
Jargespbere scatters over. flO% of the incident light in the rorward direction with gg.SC'(·
of the for,,'ard scattered light emerging from tb(· first two interfaces (p = 0 and p = 1),
Thus, only the first two terms of the series describing the rays emerging from the various
interfaces need be considered for most practical applications.
Glantscbnig and Chen obtained the following expressions for the amplitude function
6
)
ORIG'Nlil !:;:iI''''.'''' .... • ,... •• -IUi>::' ~~~ .
OF POOR QUALlTV
drs('rihingthr rays rd1c·('tNI from tllr first surfu("\, of the sph<'T(':
. 0 C' ;'''---:1 7f [ ( )] (I). Sin;, - V m~ - (,OS"-.) 1. r. . 0 S I (n. 111. 0) = 0 .. ··-···~·---·---=;=oo !:. - ex p ) .... + 20 Sill ..
. 0 C'" ,., 0 ? ? ? .' Sill ~ + V rn~ - ros~ 2 - - -
(.t)
(S)
wht'rl' suprrs('ript 1 implies thr p = 0 refir('tioll anQsubscripts 1 and 2 repres('nt til,'
pNp('ndic-ular and parallel polarizatiolls respertivdy. Th(' amplitude tundions for tlH' r:ly,;
enwrgillg from th(' second surfac-e aftl'r retraction by the sphl'f(' aregi\'en as follllws:
sil( 0 m.O) = + -C I 75~~i;,~s=t rlF':~~n~~; :o:,t~ill~~~i'j;~) (.1
X .x+( t" -20f +-~,~-=;';;;~sOl
Summing thp arnpliludp functions. thr total tor forward light scalterill~ is gin'lI a~
8)0,771,0) = Sdil 1(0,0) + S,)(o, m, OJ + 87(H. m. OJ
The dirnensionlrss intensities ij are simply
ij(I}. m, 0) = IS,;(o. 711, 0)1 2
7
j = ],2
.1
ORIGlNtl.L FF,'::;~ ~':r OF pom~ QU;\UYY
These expressions produce accurate results with the exception of s('attering at grazing or
nearly grazing incidence and for scattering into the rainbow angles as indicated by van de
Hulst. Th(' geometrical optics results can be used for values of Q~ 15 depending upon the \
information (what s('attering angles) and accuracy required. Comparisons of an ~xample
calculation with Mie theory (from Ref. 12) are sLown in figure 2. The agreement for thC'.
5J1m diamett>r droplets is very good even j hough this is near the minimum size wherein
the geomet.rical optics approximation applies.
For spheres large enough (d > 3J1m) to satisfy the above critNia. the scatt('red light
intensity appears as an obvious means for size analysis. The square of the diameter of the
spherir;ll scatt t>rE'C ('an be assumed to be proport ional to the scattered light intensity!
/..cadd, m, 0) = e(m, 0)· d'2 (10)
This rplat ionship is correct provided that the receiver fino. is smal: enough to form an
awrage over the angular fluctuations resulting fcom interference !}etween the ceflected
(p = 0) and refracted (p = 1) light. The measured light intensity is also dependent
upon tht' incident intensity 10 which is muitipl",d by the scatterir.'g coefficient, Qn,li'
In practic('. the optical collection efficiency and losses in the system are determined by
calibrations using spherical particles or drops of known size. t:nfortunately in realistic
droplet environments, the droplets wili attenuate the transmitted bea;;..:> and the scattered
light by an indeterminate amount.
For example, the light intensity scattered by a cloud of drops is
k
Qua/.N = 2: niCdi)I~cadm, 0, dil i=l
(11)
where the ni are the number of parti('les of size d j . The loss of power due to transmbsion of
the beam through a droplet. fi{'ld of path length, L is given by the wdl known Lambt'rt-Brer
lawa.s
dP = -kextlAdx
8
( 12)
..
ORIGINAL PtJ.GE ;~3 OF POOR QU.::\LITY
and the integrat.ion over the path length L gives
( 1:3)
whE.'re Jint is the incidE.'nt. intensity where x = O. It is known that for large Q the extinct ion
co('ffici('nt approarhps the value of 2 asymptotically. Tbat is,
lim Qcxt = 2 a"" co
(14)
This is often referred to as tbe extinction anomaly since large spheres would be expected
to block th(' light falling on there cross-sectional area. However diffraction whk!: i" an
edge efft'ct also scatters light proportional to the drop cross-sE.'ction;l] area. In tIl<' abs('n('p
of any absorption,
( 1:))
WhNt' a is th(' avcrage drop radius in the field. Benre,
( IG)
where'\" is the numher of droplets pet unit volum'~ and L is the optical path length through
the spray. For examplE.'. a spray with a mean drop size of 50llm at a number dE.'nsity of 100
drops/cc and a widt h 0(20 em will have an attenuation of lo/Iinc = o.gz. Assuming. thaI
Q,.cal is proportion31 to d'!., the error in tbe determination of d is approximately .1('c.";\t a
droplet concentration of 500 drops/ee, the mE.'a.sured drop size would be 18(~c smal!E.'r tlwn
it actually was barring any otiJE.'r attE.'nuations in th,:, optical path. TIH'numbE.'r dpn-;iti,>s
used in these examples are not atypical of those found in actual sprays. Thus, the simpl\'
u~eors('attered lil~ht intE.'nsity may not be a reliable m(>thod for measuring sprays. EH'n
with frE.'quE.'nt calibrations, these uncE.'rtaintips dur to attpnuation by drops in til(' L":1m
will occur.
Phase Dlle (0 Opti('aJ PatIi
ThE.' light rays emerOging from the sphere will bare diffE'TNlt path h>ngths d('Iwlldin;;
upon th(> angle of s('atter and th~ path lengths through til(> spll(>T(" For this reason, ttl('
9
'0
, <: I,
.'
>.
,. .
~1 . ".;
OR!G!Nr"lL ?~~(~:j:.: ; ..... , OF POOR Q:J,\:"'LY
.. .
~." ~ '"
intensities of the outgoing beams cannot be added directly. The beams which all originated
from the same coherent incident wave must have their complex a.mplitudes added and the
squared modulus then becomes the correct intensity.
In order to compute the phases from ray optics, van de Hulst references the actual ray
to a hypothetical ray scattered without .8. phase lag at the center of the sphere. l'\eglecting
phase shifts of 1r at reBE'ction and phase shift!> of r./2 at focal lines (all of which cancel
from the subsequent analysis), a simple geometric analysis results in the expression
'1 = 20'(sin T - pm sin r') (17)
for the phase shift witb respect to the reference ray. It is of interest to note that the phase is
directly proportional to 0' = ¥ which implies that the number of extrema in the scattering
pattern is also proportional tv the dimensionless size, 0', The change in phase which is
independE'nt of the incident intensity or scattering amplitudes but is directly proportional
to tbe drop diameter is a more practical means for obtaining the size information.
Dua.l Beam Light Scattering
One approach for extracting size information from the phase shift is to utilize th(>
dual beam seattering arrangement of the familiar laser Doppler velocimeter (LDV), figurE'
3, Assuming linearly polarized light, the amplitude functions associatl'd with scattering
from beams land 2 are
Sll(m.8,d} = V;; exp(jerd (IS)
(lg)
where the double subscript indkates only polarization 1 is considered, j is the imaginary
value /1 = --1 and (J = tJ neglecting phases shifts of 1r due to reflection, 1r/2 due to focal
. lines and the Fresnel coefficients. When a spherical partkle passes th,rough the intersection
of the two beams, it will scatter light trom e.ach beam as if the other beam W3.S not there.
Thus, the scattered ljght waves may be described as
10
... ,. ,. ~.' . ~ t';' >:.:-
~. '
1:1.,.
