el

FIGURE 5 - ANGULAR SCATTERING DISTRIBUTIONS FOR VARIOUS VALUES OF SIZE PARAMETER


FREQUENCY OF COUNT

100} D= 34.3 u f versus x,
80+
604
40
20
VJ
10 15 20 25 30 35 40

DIAMETER x, » MICRONS

FIGURE 16 - FREQUENCY VERSUS DIAMETER FOR MICROBEADS

36


(1) Microscope (2) Analytical Balance

FIGURE 14 - PARTICLE SIZE AND NUMBER
MEASUREMENT SYSTEM

au.


COUNT PER SECOND ,§

40

35

©. ex
20 L O = ax
A 2x
O 1.x
15| O 1X = 2.02 x 10° particles
— Qa ft
1
oO CI oO a oO
10h
Ap, Zs A x A.
5
L _O-
o—% ° oo —O-
1 u ! i 1 Nn !
1 2 3 4 5 6 7
POSITION

(DISTANCE BETWEEN POINTS = 0.10")

FIGURE 19 - OBSERVED COUNT PER SECOND VERSUS

POSITION FOR LYCOPODIUM SPORES

41


‘Condensing lens

Spectra-Physics model 124
Stabilite gas laser \ = 6328 A

Collimating lens

Test cell

Interference filter

RCA IP=28 photomultiplier tube

PPI Laboratory photometer

Leeds & Northrup Speedomax L
strip recorder

D.C. power supply

FIGURE 1 - OPTICAL SYSTEM USED FOR

LIGHT TRANSMISSION MEASUREMENTS (PHELPS (20))


COUNT PER SECOND, >

O = Lower limit
A= Upper limit

om Average values

SY WIN
AWW LAN WS NIN

FIGURE 27 - OBSERVED COUNT PER SECOND VERSUS
POSITION UPPER AND LOWER LIMITS

53


SECTION VII

DISCUSSION OF MEASUREMENT ERRORS

The data presented in the previous chapter illustrate
typical experimental results obtained with the system.
Due to the nature of the experiment rather large varia-
tions were observed in some of the measurements. The
source and magnitude of these variations is discussed
here.

Effect of Alignment

One of the disadvantages of this system is the sensi-
tivity to alignment. The amount of light received is
directly related to the angle between the detector and
the incident beam. One assumption that has been made
is that the detector and the beam are in the same plane
and that the pinholes and the beam are aligned. Devia-
tions from these conditions can greatly effect the re-
sults obtained at the counter. An example of this is
seen by comparing the results shown in Figures 18 and
26. For the same number concentration different counts
per second were obtained. Consequently, the actual
value of the count per second is not significant - only
the relative effect of changing the number concentra-
tion for a particular instrument alignment can be mea-
sured.

Concentration Measurement Error

The only error presented here is the error in consistent
counts. Figures 27 and 28 show the variation in concen-
tration profile and system response respectively. These
figures were obtained by taking the largest deviation
from the average. These curves show that the system re-
sponse was very good because the error in the count shown
could be expected just from the nature of turbulent flow.

Particle Suspension Considerations

To avoid the effect of particles separating from the flow
and becoming attached to some portion of the system, all
runs were made in one continuous sweep. The particles
were assumed to remain suspended throughout the run. The
effect of particles separating from the system was noted
when particles slightly heavier than water were used. For

51


SECTION Ix

REFERENCES

Anderson, T.B. and R. Jackson. "A Fluid Mechanical
Description of Fluidized Beds." Industrial and Engi-

neering Chemistry Fundamentals. vol. 8 pp. 137-144,
February 1969.

Becker, H.A., HA. Hottel and G. Williams. "On Light-
Scatter Technique for the Study of Turbulence and Mix-

ing." Journal Fluid Mechanics, Vol. 30, part 2, pp.
259-284.

Born, Max and Emil Wolf. Principles of Optics. Per-
gamon Press, 1959.

Chuang, Strong C. "Turbulence Diffusion of Small Gas
Bubbles in an Axi-Symmetric Water Jet." Ph.D. Thesis
School of Mechanical Engineering, Purdue University,
1969.

Denison, E.B, "Pulsating Laminar Flow Measurements
with a Directionally Sensitive Laser Velocimeter."
Ph.D. Thesis, Purdue University, 1969.

Fischer, M.J. and F.R. Kause. "The Crossed-beam
Correlation Technique." Journal of Fluid Mechanics,
Vol. 28, part 4, pp 705, 1967.

Goldschmidt, V.W. and S. Eskinazi. "Two Phase Tur-
bulent Flow in a Plane Jet." Journal of Applied
Mechanics, Vol. 33 Series E, No. 4, December, 1966.

Green, H.L. and W.R. Lane. Particulate Clouds, Dust
Smokes and Mist. D. Van Nostrand Company, Inc. Chapter
4, 1957.

Gurvich, A.S. "The Determination of Turbulence Char-
acteristics from Light Scattering Experiments". At-
mospheric and Oceanic Physics, Vol.4, No. 2, 1968.

Hanesian, D. and A. Rankel. "Elutriation from a Mul-
tisize Particle Fluidized Bed." Industrial and Engi-
neering Chemistry Fundamentals, Vol. 7, No. 3, August,
1968.

Hino, M. "Turbulent Flow with Suspended Particles."

American Society of Civil Engineers Proceedings, Vol.
89, Journal of Hydraulics Division, Hy. 4, July 1963.

59


a<aq

size parameter ae

radius of particle

overall system sensitivity
stream velocity

total volume of fluid

scattering volume

inlet velocity to cyclone separator

particle velocity

free fall or terminal velocity of one particle
diameter of a given particle

absorption coefficient

solid angle viewed by detector

average number of particles per unit scattering
volume

average number of particles per unit volume

additive terms to L, for traversing length

count/sec
angle subtended between the beam and the detector
wavelength of the incident beam

density of particle
density of fluid

standard deviation of particle size range

64


COUNT PER CUBIC CENTIMETER aon’)

12 OF
1X = 0.0161 gms
10
8 ok
6 Fk
4 &
27
au 1 1 n 1
1x 2x 3x 4x “5X
CONCENTRATION

FIGURE 25 - TYPICAL COULTER COUNTER COUNTS
VERSUS CONCENTRATION FOR LYCOPODIUM

47


Me (SOLID ANGLE FORMED BY DETECTOR)

FIGURE 6 - VARIATION OF DIMENSTONLESS
LENGTH WITH SOLID ANGLE ty

17


y/h vs. u/U
X w= 7.87 ft/sec
vertical
© U = 8.145 ft/sec
1.0 | horizontal
x ©,
& 5
wat $
= Q
: g
&
a
5 +64 %,
a
e 6
3
= al 8
e
: ®
= af Ko)
sal *O
3
x
°
+ + + Q +
0.0 2 4 6 8 1.0
uU ° UR RAC FT/SEC
ty RATIO OF VELOCITY TO AVERAGE VELOCITY, FT/SEC

U

FIGURE 17 - DIMENSIONLESS DISTANCE VERSUS DIMENSIONLESS VELOCITY

37


ABSTRACT

A technique for measuring particle concentrations in turbulent flows
was investigated. This technique is the measurement of the light
scattered from an incident beam by the solid contaminants present.

