Metal foam, Heat exchangers
Due to their large surface-area-to-volume ratio and tortuous structure, metal foams hold promise for heat transfer applications. Both of these factors increase the heat transfer by enhancing the mixing and surface area. The main disadvantage associated with their thermal-hydraulic performance is relatively higher pressure drop, resulting in larger pumping power requirements if they are used in a heat exchanger. In this paper, open-cell aluminum metal foam is considered as a highly compact replacement for conventional fins in brazed aluminum heat exchangers. SEM techniques are used to characterize the foam characteristics such as pore and ligament diameter. Experiments are conducted by a closed-loop wind tunnel to measure the pressure drop and heat transfer rates. The effects of different porosity, fin depth, bonding method, base metal, condensation and frost are considered. It is found that incorporating foam with smaller pores results in larger pressure drop per unit length but the heat transfer rate is higher as well. Fin depth can be changed as well to reduce the pressure drop. Furthermore, metal foams, found to perform much better compared to other designs employing plain fins or louver fins with much larger heat transfer coefficients. Permeability and inertia coefficients are determined and compared with the reported data. An appropriate length scale is suggested for the data reduction. Based on the experimental findings, a model has been developed relating the foam characteristics and flow conditions to the pressure drop and heat transfer.