New Criterion for Local Thermal Equilibrium in Porous Media

In this paper, a general criterion for local thermal equilibrium in forced convection flows through porous media under a constant heat flux boundary condition is presented in terms of parameters, including the boundary heat flux, the area of cross section, the effective thermal solid-to-fluid conductivity ratio, characteristic length for pore size, porosity, Nusselt number, fluid conductivity, and the heat source of solid phase. To check the validity of the proposed criterion for local thermal equilibrium, the forced convection phenomena in the porous medium between two parallel plates subjected to constant heat flux are studied by numerical method based on the Brinkman-Forchheimer extended Darcy model. The temperature difference between solid and fluid phases in a representative elementary volume are studied by comparing the effects of relevant parameters in this new criterion. In addition, the proposed criterion is consistent with the existing experimental and numerical results for convection heat transfer in a porous medium.