INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1949
ACKNOWLEDGMENT
1191
L. M. K., Taylor, T. M., Thomsen, E. G., and Morrin, E. H., Trans. Am. SOC.Mech. Eng., 66, NO. 2, 139-51 (1944). (6) Martinelli, R. e., Putnam, J. A., and Lockhart, R. W., Trans. Am. I n s t . Chem. Engr., 42, 681-705 (1946). (7) O’Brien. M. P., and Folsom, R. G., Univ. Calif. Pub. Eng., 3 (7), ( 5 ) Martinelli, R. C., Boelter,
This investigation, a part of the research program in multiphase flow a t the University of California, was supported i n p a r t through a grant by the Research Corporation. LITERATURE CITED
(1) Boelter, L. M. K., and Kepner, R. H., IND. ENQ.CHEM.,31, 42G-34 (1939). (2) Davis, R. F., Engineering, 140, 1, 124 (1935). (3) Gasterstadt, J., Forschungsarbeiten 2. V e r . deut. Ing., 265, 3-75 (1924). ( 4 ) Leva, M., Grummer, M., Weintraub, M., and Pollchik, M., Chem. Eng. Progress, 44, 511-20, 819-26 (1948).
343 (1937). (8) Wilhelm, R. H., and Kwauk, M., Chem. Eng. Progress, 44, 201-18 (1948). (9) Wood, S. A., and Bailey, A., J . Proc. I n s t . Mech. Engrs., 142, NO.2, 149-73 (1939).
RECEIVED January 19, 1949.
as and Solid Mixing in Fluidized Beds T h e internal flow of gas and solid in a fluidized bed has been studied by tracer gas and heat flow methods. Back-mixing of gas was found t o be relatively low in t h e smalldiameter reactors employed. T h e solid flow was sufficient t o give essentially constant temperature throughout t h e reactor.
E. R. GILLILAND AND E. A. MASON M A S S A C H U S E T T S I N S T I T U T E OF TECHNOLOGY, C A M E R I D G E . M A S S .
I
S THE past ten years the use of the fluidized powder technique
for contacting solids with gases has increased rapidly. T h e internal flow characteristics of such a system are of great importance in understanding and properly applying this operation. Several preliminary studies have been made in a n attempt t o gain a n insight into the mixing in the gas phase and the motion of the solids in a fluidized unit. The solid in small fluidization units appears to be in a high degree of turbulence. T h e temperature gradients in such units have been found t o be remarkably small even when reactions involving large heat effects are carried out, arid this has been interpreted t o indicate a very high degree of mixing within the bed. The uniformity of temperature is usually advantageous b u t mixing of the gas is undesirable in most chemical reactions. In an attempt t o obtain an insight into these mixing opera-
Figure 1.
tions, two general types of studies have been made. I n the first, gas mixing has been studied by introducing a tracer gas into t h e middle region of a fluidized bed and testing for this gas both above and below the injection point. I n the other case, solid flow within the fluidized bed has been studied by following the heat flow through the unit. GAS M I X I N G
I n the gas mixing studies, three different experimental units were employed and the pertinent information on them is given in Table I. All the units were similar in construction and operating principles and only the last is described in detail. A schematic diagram is shown in Figure 1. T h e unit was operated batchwise with respect t o the solid, and any entrained particles were removed and continuously returned
Apparatus for Gas Mixing
A . Fluidization c o l u m n
5 . Disengaglng section C . Cyclone separator D . 200-mesh screen E . Sampling ports . F . InJectlon tube, Inside diameter = 0.141 inch G. Capillary orifice H . Sharp-edged orifice J . Pressure taps every foot K. CaClz drying t u b e Bz. Gas density balance A’. Pressure adjustment bottle P . Mercury leveling bottle Q. Fine adjustment bellows R . 6 t o 1 inclined manometer S. Absolute manometer T. T h e r m o m e t e r T w . Wet-bulb thermometer U . Mercury manometer V . W a t e r manometer
VACUUM PUMP I
S
INDUSTRIAL AND ENGINEERING CHEMISTRY
1192
G
c
M,
\
M,
\
G.
Vol. 41, No. 6
comparing the results rvith gases of known molecular weight, and assuming the perfect gas laws, it was possible to calculate the composition of the helium-air mixtures. I n this unit two types of solid particles were employed. I n one run, petroleuni catalyst microspheres wcru used, the screen analysis for which i i given below. Mesh Range
7 G
65
1.6 34.7 18.4 15.6 19.0 9.8
G5-100 100-1 15
Figure 2.
