Numerical simulation of wall effect in randomly packed bed with low tube to particle diameter ratio

The wall effect in randomly packed bed with low tube to particle ratio is numerically investigated by coupling discrete element method (DEM) and computational fluid dynamics (CFD). The porosity, characteristics of fluid flow and heat transfer in randomly packed beds are carefully studied, including smooth tube wall model and corrugated tube wall model. Simulation results show that, the wall effect in smooth wall packing with low tube to particle diameter ratio is remarkable. The average velocity of the near tube wall region is higher than inner region, while the average temperature of this region is lower. Besides, the mass flow rate in the range of 0.5d_p near the tube wall is about 46% of the total flow. With corrugated structure, the leakage near the tube wall is suppressed and the mass flow rate decreases to 36%. The heat transfer characteristics and drag coefficient have a slight increase, while the overall heat transfer coefficient is lower than smooth tube wall model.