There are a large number of correlations given in literature for the prediction of volume-related liquid-side mass transfer coefficients in mechanically agitated gasliquid contactors. Significant disagreement can be observed concerning the proposed correlations, so that no single correlation exists representing all of the mass transfer data given in the literature. The observed differences can mainly be ascribed to the differences in the geometry of the system, the range of operational conditions and the measurement method used. On the basis of a comparative study of mass transfer phenomena in agitated Newtonian and non-Newtonian aerated liquids, a critical discussion of the literature results is presented in this review article, so that final conclusions can be drawn for the k L a values in the different single-and multiple-impeller agitated systems studied in the literature.

Although vortex formation is usually an undesirable phenomenon in the process industry, satisfactory process conditions and results can also be obtained in unbaffled agitated vessels in the presence of a vortex. This fact and especially the low power requirements in these systems, with their immediate relevance to the energy problem in the process industry, show the true importance of vortex formation in agitated vessels. This article reviews the literature results and the correlations proposed for the prediction of vortex depth in unbaffled agitated vessels with various types of single and multiple impeller systems and presents a critical discussion on the basis of a theoretical analysis.

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The dependence of power consumption on baffle length, L, in vessels agitated by a dual Rushton turbine system was studied within the turbulent regime, and also in relation to the impeller spacing, DH. A dependence of varying strength could be observed. The presence of baffles in the agitated systems provided a stabilizing effect with regard to the dependence of the Newton number Ne on the Reynolds number Re. A sharp decrease in power consumption could be detected for baffle lengths L < 0.3 H, with H the liquid height in the vessel. The Newton number was not significantly affected by L in the range 0.3 H < L< 0.5 H. For L > 0.5 H a sharp increase in Ne with increasing L could be observed. The two Rushton turbines act independently at DH > 1.65 d, with d being the impeller diameter. As the baffle length decreased, an increased mutual interaction between the two impellers could be observed for a broad regime of DH/d values. Ne was not affected by DH for the unbaffled agitated systems studied.

Despite the fact that the complete dispersion characteristics in agitated gas-liquid contactors are operationally important, the flooding-loading transition is widely used as a design criterion, due to its experimental convenience and accuracy. Moreover, limited data are available in the literature on the interrelation of the flooding-loading and the loading-complete dispersion transitions, although several investigators have worked on these two transition stages. Thus, knowledge of the interrelation between these two stages would be of theoretical and practical importance. In this work, the dependence of the stirrer speed at complete dispersion, n CD , on the stirrer speed at flooding, n F , was experimentally studied, in coalescing and non-coalescing systems, using Rushton turbines of two different diameters. The experimental results, having an accuracy of < 5 %, are given in the form of a dimensionless correlation.