B . Mirror and hairline C. 0,001 X 0.012 inch brass ribbon D. Balance a r m E . Balance platform F . Shell
to the unit by the cyclone separator and the enlarged section a t the top. Air was introduced into the bottom of the column through a conical scction and was distributed by a 200-mesh screen. Pressure taps were provided a t 1-foot intervals along the column. I n the experiments with this unit, helium n a s ernployed as the tracer gas in order to minimize adsorption effects. The tracer gas was injected a t a point 2.5 feet from the top of the column through a 5-mm. glass tube airanged t o inject the gas upwardly in the center of the column. T h e sampling tube \Tas a stainless steel tube 0.075 inch in outside diameter and arrangements r e r e made so t h a t this tube could be inserted a t 1-inch intervak above and below the iiijectioii point. The position of the sampling tubc was adjusted by a screw. Air and helium rates xere measured by means of orifices and the gas samples were analyzed for helium in an EdJvaids gas density balance. I n this analytical unit (Figure 2), a horizontal beam having a small hollow bulb a t one end and a mirror a t the o t h c ~ was suspended in the gas-tight chamber. The beam was brought into balance by adjusting the total pressure on thc unit; by
Experimental U n i t s
Column I.D., Height, inches feet
Herference
1
2 2
Fluidizing Gas
Solid Filtro!
Tracer
Gas
co.
.1,
Glass beads
6
150-200 200
G. Screw-on caps w i t h glass windows H . Balance f r a m e J . Check bars K . Ribbon clamp M . G a s ports
A . Float
Table I .
115-150
Gas Density Balance
I n the remaining four runs glass beads of approximately 100 mesh (0.0061 inch in diameter * 107&) were used. I n most runs the helium injection rate was such that the average composition of the final gas mixture would be approximately 10% helium.
The data obtained in one of the runs with glass beads are shown Figures 3, 4, and 5 . Figure 3 gives the composition a t the center of the tube as a function of the distance above and below the injection point. The concentration is expressed as a fraction of the calculated average stoichiometric concentration, C,, based on the air and helium feed rates. As would be expected, the concentration is very high just above the injection point and then decreases a t higher levels as the center stream becomes mixed with the surrounding gas. Below the injection point, there is a significant concentration of the helium vhich persists for a distance of over a foot, indicating an appreciable mixing of the gas. Figures 4 and 5 give similar data taken a t distances of 1.1 and 1.43 inches from the center; the wall would be 1.5 inches. These two figures show a trend in concentration below the injection point similar to Figure 3, but above this point the trend is reversed. These differences would be expected on the basis of the system employed. At a limited number of levels, detailed traverses were taken, and the results plus some of the data from Figures 3, 4, and 5 are given in Figure 6. At a given level above the injection point, there is a wide variation in the concentration a t different radii, but a t a given level below this point the concentration over a cross section is relatively constant. The data indicate that below the injection point the concentration tends to be the highest near the ni
3 50 3 00 .
3 00
2 50
2 50 AIR I/ELOC/TY = 116 f
T PER
SEC
I
I
I
I
AIR VELOCITY-1/6 F T PER SEC
I
I I I
SAMPLES A T R = 110 INCHES
SAMPLES AT R = 0 /NCHFS 2 00 I
Lo
I
CI
1.50
100
0 50
0
PO
5 /O ABOVE /NCii€S FROM POiNT O F lNJCC7lON 15
10
5
0
15
BELOW
Figure 3.
Gas Sampling Results a t Center of Column
He-air, glass beads, superficial a i r velocity 1.16 feet per second
Figure 4.
