Experimental investigation on thermal properties of paraffin/expanded graphite composite material for low temperature thermal energy storage

The technology of latent heat storage with phase change materials (PCMs) is one of the promising means to improve the utilization of renewable energy. Nevertheless, its broad application will be limited due to the low thermal conductivity of PCMs. In this work, paraffin/expanded graphite (EG) composite PCMs by paraffin having a melting point of 62 °C and expanded graphite with three kinds of particle sizes were prepared and characterized. Environmental scanning electron microscope (ESEM) micrographs showed that EG was dispersed homogeneously in composite PCMs. Meanwhile, the distribution uniformity of expanded graphite in composite PCMs was evaluated quantitatively. The thermal conductivities of composite PCMs increase as the mass fraction of EG increases, and the thermal conductivity of paraffin/EG80 (5 wt.%) was 1.492 W/(m·K) in comparison with the value of pure paraffin was 0.355 W/(m·K). X-ray diffraction (XRD) analysis indicated that the fabrication process of composite PCMs was a purely physical process without a new substance produced. Differential scanning calorimeter (DSC) demonstrated that the latent heat of composite PCM was slightly less than the theoretical value. The addition of EG could lead to the improvement of the melting temperature of composite PCMs, while the decrease of the freezing temperature.