CFD simulation of gas-liquid hydrodynamics in a rectangular air–lift loop reactor

Computational Fluid Dynamics is an increasingly important tool for carrying out realistic simulations of process apparatuses. As a difference from single phase systems, for multi phase systems the development of CFD models is still at its early stages. Moreover, gas-liquid systems are characterised by an additional complexity level, related to the fact that, as a difference with solid-liquid systems, bubble sizes are not known in advance, being rather the result of formation and breakage-coalescence dynamics, and therefore of complex phenomena related to flow dynamics and interfacial effects. In the present work CFD simulations of gas-liquid air-lift reactors are reported. All bubbles are assumed to share the same size, and a simplified approach is adopted for the description of momentum exchanges between the two phases. In particular it is shown that the only parameter needed for modelling drag forces is bubble terminal velocity. Simulation results show that. even assuming a uniform bubble diameter in the range experimental observations, there is a good agreement with literature experimental data for all the gas flow rates simulated. This result implies that, despite the many simplifications that have to be adopted in order to make them viable, fully predictive CFD simulations of gas-liquid systems can give rise to reasonably accurate predictions of real systems behaviour.