CFD simulation of hydrodynamics in a high-pressure bubble column using three optimized drag models of bubble swarm

Abstract

The gas–liquid flow characteristics in an air–water system were studied using electrical resistance tomography (ERT) in a pressurized gas–liquid bubble column with an inner diameter of 0.30 m and a height of 6.60 m. The effects of the superficial gas velocity and system pressure on the radial gas holdup were investigated under superficial gas velocities (0.120–0.312 m/s) and system pressures (0.5–2.0 MPa). Two-fluid computational fluid dynamics (CFD) was used to simulate the hydrodynamics of the bubble column in two- and three-dimensions, and the drag force, transverse lift force, turbulent dispersion force, and wall lubrication force were introduced for model correction. Based on the determination of the transverse lift force, turbulent diffusion force, and wall lubrication force in previous works of our group, three different of drag model schemes were proposed in this study. In the Model A, based on Roghair's drag model, a density correction and the gas holdup of large and small bubbles were introduced to correct the model; in the Model B, while the gas holdup of large bubbles was greater than 0.08, the influence of small bubbles was ignored. The small bubbles and liquid were integrated into a single phase (the dense phase), while the large bubbles were the dilute phase; in the Model C, an energy minimization multi-scale (EMMS) concept based on the double bubble size model was used, and relationship between the drag coefficient and the bubble diameter were introduced to modify the models. Moreover, through optimizing adjustment of the model parameter, the simulation results with the three models were found to be consistent with the experimental results obtained from ERT technique. These results may facilitate improvements in the design and scale-up of bubble columns with high-pressure and high superficial gas velocities, as well as the significance of further research.