Analysis of the Applicability of Effective Thermophysical Properties to Composite Phase Change Materials

Coarse form-stable phase change materials (FS-PCMs) can tailor the properties of pure PCMs. This is often attained by the presence of high-melting, high-thermal conductivity metallic phase which enhances the thermal energy storage/release. The evaluation of the thermal response of these composite materials in unsteady conditions, is not an easy task, and simplifications introduced to deal with them must be carefully considered. A set of FS-PCMs of prismatic geometry with polymeric wax as PCM and an Al foam with various pore sizes, modelled as BCC lattice has been considered in this paper. The thermal response under a set of boundary conditions with constant heat flux at the bottom surface, all other being adiabatic, was investigated both by direct simulations approach modelling the two phases and the ‘1-temperature model’, which considers the material as homogeneous and characterized by a proper set of effective properties. The ‘1-temperature model’ is able to closely reproduce the whole the local thermal history only within certain validity ranges, even if it can well reproduce the ‘average’ energy storage due to the transformation of the PCM phase.