Effect of the fabrication process on the thermophysical properties of Ca(NO3)(2)-NaNO3/expanded graphite phase change material composites

摘要

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) M 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 W/(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.