Free convection in a vertical, porous annulus with constant heat flux on the inner wall-experimental results

Steady-state natural convection in a concentric, tall, vertical annulus filled with saturated, porous media is experimentally studied when the inner wall is heated by applying a constant heat flux and the outer wall is isothermally cooled. Temperature profiles and heat transfer rates are obtained for two sets of aspect and radius ratios, A = 14.4, k = 3.5 and A = 11.08, k = 14. The use of several solid-fluid combinations indicates a divergent behavior by Nusselt vs Rayleigh number curves, as also reported by previous investigators. An analysis of present and previous experimental data shows that the Nusselt number for a given Rayleigh number decreases as the ratio of solid and fluid thermal conductivities increases and vice versa.