On the treatment of bed-to-wall heat transfer in CFD-DEM simulations of gas-fluidized beds

Heat exchange through confining walls is an important feature of gas-fluidized beds. However, near the wall, most of the temperature gradient exists in a thin thermal boundary layer, which is typically smaller than the grid size in the computational fluid dynamics method (CFD). This makes it hard to resolve the temperature distribution near the wall in coupled computational fluid dynamics and discrete element method (CFD-DEM). To obtain a better understanding of the heat transfer mechanism near the confining walls in fluidized beds, we adopted two approaches, i.e., by imposing a thermal boundary condition for the gas phase energy equation and by implementing a particle–wall conduction model for the discrete particle phase. Both methods were first explained in detail and then validated by available experimental results. Finally, the two approaches were compared with respect to their performance on the prediction of the overall particle temperature distribution, parameter sensitivity, and mesh resolution.