DISCRETE ELEMENT SIMULATIONS FOR GRANULAR MATERIAL FLOWS - EFFECTIVE THERMAL-CONDUCTIVITY AND SELF-DIFFUSIVITY

This study uses a two-dimensional discrete-element simulation to deter mine the effective thermal conductivity and self-diffusivity-quantitie s that depend on the random motions of particles within a granular mat erial flow. The simulations are performed for solid fractions from 0.0 15 to 0.68 and for different Biot-Fourier numbers. The assumptions use d in the simulations are consistent with dense-gas kinetic theory;henc e, the simulation results are shown to compare well with the self-diff usivity based on kinetic theory predictions. For the heat transfer pro blem, the analysis differs from classic kinetic theory since the parti cles can exchange heat with the surrounding fluid. For Biot-Fourier nu mbers much less than I, the effective conductivity from the simulation s coincides with kinetic theory predictions. As the Biot-Fourier numbe r increases above 0.1, the results deviate considerably from the class ic analysis, but can be predicted using a modified kinetic theory appr oach. The simulation is a powerful technique, which can be extended to problems that are not consistent with kinetic theory assumptions. (C) 1997 Elsevier Science Ltd.