Cfd-dem Study of the Gas-solids Flows in a Fluidized Bed with an Immersed Cylinder: Comparison of Pseudo-2d and 3d Models

In this work, a numerical study of the gas-solids flow in a 3D gas-fluidized bed with an immersed horizontal cylinder is performed using the combined computational fluid dynamics (CFD) and discrete element method (DEM). In order to investigate the wall effect, a sensitivity study of bed thickness is performed first to obtain the critical bed thickness at which the bed can be regarded as 3D. Then pseudo-2D and 3D flow characteristics are compared at the same gas inlet velocity. The effect of different structures on heat transfer between bed and an immersed cylinder is examined by comparing the values of heat transfer coefficients. The differences of the flow structure between pseudo-2D and 3D are reproduced and may be due to wall frictions and three dimensional affects. The wall shear stress in pseudo 2D is larger than that in 3D and results in larger pressure drop. Furthermore, the contribution of drag forces in bed thickness-direction to the total drag force is very small in pseudo-2D compared to in 3D. These differences of solids flow patterns result in difference heat transfer coefficient between bed and immersed cylinder.