CFD-PBM approach with modified drag model for the gas-liquid flow in a bubble column

In this work, numerical simulations of cylindrical bubble column are performed using the Euler-Euler approach incorporated with a population balance model (PBM). First, three drag models and their corresponding modified models with the wake acceleration are incorporated into the coupled approach in order to evaluate the effectiveness of these drag models. The simulated time-averaged local gas holdups and normalized axial liquid velocities using different drag equations are compared with the experimental data, showing that only the PBM-customized drag model with the wake acceleration (cf., the application of a correction factor) can reproduce the measured flow field data. Subsequently, the applicability of the coupled approach with the effective drag model is further evaluated at various superficial gas velocities and gas distributors. The simulated results accord well with the experimental data at high gas velocities. However, the model greatly underestimates the radial local gas holdup and the total gas holdup at low gas flow rates. Additionally, the simulated results demonstrate that the opening area and orifice geometry play a significant role in total aeration and the triple-ring gas distributor produces more uniform radial profiles of local gas holdup and normalized liquid velocity than the multi-orifice one, thus leading to poor mixing efficiency in the bubble column. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.