New correlations have been proposed for estimation of gas phase holdup, characteristic velocity, interfacial area for mass transfer and mean bubble size of bubble swarms under dispersed and fluidized operation of bubble columns employing singleand multi-orifice distributors. The analysis of results include available literature data of other investigators. ubble column operation in both dispersed and B fluidized regimes has become of major commer-cia1 interest and a considerable relevant literature has now developed. However, there remain uncertainties about the design and performance of such columns and in particular for the behaviour of bubble swarms produced from singleand multi-orifice gas sources.

This paper reports a detailed study of the hydrodynamics iiivolved in the operation of rotary disk contactors (RDC).

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SCOPEThe importance of axial mixing on mass transfer has increasingly been recognized. Fluid mechanical phenomena limit column performance when mass transfer rates are high. Methods for correcting the calculated height or number of transfer units for axial mixing require a knowledge of axial mixing Peclet numbers. Earlier studies on spray columns provided insights into axial mixing but gave no useful correlations for estimating the axial mixing Peclet numbers.New data on dispersion characteristics and flow behavior of dispersed phase droplet swarms have now been reported (Vedaiyan et al., 1972(Vedaiyan et al., , 1974. These studies demonstrated the changing pattern of drop size distribution in the swarms (before flooding). Studies of axial mixing in the continuous phase (Kreager and Geankoplis, 1953; Mixon et a]., 1967; Letan and Kehat, 1968; Henton and Cavers, 1970; Henton et a]., 1973) indicate that axial mixing is primarily caused by drop movement and by carry-over of continuous phase fluid elements in the larger drop wakes. The effects of continuous and dispersed phase Row rates on axial mixing dispersion coefficients E , of the continuous phase are still uncertain. Some analyses assume uniform distribution of drop sizes for all dispersed and continuous phase Row rates, while others assume a constant mean drop size, that is, at constant dispersed phase nozzle velocity. Recent reports of Ve daiyan et al. (1972, 1974) show variations in the drop size distribution and mean drop size related to the velocity at the dispersing nozzles.These results indicate that the continuous phase residence time distribution variance depends, to a great extent, on the same factors which affect the dispersed phase residence time distribution variance and, in addition, on the continuous phase velocity. CONCLUSIONS AND SIGNIFICANCEConclusions from this study are presented under three subheadings as follows. Data analyses folIow methods outlined on Table 1 (after Levenspiel, 1972).1. Conchions from the dispersed phase studies. The dispersed phase RTD variance ,d2 varied significantly with holdup and dispersed phase velocity at the distributor nozzle U N and showed a remarkable similarity to the variation of the drop size distribution variance with nozzle velocity. (The drop size distribution was measured by photographic methods.) It seems reasonable to suggest, therefore, that the factors affecting the residence time distribution of the dispersed phase are the same as those affecting the drop size distribution.The variance of the dispersed phase residence time distribution and axial mixing Peclet numbers were found to be best correlated with dispersed phase holdup rather than with either nozzle velocity or any modified -form of the Reynolds number (see Figures 5 and 6).2. Conclusions from the continuous phase studies. The variance of the continuous phase residence time dis tribution u,2 was found to be a strong function of dispersed phase velocity and holdup. The continuous phase axial dispersion coefficient E, remains nearly const...