Experimental characterization of dense gas-liquid flow in a bubble column using voidage probes

Gas-liquid flow in bubble columns under dilute flow condition has been investigated widely. In the present work, we have characterized gas-liquid flow in a pseudo 2D bubble column for a wide range of superficial gas velocities (UG = 1-30 cm·s-1) that cover dilute to dense flow conditions. In-house developed voidage probes were used to measure local gas volume fraction fluctuations, which in turn were used to characterize dynamics of column-scale re-circulatory flow and bubble-scale flow processes, under dilute-to-dense conditions. Importantly, the spatial distribution of internal composition of gas volume fraction, i.e. gas volume fraction contained in different bubble size groups, was measured. Further, the spatial distribution of chord length and bubble size was measured for a wide range of UG. With increase in UG, the low frequency oscillations caused by meandering bubble plume at lower UG were found to diminish and the fluctuations caused by bubble swarms were found to dominate under the dense flow conditions. Using the time spent by the probe in each bubble, the bubble population was classified into different size groups and the gas volume fraction for each size group was measured. Under dense flow conditions, small bubbles were seen to accumulate near column walls, as exhibited by wall peaking in gas volume fraction profiles and that large bubbles were found to flow through the column centre. The results presented in this work are important to improve the understanding of dense gas-liquid flow and also for rigorous validation of CFD models.