ORICfNAL PA1~;i7';' OF POO,'? QUA<L"n:';'
''',',.,
'E ( B .1,) - S ( 0 d)exp(-jkr + jWtt) 1 m, ,," - 11 m". 'k
J r
E ( () d) = S ( B d)exp(-jkr + jW2t) 2 m, , 12 m, , 'k '
J 'r
(20)
(21)
The total scatter is obtained by summing the complex amplitudes from each beam and
then determining the intensity which is
(22)
were 0' if the phase difference between the scattered fields, In this expression, the cross
product term 21EIIIE21 cosO' corresponds to the sinusoidaliDten~ity .... ariation of the fringE', .. ,'
pattern while the IEte + IE~d2 terms are the d,c. or pedestal components. The visibility
of the scattered fringe pattern is simply equal to the ratio of these two terms.
v == 21£111 E 21 cosO' IElI~ + IE212
(23)
Confusion can occur here by the use of the terms visibility and signal visibility. In th(>
former tase. ~1ichelson 's definition is implied which is a measure of the distinctness of th<:>
fringes formed in the space surrounding the drop, figure 4. If a point, detector was moyed
normal to the resultant fringe pattern, a signal proportional to the local light intensity
'would be produced and the visibility of the resultant sinusoidal signal would be
v = l';nax - Vmin Vrnax + Vmin
(24)
The signal risibility is the relative modulation of the signal received through the detection
optics and photodetector. This is usually produced by the integration of the scattered
fringe pattern over the area of the receiver lens. In general, the signal visibility depends
on the receiver aperture, drop size, the beam intNsection angl€', and li:;ht wavelength as
11
well as other param('ters and will always be less than or equalto the scattered interference
fringe visibility.
SiDce the rays from beams 1 and 2 intersect at a small angle. ')'( < 10°), at the sphere,
the scattering angles 81 and 82 for these pairs of ra.ys reaching a common point in space
and interfering are approximately equal. Thus, the amplitude. functions 51 and Sz are
also approximately equal. From equations 20, 21, and 23, it follows that the visibility of
thE'fl'inge pattern is approximately unity. The spatial frequency of the fringe pattern is
determined by the relative ph~e difference. (J of the interfering light waves scattered from
beams 1 and 2.
Signal visibility has been used as a means for determining the drop size [7J. When
. the drop moves through the intersecting laser beams, the fringe pattern that is produced
appears to move at the Doppler diffe.rence frequency. The DoppJer differe.nce frequency is
a function of the beam intersection angle, light wavelength, and the velocity of the drop.
The spatial frequency of the fringe pattern is dependent upon the angle of observation ..
drop index of refraction. beam intersection angle, laser wavelength and the drop diam€'ter.
Placement of a receiver lens to collect the scattered light will produce a Doppler burst
signal as shown in figure 5. The lens, in effect. acts as a length scale to measure the spatial
frequency of the scattered fringe pattern. Integration of the fringe pattern over the receiver
apert ure produces a Doppler burst signal with a signal visibility that may be related to
the drop size. This relationship is shown in figure 6.
Although the m€'tbod ba..<;:ed on measuring the signal visibility partially eliminated the
problems associated with intensity measurements, provided a means for the simultaneous
measurement of the drop size and velocity, and did this with high spatial resolution. it
bas several shortcomings. .As previously mentioned, the visibility of the scattered fringe
pattern will be equal to unity if the scattered intensities from eacb beam are equal. Since
the measured signal visibility depends on this being true. the incident laser beams must
be o·r equal intensity in addition to having the same linear polarization direction and being
coherent. These requirements may be frustrated by optical imperfections and alternate
attenuations of the beams by lar~~e drops. Because of the Bessels function relationship
between the measured signal visibility and the dimensionless drop size. the error produced
12
I
. . ",. ., .'. .; t" ~
can be telatively large at the small size end of the measurement range. Another difficulty
associated with the instrument response function is the limited size range of 8. factor of 10
or less. Typical drop size distributions extend over a factor of 30 or greater. Because of
the need to have equal intensities from each beam incident upon the drop, the alignment
of the system is also very critical.
2.2 Phase/Doppler Spray Analyzer Technique
As aforementioned, the spatial frequency of the interference fringe pattern produced
by the scattered light is linearly related to the drop size. The mathematical description of
the interrereoce pattern which includes the effects of all of the optical parameters, is then
required before this information may be utilized. With the complete theoretical description
of the s{"attered fringe patterns for the hppropriate parameters, there is no longer any need
to calibrate the system for each measurement task. The drop size measurement can then
be obtained from the accurate measurement of the spatial frequency of the interference
fringE' pattern.
The theoretical description of the fringe pattern was derived and software was generatE'd
to compute the fringe patterns at any selected optical parameters and to plot the resultant
interference fringe pattern. Three scattering regions of practjcal interest were considered:
forward scatter 10° ::s; 0 ::s; 50°, backscatter 1300 ::s; 0 S; liDO, and (j = 90° where 0 is
measured with respect to the transmitted beam direction. Light scattering by a combina
tion ot refraction and reflection at similar intensity will occur at some angles and under
certain parametric conditions. Where this occurs, tbe spatial fringe pattern is no longer a
pure sinusoidal intensity variation becauseof the multi-component scattering interference.
That is, additional interference between the refracted and. reflected rays will occur and
produ("e significant errors. Such errors can be minimized or eliminated with the proper
selection of detection and processing methods. The computational schemes were able to
accurately represent these phenomena graphically and thus, allowed the deve!opm('ot of
the optics to a\'()id these possible error sources.
An example of the computed interference fringe pattern is given in figure 7. The
sinusoidal fringe pattern was computed (or a plane normal to the beam directions. Only
13
-
I. :%« .• 4:"4 )~t;;., ps,;".v;ug;;;:;; fit ltlWIt9.mt~~·~FII(yji 'i!'.t-~~,li""",~ltI!''''II!~';i!?_?·''';'~'fl':'Iq'il'''4."WHlIt9¥fhH"I'l.~'<v.tm"1>l1'l'!'I1'i'!""~'" ~1,Jtt.~':~.~., .. :\.\"~\',~'~. '~ " . I .,.. . .• ': _~ .: ",' ,.,.;,.' .... -""~.'O'"'''' .:, : ," ", " " .. _ .... :.' ...••.•..•• :, •... ,' ';/.,.,~.).,'-: '" _,'- . " . ," i.
- .
the upper half of the symmetric fringe pattern was reproduced. As observable on the figure, .'
the fringes are hyperbolic curves showing a decreasing spatial frequency with distance from
the beam axis at x = 0, y = O. The pattern is also symmetric about x = O. Thus, the
,- spatial frequency of the fringe pattern is dependent on where the measurement is made.
Measurement of the fringe pattern would be relatively easy if the fringes were of
relatiyely high intensity and or low temporal frequency. Unrortunately, the temporal
frequency of the fringe pattern is essentially the Doppler difference frequency that will
vary according to the speed of the drop. This frequency may be as high as 2 MHz in spray
environments. The scattered light intensities will be low and will vary over several orders
of magnitude. A receiver lens and eitber photomultiplier tubes or solid state detectors are
required to pro-.'ide the necessary sensitivity.
Thescherne used to measure the spatial frequency of the scattered fringe pattern
requires tbe use of two or more detectors separated by fixed spacings. As the drop passes
througb the beam intersection region the fringe pattern appears to move past the receiver
at the Doppler differ~nce frequency. A Doppler burst 'sIgnal similar to that shown in figure
5 will be produced by each detector but with a phase shift between them as illustrated
in figure 8. The signals in .this figure have been l:igh pass filtered to remove the pedestal
component. The phase shift' is then determined by measuring the time between the zero
crossings of the signals from detector 1 and 2 and dividing by the measured Doppler period.
Th'at is.
- 1}_') 0 ~1-2 = _M X 360
1D (25)
where the measurements are averaged over all the cycles in the Doppler burst signal.
Measurements of the phase shift are then related to the droplet size using the linear
relationships shown in figure 9.
In figure g, the effect of changing the optical parameters whicb include tbe laser
beam intersection angle, collection angle, drop index of refraction, laser wavelength. and
scattering component detected is to simply change the slopes of the linear response curves.
That is, only the size scale is changed for the same range of phase angles since tbe curves
all must pass through the origin.
14
, "
'"
ORIGINAL PAGi! IS OF POOR QUALITY
Three detectors are required to ensure that measurement ambiguity does not occur.
When measuring polydisperse sprays without knowing the approximate siz.e a priori, phase
shifts of greater than 3600 could occur. Such occurrences would be measured as being
. less than 3600• The third detector provides a logical test to identiry and eliminate such
uncertainties. Pwper selection of the detector spacings also provides two sensitivity ranges
shown 3,..<; curns 91-2 and 91-3 on figure g. The two phase measurements will allow the
additional testing of the measurements in tbe overlap region and extends the size range
semitivity at on(> optical setting to a factor of approximately 100.
