Liquid‐liquid interfacial areas formed by turbine impellers in baffled, cylindrical mixing tanks

Abstract

An extensive experimental study on the formation of liquid-liquid interfacial areas was conducted using flat-blade turbine impellers in standard mixing tank geometry. The interfacial areas were measured with a light probe for different combinations of volume fraction, continuous and dispersed phase physical properties, and mechanical mixing conditions. When two immiscible liquids are combined in a mixing tank, the interfacial area, or drop size, is usually of primary concern.In the operations of extraction, emulsion polymerization, and direct-contact heat transfer, the interfacial area directly affects the rates of interphase mass and heat transfer.Previous work in liquid-liquid mixing has shown that system variables such as volume fraction of dispersed phase, fluid properties, and the mechanical mixing conditions all have an effect on the interfacial area obtained, but the quantitative relationships have not been well established. Knowledge of these quantitative relationships is extremely important for: (1) the prediction of two-phase interfacial areas in new systems; (2) the optimization of existing operations; and (3) the scale-up of experimental or pilot plant units. Thus, there is a definite need for a better understanding of the liquid-liquid mixing process.In this study, the principle variables involved in the mixing process were varied systematically in order to identify those factors that have a significant influence on the interfacial area formed. The parameters varied include the volume fraction of dispersed phase, tank size, impeller size, impeller speed, and fluid properties of both the continuous and dispersed phases. Standard mixing tank geometry, baffles, and six-blade, flat-blade turbine impellers were used throughout (Rushton et al., 1950).A light probe described previously (McLaughlin and Rushton, 1973) was used to measure the interfacial areas of the dispersions. A total of 122 different combinations of volume fraction, tank size, impeller size, impeller speed, continuous phase properties, and dispersed phase properties were studied experimentally in a design that enabled interactions well as functional dependence of the above factors to be determined. In addition, 42 replicated runs of these conditions were used to strengthen the determined functional dependence of interfacial area on the above factors and establish the statistical validity of this model. CONCLUSIONS AND SIGNIFICANCEOur detailed experimental study of liquid-liquid mixing with flat-blade turbine impellers in standard mixing tank geometry has shown that the interfacial area per unit volume of dispersion is primarily a function of seven variables: a, u, p d , pd, pc, P/ V and U. Furthermore, statistical regressions on the experimental data identified those variables that significantly affect the area of the dispersions in a mixing tank. The results are presented as regression equations that represent the effects of the mixing Correspondence concerning this paper should be addressed to Roger E Eckert.Craig M. McLaughlin is with T...

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“…Additionally, these methods might require measurement systems inside the tanks that could modify normal flow patterns and results (Quadros and Baptista, 2003). Because air bubbles affect light transmission negatively, this method is not an appropriate choice for systems in which air is entrained (Eckert et al, 1985). Nanda et al (1966) used chemical reactions for the first time to evaluate the interfacial area in gas-liquid mixing.…”

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