Computational fluid dynamics-population balance model approach with drag force of bubble swarms for polydispersed bubbly flow in continuous casting mold

This study employs computational fluid dynamics (CFD) coupled with the population balance model (PBM) to explore the sensitivity of the drag model for the predictive accuracy of the gas-liquid two-phase flow in continuous casting (CC) mold. Several single bubble drag models have been numerically evaluated for high turbulent intensity and gas flow rate operation parameters. Then, the influence of turbulence effect and bubble swarm mechanisms on bubble dynamic behaviors are investigated. The predicted mean bubble diameter and flow pattern were studied and compared with the experimental data. The results show that all single bubble drag models, except for the Grace model, can predict the bubble size distribution (BSD) well. Meanwhile, all models significantly overestimate the bubble diameter near the nozzle under high gas flow rate conditions. A novel drag correction factor based on local gas holdup and BSD is proposed, which takes into account both the hindrance effect of small bubbles and the accelerating effect of large bubbles. The proposed drag correction factor can accurately predict BSD and flow pattern transition in the CC mold under high gas holdup regions. Compared with the simulation results of the previous single bubble drag model, the mean relative error predicted by the novel drag correction factor is decreased by 69.33%.