LITERATURE CITED
(1)
Brant, R., U. S. Geol. Survey, Circ. 226 (1953). (2) Gauger, A. W., Am. Inst. Mining Met. Engrs. Trans. 101, 148 (1932). (3) Gordon, M., Lavine, I., Harrington, L., Znd. Eng. Chem. 24, 928 (1932). (4) Hoeppner, J., Fowkes, W., McMurtrie, R., Bur. Mines, Rept. Invest. 5215 (1956). (5) “International Critical T a b l e s , ” Vols. 1 and 2, McGraw-Hill, New York, 1933. (6) Klein, H., Braunkohle 29, 1 (1930). (7) Kreulen, D., Brennstoff-Chem. 36 (17/18), 266 (1955). (8) Kube, W., Proc. N. Dakota Acad. Sci. 6, 8 3 (1952). (9) Larian, M., Lavine, I., Mann, C., Gauger, A., Ind. Eng. Chem. 22, 1231 (1930).
Thermal Properties of Soybean
(10) Lavine, I., Gauger, W., Zbid., 22, 1226 (1930). (11) Oppelt, W., Proc. N. Dakota Acad. Sci., 6, 36 (1952). (12) Oppelt, W., Golob, E., Cooney, J., Kube, W., Bur. Mines, Mineral Research Invest., Prelim. Rept. 99 (1954). Kamps, ., T. W., (13) Oppelt, W. H., Kube, W. R., Chetvick, hi. €I Golob, E. F., Bur. Mines, Rept. I n v e s t 5164 (1955). (14) Pearson, R., master’s thesis (unpublished), University of North Dakota, 1950. (15) Tasker, C., Ontario Research Foundation, Div. of C h e m Research Lignite, No. 23 (1933). (16) Terres, E., Brennsloff-Chem 33, l(1952). Received for review August 29, 1956. Accept ?d February 7, 1957. Investigation supported by a grant from the National Science Foundation, Washington, D.C. (G. N. Hickox, program director for engineering sciences).
Oil M e a l
JOEL 0. HOUGEN’ Rensselaer Polytechnic Institute, Troy, N.Y.
A
nnual production of s o y b e a n s in t h e United S t a t e s exc e e d s 350,000,000 b u s h e l s a year (7), probably about o n e half (6) t h e world total. Within t h e United S t a t e s s o y b e a n s are grown widely in t h e Middle West. Cultivation of soyb e a n s is a major effort i n t h e corn b e l t s t a t e s ; over 20,000,000 a c r e s (5) are devoted t o t h i s crop i n t h a t region, almost all harvested for t h e b e a n s . Two major raw materials a r i s e from the soybean: o i l and meal. Food products, principally margarine and shortening, u t i l i z e about 80% of t h e oil; t h e remainder is used in soap, paint and varnish, and m i s c e l l a n e o u s nonfood products. Soybean meal i s consumed for the most part a s feed for livestock (about go%), smaller amounts being used for soybean flour, plywood glue, and paper coatings, and i n various industrial protein-containing materials. Soybean o i l meal i s defined a s the ground residue which remains after the oil is removed from t h e soybean, regardless of the p r o c e s s of extraction. L i v e s t o c k feed i s t h e primary market, e x c e p t for a s m a l l outlet for industrial uses. Accepted s p e c i f i c a t i o n s for soybean o i l meal obtained by t h e two standard methods of processing, expelling and solvent extraction, a r e (1): for meal from either source, carbohydrates and fiber 7 % (maximum), nitrogen-free e x t r a c t 27% (minimum), and moisture 12.5 % (maximum). Minimum p e r c e n t a g e s of protein and fat differ, depending on the s o u r c e of t h e meal. For hydraulic and expeller meals t h e s e a r e 41.0 and 3.5 and for extracted m e a l s 44.0 and 0.5, respectively. Following oil extraction the soybean meal is p r o c e s s e d for solvent removal and t o improve i t s nutritional properties. T h i s usually involves r a i s i n g the temperature of the meal by adding thermal energy through t h e w a l l s of a container, by direct steam injection, or both. Data useful i n t h e d e s i g n of apparatus used t o p r o c e s s particulate materials are not overabundant. T h i s is particularly true for materials which a r e biological in origin and h e n c e s u s c e p t i b l e t o alteration upon exposure t o air, moderate temperatures, or both. T y p i c a l of such material is soybean o i l meal. ‘Present address, Research and Engineering Division, Monsanto Chemical Co., St Louis, Mo.
1957
T h e objective of t h i s work w a s to determine experimentally the thermal properties of a typical soybean oil meal, including thermal conductivity, thermal diffusivity, and h e a t capacity.