Gas Sampling Results a t R = 1.10 Inches
He-air, glass beads, superficial air velocity 1.16 feet per second
June 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
in Figure 8 as a function of the average linear velocity. This plot also includes the d a t a obtained with the other units as listed in Table 11. The data on the three units agree reasonably well even though the ratio of length to diameter, LID, and the solid particles varied significantly. It is believed t h a t the mixing effect may be greater for small values of L I D and this condition is being studied. Owing to the scattering of the points, i t is difficult to determine whether V / E is a significant function of the velocity. However, there appears t o be a decrease with increasing velocity. The above discussion assumes that the mixing took place by a random turbulence. However, such a picture would not explain why below the injection point the concentration at the wall is higher than in the center of the tube and why the curves above the injection point show a minimum concentration as a function of the radius. Such data would be more satisfactorily explained if i t were assumed that the flow of the gas was upward and relatively turbulent in the center region but downward along the wall. Visually i t is clear that the motion of the solids is downward a t the walls, but this would not necessarily require any significant downflow of gas. However, if this is the flow pattern in the unit, it would be expected that the helium concentration which is high just above the injection point would tend to persist at a high value in the center of the tube, but i t would gradually mix with the rest of the gas. Thus, in the upper regions of the unit, there would be a relatively high concentration of the tracer gas at all cross sections and the portion of this gas along the wall would be flowing down and giving high concentration of the tracer gas a t the wall below the injection level. T h e fact t h a t concentration is relatively constant over the center portion of the tube below the injection point indicates that this region is receiving the tracer gas from the stream along the wall and t h a t the gas mixes relatively rapidly. On the basis of the curves of Figure 6 , i t is possible to make a very rough estimate t h a t the maximum quantity of gas that flows downwardly along the wall is of the order of twice the net upflow. This result is probably high, inasmuch as some of the downward mixing undoubtedly occurs by turbulence rather than
2 00
0- 50
1
L
A
B f L ow ABOVE INCH[$ FROM POINT OF /NJ€CT/ON
Figure 5.
1193
Gas Sampling Results a t R = 1.43 Inches
He-air, glass beads, superflcial a i r velocity 1.16 feet per second
walls. I n order t o correlate these data, an attempt was made to fit them to an eddy diffusivity type of equation.
where n = quantity transferred per unit area, C == concentration, 6 = time, E = eddy diffusivity, and x = distance. In the experimental techniques used, the system comes to a steady state, when the amount of helium carried down by the mixing is equal to that carried back up by the net flow of gas. I n order t o integrate the equation under these conditions, two assumptions are made: (1) The gas velocity is uniform across the cross section, and (2) the eddy diffusivity is constant. It is doubtful whether either of these assumptions is valid, but the resulting value of E should be representative of the average down3.50 mixing. The integration of the A / R YELOCfTY equation under these conditions gives 1
3 00
where V = superficial gas velocit? a n d B = constant. I n order to test this relationship, the logarithm of the concentration ratio is plotted as a function of the distance below the injection point. Only data 2 inches or more below the injection point are considered. Figure 7 gives the results of a run with glass beads at a ve1ocit.y of 1.16 feet per second. Points are given for three different radii, and within the accuracy of the data a single line is representative of the three sets. By Equation 2, the slope of this line is equal to the linear velocity divided by the eddy diffusivity and for this particular case the valur is 2.18 reciprocal feet. The ratios of V / E for the other runs are giver]
\
I
2 50
2 00
cp
ip \
\ CI
CI / 50 3
1.00
0.50
0
A
0
d
IO
05
0
RADIUS, INCHES
Figure 6.
Gas Concentration Traverses
He-air glass beads superflclal v'elocity 1.16 f e e i per second
,
air
4 8 I2 16 20 INCHES BELOW POINT OF INJECT/ON
Figure 7.
Determination of
r
VIE
He-air, glass beads, superficial a i r velocity 1.16 feet per second
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1194
Table I I . Fluid-
Refer- izing ence System 4ir-C0z Air-COa Air-COz Air-Con
'",o-/
10
I V, F E E T / S E C .
Figure 8.
VIE vs. V for
Vol. 41, No. 6
D a t a on V a n d V f ~Solid
.~...
Mesh
Type
Filtrol Filtroi Filtrol
Velocity. Feet/ V/B. Sec. L/,F'oot. 0.33 1.35 2 . l!i 0.33 1.35 2.48 1.3s 0.33 2.62 0.33 3.44 0.5
Charge, lb.
65-100 100-200 200-250 60'7 100-200 3 0 d through 325 6 0 7 100-200 3 0 4 through 325 Goyo 100-200 3055 through 325 30% 60Y0 through 100--200 325
Filtrol
Air-COz
Filtrol
Air-CO?
