INDUSTRIAL A N D ENGINEERING CHEMISTRY
1230
Vol. 16, No. 12
k, = 290 MV"'*T-1.4
SUMMARY The values of the over-all absorption coefficients, K Oand KL, have been experimentally determined for sulfur dioxide and for ammonia over a temperature range of from 10" to 50" C., and over a gas velocity range of from 0.03 to 1.5 feet per second. These coefficients have been investigated by means of the two-film theory, as developed by Lewis and Whitman.
k, = 0.72 MVO.8
(s/~)"~
lo-' T4
kL
= 5.1 X
kL
= 37.5 ( s / z ) " ~
Agreement is excellent between the observed values of the over-all coefficients ( K , and K L ) and those calculated by substituting the values of k , and k L for the foregoing equations in the general equations:
K, =
1 ~
1
E
and
1
KL =
1 1
+ HKL
BIBLIOGRAPHY t Obmved 0
1-Sims, J . Chem. SOC.(London), 14, 1 (1862). 2-Lindner (1912) in Seidell's, "Solubilities of Inorganic and Organic Compounds," 2nd ed., 1919, p. 706. a-Perman, J . Chcm. SOC.(London), 89, 2, 1186 (1903). 4-Lewis and Whitman, I n d . Eng. Chem., p. 1215, current issue. 5-Naess and Moyes, M. I. T.Thesis, 1944, not yet published.
b'4lwS
Calculated Vakrc
.......... DISCUSSION 0
0.2
0.4
0.6
a6
1.0
1.2
1.4
The dependence of the individual film coefficients upon gas -velocity, temperature, and solute gas has been calculated. Gas velocity is without appreciable effect on the liquid film in this apparatus, while the gas film coefficient is proportional to the gas velocity to the 0.8 power. Absolute temperature has a vastly different effect upon the two individual film coefficients. The gas film coefficient decreases as the 1.4power of absolute temperature, whereas the liquid film coefficient increases as the fourth power of temperature. This wide differepce in temperature effect is explained on the basis of the dependence of the gas and liquid film coefficients upon the ratio of density (s) to viscosity (2) of the film fluid. This ratio increases with temperature for the liquid film, and decreases with temperature for the gas film. Both individual film coefficients are proportional to the two-thirds power of the ratio s / x . These data also support Lewis and Whitman's statement that the molecular diffusivities of all solutes are identical. The calculations are made on the assumption that this is true for the liquid film and the ratio of the calculated diffusion coefficients through the gas films, which should, according 3.0
Referring to the decrease in the gas film coefficient, k,, with increasing temperature, Mr. Wilson was surprised that the increase in specific diffusion rate with temperature did not cause k, to increase. Was the gas saturated with water vapor before entering the tower to avoid complications due to evaporation and resultant cooling effects? Professor Haslam replied that the gas was saturated prior to absorption. He then pointed out that the ratio of density to viscosity of the gas decreases from 1 to about 0.6 as the temperature increases from 0" to 65" C., and suggested that the effect of an increase in the specific rate of diffusion per unit thickness of gas film was evidently much less than the increase in thickness of gas film due to the effect of decreased density and increased viscosity.
Constant Water-Level Devices' By Robert E. Jefferson 70 LINWOODROAD,HANDSWORTH, BIRMINGHAM, ENGLAND
An apparatus similar' to one of those described by Wilde2 was made by the writer in 1905, but was not reliable as air collected at the top of the siphon. To overcome this difficulty the apparatus shown in Fig. 1 was finally devised.
WLCULATLD AND OBSERMD
1
2.0
i P
1.0
FIG.1
0 0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
to the theory, equal the ratio of the molecular weights,is within 16 per cent of agreement with this ratio. The molecular weight ratio is 3.76 and the specific diffusivity ratio 3.3. The general equations for the individual film coefficientsfor this tower are
FIG.2
A is the water supply, B the overflow. The flask C is filled with water a t the start. D is the bath. If the flask C is not desired, the modification shown in Fig. 2 may be substituted, but the apparatus will not function so long without attention. 1 Received 9
September 26, 1924.
THISJOURNAL, 16, 904 (1924).
