The role of particle-turbulence interactions on fluid and thermal transport

Strong coupling between particles and turbulence gives rise to a variety of complex flow regimes, from dense clusters to nearly-particle-free voids. Such coupling can effectively 'demix' the underlying flow. In this presentation, results from highly-resolved Eulerian-Lagrangian simulations are reported to understand the extent to which local flow heterogeneity augment or restrict turbulent kinetic energy (TKE) and average rates of heat transfer. Simulations of homogeneous sedimenting gas-solid flows and particle-laden channel flows are analyzed for a range of volume fractions and Prandtl numbers. It is found that varying flow regimes have substantial and non-trivial effects on the budget of TKE. We also find that clusters have a profound effect on the overall heat transfer efficiency. Simulations reveal that the gas phase is cooled relatively fast in the vicinity of clusters while hot spots persist in regions void of particles. To identify the mechanisms responsible for these variations, a coarse grained temperature equation is derived for statistically homogeneous (zero-dimensional) time-dependent multiphase flows. Two-phase flow statistics are presented and a simplified model is proposed.