Filtrol
Air-COz
Filtrol
Air-COa
Filtrol
Air-COz
E'iltrol
Air-COz
Filtrol
Air-C0z
Fiitrol
Air-COa
Filtrol
Air-COz Air-COz Air-He
Filtrol Microspheres F1ltrol
Air-He Air-He Air-He Air-He
Glass Glass Glass Glass
beads
beads beads beads
6 0 7 100-200 3 0 d through 6 0 7 100-200 3070 through 8052 100-200 30% through BOY0 100-200 30% through 6 0 7 100-200 3 0 4 through Through 200
325 325
. " *
0.5
2.44
...
0.5
2.91
...
1. o
2.44
, . i
1. 3
2.04
0.33
1.5
2.07
1.5
1.82
0.33
2.01
2 ,44
...
2.6
2 , Re;
0.33 0.33 4.5
1.0 1.0 1.63
4,4(1 4 2.i
0.58 0.87 1.16 1.70
3 .0 3.34 2.18 1.39
,
326 326
325
100-200 35% 65-100 s5yo 100-200 D = 0 , 0 0 6 1 inch D = 0.0061 inch D = 0,0081 inch D = 0.0061 inch
.
I
17.2 14.3 13.2 13.0
I
1.74
All Investigators
circulation. It is possible that a st,udy of unitw with widely different ratios of height to diameter will distinguish between these two methods of mixing, and such work is in progress. At 10 inches above the injection point all the samples have a C / C , value greater than 1.0, whereas the samples taken a t the top of the unit above the fluidized bed agreed well with the metered rates. Such a result could be explained by sdective adsorpt,ion and recycling of the helium; however, this does not seem logical. Another =.= ----possible explanation is that the introduction of the sampling tube may alter the flow Dattern and give gas samples t h a t are not kpresentative. This l a t t e r problem is under active investigation a t the present time. I n order t'o obtain a more quantit,at,ivepict,ur.e of the effect of such mixing upon a chemical reaction, the eddy diffusivity formula was employed. Alt'hough this relationship niay not correspond exactly to the actual mechanism involved, it gives a satisfactory empirical picture of the experimental data. The effect such mixing would have on a chemical reaction depends on both the reaction rate mechanisin and the relat,iverates of react'ion and mixing. Thus for a aero-order reaction, mixing would have no
effect, but it would be detrimental for reactions of h i g h r ~( because it dilutrs the reactants with the products.
For purposes of comparison, a first-order gas reactioii utilizriig solid catalyst and occurring without change in volume was assumrd. It was also assumed that the linear gas velority over the cross section wab uniform. The result of the combined reactisn rate and mixing ran be given ar B
- c,
kCj
L
__-_
I - e
(3)
AI-
where Cj = concentration leaving reactor, C, = concrntratioi, PIP tering reactor, V = superficial gas velocity, L = length of reaction zone, E = constant for Equation 1, and k = first-orctri reaction rate constant. It is interesting to compare this relationship with the one tliar would have been obtained for the same assumptions in the absence of mixing and this relation is the usual first-order equatior:.
C y = Cot.-kO
=
C,e
--IZL 17
where C* = concentration leaving rcactor for conditionH of mixing.
IO0
J I ~ W ~
(4, I N #~ L H R
Equation 3 can be rrwrittrri as 095
0 90
0 85
5 *
0 80
0 75
0 70 0
0 5
10
16
20
8'E/Vz
Figure 9.
Effect of Gas Mixing on Chemical Reaction Rate Constant
and the ratio of the apparent reaction rate constant to the chwircal reaction rate constant is given in Figure 9. The important criterion of the effect of mixing is the dimensionless group roiltaining the product of the reaction rate constant and the mixing constant divided by the linear velocity squared. There is little effect on the ieaction rate constant a t low values of the dimmsionless group, as this indicates either low mixing or a low reactior' rate constant. I n the first case, the effect of mixing would be expected t o be low. I n the second case, the effect is small, hecause the low reaction sate constant implies that a long pat)) o d travel through the fluid bed would be necessary to make a sign& cant difference in concentration, and thus even though mixing occurs it is not particularly serious, owing to the small roiicrrrtration gradient.
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1949
1195
The gas mixing in this case had a rclatively small effect on the reaction-i.e., there was only 4% reduction in the apparent renction rate constant. Thus, gas mixing is not likely t o be a serioub factor in small fluidized beds with large L I D ratios. If the reaction rate were higher, the percentage effect of mixing would be larger, but in such a case the reaction velocity is so high that thc length of the reactor is not a serious problem. I n some cases the apparent gas mixing might be considerably larger because of tlir preferential adsorption of components on the solid. However, in geneyal, it is believed t h a t the best assumption to make in correlating reaction rate data for small fluidized units is that t h e effect of the gas mixing is small. SOLID MIXING
Figure 10.
