Gas-particle interactions in dense gas-fluidized beds

The occurrence of heterogeneous flow structures in gas-particle flows seriously affects gas–solid contacting and transport processes in dense gas-fluidized beds. A computational study, using a discrete particle method based on Molecular Dynamics techniques, has been carried out to explore the mechanisms underlying the formation of heterogeneous flow structures. Based on energy budget analyses, the impact of non-linear drag force on the flow structure formation in gas-fluidized beds has been examined for both ideal particles (elastic collision, without inter-particle friction) and non-ideal particles (inelastic collision, with inter-particle friction). Meanwhile, the separate role of inter-particle inelastic collisions, accounted for in the model via the restitution coefficient (e) and friction coefficient (mu)), has also been studied. It is demonstrated that heterogeneous flow structures exist in systems with both non-ideal particle-particle interaction and ideal particle-particle interaction. The heterogeneous structure in an ideal system, featured with looser packing, is purely caused by the non-linearity of the gas drag: the stronger the non-linearity of the gas drag force with respect to the voidage, the more heterogeneous flow structures develop. A weak dependence of drag on the voidage produces a homogenous flow structure. Collisional dissipation dramatically intensifies the formation of heterogeneous flow structures after the system equilibrium breaks. Quantitative comparisons of flow structures obtained by using various drag correlations in literature will also be reported.