CFD modelling of local bubble size distributions in agitated gas-liquid vessels - verification against experiments

Abstract

Abstract Gas-liquid reactors and mixing units are widely used in chemical, biochemical, petroleum and mining industries. Understanding of turbulent gas-liquid phenomena is still very limited, but basic physical laws that control these phenomena are known. Population balance models incorporated into Computational Fluid Dynamics (CFD) offer a fundamental way for modelling mass transfer in inhomogeneous stirred reactors. Time-averaged bubble size distributions (BSD) were measured from several locations at various aeration rates and stirring speeds in a 13.8 dm 3 vessel for CO 2 - n-butanol and air - distilled water systems. Parameters of the bubble breakage and coalescence models were fitted against experimental BSDs in a relatively simple multiblock model. The fitted breakage and coalescence models were then incorporated to the CFD-code. Euler-Euler approach and sliding grid technique with multiple bubble size groups was used. The CFD simulation results were compared to the corresponding experimental local BSDs to evaluate the accuracy of the fitted model. With the breakage and coalescence models and CFD it was possible to predict local BSDs when vessel scale was changed. The CFD simulation results show physically reasonable behaviour with varying levels of agitation and gas feed, when compared to the visual observations and experimental results. The validated bubble breakage and coalescence with the CFD offer a reliable tool for the simulation of agitated gas-liquid vessels.