Unsteady conjugate natural convection in a three-dimensional porous enclosure

Transient-free convection in a porous enclosure having heat-conducting solid walls of finite thickness under conditions of convective heat exchange with an environment was studied numerically. A heat source of constant temperature was located at the bottom of the cavity. The governing equations in porous volume formulated in dimensionless variables such as the temperature and vector potential functions within the Darcy-Boussinesq approach and the transient three-dimensional heat conduction equation based on the Fourier hypothesis for solid walls with corresponding initial and boundary conditions were solved using an iterative implicit finite-difference method. The main objective was to investigate the influence of the Rayleigh number 10³ ≤ Ra ≤ 10⁶, the Darcy number 10^-5 ≤ Da ≤ 10^-3, the thermal conductivity ratio 1 ≤ k_1,2 ≤ 20, the solid wall thickness ratio 0.1 ≤ l/L ≤ 0.3, and the dimensionless time 0 ≤ τ ≤ 200 on the fluid flow and heat transfer. Comprehensive analysis of the effects of these key parameters on the average Nusselt number at the heat source surface was conducted.