Characterisation of a gas-liquid PBC: Bubble size and gas holdup

A fundamental experimental study of gas-liquid contacting in an oscillatory baffled column is presented focusing on the effect of fluid oscillation on gas holdup and bubble size. The results show that beyond a critical level of fluid oscillation the Sauter mean diameter of the dispersion is substantially reduced, while the gas holdup (and, thus, the residence time of the gas phase) increases significantly. The reduction of bubble size was described in terms of bubble breakage, caused by the interaction of the bubbles with eddies. The experimental results were modeled by applying Kolmogoroff’s theory of
isotropic turbulence. The steep increase in the gas holdup with oscillation was mainly due to bubble entrainment by large vortices, formed by the oscillatory flow in the presence of baffles. A semi-theoretical expression, based on the forces acting on a bubble, was proposed, and was able to accurately match the experimental trends. The results also show that the gas-liquid hydrodynamics are mainly governed by the oscillatory operating conditions, and independent of the type of gas sparger.