Granular diffusion characteristic in moving beds with built–in pipes

Abstract

The diffusion characteristics of three different granular materials in moving beds with different pipe arrangements are studied and compared. Diffusivities of glass beads are always the highest and coarse sands the lowest in all the zones in the beds with aligned pipes. The main flow diffusivity is 1.13 × 10−6, 5.49 × 10−7 and 1.78 × 10−7 m2/s for glass beads, corundum beads and coarse sands. In contrast, the main flow diffusivities of coarse sands and corundum beads are significantly enhanced in the beds with staggered pipes, but the change of glass beads is slight. The diffusivity of coarse sands is up to 5.95 × 10−6 m2/s. In addition, low diffusivity always remains in the region above pipes. Further studies of the dimensionless diffusivities for different materials show that the granular diffusion in aligned beds could be explained by the shear–induced diffusion theory. While the diffusion mechanisms are diversified in the staggered beds.