The results show that for moderate concentrations the scattering
system gives proportional increases in count to increases in particle
concentration. The limitations of this system are the signal to noise
ratio and the condition of singular scattering by the particles.

Suggestions on refinements on the correlation technique used are
made and observed phenomena which require further investigation
are discussed.

This report was submitted in (partial) fulfillment of Contract

16070 DEP under the (partial) sponsorship of the U.S. Environmental
Protection Agency.

iii


Viscorder (5) Photomultiplier tube
Oscilloscope voltage power supply
Narrow band filter (6) Oscillator
Electronic counter (7) A.C. amplifier

(1
(2
(3
(4

PISURE 13- ELECTONICS USED IN SIGNAL ANALYSIS

29


Rosensweig, Hottel and Williams (1961) extended this
simplified expression to the signal (current) produced
by the phototube which is given by:

= _Ss fre
I-35 av, (5)
s Ve

where
I_ is the phototube signal

S is the overall system sensitivity and is constant
for a given optical arrangement and alignment

T* is given by Vv lim, q and is defined as the average
s- s

particle density contained within the control volume.

N is the average number of particles contained in Vs

The desirable relation between Ig, § and fF* is

I, = sr* (6)

Rosensweig et al (1961) state that clearly V must be small.
However, decreasing V increases all noise levels of the sy-
stem. Therefore an optimization is needed. They also show
that if a point concentration is to be obtained from equa-
tion (5) the concentration profile must not have large curva-
ture. These conditions are controlled by the geometry of the
optics and by the velocity profile in the medium.

The relation between the count from an electronic counter,
monitoring the phototube output, and the number of parti-
cles per unit volume can now be obtained. Under the assump-
tion of homogenous flow, the total number of particles count-
ed is attributed to the passage of a frozen concentration
pattern through the scattering volume V_. The pattern passes
at a velocity U - the local mean velocity of. the flow field.
The average time for one particle to pass through the scat-
tering volume is given as:

at = Pps2
U (7)

where

Dy diameter of the beam
U stream velocity

14


SECTION IV

EXPERIMENTAL APPARATUS DESCRIPTION

The experimental apparatus may be divided into various
subsystems - the fluid flow system, optical system, parti-
cle measuring system, and the electronic system.

Description of the Fluid Flow System

A schematic of the fluid system is shown in Figure 8.

The system consists of a plenum chamber, a reservoir, a
one-third horsepower centrifugal pump with a bronze head
and an Aqua-Pure water filter. All piping used was made

of Polyvinyl Chloride (plastic pipe) to insure that the
system remained as rust free as possible. The plenum
chamber was made of Plexiglass and had dimensions of 1'

x 1' x 2.5'. The inlet section from the plenum to the test
section was constructed from a cylindrical Plexiglass piece
cut at 45° angles in such a manner that when it was reunit-
ed, it formed a bell shape inlet section for a square chan-
nel as shown in Figure 9. The plenum chamber also had an
overflow weir that consisted of a 3/4 inch diameter pipe.
The reservoir was constructed from a fifty-five gallon

drum that had been treated to prevent rust. The reser-
voir had four holes located in its bottom, leading to
valves 3, 4, 5, 6. Valve No. 5 is used’ to help control

the amount of flow going to the reservoir from the con-
stant speed pump. All four valves allowed the separation
of the reservoir from the rest of the system. Valve 4 is
between the reservoir and the drain. Valves 7, 8, 9, are
for further flow control. They allow either complete,
partial, or no flow through the filter. Valve 11 is to
control the weir draining rate and valve 12 is to control
the plenum draining rate. The remaining valves (1, 2)

were to allow collection of a flowing sample from the test
region.

The test section located immediately downstream of the in-
let nozzle was made of Plexiglass and designed in such a
manner that it could be detached from this position and
interchanged with another section of the channel. The
test section is shown in Figure 9.

The velocity profiles were measured with the device shown
in Figure 9. The measuring instrument was a Pace differential

21


5 = Tt (12)

At
where
6 = count/second
V. = Scattering volume

or substituting for [* from equation 9 and for At from
equation

@

But

o qato.

A_U (13)

u
<2 <l2 la?
an
°

For a desired count the number of particles and ultimately
the weight of the particles were determined by the relation-
ship expressed by equation 13.

Resolution of the Scattering Volume

The length of the scattering volume may be determined dir-
ectly from the geometry of the optics. The angle ag is de-
termined by the diameter of the pinhole apertures which
limit the field of view of the photomultiplier tube. The
angle 9 is the angle between the photomultiplier tube and
the incident beam. These variables are all shown in Figure
4. The equation that describes the dependence of the scat-
tering length upon the geometry is given by:

_ sin O, sin a,
L, = Ld —Gos-Tte + ay + sin te Og)

(14)

where

Ld is the distance of the center of the apertures
to the center of the beam

Ls is the length of the scattering volume at the
center of the beam

The effect of different values of q and 6 on the length L

is shown in Figure 6. s

16


Particle Measuring System

This system consisted of only a microscope and an analyti-
cal balance. The size distribution of the particles was
determined by measuring a sample of the particles used
under the microscope. The microscope at high magnifica-
tion will give the diameter to + 1 micron. It was origin-
ally proposed that size determination be done optically.
While the theory was sound, the system would involve an
extensive calibration. This was not considered feasible
for the scope of the present study. Separation of the
particles by size was also investigated. The results of
this investigation showed that only for gross differences
in diameter or properties is separation by size feasible.
Particles that were obtained. from the manufacturers though
not uniform in diameter, represented the best practical
size separation that is presently available.

The analytical balance was used to measure the amount of
particles that were to be added to the fluid system. The
balance was accurate to 1/100 milligram. This system is
shown in Figure 14.

Average Concentration Measuring Device

In order that values obtained from the light scattering
experiments could be verified, a Coulter counter was used.
The Coulter counter works on the principle that the pre-
sence of particles passing through a small orifice changes
the electrical path through the orifice. This device is
thereby able to determine the particle size and concentra-
tion that is present in a small sampling vessel.

Concentration measurements from this device were determined
from small samples taken at each concentration level that
was used. The samples were taken with a bypass arrange-
ment from the, reservoir that can be seen in Figure 8 and
was controlled by valves (1) and (2).

The results obtained from this instrument proved to be un-

reliable for the fluid (deionized water) and concentrations
used.

30


equal to ninety degrees the scattering volume is minimum.
These angles are shown in Figure 4.

