Thermal hydraulic performance augmentation by high-porosity thin aluminum foams placed in high aspect ratio ducts

Abstract

High porosity metal foams are known for providing high heat transfer rates, however, the concomitant higher-pressure losses have been a concern towards the realization of enhanced thermal hydraulic performance. Present study aims towards developing metal foam-based cooling configurations subjected to forced convection in a channel by employed very thin and high porosity Aluminum foams, where the goal is to achieve maximum foam volume participation in heat dissipation. To this end, a comprehensive experimental study has been carried out to investigate the effect of foam pore density (pores per inch: PPI) and channel aspect ratio (AR) on the thermal hydraulic performance of thin metal foams. High porosity (93%) thin aluminum foams with pore densities of 5, 20 and 40 PPI were studied, where the convective heat transport was facilitated through air forced through the channel. For the 40 ppi foams, three foam heights of 3.175 mm, 6.35 mm and 19 mm were tested, for 20 ppi foams, two foam heights of 6.35 mm and 19 mm were tested, and for the 5 ppi foams, one height of 19 mm was tested. These three different foam heights yielded in channel ARs of 16:1, 8:1 and 8:3, respectively. Heat transfer gain due to metal foams was evaluated against a geometrically identical smooth channel as well as with the Dittus-Boelter correlation for developed turbulent flow in circular ducts. Experimental data reveals that, for a given AR, an increase in pore-density resulted in both, increase in heat transfer as well as pressure drop. Amongst all three channel configurations, the 40 ppi foams had highest heat transfer, where the gain with respect to smooth channel for Re 5000 was ~21, 12 and 9.5 times, for 8:3, 8:1 and 16:1 channels respectively. Increase in channel AR (thinner foams) demonstrated an increase in heat transfer performance for a given pumping power. The thermal hydraulic trends observed for thin and high pore-density foams proved them to be viable candidates for compact electronics cooling.