Investigation of the radiative heating of cubic particles with DEM/CFD and the BO/DO approach

Abstract

The combined “Blocked-Off & Discrete Ordinates” (BO/DO) approach is used within a DEM/CFD frame to model the radiative heating of stationary and moving (rotating with respect to the mesh) cubic particles. A single cube, placed inside a larger cubic box, is heated by radiation and its temperature evolution over time is investigated. Two different models for the particle heating are considered: the first one assumes a uniform cube temperature while the second model calculates the intra-particle heat transfer leading to a non-uniform temperature distribution as it occurs in thermally thick particles. Three different particle materials, wood, styrofoam and steel, are considered.Initially, the radiative heating of stationary cubes, approximated by the BO approach in a CFD mesh, is compared to the heating of cubes enclosed by a corresponding body conformal mesh as a reference. The results show that deviations in cube temperature mainly result from the artificial increase of the particle surface in the BO. When applying a particle surface area ratio to compensate for the artificial surface area increase deviations in temperature can be reduced to 5.2% compared to body conformal mesh.In a further step, the cube is constantly rotating which changes the orientation of the cube's surfaces relative to the radiation source. The evolution of the cube's surface temperatures, which is dependent on the orientation, is modelled by the BO/DO approach. As expected, materials with low thermal conductivity show larger temperature gradients over time than materials with high thermal conductivity. The temperature difference between different surfaces turns out to be in the ranges 50/14/0 K (for styrofoam/wood/steel) and 134/65/0 K between surface and core, thus reflecting the correct physical behavior. The evaluation of the BO/DO approach concerning its capability to account for radiative heat transfer in DEM simulations for particles with a regular (cubic) geometry, as examined in the current paper, forms the basis to extend the description to arbitrarily shaped particles, a great potential of the BO/DO approach as will be shown in an outlook example.