Another important parameter in scattering studies is the
ratio of the incident light. This parameter is the size
parameter defined by:

q = 2nr/r (3)
where

r = radius of the particle

X = the wavelength of the incident light

Theoretical angular distributions of scattered light were
obtained for particles used in this study from an I.B.M.
computer program called Dame. This program has the capa-
bility of calculating scattering distributions for a size
parameter up to 5000. The distributions obtained are pre-
sented in Figure 5 as a function of size parameter.

There have been several theories proposed to explain the
relationship between the incident beam and losses associated
with the scattering and absorption. For the size range of
particles used the appropriate theory is that developed by
Mie. A detailed explanation of this theory is given by Van
de Hulst (1957). For the type of scattering experiments
conducted in this study a detailed examination of Mie's
theory is not needed. The underlying assumption of this
study is that the light scattered is directly proportional
to the number of scatterers in the control or scattering
volume. This is true as long as single or independent scat-—
tering is the only type present. Sinclair (1950) has stated
that this assumption is valid as long as the distance between
particles is ten or preferably a hundred times the radius of
the particle.

The single scattering assumption has been used by many
investigators; Green and Lane (1957) give the following
simplified scattering expression:

P.

I=krn (4)
where

I = the scattered light intensity

r = the radius of the scatterers

P = parameter determined experimentally

nh = number of scatterers

11


Sinclair, D. Handbook on Aerosols. (Washington, D.C.:
U.S. Atomic Energy Commission) p. 84, 1950.

Soo, S.L. Fluid Dynamics of Multiphase System, Blaisdell
Publishing Company, Chapters 1 & 4, 1966.

Soo, S.L., G.J, Trezek, R.C. Dimick and G.F. Hohnstreiter.
"Concentration and Mass Flow Distributions in a Gas-Solid
Suspension." Industrial and Engineering Chemistry Funda-
mentals, Vol. 3, p. 98, May 1964.

Van de Hulst. Light Scattering by Small Particles, Wiley
& Sons New York, N.Y., 1957.

Wallis, G.B. One Dimensional Two Phase Flow, Chapter 8,
p. 175, 1969.

zenz, F.A. Fluidization of Particle Systems, Reinhold,
New York, N.Y., 1960.

61


SECTION I

CONCLUSIONS

It was found in this investigation that light scattering can
be used to measure concentration profiles in internal turbu-
lent flows in regions not adjacent to the wall.

Other important conclusions reached in this investigation are
presented below.

1. Changes in concentration levels resulted in
proportional changes in counts per second at
the sampler.

2. For low concentrations of solids with specific
gravity close to one, the concentration profiles
closely approximated that of the velocity. How-
ever, for higher concentrations the similarity
becomes increasing less pronounced.

3. For a given alignment the scattering system
seemed insensitive to changes of particle size
and real index of refraction.

4. The use of a Coulter counter was not feasible
as a check of concentration levels. A more
practical system would be to use-a fiber optic
probe. ‘


some of which is received by the photomultiplier tube.
The narrow band filter, which is placed directly in front
of the photomultiplier tube, limits the wavelength of
light that reaches the tube. Therefore, only radiation
that is the same wavelength as the filter bandpass ex-
cites the tube. The signal received by the tube is then
proportional to the scattered radiation from the parti-
cles, from scattering due to turbulence of the water
(Gurvich, (1968)) and from background radiation from

the room within the filter bandpass. Both of the latter
effects were found to be negligible in this study.

The entire optical system was mounted on a large alumin-
um plate which was in turn mounted on a lathe bed in such
a manner as to allow the scattering volume to be traversed
across the flow. Mounting the optics in this manner limit-
ed vibrations and allowed the whole optics to move normal
to the section where concentration gradients were taken.

Electronic System

The electronic system used in the analysis of the signal
from the photomultiplier tube is shown in Figures 12 and
13. This system consisted of an oscilloscope, bandpass
filter, an a.c. amplifier, an oscillator, a visicorder
and an electronic counter.

The signal from the photomultiplier tube was first chan-
nelled to the oscilloscope, and simultaneously to the a.c.
amplifier from which it entered the bandpass filter. The
signal was amplified to enable it to trigger the electron-
ic counter. The amplification factor was ten times the
input signal. The bandpass filter was used to improve the
signal to noise ratio. After passing through the bandpass
filter, the signal was simultaneously sent to the oscillo-
scope and to the electronic counter. Since the signal had
the appearance of shot noise, the filtered and unfiltered
signals were observed on the oscilloscope to insure that the
basic form of the signals was not changed.

The purpose of the oscillator was to serve as a standard
when in connection with the oscilloscope, by which the
electronic counter could be calibrated for sensitivity
versus accurate count setting.

The visicorder was used to double check the effect of the
bandpass filter, to compare the intensity of light received
from the different types of particles used, and also to
check on the count received from the counter at various
locations.

27


different. Even when the above conditions are satisfied,
collection of the particles by the different sizes is
difficult. Entrainment was chosen as the more practical
because it allows easy collection and because it can be
coupled with either cyclone, filter or sedimentation
chambers. The cyclone separator is thought to be the
best separator to couple with the entrainment bed because
it gives a second chance at size separation. Closer examin-
ation reveals that for particles with diameters around 100
microns free fall velocity is approximately 0.43 to 1.07
ft/sec. However, to separate particles with 4 yu range
results in air velocity control as being less than .01
ft/second. It was concluded that for the particle size
separation needed, adequate controls were not available.

‘US, GOVERNMENT PRINTING OFFICE: 1974 546-319/392 1-3 69


transducer and the probe was made from 0.035" I.D. wire
tubing. The traversing mechanism used a micrometer to
position the probe. The electronics used for velocity
measurement are also shown in Figure 10. The electron-
ics consisted of a carrier demodulator and a VIDAR digital

voltmeter with external controls allowing: time: averaging
of the velocity profile.

Optical System

The optical system consisted of a helium-neon laser, a
photomultiplier tube, a narrow band filter, and two pin-
hole apertures. The system is as shown in Figure ll.
This arrangement was chosen as a compromise between scat-
tering volume size and signal to noise ratio. In general
as the angle between the beam and the photomultiplier was
decreased, the scattering volume length increased and the
signal to noise ratio decreased reaching a minimum at the
zero degree angle. The prism shown in Figure 11 was used
just to change the direction of the beam and has no ef-
fect on the performance of the overall system. The wave-
length of the laser and the narrow band filter used was
6328 A. The apertures were approximately 310 microns in
diameter.

To aid in understanding the operation of the system and
the purposes of each component a.detailed explanation is
presented. A uniform beam is incident upon the test sec-
tion normal to the flow direction. The normal condition
was chosen to minimize any aberrations due to refraction.
The test section was chosen to have flat walls to elimin-
ate the need for a compensator box to compensate for the
effect of curvature as was found necessary in work done
in internal flows with a Doppler.system by Denison (1969).
A system that involved the use of a lens that would focus
the collimated beam down to a particular point was tried.
It was discovered that with such.a system, it would be
necessary to refocus the system at each point in the flow
field as the concentration gradient was taken. This was
due to the change in optical path and consequently the
change in effective focal length of the lens.

