INVESTIGATION MEASUREMENT OF DISPERSION COEFFICIENT AND MIXING TIMES IN BUBBLE COLUMN

Abstract

A complete model of liquid-phase dispersion was used to simultaneously characterize axial and radial mixing in bubble column of 0.15 m inside diameter and plastic plate distributor with holes of 2 mm diameter. Axial and radial dispersion coefficients and mixing times were determined in tap water for superficial gas velocities in the range 0.6-5.36 cm/s. The experiments were carried out using a transient method (the tracer response method). The dispersion coefficient was obtained by adjusting the experimental profiles of tracer concentration with the predictions of the model. The measured axial dispersion coefficients (Dax,L) were generally consistent with the predictions of the well established correlations, thus validating the complete dispersion model used in the analysis. The Dax,L values ranged from 110 to 200 cm2/s. There was evidence that the existing literature data on Dax,L in bubble columns are slightly underestimated, as consistent underestimation was found to be a characteristic of the widely used dispersion model that disregards radial dispersion. The value of the radial dispersion coefficient was typically about 1 to 2% of the Dax,L value under any given condition. The mixing time data were generally consistent with the existing literature.
 The results of this study are compared with experimental result and upper bound theory and have shown a good agreement with a minimum discrepancy