Natural convection in water-saturated metal foam

Natural convection in water-saturated copper foam is measured for 2.5 x 10(-4) < Da < 1.2 x 10(-5), 10 < Ra-m < 210, and 7.5 x 10(5) < Ra-f < 2.5 x 10(8). Experiments are reported for foam with 92% porosity and 10 and 20 pores per inch. The primary finding is that the Nusselt numbers do not follow the published heat transfer correlations with Rayleigh number for a packed bed of spheres and are 27-42% less than that predicted by these correlations at the maximum Rayleigh numbers encountered for Da similar to 10(-5). A single heat transfer correlation of Nusselt number is obtained in terms of Rayleigh and a modified Prandtl number equal to Pr(m)Da(-1/2)C(f)(-1). In comparison to natural convection in a water layer, enhancement of heat transfer is primarily via conduction. Enhancement of the advective component of heat transfer is obtained only for Ra-f similar to 10(8) and 1.2 x 10(-5) <= Da <= 2.4 x 10(-5). (C) 2008 Elsevier Ltd. All rights reserved.