Influence of grid and numerical schemes on bubble column simulation with TBPBM-CFD model

A two-bubble-groups population balance model (TBPBM) was proposed to predict the bubble size in this paper which treats gas phase (bubbles) to consist of small and large bubble groups. The population balance model was applied and solved respectively for each bubble group to predict the bubble sauter diameters. It was noted that the proposed TBPBM model effectively reflected the features of small and large bubbles in bubble column due to the coalescence and breakup of daughter bubbles. The TBPBM model, Luo's bubble breakup model and Prince's bubble coalescence model were respectively implemented into Fluent 6.3 using User Define Function (UDF). The use of two-fluid model coupled with the TBPBM was tested to simulate hydrodynamics in a bubble column with a diameter of 440 mm and the effect of grid and numerical schemes on simulation results with TBPBM-CFD model was carefully assessed. The simulation demonstrated that the influence of grid and numerical schemes was significant, especially for grid and discretisation of the convection term in volume fraction transport equation. With refinement of grid and increasing accuracy of numerical scheme, the turbulence dissipation rate and the gradient of the overall gas holdup increased but the averaged sauter diameter and volume fraction of large bubbles decreased. The simulation also indicated that the prediction accuracy for evaluation of axial liquid velocity and gas holdup distribution was improved when refining the grid. Adoption of a coarse grid gave rise to under-prediction of the axial liquid velocity.