The effect of particle shape on the packed bed effective thermal conductivity based on DEM with polyhedral particles on the GPU

Abstract

Granular material (GM) is the second most manipulated substance in the world and is present in most industries either as raw materials or finished products. Often the temperature of the granular material needs to be manipulated for example in the case of heating iron ore to induce a phase change or to be kept within a certain temperature range in the case of pharmaceutical powders and food products. Thus a detailed understanding of how heat is transferred in granular materials is essential. The most feasible numerical approach to study heat transfer in granular materials is using the discrete element method (DEM), where each particle is explicitly modeled. In terms of conductive heat transfer particle shape can be expected to have a significant effect on the heating of granular materials, due to the nature of the grain to grain contacts and packing topology which control the heat flow paths and the rate that heat is conducted along these. This paper considers the effect of particle shape on heat conduction in thermally simple or low Biot number granular materials using a polyhedral particle representation. The volume based contact model for granular heat conduction is firstly verified against the analytical solution for solid heat conduction as well as experiment with cubic particles. The resulting model is then used to study the effect of particle shape on the effective thermal conductivity (ETC) and heat distribution within packed stationary beds. It was found that for irregularly shaped (polyhedral) particles the ETC does not have a linear relationship with the packing density as found in previous studies with spherical and ellipsoidal shaped particles. Rather that there is an exponential dependence on the micro-structural quantities of contact area and isotropy, with non-homogeneity in the packing density resulting in complex conduction paths and dead zones affecting conduction thru the bed.