A particle generating system is described which is capable of breaking up agglomerations of particles and producing a cloud of uniform, submicron-sized particles at high pressure and high flow rates. This is achieved by utilizing a tubular structure which has injection microslits on is periphery to accept and disperse the desired particle feed. By suppling a carrying fluid at a pressure, of approximately twice the ambient pressure of the velocimeter's settling chamber, the microslits operate at choked flow conditions. The shearing action of this choked flow is sufficient to overcome interparticle bonding forces, thereby breaking up the agglomerates of the particles feed into individual particles

Bushnell, D. M.

Morrisette, E. L.

English

NASA Technical Reports Server

United States Patent 1191 
Morrisette et al. 
[111 28,703 
[45] Jan. 31, 8984 
[54] POWDER FED SHEARED DISPERSAL 
PARTICLE GENERATOR 
[75] Inventors: 
[73] Assignee: 
[21] Appl. No. 
[22] Filed: 
E. Leon Morrisette, Newport News; 
Dennis M. Bushnell, Hayes, both of 
Va. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
297,488 
Aug. 28,1981 
[51] Int. ( 3 . 3  ........................ B65G 53/02; GOlM 9/00 
[52] U.S. CY. .................................... 406/155; 239/568; 
241/95 
[58] Field of Search ................. 406/142, 143, 155, 47, 
406/49; 241/95, 39, 5; 239/568 
~561 References Cited 
U.S. PATENT DOCUMENTS 
1,971,376 8/1934 Hunt et al. .......................... 406/155 
2,687,593 SA954 Edwards . 
2,771,320 11/1956 Korwin ........................... 239/568 X 
3,479,857 11/1969 Bloxsom, Jr. et al. ........... 73/147 X 
3,709,026 1/1973 Rhodes et al. .......................... 73/12 
3,893,335 7/1975 Johnson et al. ....................... 73/147 
3,937,404 2/1976 Johnson .......................... 239/568 X 
4,031,748 6/1977 Cramer ................................. 73/147 
Primary Examiner-John J. Love 
Assistant Examiner-L. E. Williams 
Attorney, Agent, or Firm-Howard J. Osborn; John R. 
Manning; Wallace J. Nelson 
ABSTRACT 
The present invention discloses a particle generating 
system which is capable of breaking up agglomerations 
of particles and producing a cloud of uniform, submi- 
cron-sized particles at high pressure and high flow 
rates. This is achieved by utilizing a tubular structure 11 
which has injection microslits 12 on its periphery to 
accept and disperse the desired particle feed 16. By 
supplying a carrying fluid 19 at a pressure, Pi,, of ap- 
proximately twice the ambient pressure of the velocim- 
eter’s settling chamber 20, Psc, the microslits 12 will 
operate at choked flow conditions. The shearing action 
of this choked flow is sufficient to overcome interparti- 
cle bonding forces, thereby breaking up the agglomer- 
ates of the particle feed 16 into individual particles. 
t571 
10 Claims, 2 Drawing Figures 
PIN 
20 
https://ntrs.nasa.gov/search.jsp?R=19840008493 2020-03-22T08:12:39+00:00Z
U.S. Patent 
IO 
I 13 
I 
'IN 
Jan. 31, 1984 
19 
4,428,703 
20 
FIG. I 
e- 
f T 
300p 
12 
FIG. 2 
4,428,703 
11 
POWDER FED SHEARED DISPERSAL PARTICLE 
GENERATOR 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the U.S. Government and may be manufactured 
and used by or for the Government for government 
purposes without the payment of any royalties thereon 
or therefor. 
BACKGROUND O F  THE INVENTION 
Until recently, pitot, static and total temperature 
probes have been the primary means of obtaining flow 
information in high speed flows. These probes have 
proven to be inadequate, however, for obtaining de- 
tailed measurements of more complex flow fields such 
as three-dimensional flows. As research in this area has 
heightened, so has the need for a means of accurately 
evaluating these flows. This increased need has been the 
primary impetus behind the development of nonintru- 
sive measuring techniques. 
One such technique, known as laser velocimetry, is 
designed to measure static density, temperature and 
three components of velocity in the flow field. The 
velocimeter is actually a particle velocity measuring 
device which requires the use of seeding particles in the 
flow to act as light scatters. It, therefore, will measure 
the gas velocity only if the particle and gas velocities 
are the same. Consequently, the particle requirements of 
this system are an important factor in its successful 
operation. Initially, there must be a sufficient number of 
particles of uniform size to obtain a statistically reliable 
velocity average at a point. The particles must be small 
and low in density to follow the flow, but they must be 
large enough to scatter light sufficient for the receiving 
optics to measure. In addition, the particles should not 
