A non-linear transform approach for conduction-radiation heat transfer in the extended thermal discrete element method

Abstract

Conduction-radiation heat transfer widely exists in nuclear pebble beds, packed beds and powder materials under moderate or high temperatures. Because of the considerable computational cost, it is unrealistic to trace all possible obstructed view factors between spheres in transient particle-scale simulations. With a non-linear transform approach, an extended thermal discrete element method (TDEM) with almost the same computational cost as that required for conduction alone is proposed here. Particle-particle conduction in the contact area, particle-fluid-particle conduction near the contact point and the Knudsen effect under low gas pressures are considered in the determination of the contact thermal resistance (CTR). A particle conduction-radiation scalar is applied in the particle energy balance equation, which is a function of the particle temperature, CTR and radiation exchange factor. The numerical results of the pebble bed are in good agreement with the continuum model and measured results under high temperatures. The temperature transport process in conduction-radiation heat transfer involves anomalous diffusion by discrete and continuum methods. The proposed extended TDEM is proven to be efficient for conduction-radiation heat transfer and feasible to be applied in large-scale computational fluid dynamics (CFD)-DEM simulations.