Bubble column reactors are widely used in many industrial processes and can be operated in different modes (co-current, counter-current and batch). However, very little information has been reported on how the hydrodynamics, mixing and mass transfer characteristics vary with respect to different modes of operation. Non-invasive gamma-ray densitometry measurements have been performed to obtain the axial and radial gas hold-up profiles in co-current, counter-current and batch bubble columns. The axisymmetric tomographic reconstruction was performed using the Abel transformation, Schollenberger et al. (1997) and surface revolution methods. The present work presents (1) the effect of superficial gas and liquid velocities on axial and radial gas hold-up profiles, (2) the variation of gas hold-up profiles with respect to three modes of operation, and (3) comparison of available reconstruction methods with a new surface revolution method which does not require a function to fit the chordal values. The counter current operation shows a higher gas hold-up specifically at the center top of the column. The increment in gas hold-up with the increasing superficial gas velocity is higher for batch bubble column operation. The surface of revolution method is shown to be capable of predicting gas hold-up profiles for all three modes of operation.

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