If small particles are seeded into the flow system, they
will scatter radiation in all directions. The pinhole
apertures that are placed between the photomultiplier

tube and the flow field, together with the geometrical
relationship between the incident beam and the photomul-
tiplier tube, define the cone that intercepts the beam.
The common region between the cone and the incident beam
defines the scattering volume. The particles entering the
scattering volume will scatter light in all directions,

24


6.
7.
8.
9.
10.
ll.
12.
13.
14.
15.
16.
17.

18.
19.

20.

FIGURES

Optical System Used For Light Transmission
Measurements.

Probe With Miniature Photocell (Fiber Optics Probe).

Angular Distribution of Scattered Light For
Particles Used.

Optical Geometry Defining Scattering Volume.

Angular Scattering Distribution For Various Values
of Size Parameters.

Variation of Dimensionless Length With Solid Angle.
Effective Traversing Length.

Schematic Fluid Flow System.

Inlet Section and Test Region.

Velocity Measurement Instrumentation.

Optical System.

Schematic of the Electronic System.

Electronics Used in Signal Analysis.

Particle Size and Number Measurement System.
Frequency vs. Diameter For Lycopodium Spores.
Frequency vs. Diameter for Microbeads.
Dimensionless Distance vs. Dimensionless Velocity.

Observed Count Per Second Versus Position For Dow
Beads.

Count Per Second Versus Position For Lycopodium
Spores.

Observed Count Per Second Versus Concentration For
Dow Beads.

10
12

13
17
19
22
23
25
26
28
29
31
35
36
37

40

41

42


Section

It

IIt

Iv

VII

VIII

IX

xI

CONTENTS

Conclusions

Recommendations

Introduction

Experimental Apparatus Description
Measurements and Results
Discussion of Results

Discussion of Measurement Errors
Acknowledgements

References

Glossary of Symbols

Appendix

21
33
49
51
57
59
63
65


tal

Pinhole apertures (394 microns)
Photomultiplier Tube (detector)
Bandpass Filter for 6328 a°

Angle between detector and beam
(30°)

Solid angle formed by detector
(0.4° planar angle)

Diameter of incident beam (2mm)
Distance between apertures (2inches)
Length of’ scattering volume

Distance of the scattering volume
from origin of a, (5 inches)

AP

FIGURE 4 - OPTICAL GEOMETRY DEFINING THE SCATTERING VOLUME


No.

1.

2.

TABLES

Particle Data.

Particle Supplies and Properties.

viii


The effective length for transversing the test section is
longer than L, by a Length equal to AL) and AL. The lengths
AL, and ALy are shown in Figure 7 and are given by:

aL, = Db tan (6 + a) (15)
2

AL, = Pb tan (6 - a) (16)
2

This total length is the dimension which limits the ability
to make measurements close to the wall.

The conditions that are necessary in order that the volume
be small are:

a. large values of 9 (Max. = 90°)
b. small diameter pinholes
c. large distance between apertures

d. small distance between the center of the
aperture and the beam

Equation 14 is derived neglecting the effects of refraction

at the walls of the test section. This effect is generally
negligible provided angle a is very small.

18


EPA-660/3-74-004a
March 1974

Ecological Research Series



COUNT PER SECOND,

30

25

20

15

10

O= position ‘#1
A.z position #4
oO. position #7
1X = .0161 gms

2x 4X 6X 8X - 10x

CONCENTRATION

\

FIGURE 21 = OBSERVED COUNT PER SECOND
VERSUS CONCENTRATION FOR LYCOPODIUM SPORES

43


SECTION III

INTRODUCTION

SCOPE OF PROJECT

The stated objectives of the work sponsored under Contract
#16070DEP, were twofold. One to establish an effective
method of tracking contaminants in a liquid jet, including
the use of a laser system. ‘Two to determine the diffusion
due to turbulence of contaminants of different size and
density. The second objective was fully met. An earlier
report "Turbulent Diffusion in Liquid Jets" dealt directly
with it. On the other hand the first objective was only
partly met. It is now discussed in this report. The
second objective was met through the research of Dr. Strong
Cc. Chuang. His doctoral thesis was completed on August
1970. The research into the use of a laser as a sampling
device was conducted by Mr. Charles H. Tinsley as part. of
his M. S. studies at Purdue University.

PROJECT BACKGROUND

Knowledge of the properties of two phase flow systems,

such as solid-gas, solid-liquid and liquid-gas, is impor-
tant in manyaspects of engineering. In recent years ap-
plications in nuclear reactor development, chemical pro-
cesses, dispersion of contaminants in waterways, and the
dispersion of particulate matter into the atmosphere have
called for knowledge of the concentration and concentration
gradient of the dispersed phases.

Several techniques for the experimental evaluation of the
distributions of dispersed phases have been proposed. One

is the hot wire impact method developed by Goldschmidt and
Eskinazi (1966). This has been used to measure aerosol
particle concentrations (Householder (1968)) and Lee (1970)
and to measure bubble concentrations (Chuang (1969)), all in
free turbulent jets. This method consists of inserting a
hot wire probe into thé flow and measuring the signal re-
sulting from the impact of bubbles or liquid droplets on

the wire. Soo et al (1964) investigated several different
methods for measuring concentration distribution and mass
flow. The more successful of these was the light attenua-
tion method. In this method light is projected perpendicular
to the flow stream and the transmitted (unattenuated) light
is measured on the other side. The amount of light received
by the detector can be related to the size and the concentra-
tion of particles in the flowing medium. Phelps (1968)


SECTION II

RECOMMENDATIONS

This study was limited to the investigation of the possible
use of a light scattering probe as a particle concentration

sampler.

1.

The use of alternate sampling methods might
be considered when applicable. For instance,
when sampling droplets or bubbles the use of
a modified hot wire or hot film anemometer
may well be more convenient and reliable.

The actual sampling volume of the light scat-
tering probe has to be selected to eliminate

multiple particle scattering signals, as well
as to permit a dependable calibration of the

samples.

Techniques for signal to noise optimization
should be studied in future tests if a device
of the type described is to be employed.

Additional studies are necessary to determine
the exact count per second and particle number
density relationships. These studies should
follow the direction taken by M.J. Fischer and
F.R. Kause (1967) or that suggested by H.L.
Morse et al. These authors used a two point
correlation method by either using two beams
or two detectors. This allows correlation to
help eliminate unwanted noise.


Householder, Michael K. and V.W. Goldschmidt, "Tur-
pbulent Diffusion on Small Particles in a Two-Dimension-
al Free Jet," Technical Report FMTR-68-3 School of Civil
Engineering, Purdue University, Sept. 1968.

Lee, J.B. “Turbulent Diffusion of Particles in Plane and
Circular Jets." M.S. Thesis, Purdue University, School. of
Mechanical Engineering, January 1970.

