The critical role of scale resolution in CFD simulation of gas-solid flows: A heat transfer study using CFD-DEM-IBM method

The surface-to-bed heat transfer coefficient is an important engineering parameter for quantifying the heat transfer capability of fluidized beds. In this study, computational fluid dynamics-discrete element method-immersed boundary method (CFD-DEM-IBM method) is used to simulate the velocity and temperature fields around the immersed tube in two fluidized beds, the heat transfer coefficients of fluid-wall, particle–wall, and particle–fluid-wall are then analyzed and compared with experimental data. It is shown that in order to quantitatively predict the surface-to-bed heat transfer coefficient without using empirical correlations, the thermal boundary layer of gas phase that is of the order of particle diameter needs to be explicitly resolved by refining the fluid grid around the immersed tube up to 1/16 of particle diameter, whereas an empirical correlation is necessary to correctly calculate it in the state-of-the-art CFD studies which have used coarse grids. Present study highlights the critical role of scale resolution (specifically, the explicit resolution of the thermal boundary layer) in the study of surface-to-bed heat transfer in gas–solid fluidized beds.