The dynamic range which refers to the ultimate size range measurable at one setting
including the range of the detectors is somewhat less than 100. Because the drops scatter
light approximately in proportion to their diameter squared, the detector would require a
dynamic response over a factor of 104 or greater. A factor of 103 is realistic. However,
th€' det€'ctor gain can be easily set to select the optimum sensitivity without requiring any
optical adjustments and realignment.
Thus. the method has. several potential advantages for obtaining drop size and velocity
data. BeC'ause of the range of validity of the scattering analysis used, the overall size
rang€' is 3 micrometers to 2000 provided the drops remain spherical. Both the drop sizE'
and its velocity are measured simultaneously. This capability is useful in providing a
complete description of the spray drop size distribution (including both the. spatial and
temporal distributions). Measurements of tw(}-phase turbulent flows which requires the'
d(>termination of drop size-velocity correlations and the gas phase velocity based on small
part ides is an important capability of the method. With the use of highly focused beam~
and off-axis scatter detection, these measurements can be made with very high spatial
resolution.
In the following sections, a summary of the experimental evaluations of the method
are discussed along with a presentation or the results.
15
I'·
3.0 EXPERIMENT
The experiment.al ~ffort was directed toward the verification of the theoretical analysis,
evaluation of the phase processing method, and investigation into signal quality effects. The
early stag(> of the experiments was concerned with validating the predicted signal phase
sbifts. Tbis validation was necessary before any effort was expended on signal processor
design and development which would be a major task in itself. As a result, initial phase
measurements were obtained from individual oscilloscope traces of the detector outputs.
Although tedious, this method proved satisfactory in providing the necessary verification
to justify continuation of the experiments. Following the successful validation of the phase
shift theory for a limited number of cases, attention was given to tb~ development of an
electronic signal processing method. A breadboard processor was designed and constructed
allowing the a('cumulation of large data records at a relatively fast rate. The addition
of the signal processor permitted furtber verification of the theory over a wide range of
system parameters. Also investigated was the effect of signal degradation on the measured
phase shift. Sources of signal degradation known to adversely affect similar droplet sizing
schemes were examined to determine their effect on the pbase shift method.
3.1 Description of the Appa.ratus
The basic hardware and equipment needed for tbe experimental phase of the project
included: transmitting optics, receiving optics with detectors, electronic signal amplifiers,
filters, signal processor, oscillos~ope, data management system, and a droplet source.
Although the configuration of the system changed at times and components were added
or omitted as necessary, the basic arrangement remained the same. A photograph of the
apparatus is given in figure 10 and a description of the components follows.
Optics
The optics are divided into a transmitter and receiver package. Each was assembll'd
independentlY on an optical rail which allowed reconfiguration of the light scatter geom(>try
to any desired collection angle. The primary configuration was the arra.ngement shown in
figure 11 whicb was t.he 300 off-axis forward scatter collection geometry. A majority of thl'
data was obtained with this arrangement.
16
ORiGINAL PAGi:: t8 OF POOI~ QW\Llrv"
The transmitter package consisted of a low power He-Ne laser operating at a wavelength
of 0.6328 micrometers, a beamsplitter (BS) which allowed for a variable beam separation,
a.nd transmitter lens (Ll) with (ocal lengths of either 220mm or lOOmm. The beamsplitter
produced two paralle) beams which were caused to intersect by the transmitting lens. The l .
beam crossover is the point at which measurements are made and is referred to as the
'probe volume', Interference between the two incident laser beams occurs at the probe
volume resulting in the formation of planar interference fringes parallel to each other and
separated by a distance known as the fringe spacing gi".'en by:
(26)
where 0 = fring(' spacing, A -. laser wavelength, I = beam intersection angle, J = transmitter lens focal length, and s = beam separation at lens. The number of fringes
within the probe' "olume is given by:
N= du' o (27)
(28)
where S = number of fringes, dw = beam waist diameter, and db = laser beam diameter
at, t ransrnitter lens. Variations in the above values are obtained by adjustment of the beam
separation, S , or transmitter lens rocallength, f.
The receiver package was comprised of a lens assembly (L2, L3) which collected light
scattered by droplets v.ithin the probe volume and focused it onto the pinhole. The pinhole
acted as a spatial filter blocking the light scattered .from other than the probe volume.
Light which passed the pinhole was directed by mirrors Ml and M2 to detectors D1 and D2.
The mirrors Were adjusted so that light from different. well-defined areas of the receiver
lens ,,'a.., directed to either Dl or D2. This n ,>ulted in an effective detector separation
~cross t})e race of the receiver aperture. The separation was variable and referred to as
17
.". ","" " .... ;:~':,'·"·.w·_, ",',' -"'."""'-~"""·'·T -'''--'"P''''''''i''- '''''-,' ,- "~~""'"''''=--''-~ ... --''--''.~ . ,- ' .. ". -' A"J
ORIGINAL pp,C;?' m OF POOI~ QUALITY
the slit s(>paration. The receiver packagp was modular and thus, could be plac(>d at the
sel('c\('d angle of collection, 0, measurE'd from the bisector of tlie int(,l's(>cting laser IH'ams
(transmitter axis).
Electronics and Data .\1anagell1Pnt
Although physically a part of the receiver package, thE' dE'tectors deserve additional
consideration. Solid state silicon photodiodt"s were initially selected to act a.<; detect9rs. The
quantum effidenc), of silicon photocells can approach gOC::O at the He:\'e las(>r wavelength.
The phot.odiodes are rugged, easily manageable, require only nO,minal (-15 VDC) operat
ing voltag('s, and can be obtained with integral pre-amplifiers. A good deal of time was
sp('nt developing silicon photodiodes to act as ddt'ctors for the phase measurement sys
t('m: Unfortunately, backgro1Jnd noi~e levels could not be lowere~ ~nough to provide thl'
required signal dynamic range of which the instrument was capahh'. It is felt that silicon
photodiodes or lowN noise silicon a\'alanche photodiodes could be engineered to perform
satisfactorily but such development was beyond ,tllp se~!>,\' of this effort. A decision was
made to employ photomultiplier tubes (P~fT) as signal detectors for the duration of the
experiments. Although more fragile and bulky than solid state devi('es, P~1T's exhil>it
almost negligible background noise levels and provide enough signal gain to overshadow
their laek of quanfumeff.<'iency. They also provided a convenient means of signal len'l
seiection by adjustment of the P~lT high voltag\"
Additional instrumentation utilized in the experiments included variable high pass
filters and logarithmiC' amplifi(,fs for ('ach of the two (·hannels. Th(' high pass filters remond
the pedestal ('omponent. from the burst signals while the log amps provided compression
of the wide range of signal amplitud('s. A dual ehannel oscilloscope \\a5 used to monitor
the signals at various points along the signal conditioning path.
As mentionl'd, initial phase measurl'ments Werl' obtained from individual os('il!o~('op(,
traces which were manually analyz('d (figure 12). As confid('nC'e in tht' theory inC'rl'aspd.
seHral automat.ic processing .,~h('mes were ('onsiciprpd. Among thl'1I1 were analog ph:l-,c'
determination using a signal mixN, <,ross-correlation techniques, signal digitizing using
ana)og-to-digit a) <'onverters, and digital proeessing schemes. Tht' close a.ssociation of t h('
18
i"
,
phase technique with conventional LDV systems provided a basis of existing digital signal
processing technology. The addition of phase determination circuitry to this type or
processing scheme was deemed most suitable and straigbtforward. A prototype processor
was developed which incorporated two parallel channels of Doppler period determination
and a relative phase measurement. Signal validation included amplitude comparison
(threshold and conventional three-level logic) circuitry designed to eliminate erroneous
signal scoring. The processor also included the 'variable N' capability. The number of
fringe crossings needed to produce a valid signal was not fixed as some processing schemes
require. The minimum number of cycles was user selectable, but the processor was designed
to utilize all available signal cycles in its period and phase determination. This capability
guarantees that the most accurate central cycles of each signal burst are included in the
mea.c;urement. Subsequent testing proved this to be a bighly desirable feature of the
processor. Individual signal period and pbase determinations were output by the processor
to the data acquisition system.
An IB:\1 PC micr'oc~mputer was programmed to accept input and manipulate data
from the signal processor. Calc-ulations of droplet size and velocity from the raw phase and
period data were executeG by the computer. A real time display of the size histogram was
also provided by the computer. Upon completion of data acquisition, linear mean diameter
and. when appropriate. Sauter mean diameter were calculated for the accumulated data.
