Thermal Hydraulic Performance of High Porosity High Pore Density Thin Copper Foams Subject to Array Jet Impingement

Abstract

Metal foams have shown promise in enhancing heat dissipation from heated surfaces and find applications in forced convection cooling environments like electronics cooling. The thermal and hydraulic performance of metal foams have a strong correlation to its pore density (pores per inch: PPI) and porosity. While high pore density is desired to enhance heat dissipation (due to higher effective heat transfer area), high porosity is suitable to maintain low pressure drop in forced convective cooling applications. Towards this end, an experimental study was carried out to evaluate the thermal-hydraulic performance of high pore density (90 PPI), high porosity (95%), thin Copper foams (3 mm thick) strategically placed over a heated surface of base area 20 mm x 20 mm. Heat transfer was facilitated with air as the working fluid impinging through a 3x3 array (x⁄dj = y⁄dj = 4) of circular nozzles of diameter, dj = 1.5 mm. Two metal foam-heated surface configurations were tested, a full foam configuration; where the metal foam covered the entire heated surface area, and a foam stripes configuration, where metal foam stripes were strategically placed over the heated surface, were studied for their heat transfer, pressure drop and thermal hydraulic performance at Reynolds numbers (Rej) between 3000 and 12000. A smooth surface, without metal foam, served as the baseline case. Additionally, the effect of varying jet-to-target plate distance (z) as z⁄dj = 2, 3, 5, 7 was studied. From experiments, it was observed that the stripes configuration had highest heat transfer enhancement of about 1.45 times that of the smooth surface target, at the expense of a marginal increase in pumping power, thereby making it the best configuration in terms of thermal hydraulic performance.