McGill, D.R. "Scattering Experiments." Development of
Four Experiments for Applied Optics Laboratory. M.S.
Thesis, Mechanical Engineering, Purdue University, 1968.

Moder, J.J. and D.A. Dahlstrom. "Fine Size, Close-Specific-
Gravity Solid Separation with Liquid-Solid Cyclone." Chemi-
cal Engineering Progress, p. 75, 1952.

Morse, H.L., B.J. Tullis, W.R. Babcock and H.S. Seifert.
"Development, Application and Design Specifications of a
Laser-Doppler Particle Sensor for the Measurement of
Velocities in two Phase Flow Rocket Exhaust." Volume I,
Sudaar, No. 356, p. 56.

Perry, R.L. and S.M. Henderson. Agriculture Process Engi-
neéring, pp. 184-189, New York, Wiley, 1955.

Peskin, D.L. and P.S. Baw. "Solid Density Distribution in
Gas-Solid Pipe Flow." Technical Report No. 108-ME-F NYO
2930-6.

Petrie, J.C. and D.E. Black. "Improved Air Distributor
Caps for Fluidized Beds." Chemical Engineering Progress,
Vol. 62, No. 3, March, 1966 p. 82.

Phelps, Jean P. "Particle Size Determination Using A Laser
Light Transmission Technique." M.S. Thesis, U.S. Naval Post
Graduate School, March 1968.

Rosensweig, R.E., H.C. Hottel and G.C. Williams. "Smoke-
Scattered Light Measurement of Turbulent Concentrations
Fluctuations." Chemical Engineering Science, Vol. 15,
pp. 111-129, 1961.

Rouhiainen, P.O. and J.W. Stachiewieg. "On the Deposi-
tion of Small Particles from Turbulent Streams." Journal
of Heat Transfer, Vol. 92, Series 1, February 1970.

Scholz, J.T. and D.R. Uhlmann and B. Chalmers. "“Elutria-

tion Particle Separator." The Review of Scientific Instru-
ments, Vol. 36, Number 12, pp. 1813-1816, December 1965.

60


- 9. Electronic Counter was set back to maxi-
mum sensitivity (55 m.v.).

10. Steps 2-19 were repeated.

The data for the point concentration measurements were
taken as an arithmetic average of the values taken at
the point. Typical distributions for each type of par-
ticle run is presented in Figures 18-23.

Coulter Counter Results

Typical results obtained for a few of the runs from the
Coulter counter are presented in Figures 24 and 25. The
Coulter counter proved to be a poor choice of a check for
the results obtained from the scattering system. The
primary reason is that the Coulter is extremely sensitive
to contaminants in the water used. The Coulter counter
would give high counts for clear water and give counts on
the ‘same order of magnitude for samples obtained from the
particulate system. In fact, in some cases higher counts
were obtained for clear water (uncontaminated deionized
water). The scattering system did not show this sensi-
tivity to clear water contamination; however, if it had

a zero level could have been set and exact counts could
have been obtained by substracting this known zero level
from obtained values.

39


(1) Laser (3) Apertures ani banIps:s
filter

hi F
ts (4) Photomultiplier tude

(5) Laser power supyly

Tare” Tf — YPTICAL SYS

26


COUNT PER SECOND,

2st
ie}
20 [L J/TM O= point #1
O= point #4
A- point #7
151
10 f—-
5}
40 60 80 100 120

COUNTER SENSITIVITY (mV)

FIGURE 22 - OBSERVED COUNT PER SECOND
VERSUS SENSITIVITY FOR DOW BEADS

440


) External timer (5) Carrier demodulator

) External start and:stop (6) Probe and transversing
) Vidar digital voltmeter mechahism

) Calibration mechanism (7) Transducer

ann
FUNr

FIGURE 10- VELOCITY MEASUREMENT INSTRUMENTATION

25


Entrainment

Entrainment may be defined as the carry-over of the
particle by the fluid, from the particle bed to and
through the dispersed phase. The rate of entrainment
depends on factors that involve the apparatus, charac-
teristics of the solid and fluid, for all of these.

The entrainment process can be described in terms of the
free fall or terminal velocity of the particle. When

the fluid velocity exceeds the velocity of the free fall
of the particle, the particle is carried by the fluid
until either the particle is carried completely from

the column or the particle forces exceed the momentum

of the particle and it returns to the bed. Unfortunately,
the entrainment rate cannot be modeled by the terminal ve-
locity alone, other effects such as the throwing up of
the particles by the bursting action of the gas at the
particle bed and the concentration of the particles are
important. Since the entrainment rate is dependent upon
free fall velocity it also allows particle separation by
size.

Conclusion
The methods surveyed were:

(1) Filters

(2) Sieves

(3) Impingement Separators

(4) Cyclone Separators

(5) Gravity Chambers

(6) Entrainment Columns
Of these methods filters do not prove adequate because of
the nature of their operation. Filtration is essentially
a catch all operation. Sieving is used by most of the
manufacturers and if this method was chosen no finer dis-
tribution could be obtained. Impingement separation while
theoretically possible is experimentally infeasible because
it would require a test program for different types of

collector designs.

Gravity separators are useful only when all particles are
to be separated or when the densities or size are widely

68


21.

22.

23.

24.

25.

26.

27.

28.

Observed Count Per Second Versus Concentration For
Lycopodium Spores.

Observed Count Per Second Versus Sensitivity For
Dow Beads.

Observed Count Per Second Versus Sensitivity For
Lycopodium Spores.

Typical Coulter Counter Counts vs. Concentration
For Dow Beads.

Typical Coulter Counter Counts vs. Concentration
For Lycopodium.

Observed Count Per Second Versus Position For
Lycopodium Spores (Different Alignment).

Count Per Second Versus Position Upper and Lower
Limits.

Observed Count Per Second Versus Concentration
Upper and Lower Limits.

vii


The length D/2 represents an average cross-sectional
length for the circular beam. The time it takes for

a length V./Ag to pass through the scattering volume
1s: ‘

Vv,
s
Un = At (8)
“Ss
where
V, = scattering volume

A, = cross-sectional area of the scattering
volume defined as LD:

L., = the length of the volume formed by the
interception of the solid angle and the
beam. (shown in Figure 4)

If the average number of particles per unit scattering
volume is given by:

Te = q (9)
s
where
WN = total number of particles contained
in V,
s
V. = scattering volume

and the total number of particles contained in the system
volume is N then the particle density is given by:

WN
r=8 (10)

and for homogenous flow

Vv (11)

~
NN
Vs
The number of counts per second is then given by the number
of particles per unit scattering volume divided by the time

for one scattering volume to be convected through the volume.
In equation form this is: .

15


SECTION VIII

ACKNOWLEDGEMENTS

The reported work was the result of the Master of
Science research of Mr. Charles H. Tinsley, Jr.
Professors Victor W. Goldschmidt and Warren Stevenson
acted as supervisors of his work.

