Non-Darcy natural convection in high porosity metal foams

We present numerical and experimental results for buoyancy-induced flows in high porosity metal foams heated from below. A Brinkman-Forchheimer-extended Darcy flow model and a semi-heuristic two-equation energy model obtained by relaxing the local thermal equilibrium (LTE) assumption are adopted. Experiments conducted under natural convection conditions for the same configuration are used to test the numerical model and the validity of the thermal equilibrium assumption for metal foams. Aluminum foam samples of different pore sizes (5-40 PPI) and porosities (0.89 less than or equal to epsilon less than or equal to 0.97) are used to illustrate the effects of metal foam geometry on heat transfer. In addition, several metal foam-fluid combinations (aluminum-air, carbon-air, aluminum-water, and nickel-water) are used to study the heat transfer enhancement relative to the base case in which there is no metal foam but only a heated plate. Thermal dispersion effects and the effects of Darcy number on heat transfer are reported. Our results indicate that the thermal non-equilibrium model provides a superior description of heat transfer in metal foams, especially in the presence of fluid-porous interfaces. (C) 2002 Elsevier Science Ltd. All rights reserved.