Continuous-phase mass transfer coefficients and drop sizes in agitated vessels are correlated with operating variables and physical properties of liquid-liquid systems. In formulating mass transfer coefficients, a realistic mechanism has been developed, involving periodically varying rates of surface renewal associated with droplet circulation through varying degrees of turbulence around the vessel. Relationships are obtained for optimized design and scale-up.
SCOPEThe rate of mass transfer between two immiscible liquids in mixing vessels depends on the concentration difference, the interfacial area, and the mass transfer coefficient. The comprehensive correlation of mass transfer coefficients and interfacial areas are therefore essential for the optimized design and scale-up of such equipment. Schindler and Treybal (1968) and Keey and Glen (1969) studied liquid-liquid mass transfer rates in agitated vessels.Both investigations were confined to single systems, so that comprehensive correlations over a range of physical properties were not established.The objects of this research are to measure and correlate such continuous-phase mass transfer coefficients and the corresponding drop sizes in the presence of mass transfer. Relationships for optimized design and scale-up will then be formulated.
CONCLUSIONS AND SIGNIFICANCEThe continuous-phase mass transfer coefficient has been correlated and separate correlations for high and low interfacial tension systems have also been attempted for a better fit of the data.Comparison between our correlation for k, and expressions derived from the penetration theory with Kolmogoroff s time scale and from turbulent boundary layer theory show significant differences between the exponents on any given variable, suggesting the need for a new model. Accordingly, a theory based on a periodically varying rate of surface renewal has been developed and the average rate of surface renewal sa in this theory has been correlated.Droplet size was determined from photographs of the dispersion taken through a plane glass water pocket. A correlation was obtained for the Sauter-mean drop diameter when about 50% of the possible mass transfer had occurred; this was chosen as an average value during batch operation.These correlations have been used to develop relationships for optimized design and scale-up.This study included h e liquid-liquid systems, two sizes of six-flat-blade turbines, two vessel diameters, two principal liquid heights (T = H), impeller speeds between 3 and 8 rps, and dispersed-phase volume fractions between 0.03 and 0.09.
7r(2X*¿2)m¡xt, 7r(EX*,3)m;x, = osmotic pressure of mixed solute aqueous solution corresponding to total mole fraction of all ions in solution, in solution phase 2 and solution phase 3, respectively, atm Literature Cited
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