Thermal conductivity evolution of a compressed expanded natural graphite-Phase change material composite after thermal cycling

Compressed Expanded Natural Graphite (CENG) impregnated with Phase Change Material (PCM) is an interesting material for latent heat storage application requiring a high heat transfer rate. This composite material, that has orthotropic properties, undergoes expansion while the PCM changes phase that might affect its thermal properties and its mechanical integrity. In order to assess this possible evolution, the CENG-PCM thermal conductivities in the two principal directions have been measured before and after a 1500 thermal cycling test. The thermal characterisation was performed using two methods: a classic hot guarded plate method and a more originally inverse method. The results show no significant change of the thermal conductivity values after ageing cycles in spite of the appearance of cracks in the planar direction of the composite. We can conclude that the delamination of the CENG was not sufficient to affect the thermal conductivities. In addition, a DSC analysis shows that the latent heat is also almost unchanged after the thermal cycling.