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An analytical study of the stability of horizontal two-fluid layers encountered by interphasial mass transfer is reported. A linear stability analysis for two immiscible viscous, initially motionless fluids, confined between horizontal solid walls of constant concentrations and subjected to both the Rayleigh and the Marangoni driving mechanisms, is presented. The effect of interfacial contamination is also involved. Stability criteria for the cases of transfer of acetone or acetic acid through benzenewater interface are presented. As for acetic acid, instability is predicted for either direction of transfer, showing the importance of the Rayleigh driving mechanism. It relaxes the discrepancy between experimental results and the theoretical result of the purely Marangoni effect model of Stemling and Scriven. Stability criteria are strongly dependent on the ratios of properties of fluids, the total depth, and also the depth ratio of layers and the presence of interfacial contaminant. This analysis is readily applicable to predicting the stability of two-fluid layers encountered by heat transfer.

An analytical and experimental study of thermally induced instability in horizontal two-fluid layers is reported. The earlier reported linear stability analysis is applied to predict the stability criteria of benzene-water and water-carbon tetrachloride layers. Calculations predict instability in benzene-water layers of whatever depth ratio of layers for heating from above or below, but only for heating from below in equi-depth water-carbon tetrachloride layers. Results of experimental measurements of the critical Rayleigh and Marangoni numbers in these two-fluid layers of various total depths, heated from below, confirm the consistency of the theory both in clean and contaminated systems.