Effect of Solid And Liquid Heat Conductivities on Two-Phase Heat and Fluid Flows

Abstract

Liquid-solid two-phase flow with heat transfer is simulated, and the effects of temperature gradient within a solid object and particle mobility on heat transfer are studied. The interaction between fluid and particles is considered with our original immersed solid approach on a rectangular grid system. A discrete element model with soft-sphere collision is applied for particle-particle interaction. Governing equation of temperature is time-updated with an implicit treatment for the diffusion term, which enables stable simulation with particles of very high/low ratios of heat conductivity (from 1/1000 to 1000) to fluid. The local heat flux at the fluid-solid interface is carefully discretised and incorporated into the implicit scheme of temperature. The method is applied to a 2-D confined flow including multiple particles under a high Rayleigh number condition. Heat transfer and particle behaviours are studied for different ratios of heat conductivity (solid to liquid) and solid volume fractions. For a relatively low solid volume fraction, a transition of particulate flow pattern is observed depending on the heat conductivity ratio; the cases with high ratios of heat conductivities exhibit simple (single or double) circulating flows, whereas low heat conductivity ratio causes complicated flow patterns involving multiple circulation of particles, resulting in low Nusselt number. The above simulation results, together with the heat transfer properties under a near-packed condition, highlight the effect of temperature distributions within the particles and liquid.