The support of the project by the Water Quality Office
Environmental Protection Agency, and the help provided

by Mr. George Ditsworth, Project Representative is
acknowledged.

The assistance of the staff of the School of Mechanical
Engineering and its Ray W. Herrick Laboratories during
the final stages of the work reported is also gratefully
acknowledged.

57


striking the object, the particles are held into place

and collected - usually at shut down. Collection can be

made by counter current flow or by centrifugal force im-
parted on the carrier gas. Zenz (1960) gives a theoretical
explanation of this type of separator. The important para-
meter is the stopping distance (L_). The stopping distance
is a function of the particle vel8city, free fall velocity,
and both particle and fluid densities. For a spherical parti-
cle the stopping distance is given by:

= =VY, Pp v
L pp _¢ (a)
I) o- Pg)
where
‘p= particle velocity
ve = free fall velocity - ve
Pp = particle density
Pe = fluid density
g = 32.2 ft./sec/sec

Cyclone Separation

The cyclone or centrifugal separator is a device utiliz-
ing radial acceleration for separation of particles suspend-
ed in a gas stream. It consists of an outer cylindrical-
shell and a cone attachment, and is so arranged that the
dust-laded gas enters tangentially. This causes a vortex
of gas which ascends up the cone and finally ascends to an
outlet concentric with the outer cylinder. The particles,
however, are impinged against the curved wall and swirl in
a downward spiral path due to the effect of an outward
centrifugal force imparted by the momentum due to inlet
velocity and the force of gravity. The minimum diameter,
of the particles separated by this process, is given as a
function of fluid dynamic viscosity, free fall velocity,
fluid inlet velocity, and the difference in particle and
fluid densities.

In order to obtain the function which determines the dia-
meter of the particles to be separated, the distance traveled
by the particle laden gas must be determined. This distance
is simply anr N of the cylindrical portion of the cyclone.
The time that°if takes the gas to travel this distance is
t= amr Ns/v, where Vig is the inlet velocity to the

66


The frequency of occurrence of sizes for Lycopodium and
for microbeads can be found in Figures15 and16~. The
density and other properties of Lycopodium were taken
from Rouhiainen and Stachiewicz (1970). The other par-
ticle properties were taken from manufacturer's data and
can be found in Table II.

TABLE II

PARTICLE SUPPLIERS AND PROPERTIES

MANUFACTURER INDEX
OR MATERIAL DIAMETER OF SPECIFIC
SUPPLIER REFRACTION GRAVITY
Carolina Lycopodium 32.2 uy - 0.621
Biological Spores
Supplies
Dow Styrene 34.3 u 1.587 1.05
Chemical divinyl-
benze

Microbeads Soda-lime

silea glass 1.51 1.5
Minnesota Glass 1.5 1.5
Mining
Reflective
Products

Velocity Measurement

The measurement of the velocity was done prior to any of
the concentration runs. The nozzle and flow field is
shown in Figure 16. The mean velocity in the test sec-
tion was found to be 8 feet per second. The correspond-
ing Reynolds number based on the hydraulic diameter is 5.76
x 105. Velocity profiles were found to be flat over most
of the test section in both horizontal and vertical direc-
tions. A typical profile is shown in Figure 17.

Concentration Measurements

‘The particles were injected into the plenum chamber and

34


110

100

90

80
70

60

50

40

FREQUENCY OF COUNT, £

30

20

10

9

u f versus x
u J

24

25 26 27 28 29 30 31 32 33 34 35

DIAMETER x y? MICRONS

FIGURE 15 - FREQUENCY VERSUS DIAMETER FOR LYCOPODIUM SPORES

35


CCUNT PER SECOND, :

5
1X = 2.02 x 10° particles
Mm = 16x ft
@ - «x .
300. L ‘ ner water
O =-1x
g a A =x
250.
2 7 a
a
i |
200.
150. Ee
e —o— e e
100. [— e e ~~
oN
50. u u w a —o-— 5
ae

2 3 4 5 6

POSITION

FIGURE 26 - OBSERVED COUNT PER SECOND VERSUS
POSITION FOR LYCOPODIUM SPORES (DIFFERENT ALIGNMENT)

52

o- 6 SA
S—_———


Sampling
bypass ay

og

(6)

reservoir

Lg \

@)

22

FIGURE 8 ~ SCHEMATIC -FLUID FLOW SYSTEM

plenum
10) (1)
filter (99)
Hoy
(4)
)

Ik
orifice
meter

drain


these particles the count first steadied and then rapidly
began to decrease. The lighter particles seemed to remain
suspended in the fluid rather well. This was determined
by allowing the system to run for several hours and then

rechecking the count/sec of particles.

55


cylindrical portion of the separation. This also is the
maximum time allowed for the particles to travel the dis-
tance Ly. This is given by: :

LSM = anr N./Vio (b)

The terminal velocity can be determined from an equation
given in a succeeding section if the drag force is com-

puted by Stoke's law for a centrifugal field. The terminal
velocity is then given by:

v= 9D, (6, - pg)/18 Uy (c)

Substituting and solving for D_, the following is
obtained: P

D, = 9 Hel, / (TN,V5 (0, - p,)) (a)

Gravity Separator

Gravity settling chambers are the simplest type of parti-
cle-collection equipment. The principle of operation is
that the fluid velocity is reduced below the free falling
velocity of the particle. This allows the particles to
settle from the carrier fluid by the influence of gravity.
The rate at which this occurs is dependent upon both fluid
and particle properties. For similar shapes, the settling
rate (free fall or terminal velocity) becomes dependent
only upon the characteristic length usually the hydraulic
diameter. In Wallis (1969) a derivation and also the
correlation are given for the terminal velocity.

Any expanded section in line can constitute a gravitational
settling chamber, however they are usually a long, empty,
horizontal vessel or a long vertical cylinder. For the
horizontal vessel, the basic idea is to allow the particle

to travel a vertical distance in free fall in less time :
than it takes the carrier fluid to flow from inlet to outlet
of the settling chamber. For the case of equal densities but
different sizes the larger particles will fall out first and
therefore the length of the chamber determines which diameter
particles will settle. The cylinder settling chamber consists
of a stagnant or very slow moving fluid in which the particles
are dropped. The time at which a certain diameter particle
reaches a predetermined depth can be determined thereby al-
lowing a known range to be collected.

67


EPA REVIEW NOTICE

This report has been reviewed by the Office of Research

and Monitoring; Environmental Protection Agency and approved
for publication. Approval does not signify that the con-
tents necessarily reflect the views and policies of The
Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.


COUNT PER SECOND, &

25.0

20.0

10.0

5.0

roob
a

position #7

position #4
position #1

1 milliter of
10% concentration

1x 2x 3x

CONCENTRATION

FIGURE 20 - OBSERVED COUNT PER SECOND
VERSUS CONCENTRATION FOR DOW BEADS

42

4X


COUNT PER SECOND, é

25.