Effect of Gas Mixing on Fraction of Reactant Converted
2 00
I80
1.60
"a \
940
1.20
IO0 0
I O FfElVZ
05
Figure 11.
I5
20
Effect of Gas Mixing on Fraction of Reactant Unconverted
The effect of such mixing on the reaction rate can also be shown rn the effect on the fraction converted and the fraction unconverted. Figure 10 gives the ratio of the fraction converted with mixing t o t h a t without mixing and Figure 11gives the corresponding ratio for the fraction unconverted. The most serious effect of mixing occurs when there is a significant concentration gradient-Le., when the conversion is high-and the effect becomes small at low conversion. T o give a more quantitative picture of the magnitude of this effect, assume (1) that a first-order reaction is t o be carried out in a fluidized bed under the flow conditions assumed above, (2) that the chemical reaction rate data are such t h a t without gas mixing one would expect a 95y0 conversion for a bed depth of 15 feet, and (3) t h a t t h e fluidizing velocity is 1 foot per second. From Figure 8, a value of V / E equal t o 2.6 is obtained, and from Equation 4 a value of the chemical reaction rate constant, IC, is obtained as 0.2 reciprocal second, giving a value for the dimensionless group of
The actual conversion can be calculated from Equation 3. r
C" - -1
c,
' c6
0.2
=
( 1 ) [I - 4~i-I
(0.77) =
16.6
=
0.057
Thus a conversion of 94.3 would be obtained and the depth of bed would need t o be increased to 15.7 feet t o make t e d e s i r e d conversion I n this case, the ratio of k' t o IC is 0.96.
I n a n attempt t o investigate the flow pattern of the solid, a fluidized unit was built with the upper section electrically heated and the lower section water-cooled. Thermocouples were arranged t o meamre the wall temperature, and the temperature of the cooling water entering and leavine the iacket was determined; a movable thermocouple was arranged along the axis of the fluidized bed. Care was taken in winding the electric furnace, so t h a t the heat influx per unit length would be constant. Air was used as a fluidizing medium in all cases, and several different finely divided solids were employed. The results of temperature measurements along the axis when only air is present (no solids) are shown in Figure 12. The air entered at, room t e m p e r a t u r e 5 0 1 f and flowed through COOLED HEA TED the water-cooled section with no tempera0 0 8 /6 24 32 40 ture rise and then 4 I showed a rapid inINCHES FROM BorroM OF COLUM! crease in temperature Figure 12. Center-Line Temperatures i n Heated-Cooled C o l u m n in the heated section. The e x p e r i m e n t a l Filtrol, superficial air velocity 1.2 feet per second heat transfer coefficient for the heated section was 1.15 B.t.u./hour/sq. ft./'F., as compared t o 1.1 predicted from Equation 12 (3,page 186). The same figure shows the temperature distribution obtained when solid is present in the bed. The center-line temperature is very much more constant than in the case with no solids. The temperature of the inlet air rises rapidly to approximately 95' F. and then shows only a slight further increase. The heat supplied t o the unit was 52% higher in the test with the solid present and the fact t h a t the gas leaves a t a lower temperature in this case is due t o the heat transfer to the cooling section. For the run shown, the rate of heat transfer to the lower section mas approximately 208 B.t.u. per hour, which was 89.8% of the total heat supplied. Heat transfer coefficients were calculated on the basis of the measured heat flow through the walls of the unit and the temperature difference between the wall and the center of the fluidized bed. The heat transfer coefficients for the heated and the cooled sections are 22.6 and 124 B.t.u./hour/sq. foot/' F., respectively. T h a t these values are much higher than with the gas alone indicates the large effect of the solid.
:-1
-,
;
+-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1196
ture in a fluidized bed, and in cases where heat is being transferred into and out of the bed, there may be significant radial differences. The data in Figure 13 do not alloiT one t o determine which of the two methods of inixing is the more effective. Heat is undoubtedly carried down to the lower section by solid flow down along the walls, but there are no data available to indicate the magnitude of the flov-.
