(218g) CFD Simulation of Gas-Liquid Flow in Stirred Tanks: Effect of Drag Models

Stirred tanks of gas-liquid flow are widely used in chemical and biochemical processes, such as wastewater treatment, fermentation and crystallization due to good contact between phases and intensive liquid mixing. Knowledge of gas dispersion in stirred tanks is of great significance as it determines interfacial contact area and heat and mass transfer between phases.

Drag force plays important roles in the prediction of gas-liquid flow in stirred tanks, but systematic studies on drag models are still lacking. In this study, we evaluated the effect of four different drag models (DBS-Local, DBS-Global, Brucato, Schiller-Naumann) in which the DBS model was originally developed for bubble columns. The flow regime, liquid flow field and gas holdup predicted by the four drag models are compared with experiments. The DBS-Local and DBS-Global models show the advantages over the other two in the prediction of gas dispersion and flow structure, since the ratio of effective drag coefficient to bubble diameter is either one or two-orders of magnitude over-estimated by the Brucato model or under-predicted by the Schiller-Naumann model. The flow regime at different rotational speeds and the effects of gas dispersion on the liquid loop structure can be correctly predicted by the DBS drag models. This study demonstrates that the drag model is extremely important to accurately predict the gas-liquid flow in stirred tanks.