Impact of surface roughness on heat transfer through spherical particle packed beds

A new thermal discrete element method-based model relying on a resistance network and considering conduction at the particle contact point, conduction in the surrounding fluid and particle conduction was developed. The model was validated using measurements of temperature evolution in four packed beds of glass, steel and two types of aluminum alloy beads whose roughness was characterized by AFM. The detailed analysis of every resistance in the network for the four materials showed that conduction in the fluid in the macrogap between the particles is not negligible for any material and is even preponderant, especially at low particle-to-fluid thermal conductivity ratios (lc). The model simulations also revealed that roughness has a significant impact on the effective thermal conductivity of packed beds with a K > 3, 000. This finding explains, for the first time, the large increase in the scattering of effective thermal conductivity data observed in the literature as K is increased. (C) 2020 Elsevier Ltd. All rights reserved.