Direct numerical simulation of heat transfer in fluid-particle two-phase flow by coupled immersed-boundary and discrete-element methods

摘要

To discuss the heat conductivity of fluid-solid mixture, we analyze the natural convection of solid-liquid two-phase media by developing a direct numerical simulation method that deals with the heat-transfer at moving boundaries. The interaction between fluid and particles is treated by our immersed solid approach: the momentum-exchange is imposed by a volume force which facilitates the computation of the solid behavior. A discrete element model with inelastic collision is applied to particle-particle interaction: it enables us to simulate particle-laden flows under a highly-packed condition. Then we propose an improved heat conduction model with a flux-decomposition scheme. The present method is applied to a direct numerical simulation of 2-D confined flow including multiple particles under a high Rayleigh number condition. In case of relatively low solid volume fraction, transition of particulate flow pattern is observed depending on the heat conductivity ratio; the cases with high ratios of heat conductivities exhibit simple circulating flows, whereas low heat conductivity ratio causes complicated flow patterns. Under a near-packed condition, our result highlights the effect of temperature distributions within the particles and liquid.