Experimental study of buoyancy-driven flow in open-cell aluminium foam heat sinks

Abstract

Air-saturated buoyancy-driven flow in a heat sink with open-cell aluminium foam as extended surface is studied. The experiments were performed in a carefully validated test rig. Influences of the pore density, the foam height and the bonding method are examined in this paper for Rayleigh numbers varying between 4000 and 6500, while maintaining the length-to-width ratio of the substrate on 10. The studied foams have a pore density of 10 and 20 PPI, both with a porosity of 93%. The height of the 10 PPI foam is varied between 6 and 40 mm and for 20 PPI between 6 and 18 mm. The bonding of the foam is done via brazing or by applying a single epoxy.A difference in heat transfer rate is observed between both bonding methods: the brazed samples are superior in all cases. The pore density, has a more pronounced influence. The strongest influence can be attributed to a variation in sample height. A correlation for the Nusselt number is derived, for the studied 10 and 20 PPI foam.