and Pratt (1933) contained lower values of holdup (most values were < 10 % ) , and V, was shown to be more nearly constant. At low values of holdup, there is little difference between V, and V,. Generally, V, is believed to be a more useful correlating parameter over a wide range of holdup values. However, neither of the parameters is as accurate as one may desire, and improved correlations, especially those with a theoretical basis, are needed. ACKNOWLEDGMENT This work was sponsored by the U.S. Atomic Energy Commission under contract with Union Carbide Corporation. The authors would like to express their appreciation to John S. Taylor, R. 0. Payne, and several students and Directors of the Massachusetts Institute of Technology Chemical Engineering Practice School who made most of the measurements and otherwise assisted in the study.NOTATION a = d p = vc = Vc.f -v d = --Vd,f v, = cm2 of packing surface/cm3 of packing volume diameter of packing, cm superficial velocity of the continuous phase, cm/s superficial velocity of the dispersed phase, cm/s superficial continuous phase velocity at flooding, cm/s superficial dispersed phase velocity at flooding, cm/s characteristic velocity defined by Equation (6), cm/s V, Greek Letters Ap phases, g/cm3 E p = viscosity, poise AVc,01/2 = defined by Equation (5) AV,,01/2 = defined by Equation ( 5 ) Subscripts c, d = continuous and dispersed phases, respectively o = intercept value; flow rate of other phase ap-= superficial slip velocity, cm/s = difference in densities of dispersed and continuous = void fraction of the packing, dimensionless proaching zero A group-contribution method is presented for the prediction of activity coefficients in nonelectrolyte liquid mixtures. The method combines the solution-of-functional-groups concept with a model for activity coefficients based on an extension of the quasi chemical theory of liquid mixtures (UNIQUAC). The resulting UNIFAC model (UNIQUAC Functional-group Activity Coefficients) contains two adjustable parameters per pair of functional groups. AAGE FREDENSLUND, RUSSELL L. JONES, and JOHN M. PRAUSNITZ V IBy using group-interaction parameters obtained from data reduction, activity coefficients in a large number of binary and multicomponent mixtures may be predicted, often with good accuracy. This is demonstrated for mixtures containing water, hydrocarbons, alcohols, chlorides, nitriles, ketones, amines, and other organic fluids in the temperature range 275O to 400OK.
