Effects of gas distributor on hydrodynamics in gas-liquid bubble column by visual experiments and CFD simulations

Visual experiments and simulations are conducted to study the effects of varying the size and arrangement of apertures in gas distributors on gas-liquid flow in bubble columns. Flow characteristics, such as bubble size distribution and flow pattern, are investigated using swarm velocity and drift flux methods, which show that the global gas holdup and the flow regime transition point are primarily determined by the opening size of orifices rather than their spatial arrangement. With the aid of high-speed photography and the dynamic gas disengagement method, two mechanisms for flow regime transition are identified, namely "coalescence-induced transition" and the "distributor-induced transition". In addition, a modified two-fluid model-population balance model (TFM-PBM) framework relating gas distributor shape and initial bubble size is established and validated using experimental data. Simulations indicate that a gas distributor with a central aeration mode leads to improved mixing owing to high rising velocity and shear rate, which may benefit mass transfer-limited reactions. In contrast, a distributor with a peripheral aeration mode results in a lower shear effect, which may be applicable to cell growth processes.