An accompanyinls printer provided a hard copy record of the reduced data.
Drop Sources
Drops necessary to. evaluate tbe system and verify the theory Were generated from
three different de .... ices.
The Berglund-Liu generator 13 device produces a: stream of monodisperse drop:'. ThE'
range of useful drop sizes obtainable was roughly gO to 160 micrometers which often
depended "pon the operating peculiarities oftbe generator. Since the device wa.s operated
off the manufacturers recommended conditions, the drop stream would sometimes becomr
unstablE' producing a scattering of drop sizes instead of the desired monodispersit)'. r'\ot
only could this device produce a known-sized, variable, monodisperse drop field, but the
19
.. ~
v
ORIGI]\J,QL PAC~ m OF POOR QUAUrV
strl'amwise nature of the drops also allowed them to be selecti\'ely directed through specifiC"
parts of the probe volume, The Berglund·Liu was the only drop size standard used for till'
phase m('a~ur<'ment exp<'riments.
Til<' highly controllable nature of the Berglund-Liu device was necessary for verificatioll
of the theory, but did not represent the true environment of most drop fields. Polydisp<.>rsions
of drop siz('s and a certain randomness of drop trajectory, velocity, and arrival at the
prob(> volunw are more characteristic of a spray l'nvironml'nt. Cnfortunat.ely, there are no
'calibrat<,d' drop SOUTces of the type described, due in part, to the lack of instrumentation
capable of p<'rforming such calibrations.
To better simulate the actllal spray environment, several spray nozzles were u~(>d.
TIl(> watN suppl;' Ils(>d in the laboratory had a maximum line pressure of 80 psi. TIl(>
pr('ssur(> was regulated to produce var;:ing spray characteristics. Th£' nozzles used Wl'rt'
low to mociNatt' flow rate (.S to sHl>ralgallcns pt'r hours), solid conl' type. Garden \'ari('ty
nozzles \\('re ~ometimrs used to produc'c larger drops ina hollow cone spray patt~rn. ., "'~":'~ r... "
A spinning disc atomizt>r was utilizPd for onE' !;('t of tests. This dpvice is used for room
humidification and is known ((, g(>n('ratt' very small ("'-' 4-30 JIm) drops in a very n:lrrOW
distrihution. Both of these features wert' used in estimating the performance of the phase
mt'asuremrnt syster:1.
3.~ Experimental Verification of the Theory
Experinwntal data were obtain('d to validate the throretical predictions. Of particubr
importancr was the verification of the linear rrlationship betw('en nwasur(>d signal pha,;e
shift and drop size. Paramrters other than drop size which \\We known to affrc! the
measurement include r~inge spacing. receiving lens g('omet ry, and rt'ceiving angle. Eaeh of
these param('ters was investigated individually. The system response to more realistic spray
environments was tested using a series of spray nozzles and thr spinning dise atomiZ(>r.
Droplet Sizl' Varial ions
TIl(' s),st(>m' was aligned into the 30° forward scatter configuration (figure 11). TIlt.>
monodispt'fse droplet gcnerator \\'as the drop sourcf'. Tlw g('nl'rator ('ould bl' (unrd OY(>f
a range of operating frequencies to produce drop sizes from no to 160 l1licronl('t\'r~ ill
20
J.
,
diameter. This narrow spread in drop diameters was limited by the droplet generator and
represented only a small part of the dynamic J'ange of the instrument, To test the method
at both the upper and lower ends or the size range, the effective detector separation was
changed to double the maximum drop size t.hus lowering the phase shift for the drops
produced by the monodisperse generator. The individual data listings a.re given in figure!>
13 tbru 18. Tbis size data has been converted to phase angle a.nd is compared to the theory
in figure lQ sbowing excellent agreement.
Fringe Sparing Va.riations
Tb(> re5ultant. size range sensitivity for tbe phase measurement instrument is a fUD(,·
tion of fringe spacing, detector separation, receiver collection angle, and drop index or
refraction. The fringe sparing was cbanged with tbe accompanying size range variation in
the next series of tests. Each change in fringe spacing also incurred a proportional cbange
in signal frequency, number of fringes, and signal amplitude. Again, tbe Berglund.Liu
monodisperse generator was used to produce dropsofcODS\sti?nt size and velocity so that' '" .
th(> above changes could be anticipated as the fringe spacing was varied. A cbange in signal
frequency required a similar change in the higb pass filter cutoff while a variation in signal
amplitude required a detector gain adjustment. Compensation for the change in number
of fringes also affected tbe high pass filter setting. Every attempt was made to minimiz(>
the effect of these secondary factors during these tests, The fringe spacing was varied from
10,7 to 44.9 micrometers by adjustment of the beam separation at the beam splitter.. Data
listings for one representative test are given in figures 20 thru 23. These data are converted
to phase angle and plotted against theory in figure 24. Further substantiati,ng data from
similar tests are also shown.
Lens Geometr), Va.riations
Scattered light intercepted by the receiver lens was selectively directed to each of
the two detectors employed in the experiments. This wasac('omplished by masking the
receiver lens into two separate regions such that mirrors could be used to separate and
direct light to respective detectors. Since the receiver masking determined the effective
detector separation, this parameter was very importa.nt in fixing the size sensitivity of the
21
t. I ...
instrumt'nt. In fact, size sensitivity is lineal' with· effective detector spacing. Thus, size
sensitivity could be cODveniently varied by changing the receiver lens masking without
changing other signal characteristics.
To test the response of the instrument to effective detector spacing, a series of receiver
masking geometries was employed. The centroids of the rectangular apertures were taken
as the detector (~enters. The size sensitivity was varied over a factor of six by chang
ing the receiver lens masking from 12.7mm centroid spacing to 76.2mm centroid spar
ing. Except for some variation in the signal amplitude due to changes in receiver lens
! /number, no changes other than receiver masking were necessary to vary the size sen
sitivity. Representative results of this testing using the monodisperse droplet generator
are given in figures 25 thru 28. Receiver masking geometry is shown overlayed on each
data listing with the centroid spacing specified uncler the parameter 'SLIT SEPARATIO:\'.
Measured drop size agrees very well with Berglund-Liu drop size ('B-L SIZE') in all cases.
It was assumed that the centroid of the masked area was tbe appropria.te choice
for detector location. To test this assumption, several masks W('re designed with similar
centroid spacings but dissimilar geometries. typical results from these tests are given in
figures 2Q thru 31. Again, mask geometries are overlayed on tbe data histograms. In
each case the centroid separation was fixed at 50.8mm. Changes in lens aperture resulted
in chariges in signal amplitude which were corrected by defector gain adjustmeLt when
necessary.
Spray Sozzle and Atomizer Tests
This series of tests involved the measurement of polydisperse droplet spray field~
produced by industrial spray nozzles using water. Although the signal processor and
data acquisition system lacked much of the sophistication necessary to makE.> accurate
mea.surement in this type of flow, the data obtained show rema.rkably good agreement with
other measurement sources. In particular, signal rejection based on Doppler frequency and
signal amplification over a dynamic size range greater than 35 were not available with the
breadboard system. Kol' was the third detector required (or additional signal \'~lidatioD
and ambiguity availabJe.
22
OHlGINAL PAG.2 m ,)F POOR QUALITY
The majority of the spray testing utilized spray nozzles from the Delavan Inc with fl()~'
capadties ranging rrom .5 to 1.0 GPH. Typical resu\.s ror two different flowrate nO'z1Ie~
at 60 psig are shown in figures 32 and 33. These particular spray conditions were selected
because of comparative drop size distribution information provided by Deiavan(H). Figure~
34 and 35 show the phase Doppler measurements overlajed with the Delavan data.
Several other spr~y sorr,eswere used including garden variety nozzles and hand or
finger operated pump bv!t1es. Results from these tests were not included as no corroborat·
ing data was available.
A spinning di.'"c atomizer was used to test the small drop size sensitivity of the
instrumpnt. A typical distribution is shown in figure 36. As expectpd the size distribut ion
produced by the atomizer was very nanow with the majority of drops less than 40
minometers dia.meter. Thp distribution of figure 36 can be compared to those of figun·s 37
and 38 in which thp size sensitivity of the instrument was varied in an attempt to shift tnt'
location of the ffip.asurpd phase information. The selr·consistency of tbese measllremc'nb
can bt' seen when they are overlayed with normalized ordinates as in figme 39. The oat a
presented in these tests is in tbe 'raw' form with no probe volume corrections (,\'(,D th()ugb
thi::. type of correction is bt'lieved to be necessary at the small size end of a gwen size rang(·.
