A combined hydro-thermal characterization of high-porosity metal foam test sections with discrete pore-size gradients

Abstract

In this study, aluminum foam test sections with discrete pore-size gradients were experimentally investigated. The test sections, which were created by combining foams with up to three different values of pores per inch (PPI), were uniformly heated from below by a flat heater and cooled by a controlled air stream flowing through the foam. The overall dimensions of the foams tested were 25.4mm wide and 6.4mm thick, and the individual length of a foam section varied between 101.6mm, 50.8mm, and 25.4mm, depending on the number of segments with different PPIs being tested. The pressure drops were measured, and the heat transfer coefficients were calculated for all foam combinations considered. The hydrodynamic results showed that the number of sections did not affect the overall pressure drop across the test section if all segments had the same PPI. Also, a higher heat transfer coefficient was observed when air flowed first through the foam with the larger pores (smaller PPI) compared with that of the test section in the reversed orientation. However, the heat transfer coefficients of the mixed-foam test sections were not greater than their better performing whole-foam counterpart, at least for the samples tested. This suggests that, perhaps, metal foams with more refined geometric features could be exploited to allow the tradeoffs between heat transfer, required pumping power, weight, etc., to become identifiable.