Numerical studies of bubble formation dynamics in gas–liquid–solid fluidization at high pressures

A discrete phase simulation (DPS) is conducted to investigate multi-bubble formation dynamics in gas–liquid–solid fluidization systems. A numerical technique based on computational fluid dynamics (CFD) with the discrete particle method (DPM) and volume tracking represented by the volume-of-fluid (VOF) method is developed and employed for the simulation. A bubble-induced force (BIF) model, a continuum surface force (CSF) model, and Newtonʹs third law are applied to account for the couplings of particle–bubble, bubble–liquid and particle–liquid interactions, respectively. A close-distance interactive effect between colliding particles is considered in the formulation of the particle–particle collision model. Two-dimensional simulations of the behavior of bubble formation from multi-orifices in liquids and liquid–solid suspensions are conducted at high pressures up to 19.4 MPa under constant gas flow conditions. Experiments are also conducted in this study to quantify the bubble formation behavior from a single orifice under comparable gas flow conditions. The study indicates that the liquid flow dynamics induced by adjacent bubbles and bubble wake significantly affects the multi-bubble formation process. The simulation results on the initial bubble size and bubble formation time under various pressures and solids hold-up are found to be in good agreement with those obtained experimentally as well as those predicted based on the analytical model developed earlier by the authors.