The atomizer used in the above tests produces a spray field of moderately high drop](·t
Dumber deosity. Simultaneous droplet probE' cr~iDgs (multiple events) were obseTnd
from timp to time on the oscilloscope. Although this path was not pursu£>d, tbe Syst('Dl
response to multiple events does Dot appear to- preclude its us€' in high droplet number
density environm£>ots.
Backscatter
In many applications, access to a spray field undl'r test can be obtained from only
one side of tbe test rig. At other times it is desirable to locah' tl'ansmittH and re('Pi\ ('r
packag('s nE'xt to each other to provide system rigidity. In some situations the dropkt~
themsel\"f;>s may be opaque to visible light (( •. g. liquid metals) sl,I('h that rt'fractive scatter
does not exist. In all of the above cases, the measurement of backscatteied light could be'
utilized, The backscatter configuration involves arrangement of transmitter anu H'(,(,j\'l'r
23
- .... , "'. !j. ~.
f
! .
su('h tbat light scattered back toward the source (0 = 1500 in ihis case) is collected and
analyzed. For the situation involving opaque drops, this light would be scattered by first
surface reflections. For non·opaque drops,backscaUer may also involve light scattered
from secondary internal refiections which complicate the analysis.
Cal<'ulations of relative scatter intensities were performed prior to experimentation.
The results showed that the light scattering intensity from the droplet surface (first surface
refi(>ctiou) of pure water drops was a.ctually less than the light scattering intensity from
light reCracted into and internally reflected out of the droplets in the same backscatter
direction. It was believed that if the relative intensities of light scattered between the two
modes were sufficiently diff(>rent, onl)' the dominant mode should be detected. To support
this as::umption, phase shift calculations for th(> internal reflection mode (0 = 150°) were
completed and found to be nearly identic .. } to the forward scatter refraction mode (0 = 30°).
A wat er baSed dye was used during these experiments to vary the opacity of the
droplets and suppresstbe internal reflective scatter by absorption or the incident light.
Pure dye used to form droplets eliminated all internal refledions allowing only first surface
reflection. Results involving pure dye are shown in figure 40 to accurately follow the
predktion for first surface backscatter. Results using pure water and the prediction for
internal refi(>ction at (j = 1500 are shown in f:.gurc 41. When the dropiet op2.city rea('hed
a certain value the results fell between the two extremes of figure 40 (essentially 100'[
opaque) and figure 41 (nearly transparent) and often contained data from both modes.
3.3 Signal Quality Effects
Several sources of possible signal degradation were investigated to observe their effect
oIl.the phase measurement scheme. These sources were ideDtified by the investigators based
OIl previous experience with similar light scatter instrumentation. The two ca.tegories into
which these ;>ossible sources fall are optic",l aiignment and incident beam interference.
The probe volume of the phase measurement method is physically limited by the beam
intersection rel!.ion and the receiver ~)inhole. Only light which enters the pinhole will reach
the detectors and this light must origin~teJ!om the beam overlap region. This critical
24
, "
F!i~~'i''iWI'!'"I''~~'''''';''''''"''''''~''i''':=~O''''~''~'~''''l'I''''"'''~''C':''''"''':'-'''""",~,,,,,o"'''''''~:.''~''''''--7,~,"''''I''''wP''''''''''''''''~''''''''''''7'''''''''7~l!!'!':':'~'--"~r;;
, ~
alignment between transmitter and receiver can be affected in ways which could possibly
produce deleterious effects on the size measurements. Perhaps even more crucial to signal
phase measurements is the quality of the incident beams which (olm the probe volume.
Incident beam quality directly affects the quality of the interference fringes. Beam drop-out
or selt'ctiH' attenuation can alter fringe formation and contrast. The phase measurement
technique was promoted because it was potentially less sensitive to loss of signal quality
than existing instrumentation.
Alignment
During thege evaluations, light gathered by the receiver lens was brought to a focus
and passed through a pinbole spatial filter whose size was selected to match the beam waist
at the probe volume. The purpose of the pinhole is two-Cold: first, it prevents light from
other sources (other parts of laser beams or background light) from reaching the detectors
and second, it guarantees signal coincidence at both detectors. Pinhole misalig;nment can
result in 'receiver aperturing' which alters the character of the detector signals. The
monodisperse generator was especially useful when studying' pinhole effects as its droplet
stream could be directed through select parts of the laser beams effectively scattering light
from a single 'point'. When first applied in the receiver package, tests were conducted to
verify that the pinhole did not adversely affect the drop size measurement. The results of
one such test is shown in figures 42 thru 45. A range of pinhole sizes was used including the
smallest which was not expected to transmit all of the focussed light. 1':0 appreciable shift
in measured size could be detected although the smallest pinbole produced a broadened
distribution which may bave been indicative of aperturing problems.
A second series of tests were run to observe induced aperturing effects on size mea..<;ure-
, ments. These tests involved intentional focussing errors at the pinhole plane. Due to the
nature of the focussed light, selective aperturing of light intended for individual detectors
could occur. This apel'turing led to signal distortions with the potential fOT errors and
were, in fact, processed as erroneous drop sizes. A set of data from one such test is given
in figures 46 thru 48. The errors induced in these tests were much more severe than those
expected in practice.
25
The effe('t. of receiver alignment on other than the center of the probe volume was
investigated. At the extremes of the probe volume, a hyperbJlic spreading of the inter
ference fringes may take place. The monodisperse droplet stream was centered on the beam
crossover and then moved to the detectablf> extremes of the crossover region. The receiver
pinhole was removed for these tests. Figures 49 thru, 54 show the datarrom these tests, A. ('ombination of loss of signal intensity and signal distortion determined the detect(l.bility
limits. No appreciable change in droplet size was observed, although broadening of the
distributions did oceur and was attributed to the decrease in signal·to-noiseratio.
B£>a.m Qua.lity
fringe ('ontTast at the measurement probe volume is dependent upon relative beam
int(>nsity, beam polarization and coheren<.'e. Loss of fringe contrast is disastrous for sizing
techniques based on sign~l visibility since this quantity is directly related to the fringe
contrast or visibility. Although fringe contrast is easily affected, fringe spacing is not. The
phase te('bnique is directly dependent upon fringe spacing but not upon fringe visibility
and thus, should not suffer from losses of contrast. To verify tbis, tests were conducted
in which th£> {ring£> visibility was intentionally lowered. The monodisperse generator was
used as the droplet source. Figure 55 shows results for the case of IOOSC fringe contrast
in which incident beam intensities were nearly equal. A neutral density filter of optical
density 1.0 was then inserted into one of the two beams changing the intensity ratio from
50:50 to {H:9 and reducing fringe visibility to only 20%. The test was repeated with tbt'
results given i:o figure 56. The size measurement was not affected.
Losses of beam intensity and fringe visibility do not occur as cleanly as was sllggestcd
by tbe previous testing. In a spray environment, droplets pass randomly through the
incident beams scattering light away from the incident direction, affecting both beam
intensity and (:oherence. Droplets with sizes comparable to that of the beam diameter can
cause beam drop-.out. The combined effect of many small droplets in the incident beams
can n .. >sult in a severe decrease in signal-t~noise ratio. The oscilloscope trace of figure
57 shows a typical beam attenuation due to droplet interference. SiDce each of the' two
incident beams is affected similarly, but not identically, by droplet passage, the ('haractt'r
of the beams which intersect at the probe volume at any instant cannot be easily predicted.
26
\ ..
""',(.,-.. ' • < .~., •• ,., L ,. ,',
Spray interrereD('e effects on droplet measurements was investigated by introdl,lCing a spr .. y
into tbt' path of the incident beams while measuring the monodisperse droplet stream.
Sin('e droplet sizt' to beam diameter is an important parameter in this test, iwo spray
droplet distributions ot wideJy differing mean drop sizes were used. Spray interference will
also affect light scattered from the probe to the receiver lens. This interference, however,
is not as severe as beam drop-out. The results of a spray interrerence test is given in
figures 58 thru 60. In each case the intertering spray was judged to contain a moderate
to high droplet number density. Test results show that mean siZe measurements did not
('hange although some broadening or the distribution did oc('ur and is attributed to loss of
signal-ta-noise ratio and spray interference directly with the monodisperse droplet stream.