20.

15.

10.

O = 1x

FIGURE 18 ~ OBSERVED COUNT PER SECOND
VERSUS POSITION FOR. DOW BEADS

40

O = 2x
A = 3x
5 . 4 el
1X = 7.76 x 107 Baytistes
A
A A _
a A A
L
Q oO -. n = oO
Lt =)
Q fe) _O—
) “0 v
! ! L ! 1 _t
1 2 3 5 6 7
POSITION


a

3. Accession No.

SELECTED WATER Rented Wo,
RESOURCES ABSTRACTS a

INPUT TRANSACTION FORM

4. Title
TURBULENT DIFFUSION IN LIQUID JETS: PART I 2 Besteiib
7, Author(s) . = Report reve.
Charles H. Tinsley, Warren S. Stevenson & Victor W. Goldschmidt} i. Project No.
—— 16070 DEP
9 Organization Engineering Experiment Station [ii Contract] Grant No.
001 of Mechanical Engineering
‘ Purdue University iF eee
Lafayette, IN 49707_ - " Period Covered

15. Supplementary Notes pART 1 I$ SUBTITLED: Measurement of Particle Concentration by a
Light Scattering Probe.. Environmental Protection Agency. Report number 660/3-74-004m,
March 1974

16. Abstract

A technique for measuring particle concentrations in turbulent flows was investigated.
This technique is the measurement of the light scattered from an incident beam by the
solid contaminants’ present.

The results show that for moderate concentrations the scattering system gives
proportional. increases. in count to increases in particle concentration. The
limitations of this system are the signal to noise ratio and the condition of
singular scattering by the particles.

Suggestions on refinements on the correlation technique used are made and observed
phenomena which require further investigation are discussed.

17a. Descriptors

Equations, Instrumentation, *Particle Size, Suspension, Turbulent Flow

17b. Identifiers

Lasers, Light Scattering, * Particle Concentration, * Particle Size Measurement

I7c. COWRR Field & Group , 08 B

18. Availability Send To:

U.S. DEPARTMENT OF THE INTERIOI
WASHINGTON, D. C. 20240

WATER RESOURCES SCIENTIFIC INFORMATION CENTER

Abstractor gop. Ditsworth T Institution Envi vironmental Protection Agency |

* WRSIC 102 (REV. JUNE 1971)



FLOW

GLASS ROD.
PHOTOCELL
TO VOLTMETER.

LIGHT BULB

FIGURE 2 PROBE WITH MINIATURE PHOTOCELL

PESKIN AND BAW (18)


COUNT PER SECOND, 5 -

30 OL

25

20

15

10

4A. Upper limit
O = Average value
O = Lower limit

CONCENTRAT ION

FIGURE 28 - OBSERVED COUNT PER SECOND VERSUS
CONCENTRATION UPPER AND LOWER: LIMITS.

54


a ul op

Q

Iz

n'

SECTION X

GLOSSARY OF SYMBOLS

cross-sectional area of scattering volume defined as LD,

average particle diameter

diameter of beam

frequency of occurrence for that particle diameter
32.2 £t/sec/sec -
scattered light intensity

phototube signal

f-1

ath

4n

length of the volume by interception of solid angle as
stdépping distance for impingement separators

free fall travel distance in a cyclone separator

millivolts

total number of particles added to water

average number of particles in Vs

number of times particle encircles cylindrical portion
of cyclone separator

number of particles sampled
real part of refractive index
relative index of refraction
number of scatterers

parameter determined experimentally used to determine
light scattered

63


oT

(Microbeads) n= 1.13

(Dow) ae «== 1.19
| L
+ + T T
107 104 10° 10°

FIGURE 3 - ANGULAR DISTRIBUTION OF SCATTERED LIGHT FOR PARTICLES USED


EPA 660/3-74-004a
March 1974

TURBULENT DIFFUSION IN LIQUID JETS: PART I

Measurement of Particle Concentration
By a Light Scattering Probe

Charles H. Tinsley, Warren S. Stevenson and Victor W. Goldschmidt
Engineering Experiment Station
School of Mechanical Engineering
Purdue University
Lafayette, Indiana 47907

Project No. 16070 DEP
Program Element 1BA025

Project Officer

George R. Ditsworth
Pacific Northwest Environmental Research Laboratory
National Environmental Research Center
Corvallis, Oregon 97330

Prepared for

OFFICE OF RESEARCH’AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C, 20402 - Price $1.15


SECTION V

MEASUREMENTS AND RESULTS

Particle Size Measurements

The particle size was determined by measurement with a
microscope. The standard deviation and average were
calculated from the following equations:

N
= l=
D=s+r ff x.
N ce)
d=1
N
1 r 2
T= £ .-D
wT’) *4 (5 - D)
where
N=

meter:
Tt = Standard deviation of
D = Average diameter

The results obtained are given

Table

(17)

(18)

Number of particles sampled
= Diameter of a given particle

x,
£ = Frequency of occurrence for that particle dia-

the particle diameter

in the following table:

TYPE OF PARTICLE D

Lycopodium Spores 31.66
Microbeads 34.3
Dow Beads 45.4

vy 2.23 y Unavailable
ve 4.74 1.51
ve 8.9 1.587

33


fo INCIDENT BEAM

L

AL.

—+
WA
L

PINHOLE
APERTURE

a

FIGURE 7 - EFFECTIVE TRAVERSING LENGTH

19


RESEARCH REPORTING SERIES

Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:

1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research

4. Environmental Monitoring

5. Socioeconomic Environmental Studies

This report has been assigned to the ECOLOGICAL
RESEARCH series. This series describes research
on the effects of pollution on humans, plant and
animal species, and materials. Problems are
assessed for their long- and short-term
influences. Investigations. include formaticn,
transport, and pathway studies to determine the
fate of pollutants and their effects. This work
provides the technical basis for setting standards
to minimize undesirable changes in living
organisms in the aquatic, terrestrial and
atmospheric environments.


COUNT PER SECOND § .

25

20

15

10

n O = point #1

Oo. point #4

A- point #7

i

0 25 50 75
COUNTER SENSITIVITY, (mV)

FIGURE 23 - OBSERVED COUNT PER SECOND
VERSUS SENSITIVITY FOR LYCOPODIUM SPORES

45

100

112.5


82

iphotomultiplia
tube

filter

oscillator

amplifier counter
loscilloscope
ta —______] \visicorde

FIGURE 12 - SCHEMATIC OF THE ELECTRONIC SYSTEM USED


allowed to disperse for one hour to one and one-half
hours before any data was taken. This time was deter-
mined experimentally as the time delay necessary for a
consistent count. The procedure for data collection
was as follows:

1.

