Improving the Cold Thermal Energy Storage Performance of Paraffin Phase Change Material by Compositing with Graphite, Expanded Graphite, and Graphene

The goal of this research is to compare the thermal energy storage of the composites of graphene/paraffin and expanded graphite/paraffin for low-temperature applications and understand the role of graphene and expanded graphite in this regard. Paraffin with 5 °C phase change temperature (Pn5) was employed as the phase change material (PCM). It was integrated into graphite, expanded graphite, and two types of graphene to improve its thermal energy storage performance. Expanded graphite and graphene absorbents with porous structures could efficiently absorb Pn5 with only a minor drop in the latent heat of fusion (below 6%). Moreover, 1:10 weight ratio expanded graphite-Pn5 and 1:10 graphene-Pn5 composites possessed 0.923 and 0.660 W m−1 K−1 thermal conductivities, which are about 4.8 and 3.4 times that of the neat Pn5, respectively. Besides, regarding the differential scanning calorimetry (DSC) results, the variation in the phase change temperatures of the fabricated composite PCMs in comparison with the pure PCM was negligible. The heat storage behavior of the probing PCMs in cold environments was simulated. The simulation results exhibit that when the charging target temperature for the PCMs placed in the four side walls of a modeled room is 0 °C, Pn5 reaches this temperature from the initial 23 °C temperature after 30.6 h, whereas the storage time for 1:10 weight ratio graphene-Pn5 is 10.8% shorter than that of Pn5. Finally, the 1:10 graphene-Pn5 composite PCM is the most propitious one for cold thermal energy storage applications in buildings and containers due to its extreme thermal conductivity, satisfactory phase change temperature as well as the superb latent heat storage capacity.