Critical analysis of the experimental determination of the thermal resistance of metal foams

Abstract

This paper addresses experimental and numerical analysis of the thermal resistance of M-Pore® copper foam. The findings suggest a separation of the thermal resistance into two components: material resistance and contact resistance. Finite element analysis is used to calculate the thermal material resistance. Calculation models are based on micro-computed tomography data in order to account for the complex material geometry. The same samples are used for experimental analysis. A transient method is applied where a time-dependent temperature change is related to the thermal resistance. In addition to material resistance, experimental measurement values inevitably include thermal contact resistance. Although a thermally conducting paste is used in order to minimise this effect, a significant thermal contact resistance is found. As a result, the experimentally measured thermal resistance can no longer be considered as a material property but depends on the sample size and the particular shape of the contact surfaces. Furthermore, it is demonstrated that the traditional approach to experimentally obtain thermal contact resistance by changing the specimen size is impractical for cellular metals. Instead, the contact resistance is obtained by comparing experimental and numerical results.