combust or evaporate in the high temperature and pres- 
sure of the setting chamber, and they should be both 
nonabrasive and noncorrosive. 
This invention relates to a particle generating system 
which is capable of breaking up agglomerations of parti- 
cles and producing a cloud of uniform, submicron-sized 
particles at high pressure and high flow rates. Conven- 
tional particle generators are incapable of meeting the 
rigorous demands imposed by the laser velocimeter. 
Smoke generators, although commonly used in other 
settings, are nonfunctional at the high mass flow rates 
(higher densities) and high pressure of the velocimeter’s 
hypersonic tunnel because of the resultant interference 
with the generator’s evaporation and condensation pro- 
cesses. In addition, such systems are very sensitive to 
small changes in the stagnation pressure of the tunnel. 
Another object of the invention is to provide an appa- 
ratus which will effectuate consistent and uniform sepa- 
ration of particle agglomerations. 
SUMMARY OF THE INVENTION 
The foregoing and other objects of the invention are 
achieved by providing a particle generating system 
which utilizes a convenient particle feeding system such 
as a fluidized bed. In this system, the desired particles 
10 are mixed with a chemical which acts as a hydrophobic 
agent and electrical charge neutralizer, and are stored in 
an upright cylindrical casing. A fluid source is intro- 
duced from beneath, thereby lifting the particle mixture 
through a fairing and into a tube with extremely small 
15 slits (25-5Op) on its periphery. By supplying a fluid at a 
pressure of approximately twice the ambient pressure of 
the velocimeter’s settling chamber, the slits will operate 
at choked (sonic) flow conditions. The shearing action 
of this choked flow is sufficient to overcome inter-parti- 
20 cle bonding forces, resulting in the generation of uni- 
form, submicron-sized particles. 
Other advantages and objects of the present invention 
will become apparent from the following explanation of 
an exemplary embodiment and accompanying drawings 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a side elevational view of a particle genera- 
tor in accordance with this invention; and 
FIG. 2 is an enlarged sectional view of the tubular 
structure of FIG. 1. 
In describing the preferred embodiment of the inven- 
tion illustrated in the drawings, specific terminology 
will be resorted to for the sake of clarity. However, it is 
35 not intended to be limited to the specific terms so se- 
lected, and it is to be understood that each specific term 
includes all technical equivalents which operate in a 
similar manner to accomplish a similar purpose. 
DETAILED DESCRIPTION OF THE 
INVENTION 
Referring now to FIGS. 1 and 2, there is seen an 
embodiment of the present invention, designated gener- 
ally by the reference numeral 10. The particle generator 
45 PO consists primarily of a tubular structure 11 which has 
injection microslits 312 on its periphery and is attached 
atop a particle feeding system 84. 
The feeding system 14 coaprises an upright cylindri- 
cal casing 15 which is used to store and supply the 
50 desired particle feed 14. The dimensions of the casing 95 
are determined by the mass flow rate required for any 
particular application of the system. At the bottom of 
the casing 95 is an inlet structure 18 which is used to 
introduce the carrying fluid 19 to the particle feed 14. 
55 Although the fluid used in this embodiment is air, any 
5 
25 thereof. 
30 
40 
other fluid which the velocimeter can tolerate may be 
Fluidized bed systems are also inadequate because of used. 
ates of particles rather than single particles. This inven- up agglomerations, the experimentor will achieve the 
tion was designed to overcome the deficiencies of these 60 best results by utilizing particles which are manufac- 
previously utilized systems. tured in submicron size. In the disclosed embodiment, a 
Accordingly, it is an object of this invention to pro- submicron Teflon powder is used in the particle feed 14. 
vide an apparatus which is capable of Producing a cloud There are, however, other commercially available dry 
of uniform, submicron-sized particles at high pressure powders, such as aluminum oxide, silicon carbide and 
and high flow rates. 65 talcum, which also may be used. Depending on the size 
Another object of the invention is to provide a parti- of the injection microslits 12, the generator EO will pro- 
c!e generating system which remains independent of duce particles of a uniform size down to that of the 
external environmental conditions. smallest particle in the feed 16. 
