Role of thermal disequilibrium on natural convection in porous media: Insights from pore-scale study.

The present study investigates the role of thermal nonequilibrium on natural convection in a fluid-saturated porous medium heated from below. We conduct high-resolution direct numerical simulation at the pore scale in a two-dimensional regular porous structure by means of the thermal lattice-Boltzmann method (LBM). We perform a combination of linear stability analysis of continuum-scale heat transfer models, and pore-scale and continuum-scale simulations to study the role of thermal conductivity contrasts among phases on natural convection. The comparison of pore-scale lattice-Boltzmann simulations with linear stability analysis reveals that traditional continuum-scale models fail to capture the correct onset of convection, convection mode, and heat transfer when the thermal conductivity of the solid obstacles does not match that of the fluid.