DEM-CFD simulation of a dense fluidized bed: wall boundary and particle size effects

We simulate a small-scale dense gas-solid fluidized bed using an approach coupling the averaged Navier-Stokes equation with a discrete description of particle dynamics. The simulation results are compared to the voidage, solid velocity and granular temperature measured using magnetic resonance (MR) and other experimental measurements for the same fluidized bed. It is found that the simulation is able to predict the minimum fluidization velocity and pressure drop with reasonable agreement and qualitatively capture the solid circulation pattern to a similar degree achieved by previous such simulations. The discrepancies for the solid velocities near the walls and in the central region at upper and lower bed heights were investigated by examining various models of the physical system and the sensitivity of the simulation results to these models. We demonstrate that the particle–wall interaction dominates the particle dynamics in a boundary layer of about 5 particle diameters to the wall and that modelling the wall using fixed particle of comparable size to the fluidized particles provides enhanced resistance reducing solid wall- slip velocity and granular temperature at the boundary layer. Modelling of particle size is shown to be important for capturing the variation of bed dynamics along the bed height direction.