their tendency to produce only aggregates Or Because the particle generator BQ is designed to break 
4,428,703 
3 4 
A difficult problem with developing a particle gener- In order for this generator PO to operate as desigrled, 
ator for operation at high back pressures is that the the pressure of the inlet carrying fluid 19, Pin, must be 
particles cannot be maintained for long periods of time. appmximately twice the ambient pressure of the velo- 
The natural inclination of small particles is agglomera- cimeter’s settling chamber 20, Psc, thereby ensuring 
tion and deposition if a surface is near. To overcome 5 sonic flow through the microslits 12. Specifically, Pin 
that agglomeration problem, silicon dioxide, SiOz, is for any gas is calculated by the following equation: 
added to the Teflon, coating the agglomerations and 
acting as a hydrophobic agent and electrical charge 
neutralizer. This ensures as easier and longer lasting 
Y I-” psc = (1  + f - 1  ‘+f2 primary particle dispersion and improves the fluidizing 10 Pm 
characteristics of the particle feed 16. The Si02 may be 
added to any other particle feed 16 with the same result. 
Immediately above the particle feed 16 is an exhaust 
fairing 17 which accepts and guides the flow from the 
particle feed 16. The fairing’s 17 primary function is to l5 
provide a smooth outline for the flow which will reduce 
drag and ensure a more laminar flow in the tubular 
structure 11. Any acceleration through the fairing 17 is 
minimal and does not bear on the generator’s 10 opera- 
upper portion of the casing 15 thereby providing a 
connection for the tubular structure 11. Maintenance of this pressure ratio, which is approxi- 
structure l1 is attached to the feeding mately 1:2 for most gases, will ensure that the microslits 
system 14 by means of a ball valve 13. This connection 25 12 operate at choked (sonic) flow conditions. 
keeps the flow uniform and smooth as it enters the tubu- simply that the flow 
lar structure l1 and Prevents Of through the microslits 12 is not affected by the pressure 
particles. Along the periphery of the tubular structure of the settling chamber 20, Psc. The velocity of the 
11 are numerous injection microslits 12. To minimize particle flow in the tubular structure 11 increases stead- 
the agglomeration-deposition Problem, the tubular 30 ily as the pressure of the inlet carrying fluid 19, Pin, 
structure 11 is placed in the Velocimeter’s Settling cham- approaches twice the ambient pressure of the settling 
ber 20 SO that the final particle generation iS into the chamber 20, psc. Near this point, as calculated by the 
tunnel environment. This connection is achieved by a above stated equation, sonic velocity is achieved in the 
high pressure fitting 21 which ensures that uniform microslits 12. It is well known physical phenomenon 
pressurization in the settling chamber 20 is maintained. 35 that Once this pressure ratio is attained, the velocity o fa  
Once generated, the Particles may then be utilized flow through an orifice will not exceed sonic velocity 
quickly and effectively. (Mach 1 flow). Consequently, to increase further 
FIG. 2 presents an enlarged view of the tubular struc- will result in an increased mass flow, but no change in 
ture 11, emphasizing the injection microslits 12 thereon. the particle exit velocity. Because this choked (sonic) 
The tubular structure 11 in the disclosed embodiment 40 condition is a function of pressure ratio and not pressure 
has an outside diameter of 0.375“ while the microslits 12 level, the generator 10 is independent of small variations 
have a width OfaPProximatelY 25-5oP and a length of in Psc and, thereby, capable of generating particles even 
approximately 3 0 0 ~ .  Depending on the desired particle at high ambient pressures. 
size and recognizing the limitations imposed by particle The advantages of this invention are numerous and it 
manufacture, the dimensions of the individual microslits 45 is particularly adapted for laser velocimeter particle 
12 may be altered accordingly. In addition, the injection generation. Because the system is capable of producing 
microslits 12 will operate as designed regardless of their a cloud of uniform, submicron-sized particles at high 
position on the tubular structure 11. Such positioning, pressure and high flow rates, it can attain the rigorous 
therefore, is controlled only by experimental need. particle requirements of the laser velocimeter. 
Another advantage of this invention lies in its ability 
to generate submicron particles regardless of external OPERATION OF THE INVENTION 
In operation, the carrying fluid 19 is introduced to the environment conditions. 
