On the electrical and thermal contact resistance of metal foam

This paper addresses the electrical and thermal contact resistance in metal foam-graphite assemblies considered for use in next generation air-cooled fuel cells as replacements of currently available water-cooled ones. Their successful application requires minimization of thermal and electrical contact resistance between components. The current study investigates the evolution of both resistances with increasing compressive force between metallic foam and graphite plates. Reducing these contact resistances through compressive force instead of brazing significantly reduces the manufacturing cost. Our results show that both electrical and thermal resistances monotonically decrease with increasing compressive force when moving from no compressive force to a slight one about 100 N (corresponding to a compressive stress of 0.01 MPa). Interestingly, compared with the thermal contact resistance, the electrical contact resistance shows more sensitivity to compressive force within this range of force. Furthermore, it has been noted that increases in compressive force beyond 300 N (i.e. 0.03 MPa) decrease the resistances only marginally. Electrical contact resistance was found to govern the total resistance of the metal foam-graphite assembly since electric bulk resistances are several orders of magnitude lower. Similar observations are made for thermal resistance where the minimum contact resistance exceeds the thermal resistance of the foam in our experiments.