PROPERTIES OF MEAL, EXPERIMENTAL APPARATUS, AND PROCEDURE T a b l e I l i s t s some of t h e physical and chemical properties of the soybean oil meal u s e d in t h e s e s t u d i e s . T h e meal w a s extracted in conventional H a n s a M e u h l e type e x t r a c t o r s using Skellysolve B as t h e solvent. Following t h e oil extraction t h e solvent w a s removed by heat and by direct steam injection a t about 200 O F . Solvent removal w a s considered complete. R e s i d u a l o i l content w a s found to b e 0.7 t o 0 . 8 % , a s shown in T a b l e I. Toble I. Properties o f Soybean Oil Meal after Solvent Removal Size
Oil content, 70 Moisture content, % Total protein, 70 Water-soluble protein, 7’’ Variety of bean
Will p a s s 48 mesh 0.7-0.8 13.2 51.55 (dry stock b a s i s ) 39.57 of total protein* (dry stock b a s i s ) Lincoln (probably)
eDetermined by tentative procedure recommended by Soy Flour Association, revision of Dec. 10, 1946.
T h i s meal may b e further processed before being soid. It i s frequently packaged in metal c a n s prior t o final treatment. Meal which w a s canned but had not received i t s final (heat) treatment was supplied by t h e A . E. Staley Manufacturing Co., Decatur, Ill. Thermal conductivity w a s obtained by using t h e concent r i c cylinder technique with a material of known conductivity as t h e reference. (Figure 1). Concentric copper t u b e s were arranged a s indicated, with provisions for producing an atmosphere of saturated steam within t h e innermost tube. T w o small iron-constantan thermocouples were located a t points about diametrically o p p o s i t e e a c h other on e a c h tube a t the mid-point of the vertical s e c t i o n s . T h e reference material used w a s Grade 6 Spheron carbon black furnished by Godfrey L. Cabot, Inc., Boston, Mass. At a mean temperature of 118’F. and a bulk density of 20.2 CHEMICAL AND ENGINEERING D A T A SERIES
51
pounds per c u b i c foot, t h e thermal conductivity of t h i s m a terial h a s b e e n reported a s 0.182 B.t.u., hr.-’, ft.-’, inch, OF.-’
Table
II.
Measurements for Determination o f Thermol Conductivity
(3).
With carbon black in one annular s p a c e and soybean oil meal i n t h e other, t h e system w a s allowed to come to thermal equilibrium and the various s u r f a c e temperatures were determined. T h e position of t h e two materials w a s then reversed, using fresh material, and t h e p r o c e s s w a s repeated. In e a c h c a s e the soybean oil meal w a s obtained from a freshly opened can in which i t had b e e n preserved. Data a r e shown in T a b l e 11. A s t h e soybean oil meal w a s available in s e a l e d c a n s , t h e transient method appeared to be most suitable for obtaining thermal diffusivity data. Iron and constantan therrnccouple wires of small diameter were butt-welded and p a s s e d through t h e c a n of meal on i t s longitudinal axis. T h e junction w a s located at the geometric center of t h e c a n , t h e h o l e s were s e a l e d , and t h e c a n w a s properly supported ins i d e a n autoclave. T h e thermocouple l e a d s were extended t o a Brown Electronik self-balancing potentiometric pyrometer by which c h a n g e s in temperature could b e followed. T h e heating medium w a s steam admitted through a control valve positioned by a Plodel 40 Foxboro pressure controller.
CONDENSER
THERMOCOUPLE JUNCTIONS
-12
.I
Outer annulus Ti, ZCT i , oC. T3, C.
T1 - TI AT^ = TI - T3
AT1 =
Bulk density carbon black, lb./cu. foot Bulk density meal, lb./cu. foot
Test 1
Test 2
109.6 grams of carbon black 129.1 grams of soybean meal 98.56 50.16 44.78 48.40 5.38
171.1 grams of soybean meal 81.4 grams of carbon black 100.65 62.35 4 8 95 3 7.70 13.40
24.4
24.5
38.9
38.1
T h e position of t h e c a n of meal within t h e autoclave i s indicated in Figure 2. After initial thermal equilibrium had been attained, steam w a s quickly admitted to t h e autoclave, using a manual byp a s s valve. When the desired p r e s s u r e had been achieved, t h e b y p a s s w a s closed and t h e controller assumed operation. T h e time required to attain t h e desired pressure level w a s never longer than 1 minute. A duplicate s e t of d a t a w a s obtained on a s i n g l e sample and t h e r e s u l t s were averaged. Data taken from a smoothed curve a r e shown in T a b l e 111.
