Bubble size distribution and gas–liquid mass transfer in airlift contactors

Abstract

This work investigated the distribution of bubble size in annulus sparged airlift contactors (ALCs). Increasing gas velocity in the ALC considerably reduced the size of the bubble and shifted the distribution of bubble size from the normal to log-normal types. Bubble size was found to decrease along the axial distance in the riser of the ALC. Moreover, an increase in the ratio between the cross-sectional areas of the downcomer and riser was found to result in the decreasing bubble size at high superficial gas velocity. Spargers with a large number of orifices led to a larger bubble size in the system. In contrast, it was found that a comparatively broad bubble size distribution was caused by employing a gas sparger with less number of orifices. This work also examined the gas–liquid mass transfer characteristics of the ALC in forms of mass transfer coefficient and specific interfacial area which were individually evaluated. It was found that the specific interfacial area, rather than the mass transfer coefficient, played a more significant role in controlling the overall rate of mass transfer in the system.