Numerical and experimental investigations of melting process of composite material (nanoPCM/carbon foam) used for thermal energy storage

Paraffin wax is considered as stable and environmentally convivial phase change materials (PCM) for thermal energy storage systems (TESS). However they suffer to low thermal conductivity which reduced the rate of heat storage and energy conversion, as well as the leakage of materials during the melting process. In this paper, nanocomposites consisting of a paraffin / graphite mixture embedded in carbon foam by vacuum impregnation were prepared in the aim to develop a new formulation of phase change material (PCM) with excellent shape stabilization, thermal conductivity improved and exceptional thermal reliability. Different tests such as Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermal conductivity analyzer are proposed to determine thermal properties of the composite PCM. After the validation of numerical model with experimental results, the numerical analysis is extended to investigate the melting process of the composite PCM under constant temperature. A regular three-dimensional (3D) foam structure was designed. The effects of carbon foam porosity and nanoparticles' volume fraction on the thermal behavior of composite PCMs were investigated. The results show that the addition of both graphite and carbon foam to paraffin wax enhance the thermal properties and prevent the leakage of the melted paraffin which preserve its stable thermal performance. This is due to the conductive network path created by the 3D structure of the carbon foam and the percolation of graphite, which might facilitate an increased phase change speed of composite PCM.