THEORETICAL
1
,I
Inner annulus
CONDENSATE [RETURN
T h e thermal properties of interest in predicting h e a t transfer by conduction a r e contained i n the thermal diffusivity term, x = k/c,p. From t h e transient s t u d i e s x may be obtained, while from t h e steady-state performance k c a n b e found. T h e bulk density, p, may b e obtained in any convenient manner, but for t h e s a k e of greater c o n s i s t e n c y w a s measured in connection with t h e conductivity t e s t s . Heat capacity may b e computed as cp = k/icp. Calculation of conductivity from t h e steady-state d a t a using t h e concentric tube technique i s straightforward, except that where t h e s p a c e is filled with finely divided s o l i d s , such as carbon black, t h e conduction equation should be kAAT kAAT rather than - (4). L -2d L T h u s two s e t s of d a t a a r e required to find t h e unknown conductivity and simultaneously t h e “surface r e s i s t a n c e ” factor, d , or d may b e found first by using Equation 1 below and conductivity, subsequently, by using Equation 2:
BOILER -
Figure
1. Concentric tube apparatus for determination o f thermal conductivity L i n e a r Dimensions i n Inches
d, = 0.62 d, = 1.62 d, = 2.15 r1 = 0.31 rp = 0.74 r: = 0.810 r, = 0.995 h = 12.07
52
I, I,
= 0.43
= 0.185
rml = 0.496 (log mean radius) rmr = 0.895 (log mean r d i u s ) A , = 27rr,, h = 0.260 h sq. foot AI = 2nrm h = 0.470 h sq. foot V I = 1 7 . l d c u . inches (inner annulus) Vr = 12.68 CU. inches (outer annulus)
INDUSTRIAL AND ENGINEERING CHEMISTRY
.
where s u b s c r i p t s 1 and 2 refer to the t e s t data shown in T a b l e 11. It i s assumed that conductivity is independent of temperature in t h e range encountered. To find t h e thermal diffusivity, the equations describing t h e unsteady-state h e a t transfer to a right circular finite cylinder a r e employed and t h e value of X i s selected s u c h that t h e theoretical transient heating curve f i t s t h e experimental curve reasonably well. T h e theory h a s been outlined by Olson and Schultz ( 2 ) and convenient numerical tables h a v e been prepared from which rapid solutions for timetemperature relations for a number of geometric s h a p e s may b e obtained. V O L . 2,
NO. I
TO BROWN SELF- BALANCING ELECTRONIC POTENTIOMETER
GAUGE
\I
..
E a c h s e r i e s represents t h e solution of the appropriate partial differential equation d,scribing t h e physical situation. Finally, for a finite cylinder with T measured a t t h e geometric center i t c a n b e shown that
Olson and Schultz present t a b l e s where, for various v a l u e s of xt/rz or X t / a z , t h e corresponding v a l u e s of C and S may be found.
EXPERIMENTAL RESULTS In t h i s c a s e , from experimental observations, v a l u e s of u a s a function of time, t , h a v e b e e n found. r and a were obtained f r o m t h e dimensions of t h e cylindrical container. T h e problem is to select, by trial and error, t h e appropriate v a l u e of x s o that t h e product, C x S , gives a value of u in agreement with t h e observed v a l u e s over a reasonable portion of t h e experimental region. In T a b l e I11 experimental v a l u e s of T are given along with t h e calculated values of u with a value of thermal diffusivity taken a s 0.0048 square foot per hour and in F i g u r e 3 r e s u l t s a r e compared graphically. A reasonable tit is obtained.
+.* ~
TRAP
F i g u r e 2. Apparatus for heating canned soybean o i l meal a t constant surface temperature
T h e e s s e n c e of t h e mathematical treatment may b e described a s follows. If a “theoretical” temperature b e defined a s u = ( T , - T ) / ( T ,-
To)
-
0 2
EXPERIMENTAL --\
0-
CALCULATED A$¶”YI*G
*-
000411
-.-
r14*a
I
c
i t may b e shown that t h e value of u for an infinite cylinder of radius r with T being t h e temperature a t t h e a x i s may b e found a t any time t by t h e formula u = C (xt/rz) where function C i s t h e infinite s e r i e s of t h e form -0:
n iexp (-
R: X t / r z )
i=l
For infinite s l a b s of t h i c k n e s s a with T taken a t t h e midpoint
u = s (xt/a’) Table
T a b l e 111.
t , Sec.
0
500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Thermal Response D a t a for F i n i t e C y l i n d r i c a l Section o f Soybean O i l Meal
T,OF. 65 66 70 91 118 147 168 183 192 197 20 2
TI
-T
168 167 163 142 115 86 65 50 41 36 31
u
(Exptl.) 1.000 0.994 0.971 0.845 0.685 0.511 0.386 0.297 0.244 0.214 0.184
T I 233’F., To = 65’F., Ti - To= 168 r = 1.65 inches
1957
u
a = 4.25 inches
(Calcd.) 1.000 0.998 0.944 0.818 0.672 0.538 0.425 0.333 0.259 0.202 0.156
IV. T h e r m a l Properties o f Soybean O i l M e a l T e s t e d 0.0048
Thermal diffusivity, CC, sq. f t {hr. Thermal conductivity, k, B.t.u. /hr.-sq. ft. (OF./ft.) Heat capacity, c p , B.t.u./hr.-OF.