particle feed 16 via the inlet structure 18. In the dis- Still another advantage of this invention is its capabil- 
closed embodiment, air is supplied at a pressure, Pin, of ity to effectuate consistent and uniform separation of 
lo00 psia, thereby lifting the particle feed 16 into the 55 particle agglomerations. 
exhaust fairing 17 at a rate of 5 billion particleshec, a The specifications herein discussed are not meant as 
velocity of 4X limitations on the scope of the invention and its underly- 
lbm/sec. Once guided through the fairing 17, the parti- ing theory as described in connection with the disclosed 
cles 16 will enter the tubular structure 11 for injection embodiment. Various changes may be made without 
into the velocimeter’s settling chamber 20. 60 departing from the scope of the invention as defined in 
The injection microslits 12 along the periphery of the the following claims. 
tubular structure 11 are designed to provide a shearing What is claimed as new and desired to be secured by 
effect on the agglomerated particles. The increase in the Letters Patent of the United States is: 
velocity gradient of the flow between the microslit 12 1. An apparatus to supply a cloud of uniform, submi- 
wall (velocity=O) and the center of the microslit 12 65 cron-sized particles to a high pressure environment, 
(sonic velocity) provides shear forces greater than inter- 
particle bonding forces, thereby breaking up the ag- feeding system means for storing and supplying the 
glomerates into individual particles. 
where, 
M =Mach number of flow through microsIits 12 (= 1 
y=specific heat ratio of the gas 
P,,=ambient pressure of the settling chamber 20 
P;,=pressure of the inlet carrying fluid 19 and, 
for sonic flow) 
c~ s ecific heat at constant ressure 
= 7= &cific heat at constant:olome tion. The top of the exhaust fairing 17 exends from the 2o ’ 
The 
Operation at choked flow 
Or 
50 
fthec, and a mass flow of 3 X 
comprising: 
desired particles; 
4,428,703 
5 
conduit means for accepting said particles from said 
feeding system means, said conduit means having 
microslits on its periphery for separating and in- 
jecting said particles; 
settling chamber means for receiving the injection of 
said particles from said conduit means; and 
carrying fluid means for transporting said particles 
wherein said carrying fluid means is supplied at a 
pressure sufficient to cause said microslits to oper- 
ate at choked flow. 
2. An apparatus as in claim 1 wherein said feeding 
system means comprises a casing whose dimensions are 
determined by the required mass flow rate of said parti- 
cles. 
3. A casing as in claim 2 having an inlet for supplying 
said carrying fluid. 
4. A casing as in claim 3 having fairing means for 
guiding both said particles and said carrying fluid into 
said conduit means and ensurine a laminar flow therein. 
6 
agent thereby ensuring easier, longer lasting primary 
particle dispersion. 
8. An apparatus as in claim 1 wherein said particles 
are mixed with a chemical which acts as an electrical 
9. An apparatus as in claim 7 wherein said chemical is 
5 charge neutralizer. 
Si02. 
10 
15 
20 
Y 
5. An apparatus as in claim 1 wherein said microslits 
have a width of approximately 25-5Op and a length of 
approximately 300p. 
6. An apparatus as in claim 1 wherein said carrying 
fluid is supplied at a pressure of approximately twice the 
ambient pressure of the velocimeter’s settling chamber 25 
so that said microslits will operate at choked flow con- 
ditions thereby resulting in shearing forces adequate to 
overcome interparticle bonding forces. 
7. An apparatus as in claim 1 wherein said particles 
are mixed with a chemical which acts as a hydrophobic 30 
10. An apparatus as in claim 1 wherein: 
said feeding system means comprises an upright, cy- 
lindrical casing; 
said casing has an inlet at its bottom for introduction 
of said carrying fluid means; 
said carrying fluid means is air supplied at a pressure 
of approximately twice the ambient pressure of the 
velocimeter’s settling chamber; 
said particles are mixed with Si02; 
said conduit means is attached to said feeding system 
means by means of a fairing at the top of said cas- 
ing; 
said conduit means is tubular in shape; 
said conduit means has microslits measuring 25p in 
width and 300p in length on its downstream side; 
said microslits operate at choked flow conditions 
thereby effectuating uniform particle separation; 
and 
said conduit means is placed in the flow of the velo- 
cimeter’s settling chamber injecting the separated 
particles therein. * * * * *  
35 
40 
45 
50 
55 
60 
65 


Powder fed sheared dispersal particle generator

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