Computational study of fluid flow and heat transfer in randomly packed bed with different tube walls

In the present paper, the flow and heat transfer performances in randomly packed beds of spheres with low tube-to-particle diameter ratio and different tube wall structures were numerically investigated, including smooth tube wall model and hemisphere tube wall model. The randomly packings were generated with discrete element method, and the influence of the wall effect on the flow and heat transfer in the packed beds were carefully studied. Firstly, it is found that, the wall effect on the velocity and temperature distributions in the smooth tube wall packing with low tube-to-particle diameter ratio were remarkable. The average velocity of the near-tube-wall region is higher than that of the inner-tube region in the bed, while the average temperature of the near-tube-wall region is lower. Meanwhile, with hemisphere tube wall structure, the radial porosity in the packed bed would be more uniform, and it would lead to more uniform velocity, temperature distributions, and stronger lateral flow mixing inside. This would be beneficial to restrain the wall effect and improve heat transfer performance in the packed bed with low tube-to-particle diameter ratio.