0.040 0.215
ACKNOWLEDGMENT T h a n k s a r e extended t o Frank Bunk, J a m e s Codding, and Raymond Gerow, former s t u d e n t s a t R e n s s e l a e r Polytechnic Institute, for their a s s i s t a n c e in obtaining some of t h e experimental data.
NOMENCLATURE a = height of cylinder
A , A I , A 2 = area for heat flow
A i = coefficients in Bessel-Fourier expansion b , = exponents in s e r i e s for .S(‘&t/a’) B i= coefficients in series for S ( a t / a ? cp = h e a t capacity d = “surface resistance”
CHEMICAL AND ENGINEERING D A T A SERIES
53
k , k s b , k , b = thermal conductivity k s b for soybean oil meal k,b for carbon black a = thermal diffusivity L, L1,L, = length of path for heat transfer r = radius of cylinder t = time T = temperature at geometric center of finite cylinder except a s noted To= initial temperature of cylinder TI= surface temperature of cylinder at time 8 (forcing temperature) u = 6'theoretical" temperature, Tl - T / T I - To p = density
LITERATURE CITED (1) Markley, K. S., "Soybeans and Soybean Products," p. 436, Interscience Publishers, New York, 1950. (2) Olson, F. C. W., Schultz, 0.T., Ind. Eng. Chem. 34, 874 (1944). (3) Smith, W. R., Wilkes, G. 5 ,Ibid., 36, 1111 (1944). (4) Smoluchowski, M., Proc. 2nd Refrig. Congr. 1910, 187-93. (5) U. S. Dept. of Agriculture, Agricultural Statistics 1955, Table 181, p. 126. (6) Ibid., Table 182, p. 127. (7) Ibid., Table 184, p. 128. Received for review May 13, 1954.
Accepted September 24, 1956.
Thermal Conductivity of Some Organic Liquids
High Temperature Measurements 0. B. CECIL, W. E. KOERNER, AND R. H. MUNCH Organic Chemicals Division, Monsanto Chemical Co., St. Louis 4, Mo.
A lthough thermal conductivity v a l u e s a r e becoming more numerous i n t h e literature, they represent for t h e most part v a l u e s determined a t relatively low temperatures-i.e., below 100" C. Engineers desiring to u s e t h e s e data for high temperature problems must extrapolate low temperature v a l u e s to t h e desired temperature. In many cases, only one v a l u e e x i s t s and t h i s must b e used for a l l calculations. Such extrapolations a r e obviously questionable. T h i s report d e a l s with t h e extension of a technique for determining a b s o l u t e v a l u e s of thermal conductivity (1) t o temperatures a s high a s 200" to 250' C. T h i s work d o e s not represent a limit for thermal conductivity measurements but serves t o i l l u s t r a t e how v a l u e s a t higher temperatures can b e determined.
F T O C a r t e s i a n Monostot
II".
Condeniser 241
3
EXPERIMENTAL T h e method u s e d [described in detail elsewhere (I)] is a highly refined modification of t h e hot-wire technique. T h e thermal conductivity cell proper employs a four-lead arrangement analogous t o a four-lead platinum r e s i s t a n c e A l l conthermometer, thereby eliminating end effects. s t a n t s n e c e s s a r y for thermal conductivity measurements a r e determined from t h e dimensions of t h e cell. T h e determined thermal conductivity v a l u e s a r e t h u s absolute. Of prime importance i n t h e s u c c e s s of t h i s method is t h e constancy of t h e temperature of t h e thermostated bath. In t h e previous low temperature work, simple on-off control of t h e thermostated bath provided a temperature which w a s constant t o within about k 0.003" C. Duplicate measurements a t 30' C. had shown a n average deviation from t h e mean of *0.3%, and t h i s deviation had increased to +0.5% a t 80' C. T h e s e d a t a demonstrate o n e of t h e inherent that progressively l e s s f a u l t s of on-off control-namely, satisfactory performance is obtained a s t h e desired operating temperature differs more widely from ambient temperature. For t h i s reason other t y p e s of controls and thermostating were considered. T h e final c h o i c e for t h e high
54
INDUSTRIAL AND ENGINEERING CHEMISTRY
F i g u r e 1. Thermal conductivity cell and condensing vapor thermostat
A. S i l i c o n e o i l reservoir
B . Condensing vapor i a c k e t C. 1%-inch thick magnesia insulation D. 1-liter pot heated with spheri ea I mantle
E. T r a n s i t e top and c e l l holder F. Gloss wool insulation
VOL. 2, NO. I
