Solar Energy Materials and Solar Cells | 2019
Effect of the fabrication process on the thermophysical properties of Ca(NO3)2–NaNO3/expanded graphite phase change material composites
Abstract
Abstract Studying the influence of various fabrication steps on the thermophysical properties of the shape-stable phase change materials (SSPCMs) is pivotal to adjust the thermophysical properties of the PCM/expanded graphite (EG) SSPCMs. In light of this, three kinds of PCM samples involving different fabrication steps (impregnation, cold-compression and sintering) were fabricated and characterized, to investigate the effects of the different fabrication steps and molar ratios of the Ca(NO3)2–NaNO3 binary salts on the microstructure and some thermal properties of the SSPCMs. The results show that the cold-compression and sintering led to a quite compact arrangement of EG regions separated by salt particles, which constrained the Ca(NO3)2 crystal arrangement and orientation of nitrate molecular chains within the mesopores of EG. As a result, two overlapped or convoluted DSC peaks, instead of one peak, and a wider melting temperature range appeared during the melting process of the SSPCMs when the Ca(NO3)2\u202fM ratio was no less than that of the eutectic binary salt. The cold-compression and sintering also caused evident increases of the melting temperature range, reductions of the phase change enthalpy by 21–23%, and significant increases of the thermal conductivities of the SSPCMs by over 2.5 times from 1.56 to 1.9 to 5.02–6.27\u202fW/(m ⋅ K). The cold-compression and sintering are suggested to be employed in the fabrications of the SSPCMs to establish a better conductive passageway and surge the energy storage density.