EFFECT OF
TRANSFER ON DROP FOR MATIO N
Downloaded by UNIV OF NEBRASKA-LINCOLN on August 24, 2015 | http://pubs.acs.org Publication Date: August 1, 1968 | doi: 10.1021/i160027a028
The size distribution of drops formed b y injection of one liquid into another was quantitatively determined as a function of the direction of mass transfer between the phases. The experiments indicated a profound influence of mass transfer on the character of the drop size distribution. OR liquid-liquid mass transfer operations in which drops of F o n e liquid are dispersed throughout another, the size distribution of the drops is of great importance because the rate of mass transfer depends directly o n the interfacial area. The size distribution of drops resulting from the injection of one liquid of an immiscible pair into the other has been studied as a function of flow conditions and the physical properties of each phase by Hayworth and Treybal (1950) and Keith and Hixson (1955). No work, however, is known which treats drop formation with simultaneous mass transfer. This paper describes preliminary experiments in which the size distribution of drops formed by injection of one liquid into another was quantitatively determined as a function of the rate and direction of mass transfer between the phases.
Experimental
In a device thermostated to 75' + 0.2' C., a paraffin waxtetrabromoethane solution was injected through stainless steel hypodermic needle tubing into, and parallel with the streamlines of, a laminar stream of distilled water. The injection tubing had an inside diameter of 0.006 inch and a length to diameter ratio of 145. The wax solution melted a t 51' C. and was of such a composition that a t operating conditions its density matched (to within 0.0001 gram per cc.) the density of the water. Ethyl carbamate was the solute transferred between phases. The change in density of the dispersed phase due to carbamate transfer was negligibly small, because the initial concentration of carbamate was low and its density is close to 1 gram per cc. Sampling was accomplished by collecting the entire dispersion in chilled water in such a way that the wax drops solidified individually. The size distribution of the solid drops, after they had been rinsed and dried, was obtained by sieve analysis.
A complete description of the equipment, designed to
serve another function and having little bearing on the information presented here, is given by Bayens (1967). Results
A series of runs was conducted in which drops were formed by injection of wax into water while ethyl carbamate was transferred from one phase to the other. Injection velocities were considerably above the jetting point-a state described by Keith and Hixson (1955). The driving force for mass transfer was varied from run to run by changing the concentration of ethyl carbamate in the continuous phase. The effect of mass transfer directed from the disintegrating jet on g ( u ) , the weight distribution function for drop diameter, is illustrated in Figure 1. CE - C, is the difference between the equilibrium and initial concentrations of ethyl carbamate in the jet phase. An increase in the driving force for mass transfer from the jet resulted in substantial broadening of the distribution function and a loss of its bimodal character. The interfacial area per unit volume of dispersion is inversely proportional to the Sauter mean diameter, ."/a", the ratio of the third and second moments of the number distribution. The weight and number distribution functions are related in the following way:
Figure 2 is a plot of the reciprocal of the Sauter mean diameter as a function of CE - C,. For mass transfer from the jet the interfacial area of the resulting dispersion significantly decreased as the driving force for mass transfer increased. For mass transfer to the jet an increase in the driving force did not markedly change the interfacial area.
0 Drop Diameter, a , c m
Figure 1 .
Effect of mass transfer on the weight distribution function for drop diameter VOL. 7
NO. 3
AUGUST 1 9 6 8
521
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2
1 -0.008
1
I
1
-0.004
I
1
0
1
t0.004
tc 108
CE-CO,moles/liter
Downloaded by UNIV OF NEBRASKA-LINCOLN on August 24, 2015 | http://pubs.acs.org Publication Date: August 1, 1968 | doi: 10.1021/i160027a028
Figure 2.
Effect o f rate and direction of mass transfer on total interfacial area
Visual observations of injection revealed that mass transfer from the jet caused abnormally large drops to form directly from the disintegrating jet and not as a result of the coalescence of drops already formed. These limited experimental results indicate that mass transfer can alter the mechanism of jet breakup. Acknowledgment
C, = initial solute concentration in the jet phase, moles/cc. f ( u ) = number distribution function, particles/cc. g ( u ) = weight distribution function, particles/cc. literature Cited
Bayens, C. A., “Mass Transfer in a Dispersion,” Ph.D. dissertation, Johns Hopkins University, 1967. Hayworth, C. B., Treybal, R. E., Ind. Eng. Chem. 42, 1174 (1950). Keith, F. W., Jr., Hixson, .4. N., Znd. Eng. Chem. 47, 258 (1955).
The authors express their thanks to the National Science Foundation for its support of this research. Nomenclature a u2 u8
= diameter of a drop, cm.
average of square of drop diameter, sq. cm. average of cube of drop diameter, cc. CB = equilibrium solute concentration in the jet phase, moIes/cc.
522
= =
I&EC FUNDAMENTALS
C. A. BAYENS‘ R . L. LAURENCE T h e Johns Hopkins University Baltimore, Md. 21218 RECEIVED for review September 27, 1967 .ACCEPTED April 10, 1968 Present address, Shell Development Co., Emeryville, Calif. 94608