27
;J;'_
, " :, l--~" ."" ', ..
4.0 SUMMARY AND CONCLUSIONS
An innovative approach (or spray drop size and velocity characterizations has been
described. The mt'thod, which obtains the drop size information Crom the interrerence
Cringe pattern produced by the scattered light, bas been shown to have severAl advantages,
Pt'rbaps th(l most significant adva:ntage is the relative insensitivity of the method to un
certainties in the scattered light intensity and Cringe visibility which occur when the laser
beams are attenuated by the droplets or other optical contamination. The linear relation
ship between the measured signal phase and the dimensionless drop size simplifies the im~
pl('mentatioD of the method and creates a uniform. size sensitivity over the measurement
range. The dynamic size range of the technique is essentially limited only by the dynamic
range of the dete('tors and the prevailing signal-to..Doise ratio.
~fonodi5pel'st' droplet streams were used as a basic test of the theory and to test sus
ceptibility of the m('thod to practical effects experienced in tbe application of the method. , , !";" 1
These effects includ<>d optical imperfections, environmental conditions and simple align
ment errors. In terms of the operating requirements and errors produced, the operation
was analogous to the conventional laser Doppler velocimeter.
~1ethods for size range selection were desctibed and tested. Either the beam inters('C'
tion angle (fringe spacing) or the detector spacing can be changed to achieve the same
r('sult. The detector or slit spacing was easy to implement, did not require realignment
and did not change the Doppler difference frequency. Also, this method has only a minimal
effect on thE" probe volume. '
Sprays were measured in this preliminary assessm('ut of the technique. Comparisons
of the measurements to other methods were presented and tbe results showed reaSonably
good agreement. However, this cannot be used to make conclusions about the relative
mea.surempnt accuracy. Measurement.s at different size range selections Were also made
to determine theseH-consistency of the metbod, The availability of a "standard spray"
would facilitate the evaluation of these new diagnostic techniques.
Although the tests conducted using the breadboard processor were as extensive as
possible, turther tests are required using the more advanced prototype processor currently
28
under, development. The processor will produce two'simultaneous phase measurements
to prevent ambiguity and toreject spurious signals that may occasionally pass the noise
rejection logic. Testing of the processor's automatic setup runctions and signal qualification
logic will be the first priority in the future work. The processor will be capable of a data
rate greater than 10,000 samples per second so that tests on tbe probe volume effects and
mass flowrate determinations can be considered.
In summary, the recognized potential characteristics of tbe method are:
• linear relationship between tbe measured phase angle and drop size
• size range of 30 or greater at a single optical setting
• overall size range of 3 to 2000 microns
• simultanl?ous size and velocity measurements
• relative insensitivity to beam or light scatter attenuation
• high spatial resolution il.·.
• operation is similar to an LDV
• adaptable to existing LDV systems
• ('an distingui~h between gas phase and droplets
• reduced sensitivity to misalignment
• can perform measurements independent of refractive index.
A patt'nt application has been filed.
29
, . ,
REFERENCES
1. A.;~1. TaweE'l, and J. Landau, "Thrbulence Modulation in Two-Phase Jets," Journal
of Multiphst> FJow,Vo! 3', Hl77, pp. 341-35l.
2. \.;. H. Snyder, and j. L. Lumley, "Some Measuremen.ts of Particle Velocity Autocor
relation Functions in a. Thrbulent Flow," Journal of Fluid Mecbanics,Vol. 48, Hl71
3. V. Goldschmidt, and S. Eskinazi, "Two-Phase Thrbulent Flow in a Plane Jet," Journal
of Applied .\!ecbanics,Vol. 33, Ser. 3, !\o. 4, 1966.
4. D. Modarress, J. Wuerer, and S. EIgbobashi, "An Experimental Study of a Thrbulent
Round Two-Pha.<;e Jet," St. Louis, Missouri, AIAA Paper !\o. 82-0964, June 1QS2.
5. R. A. Dobbins, L. Crocco, and I. Glassman, "Measurement of Mean Particle Sizes of
Sprays From Diffractively Scattered Light," Am. Inst. Aerollaut. Astronaut. J. Vol. 1,
p. 1882.
6, J. Swithenbank, J. M. Be,';, D. S. Taylor, D. Abbott, and G. C. McCreath, "A laser
Diagnostic for the ~1easuremcnt of Droplet and Particle Size Distrihution," Al'\.A.14th ,
Aerospace Sciences ~feting, Washingtou, D. C., Paper :\0. 76-79, Jan. Hl77.
7. W. ~1. Farnwr, ~~1easurement of Particle Size, !\umber Density, and Velocity Fsing a
Laser Interf€'rometer," Appl. Opt.,rm \'01. 11, lQ72, p. 2603.
8. A J. Yule, .\'. A. Cbigier, S.Atakan, and A. Ungut, "Pa.rticle Size and Velocity
Mea..<;urement by Laser Anemometry," Al·iA 15tb AerospacE' Sciences .\ieeting. Los
Angeles, Paper no. 77·214, 19i7.
9. W. D. Bachalo, ~.\!etbod for .\1easuring tbe Size and Velochy of Spheres by Dual·Beam
Lighl-Scattn Interferometry," AppJ. Opt.," Vol. 19, :0\0.3, IS80.
10. H. C. van de Hulst, Light Scattering by Small Particles, \Vile)', !'\ew 'York, 11)57.
11. J. R. Hodkinson and 1. Greenleaves, "Computations of Light-Scattering and Extinction
by Spberes According to Diffraction and Gl'<)metrical Optics, and Some Comparisons
with the Mie Theory," Journal of the Optical Society of America,Yol. 53, No.5, 19G3 . . .," p. :)/ I.
12. W. J. Glanschnig and S. Chen, "Light Scattering From Water Droplets in the Geo
metrical Optic's Approximation," Applied Optics," Vol. 20, No. 14, 15 July , Hl81. '.,
30
13. Berglund-Liu MODQdisperse Droplet Gt'nerator, Thermo Systems Inc., Minneapolis,
Minn.
14. Correspondence with Dr. Roger Tate, Delavan Inc, We.<;t Des Moines, Iowa.
31
) ..
. \
~
FIGURF. 1. - Geometrical ray trace of an incident light ray through a sphere.
v
00 "T1;:o .,Q O 2 0:..> ;Or-.0-0 C:~ ):-0 r "I """'; .... ~(t;1
"
-..
· ORIGINAL PAGE (S OF POOR QUALITY
orl' ...... --------------,
I~·
,.. !l ~rn w.,t.f o.opt" -- Gtotl'lt'u". Oph" ---- Mil Tf\tof,
610EGREESl
\~~.---------------.
,::'~--...... - ...... --'--...... -..,.....,__ ........ --....l lIe.O 400
8(OEGREESI
~~r--~-------------~
IC·r-----------------------~
~~O
fJ ItxGllfESI
FIGURE 2. - Comparisons of angular scattering diagrams for 5 micrometer droplets computed from geometrical optics and Mieapproaches.
33
Probe
FocusIng Lens
Beam SpUtter
,.. ;g
Collecting Angle
Laser
Coffectfng System - .
TransmItting System . -.~
,tramr. 3._ ~ch ... m"tic or t.1I ... nntir;d ~y"td;" for an 1.[lV "n,1 (~ropl ... t sizin'1 "ystt"m.
~ ...
OC ..,,~
-0(.) 0:';; 0--;;;:f! re· r.a ~ ~) S S~l
':;1 ~~
. . \."!
ORlGINt\t P.n.GE ,8 OF POOR QUALlT't
'FIGURE 4.' '-. Far field scattered light interference fringe pattern produced by a droplet.
FIGURE 5'. - Laser Doppler burst signal.
35
'J
\
...,;;../
w OJ
>!:. ~ en (J)
>
1.0
0.8
0.6
0.4
I •• 629 • L ... 12S • ."I.}) IS .. 2!l ~ A .. .5145 IlIl lEFRACTION.
S2 ONLY
0.2L' .
0.0_ r" " 1 "r~ OJ -.
