Numerical simulation of bubble-driven liquid flows

Abstract

The governing equations of mass and momentum conservation for both continuous and dispersed phases in the bubble-driven flow are analysed by a volume-averaging technique. It is found that two additional terms could be added into the classical two-fluid model to improve the predictions of flow behaviour in the gas-phase. Firstly, the gas-phase dispersion is attributed not only to the convective transport but also to the phase diffusion caused by the non-uniform distribution of gas. Therefore, it is essential to include a diffusion term in the mass conservation equation of the gas phase. Secondly, the viscous forces were normally neglected in the momentum equation of the gas phase in previous studies. This has restricted the validity of model predictions on the gas-phase flow behaviour. Hence, the viscous force terms are included in the gas-phase momentum balance to examine the prediction on gas-phase flow characteristics. Both laminar and turbulent flows with bottom gas injection into a liquid bath have been investigated by computer simulation. For the turbulent bubble-driven liquid flows, a two-equation k– ε turbulence model is used to examine the contribution of the mean flow of liquid. Comparisons between the predictions and the literature experimental data illustrate that the present model is capable of capturing a reasonable agreement with experimental results for both the liquid and gas phases.