Flow structure formation in high-velocity gas-fluidized beds

The occurrence of heterogeneous flow structures in gas-particle flows seriously affects the gas-solid contacting and transport processes in high-velocity 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 cluster and the core/annulus structure formation. Based on energy budget analysis including work done by the drag force, kinetic energy, rotational energy, potential energy, and energy dissipation due to particle-particle and particle-wall collisions, the role of 1) gas-solid interaction and 2) inelastic collisions between the particles are elucidated. It is concluded that the competition between gas-solid interaction and particle-particle interaction determines the pattern formation in highvelocity gas-solid flows: if the gas-solid interaction (drag) dominates, a uniform flow structure prevails. Otherwise, a heterogeneous pattern exists, which could be induced by both particleparticle collisions and gas-solid interaction. Although both factors could cause the flow instability, the drag force is demonstrated to be the necessary condition to trigger the heterogeneous flow structure formation.