Check to insure the following equipment
was turned on at least one-half hour be-
fore a run.

a. Oscilloscope

b. High voltage power supply

¢. Visicorder oscillograph

d. Laser

e. Electronic Counter (set at maximum
sensitivity)

The inner wall of the test section was

located. (The location of the wall was
determined by the scattering pattern at
the interface between the wall and the

air.

Dial positioner was zeroed. (This dial
was used to determine step size of tra-
verses of the scattering volume in the
test section)

All room lights were turned off.

Readings of the count per second were
obtained at positions spaced 0.10 inch
apart.

Visicorder oscillograph and count per
second readings were obtained at posi-
tions 1, 4 and 7 which correspond to
the two wall regions and the center of
the test section.

Electronic counter sensitivity was varied
from a voltage threshold of 55 m.v. to
104 m.v.

The concentration level was changed.
(For lycopodium spores a wetting agent
must be used. For this investigation
Industroclean cleanser was added to the
system.)

38


(1) Test section (3) Pilot tube with
(2) Inlet nozzle traversing device

(4) Photomultiplier tube

FIGURE 9 - INLET SECTION AND TEST R2G1CN

23


evaluated this dependence of light transmitted on the aver-

age concentration, particle diameter and particle properties.
The experimental arrangement is shown in Figure 1. Soo et al
(1964) used a modification of this method employing a fiber
optic probe. This has the same dependency on particle size

and properties and particulate concentration as shown by Phelps
for the amount of light received. The primary difference bet-
ween these two methods is that the test section for the experi-
ments of Soo et al is defined by the geometry of the probe,

and the test section for Phelps is defined by the cross-section
of the flow. Consequently, Soo et al are able to obtain a
gradient and Phelps is only able to obtain an average concen-
tration. The disadvantage in the method of Soo et al is that

a probe must be inserted into the flow field. An example of
the type of probe used by Soo et al is shown in Figure 2.

This probe was used by Peskin and Baw to obtain concentration
profiles in pipe flow with solids and air as the two consti-
tuents.

The method used for the measurements reported herein was
light scattering. In this method no physical probe is in-
serted into the flow. The concentration is measured in a
finite volume which is determined by the geometry of the op-
tics. This method has been used previously by Rosensweig,
Hottel and Williams 1961, while studying the concentration
gradient in free turbulent flows of a gas-solid mixture. In
this study the phases are solid-liquid and the turbulent flow
under consideration is an internal flow. The object of this
study was to evaluate the feasibility of using a light scat-
tering system to determine the concentration and concentra-
tion gradient of the solid particles in a turbulent internal
flow.


SECTION XI

APPENDIX

In many experimental investigations, it is necessary

to have a supply of uniformly sized particles. Parti-
cles obtained from various manufacturers, in a range of
10 to 100 microns, do not adequately meet the uniform
size specifications. Examples of the types of variance
encountered are given in Table 1. The objectives of
this appendix are to present a survey of the various
techniques suitable for separation of micron range
particles by size and to examine the most practical
system.

Filtration Separators

Filtration separators are usually made of cloth or of a
porous element. This type of separator is commonly used
in conjunction with the removal of a particulate from a
gas stream. Filter efficiency is dependent on the length
of time in operation. Filters start at a low efficiency
but increase to values as high as 99.9%. After a short
period of operation, the pores become elogged from im-
pingement, adherance of fines or by blockage owing to the
larger-sized fractions in the dust being separated. The
filter will then build up a "precoat" layer on its up-
stream surface and thus the precoat actually serves as a
high efficiency filter bed.

Sieving is another form of filtration separation. Siev-
ing is a method used to separate the fine particles from
the course ones by means of nested screens. The sieving
screens are mounted on a metal rim to form cylindrical
pans. Such pans, each of different screen size, are
nested one atop another with the finest at the bottom and
the coarsest at the .top. The material is placed on the
top and then the screens are shaken. The difference be-
tween the pans of the nest represent a certain size range
of the material separated.

Impingement Separator

Impingement separators depend on the inertia of the parti-
cle. The carrier fluid flows the streamline around an ob-
ject which the particle cannot immediately follow, due to
the particle momentum. The particle is, therefore, decel-
erated to zero velocity by striking the object. After

65


COUNT PER CUBIC CENTIMETER (107°)

2.5r

1X = 10 ml of 1%
concentration
2.0,
°
1.5,
1.0F-
Sr
.2F
1 L L 1 1
1x 2x 3x 4x 5x
CONCENTRATION

FIGURE 24 - TYPICAL COULTER COUNTER COUNTS
VERSUS CONCENTRATION FOR DOW BEADS

46


SECTION VI

DISCUSSION OF RESULTS

The primary results obtained are presented in Figures
18 through 24; they illustrate typical data. Figures

20 and 21 show that a change in concentration results
in a corresponding change in counts per second and is
expressed by a linear relationship for moderate concen-
tration levels. It can be seen by comparing Figures 18
and 19 (which show the response of Dow beads and lycopo-
dium spores) that similar concentrations levels give
similar counts per second. Figures 18 and 19 also show
that the concentration profile, like the velocity pro-
file, is flat across the test section for moderate con-
centrations. At high concentration levels a noticeable
assymetry in the profile was observed. The exact ex-
planation for this effect is not known. Figures 22

and 23 show the response of the system to varying de-
grees of sensitivity. These figures show that a corres-
ponding response to a concentration change was obtained
at all levels of sensitivity tested.

Figures 24 and 25 show the response of the Coulter count-
er to various concentrations. -For lycopodium spores the
response is almost linear; however, for dow beads the
response was nonlinear. It was concluded from these
results and attempts at calibration, with this fluid and
these concentrations levels, that the Coulter's results
were not accurate.

49


THEORETICAL BACKGROUND

Scattering Parameters and System Response

Light that traverses a medium may be transmitted, absorbed
or scattered. There are certain parameters of the medium
and of the incident light that determine to what degree
transmission, absorption, and scattering occur. These
phenomena are related such that the amount of light not
transmitted (extinction) is equal to the sum of losses
due to scattering and absorption.

In equation form:

Extinction = Absorption + Scattering (1)
A brief summary of these parameters and their effect on
extinction, primarily taken from Green and Lane (1957),
is given here.
The relative index of refraction of a particle suspended in
a medium affects extinction. The relative index of refrac-
tion is given by:

n'= n particle (2)

D fluid

where n = real part of the complex index of refraction (n - ik,)

i= -1
= ad
Ko an
with a = absorption coefficient, and } = wavelength of the

incident beam

Scattering systems generally utilize particles which have a
zero absorption coefficient, thereby maximizing the amount
of the signal obtained by scattering alone. The effect of
the index of refraction on the angular distribution of scat-
tered light is shown in Figure 3 for the two types of parti-
cles studied.

Two other important parameters for scattering systems are the
angle @ subtended between the beam and the detector, and the
solid angle, a viewed by the detector. These angles help
determine the length of the scattering volume. When the angle,
6, is zero the scattering system reduces to a transmission
system and the scattering volume is maximum. For angle, 0,