Heat transport in granular materials during cyclic fluid flow

Heat transfer takes place between grains and the fluids that saturate the pore space in granular materials, when the fluid is static or moving. This study explores effective heat transport in granular materials during cyclic fluid flow. Controlled particle-scale experiments, complementary analyses and numerical simulations help us identify the governing variables and ensuing time scales. We show that fluid-grain heat transfer leads to effective heat transport along the granular medium during cyclic fluid flow. At the macro-scale, the process resembles diffusion where the effective diffusion coefficient is proportional to the square of the fluid invasion length in each cycle and inversely proportional to the cycle period. Both experimental and numerical results confirm improved heat transfer by cyclic fluid flow over thermal diffusion under hydrostatic conditions. The formulation can be used to identify optimal operation conditions for maximum transport.