0.0 1.6 3.0 4.6 6.0 7.6 9.0 10.6 12.0 13.6
D/DELTA
FT~URE 6.- Siqnal visibility verRUS dimpnsionlcss drop size; {IS and collection anqlc ]0
.~
00 "';:0 "00 0::; 0 """:", ;op .0 " (::';.:' j:> [::. r"" ~n .. ~ _, r
_~ ~.r;~~
'. ;.'C
ORlC:N.ql PP,GiZ iSj
OF POOH QUALITY
DROPLET DI~~ETER. RE:ElvER 'OCAL lE~C~". DIA~ETER P£CElvEft • THE'fA 'R!NCE S~~=!NC • LASER wPvE~E~CTH • IN~E~ O~ RE~A~T!vN •
168,080e '3',B0ee 125,090e .,8009 ,,,,aaee
,6329 1. nee
Droplet
-240 -leu -lie "". e ill X,mm
241 Jae
FIGURE 7.- Computed interference fringe pattern produced by a droplet
37
v , :~
. ,~i~~~~ ' . . ' . . ,
~ ~ !
P.e , ... <:", ~(1
ORIG\NAL j.\u:' :~. Of POOR QUALII (
Collect1ng Len~tS
:FIGURF. 8. - Schematic of the detector arrangement and the resulting high pass filtered signals.
38
OKtKtors
OJ
w (!)
fid ~
S60
210
< 1$0 x t:l.
90
o 5 10 16 20 25
P/Dl!lTA
FIGURF. 9.- Theoretical prediction showinq the phase variation with the diMcnsiortless drop size
, ,
30
00 ":.:0 -vG3 O 2 0;.:. ;Or-
Du, ep 1>0 r f"~ ~ .. -~ -<! Q..~
,;., ,
~ -~
[1 rJ i~ :~
~-J
,
.t+)
~ '~ '0 .-~
I j
'~'i , . • ·r ;
d ~
ORIGINAL F.c\Ci ;~ OF POOR QUAUi'Y
40
l;...:
c ..r:: c. r.: \..< t"" o
.;.J C
..r:: :::...
..,. I-'-
;OJ
LASER
,
~ BS •
OPTICAL PRonE VOLUHE
DE'l'F.CT()R HJ\SK
DROPLET sou RCI-:
~
~,--~J , ~e-
DETF.CTOR 1
DETECTOR
1·'TGtlI1E 11 - Optical Component l·.:tYo1.lt
COLLECTION ANGLE
M2
00 "":::0 ..,0 0--0 2
=o~ .0.., c :r;. » (.) r ft'l
~ ~c
_ • ...A ;~
··"-· .. ·11 -)j ;!1 ~
j ..<1'
.1 ·f
a;
','
j ~ ,~
1 ,
, (+)
OfHGtNi\L ;;;M'.E \:] OF POOR QUALi"\'l
42
, . ,
I:l Co U If. o ... ... u
'" C .. N
H )1.
~--~----~I--~--~ i.,
II IIItl III .1 eMU)
m~:~n .. ~.~[: It a, nil un : ~ 1 lUI nOr[ : .~, WfUS : l~
Figure 13 - Drop size variations
""I~ 221fl1 ~I~ m 114,.. ~ S~, 11 2 .1(1'9f6 ~!Ir til ZIl ~lmtl 111M CVCU • Figure 14 - Drop size variations
111 II>4C/'QA1
4
\ll!IT lOO n:c .... IVA S[J 11.4 III ~ ~I'A( H lllltNIt lalH ~IA 4llU\Mi I'iIK.croJ • Figure 15 - Drop size variations
43
'I'l.C~: (1.
OH1GIl\lAL Pl;G2 ;S OF POOR QUt:.lITV
, "
Figure 16 - Drop size variations
H.U: 1'" 11(I'0Il1
i
i .. ~\ '.,r--"i
~;f I ~
' .
j I ~
Fibure 17 - Drop size variations
Figure
UIlf.\ll 1I~1U ! l.l ftl tn'IIi m_1C~ j,
18 - Drop size variations 44
, ... ..,
»18: ua aleNt!
til 0) GJ ~ t1' GJ
"Cl ......
360
300
240
(I) 180 rl Ol
,§ " (I) n Ul
m .c p.. 120
60
0
,!./
0 1
0
e DATA, listings included in report
o DATA, listings not included
THEORETICAL CURVE Phase vs d/delta for f/S=[ 9.741 9=30 deg., m=1. 33
, 19.49J,
2 3 4 5 6 7 8 9 10 d/delta (f/s=9.74)
1 2 3 4 5 d/delta (f/s=19.49)
FIGURE 19 - Plot of Phase Shift vs Non-dimensional Size;
Theoretical Predictions and Experimental Data
11
00 "";0 "tl C) 02 0:>:, AlT'
.0-0 c.: ;:~ -p Iz', r- !':j ...-0; ,.,,-..
2'~6~
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r 1/ ~-i-I -+----+----i !!fir:
13:13:25
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1\-:·., 11 • "1"". C.~'lfII" y •••• ' " .. ".
334
-
J{ DI~;Il"ltl'!lnsl
"':1 LIl!) m ... B!Q~ m D.· fli~.; '·fQ,: Ii ~ Oleron, 1Jl\l ~!A 2IJ Oimn~ -! Ii :'!': Lf ~
~R lOIS: m "" (~ll *~~!: J~ i, j SLl! \Elk : ~i S •• mrr : m SAIt:'LfS • I~?)
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360
~ 300 ~ 240
180
120
60
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• DATA, listings included in report
o DATA, listings not included
THEORETICAL CURVE Phase Angle vs d/delta for f/s=9.74, 8=30 deg., m=1.33
00 ." :'J "0 r.) o -... ( ) ;.:; .~ ::Or
.() .... , c.: ;.~"
E r; -1, ~ (,.
I . J
2 3 4 5 6 7 8 9 10 11 12 d/dc1 ta
FIGURE 24 - Plot of 1'11.:1<;e Shift vs Non-dimensionCll Size;
Theoretica1 Predictions and Experimental Data
'\
... ~. --'
.j::. ;xl
v tr
11m·:, rH!-!m
TIl(: lU6:14
H lin: It'.3 Il C11AS
Jtf,I mt 111.1 ilCl'tftS
iT l<J I f\ ~ f=1)
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1i'$Y, m. : 8~U II CPt_! SlQ"ilS : m
.. y COOICT 117
I PlIt\t' C~IC1S
M~iH • C~H1S
Figure 25 - Detector spacing variations; S- 12.7 mm
t~h'lm
n',e HUll: i~,l PleNti
,,'~mt 111' Rl~
v ,;' /1
\ l "-
I"-
" ~ \
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Sln.C~1IT m
I P'l!1{: CCJ;1(j\
",/11m • C~It1)
Figure 27 - Detector spacin~ varlatlon~; s~ 50.B mm
,,~.
ITt: 8HHMJ
nJi' IU':Z1
BUD: I'U II("U
IiAlI tlIl: UU IICrtlll
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111< I~C .91 EtMS !lIIST til ~ Ilena, RIM,ClCU
~.~ Mr ,sur ,:.f III mUla:.' D
~; .111i,*,
~IMit m
I~~ ~Mt: • C~J!fS
Figure 26 - Detector spacing variations; s- 25.4 mm
I!J;'19U n'~:14
I / y .........
"- I I I
/ \1 ~J SI%[: I .1 Imons
~" SIn: 1 .7 lit,,"'
) l
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Flgu~e 2R - Detector spacing variations; 5- 76.2 mrn
00 -n;:tJ
-OC-; O ---" 0 ·:;.., ?Jr rO"Z1 c: ):.0 ~,-.. [;} ~ r:~, -. .--.. ;! t.~.
~ , :..;.
~
\
---"- , '+ ~ _" .4.~ ., \:!.
l~i'ltn n,.:zt
rJJI~~ IDII U%.t: 118.1 altl'Oll
/, v
/
\ I
'" ~
........... 0.,
I ~ I
,I v " ./
/'
Figure 29 - Detector area variations
ITt" M·ll·I"]
T1~' l?:z;:e
Hmz' IIIU II'*'
'I'C« Ul,t 1lG ~ Illl"Cti
IW.~ r~t:
Figure 30 - Detector area variations
\'II'I li'~li·l~J TIl[' 11:0141
Hun: 1.9.1 rUCPMI
putt' UUIIlC*1
Figure 31 - Detector area variations
49
ORlGlNAl ").'1"",., rey o ' Y"''''l''t'' I" F POOt? Q! ::", 'j __ 1 '
-,,'- i
~,
;/
CJl o
.
DATE: 10-19-1983 \ I I TIME: 13;15:14
l_____ __l_~ ___ J .' r---~-- -~--~---l i I I
..
