Spray-Formed, Metal-Foam Heat Exchangers for High Temperature Applications

Open pore metal foams make efficient heat exchanger because of their high thermal conductivity and low permeability. This study describes a novel method of using wire-arc spraying to deposit Inconel 625 skins on the surface of sheets of 10 and 20 pores per linear inch nickel foam. The skins adhere strongly to the foam struts, giving high heat-transfer rates. Tests were done to determine the hydraulic and thermal characteristics of the heat exchangers and correlations developed to calculate Fanning friction factor and Nusselt number as a function of Reynolds number for airflow through the foam. Measured heat-transfer coefficients for the foam heat exchangers are greater than those of straight flow channels at the same flow rate. A ceramic thermal barrier coating was deposited on one face of the heat exchanger using plasma spraying. The coating and heat exchanger survived prolonged exposure to the flame of a methane-air burner.