100
80
P -&
Vol. 41, No. 6
60
2
L
SUMMARY
I
2 40
The experimental data on gas mixing indicate that the backmixing of gas in small fluidized beds with high L I D ratios is relatively small and in the case of most reactions not particularly detrimental. On the basis of these data, it is recommended t h a t reaction rate studies conducted in such units be correlated on the basis of piston flow, neglecting mixing. The data on the heat flow in the fluidized bed indicate t h a t solid mixing is relatively rapid and t h a t the sensible heat carried by the solid can serve to maintain relatively constant temperature throughout the bed, despite a wide vaiiation in rate of heat release.
2
?. PO
__----
COOi€D
_/---
0
Figure 13.
5
-+-H€A7tU.4
20 25 /NCVLS FROM BOTTOM OF COLUMN 10
15
30y'
Radial Temperature Differences in Heated -Cooled C o l u m n
Filtrol, superficial a i r velocity 1.2 f e e t per second
It is intcrcsting to consider the mechanism by which the heat is transferred from the upper to the lower section. The thermal eddy diffusivity for the gas only JT-as estimated from the gas mixing eddy diffusivity, and a n estimate of the heat transfer from the upper to the loner section on this basis accounted for less than 3% of the total. Thus i t appears that the heat must be mainly transferred by the mixing of the solids This downflow of heat corresponds t o a relatively rapid mixing of the solid, which could be of tlyo types. First, the mixing could be due simply t o general turbulence, which progressively transmitted the heat to a lo\yer level, or it could be the dovnflow pattern similar t o that suggested above-Le., the solid would flow up the center and down the \$all. This would not imply that there Kas not considerable random inixing but simply that such ciiculation x a s superimposed upon the vertical pattern. I n order to investigate the mixing pattern, temperatures Tyere measured by a thermocouple approximately 0.1 inch from the wall along the length of the reactor. The data are given in Figure 13 as the difference between this temperature and the center-line temperature. At the bottom of the unit this temperature difference 1s relatively small but it rises to a fairly high value a t the top of the cooling section. This indicates t h a t temperature gradients along the renter line may be misleading as to the constancv of tempera-
NOMENCLATURE
B C CJ Cy
=
= = = = =
C, D E = k =
8' L n
R 77
-V
e
=
= = = = =
=
constant concentration concentration leaving reactor concentration leaving reactor, no gas mixing concentration entering reactor diameter eddy diffusivity first-order reaction rate constant apparent first-order reaction rate constant length of reaction zone quantity material transferred per unit area radius superficial gas velocity distance time L I T E R A T U R E CITED
(1) Ciboron-ski, J. IT., 10-90 R e p o r t , C h e m . E n g . , M a s s a c h u s e t t s I n s t i t u t e of Technology, 1947. ( 2 ) K e n n e l . W. E., S.M.thesis i n chemical engineering, M a s s a c h u s e t t s I n s t i t u t e of Technology, 1946. (3) ,McAdams, W. H . , " H e a t Transmission," 2 n d ed., p. 186, New York, McGraw-Hill Book Co., 1942. (4) Sweeney, G. C., Jr., S.M. t h e s i s i n chemical engineering, Massac h u s e t t s I n s t i t u t e of Technology, 1948. KECEITEDJanuary 19, 1049.
ue to Dust Particles in a Gas Stream A few experiments were made i n a n effort t o evaluate some o f t h e basic factors of erosion t h a t can arise in gas-solid flow systems of high velocity. In essence theexperimental method was one of sandblasting targets a t different j e t velocities and angles of impingement w i t h different entrained dusts. T h e a m o u n t of erosion was determined f r o m t h e change i n weight of t h e targets. R. L.STOKER1 WESTERN PRECIPITATION CORPORATION, LOS ANGEI-ES, C A L I F .
E
ROSIOK can occur v h e n small solid particles carried in a fast-moving gas stream impinge upon a solid surface. In sandblasting operat'ions such as cleaning castings and et'ching glass this eroding action is emphasized. Considering how long sandblasting has been used, one would expect to find literature describing all phases of the art, and technical and experimental 1
r.08
Present address, Department of Engineering, University of California, Angeles, Calif.
inforination o n the essential factors, and the relationships existing between them, that are responsible for this type of erosion. Although much has been written on the qualitative nature of sandblasting, quantitative, basic information is surprisingly scarce. Current erosion studies a t high gas velocities have been reported by Fisher and Davis (1). The experiments described here were exploratory and preliminary steps taken a fen. vwrq a g o in an attempt to solve certain