6 DIAHETER(Microns) 224
XHIT LENS : 22e ~M BEAM SEP: 7.74 M~ FRHG SPAC : 17.9 Microns WAIST DIA : 213 Microns MIH,CYCLE: 4
RCUR LENS : 495 MM COLL.ANGLE: 30 deg SLIT SEPR,: 50,8 MM SLOPE' : .758 SAMPLES : 1~~3e
FIGURE 32 - Drop Size Distribution: Delavan 45B .6 GPH
60 psig Water, 10", below nozzle centerline
HAX.COUNT 583
MEAN SIZE: 47 Micflons
SHD: 102 Micl'ons
00 .,,~
"'05 0-' ::2
~F () ";:I r- "tj)
?~ ~;.; :) ~:'}
~
' ..
-.;~
:,/
C;' J->
MrE: . 10-19-1983
TIME: 17:19:24
6 DIAMETER(Microns)
XHITLENS: 22~ MM BEAN SEP: 7.74 "" FRNG SPAC : 17,9 Microns WAIST DIA : 213 ~icrons HIN.C~CLE : 3 .
RCVR LENS : 495 Hr.. COLL.ANGLE: 30 deg SLIT SEPR~: se.8 MM SLOPE : .758 SAMPLES : le~g0
224
FIGURE 33 - Drop Size Distribution: Delavan 45B 1.0 GPII
60 psig W~tcr, 10" below nozzle centerline
MAX. COutU .. 685
MEAN SIZE: " 48 Mict'ons
SHD: lea Mi Cl'ons
00 ." ~
"On 0::;':: 0:;; ;J;Jr 0,::; c: ;..~,~ :t=- !'j
r:; ~ ... ~~.)
". . ..... -~ . ~ ..
I "'"~~-- _-:,,_,,4,' __ -,'- ,.5'_- '," __ "- '"""'"."..".. a ii, .~, .. >i -em! ,a
f ~
...... ::: .I-l '0 .....
".. ~ z c..:c: c· .... ~.Q ;:.J ~>..
.Q e:: ::.1 '0 c::l ~ ::2N ~,,,,,
fj z~ ":: ::= l-i 0 c -
131n 12 jtt 11 I • 10
9
S
7
6
5 i I 4
3
11 2
1
0
0 40
r·. er w
80 120
n DATA SUPPLiED BY DELAVAN INC 010" 44.8
D32= 99.7
e PHASE/DOPPLER DATA 0 10"'" 47 0 32= 102
160 200 240 280
Droplet Diameter (micrometers)
FIGURE 34 - Drop Size Distribution Overlays
;. Delavan 45B .6 GPH, 60 psig, 10· below CL
oc ":c "00 0
_--:>
o~ ;of-.o-u c :i~ ;t;. r ' c: i'.i _1 ~..! ,~.;;
. ,-1
"
~
c.n CAl
.) ,.,.
--
15
14
13 11
12 1 11
:5 10 'U .,../
E-'~ Z ~~ c U . .-4
r::: ,Q ~1 0...>,
..Q c::; C:G1J ;:J Ci ~t-.; ~.,../
z---,.. ~ ~I
o ~
9
e
7
:j 4
J
2
1
o
(9
•
•
eet 0.
n DATA SUPPLIED BY DELAVAN INC
0 10'" 38.7
0 32= 83.7
o PHASE/DOPPLER DATA
010= 48
032= 105
o 40 80 120 160· 200 Droplet Diameter (micrometers)
FIGURE 35 - Drop Size Distribution Overlays
Delavan 4SB 1.~ CPH, 60 psig, 10· below CL
.':
00 "";0 "0.5 0-0<-~F! .0" C.h ,p. C) r: ftl -'--< i,";2
" I !
I
~
.~
"-f+
1m 'HHHl tlK! .lll.U
• DI..r1[)lftIC,..,.ll m ~:l I.1'IlS : III .. fro ~ : m till JI&I UP: t 1 III 00 tl(ll: )f /II, nx spac : U IIltpttS illl un: Z~ 4 .... It lSI JIA: " alC""'S ,.1 )ia.; m 'lC"~S K\h C'I~ : l Wf:.n : ~ Figure 36 - Drop size distribution:
spinning disk atomizer size range 229 micrometers maximum
SKt 41 "It R"'.'
YJI:l ~ llil NO liOJ UY. : ~l .. 1(U m u... (O~ 1'1;.(: 1i Or, ~ nl: t, •• c,...\ ~~!l \[]i. : ~i I .. .. al ':1 '1'HPOC'S All ":1 : 1I~ 'IC"'.I 1I.l- CYCJ l Sa.w:t.ll : ~
Figure 37 - Drop size distribution: s?inuing disk at0~izer
size range 114 micr~weters maximum
":1 1f·14·HIl
tiKI IUrI'
1m T l.Dfl llli 1111 lOt i.OO: 4'~ "" l't~ m '1.. COu. U(J: » 4fj r~ Sl1: U Illm\ HI! mI.: "Ill> 9111 lil n '11ttAI ~I )it : 14 "it,...\ 1111 mu 2 stem : ~
I'l .... ml tI lott",,1
1IO ta I&CK'l\
Figure 38 - Drop s1ze distributlnn: spinning disk atomiZer
s:!ze' range 76 micrometers maximum
5<1
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~ Sizc Ranqc MaxiMum 229 micrometers - 3.2 micrometer Bin Width
.... -. Si 7.0 HnntJ0 HllXimtlM 114 micrometers 1.6 micrometcr Bin Width
-+- Sizc Range Haximum 76 micrometers 1.1 micrometcr Bin Width
DROP DIAnETER (Micromcters)
FIGURE 39 - Drop ~ize Di~lril)ution Ovcrlays: spinning Disk Atomizer
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DA:E: 19-11·1983
TlHf: 11:34:38
B-L SIZE: 123 l'Ii Cl'ons
B-l SIZE: 123 1'I1Cl"Ons
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XHIT LINS : 223 ~~ BEAM SIP: 18.6 I'I~ fRHG SPAC : 7.4 Microns ~AIST DIA : 213 Microns KIN,CYCLE : Ie
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-
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RCVR LENS: 495 "~ COLL.ANGLE: 159 dey SLIT SEPR,: Se,B K~ MAX, DIA, : ZBB ~icrons SAKPLES : 8237
. KAX.COUNI 6714
MEAN SIZE: 124 Microns
FIG':F.! 4: - B"ck."ata< Test: 100\ P)'e !Opaque) Drops;
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.. XMiI LfHS : 22B M BEAH Sf?: 5 ~ FRKG SPAC : 27.8 Microns WAIS1 DIA : 213 Microns HIH,C~CLr : 3 .
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RCUR LENS : 495 ~~ COLL.ANGLE: 159 dey ~LII SEPR,: Sa.8 MI'I I~I~X, DIA. : 357 I\icl"ons SAMPLES : legS
fIGURr u - ii"'C".C6tt\!r ~'est' Water (Nearly .'l'r"n'parent~ Dro,,':
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Ffgure 42 - Plnhol~ effect test: no pinhole, baseline data
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Figure ~3 - Pinhole effect test: 800 mIcrometer pinhole
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Ft~IJrf' 45 - Pinhole ('ffet:'t tCllt: ~OOmlcromet('r pinhole
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Figure 46 - Pinhole focus test: 400 micrometer plnh'ole in focus
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Figure 47 - Pinhole focus test: probe ima~ed behind pinhole
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probe imaged before pinhole
58
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Figure 49 - Optical alignment test: probe center. reference data
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Figure SO - Optical alignment test: probe center, pinhole removed
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Figure 51 - Opttcill 7 .mro downstream of
alignment teat: probe center
59
ORIGINAL PAGE to' OF pom? QU/'.~ ITY
IlITE GI·u·nu til( .Utl7
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Figure 52 - Optical alignment test: 6.5 mm upstream of probe center
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Figure 53 Optjcal ali~nment test: nearside limit of probe
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•• n<l Orop-out iJuc to Spr"lY, 'Interference'
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ORIGfNAl PAGE rt'4 OF POOR QUALlT'r
. Figl,ire 58 - Spray fnte'rference te~t: monodisperse generator without spray, baseline data
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Figure 59.-Spray i~terf€rence test: 40 micrometer Clean drop dia;:'leter spray upstre.arn of probe
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Figure 60 - Spray interference test: 100 micrometer~ean drop diameter s~ray upstream of probe ,..'>
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End of Document