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Measurements of flow pattern in a 150 mm i.d. bubble column were carried out using a laser doppler anemometer (LDA) in a forward scatter mode. A superficial gas velocity of 20 mm/s was used in all the experiments. Two different spargers (perforated plate and porous plate) were employed. The liquid flow starts developing from the sparger where non-uniformities in the gas sparging exist. From z/D ≥ 2 (z = axial location; D = column diameter), the fully developed axial liquid velocity profiles are seen. The radial variation of mean axial velocity shows gross liquid circulation in the column. Circulation velocities are smaller for the bubble column with porous plate sparger mainly due to the fact that the mean bubble size is small and the gas distribution is relatively uniform over the column cross-section. The difference in the hydrodynamic behavior with two different spargers is also apparent from the profiles of the turbulent kinetic energy and Reynolds stress measured from the velocity−time series.

In the present work, a computational fluid dynamics study has been carried out to bring out the mixing characteristics of bubble column and external loop airlift reactor. A comparison of mixing time for two reactors has been presented on the basis of the same reactor volume as well as the total power input. The CFD model was validated by simulating flow, both in bubble column and external loop airlift reactor. An agreement was observed between the predicted and the experimental data available in the published literature. The validated CFD model has been extended for the simulation of the mixing time for both the reactors. The CFD predictions of mixing time show good agreement with the experimental values published in literature. A systematic numerical study was then carried out to bring out the mixing characteristics of both the reactors. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

A CFD analysis has been carried out to elucidate the characteristic features of axial mixing in gas-liquid dispersed upflow when the flow changes between two extremes: from bubble column, with very low/no liquid velocity, to pipe flow with very high liquid velocity. The CFD model was validated by simulating flow both in multiphase and in single phase. An agreement was observed between the predictions and the experimental data available in the published literature. The validated CFD model has been extended for the simulation of the axial dispersion coefficient for both multiphase and single phase. CFD predictions of the axial dispersion coefficient show good agreement with experimental values published in the literature. A systematic numerical study was done by varying the superficial liquid velocity, from a very low value to a very high value, to understand its effect on axial dispersion.