Influence of confining wall on pressure drop and particle-to-fluid heat transfer in packed beds with small D/d ratios under high Reynolds number.

• The pore-scale CFD is performed to study fluid flow in packed beds at D / d < 10. • The quasi-regular packed bed is identified at very low D / d ratios. • The typical confining wall effect is found in packed beds with large D / d ratios. • The regularity from the wall dominates the packing and flow field at D / d < 4. • The simulations results are compared with well-known empirical correlations. The presence of the confining wall exerts critical influences on packing structure, as well as transport properties of packed beds with small D / d ratios. In the present work, the variations of pressure drop and particle-to-fluid convective heat transfer in the packed beds of strong wall interference were evaluated under the high Reynolds number regime (Re m ∼ 104) by using the CFD simulation combined with the DEM method for random packing generation. The variations upon the D / d ratios were discussed, and the applicability of empirical correlations was examined. It found that the lower D / d ratios, the lower pressure drop and heat transfer performance, and the Carman correlation and the Wakao correlation provided predictions of better accuracy for the two parameters respectively than the other empirical correlations. Then, the discussion was extended to the packing structure and fluid flow distribution. A packed bed with distinct features—the quasi-regular packed bed—was encountered at D / d = 4, in which the packing structure regularity from the wall extents over the entire bed. Accordingly, much uniform flow velocity and temperature distributions were observed in the bed. Finally, some literature results in the range of 1 < D / d < 4 were revisited in conjunction with the present findings to reach a complete picture of the confining wall influence on the packing structure and related transport properties. It suggests that the studies for packed beds in the range of D / d < ∼ 4 should be isolated from the other packed beds of higher D / d ratios and the related analysis should be developed on a case-by-case basis. These findings may provide a new perspective to address the confining wall influence in packed beds with small D / d ratios. [ABSTRACT FROM AUTHOR]