Particle-scale study of gas-solid flows in a bubbling fluidised bed: Effect of drag force and collision models

Abstract

Inter-particle and inter-phase interactions of gas-solid flows dominate macro-scale bed hydrodynamics in fluidised bed systems. In this work, typical fluidisation behaviours are presented. The effects of different drag models (i.e., Di Felice drag model, Gidaspow drag model) and collision models (i.e., hard-sphere model, soft-sphere model) on gas-solid behaviours in a bubbling fluidised bed are comprehensively compared. Besides, the influence of critical operating conditions (i.e., superficial gas velocity) is discussed. The simulation results show that Di Felice drag model shows better agreement with the experimental data than the Gidaspow drag model. Both the hard-sphere model and soft-sphere model can well predict particle velocity profiles. Larger superficial gas velocity and hard-sphere model respectively cause more vigorous inter-phase momentum exchange and more frequent collision events, indicating the more intense bubble evolution and the resulting fluctuations of void fraction. The rotational velocity obtained from the soft-sphere simulation is larger than that from the hard-sphere one, but the rotational velocity fluctuation is much weaker.