A numerical evaluation of a latent heat thermal energy storage system in the presence of various types of nanoparticles

Due to the high demand for using phase change materials (PCMs) in thermal systems and to the goal of improving the thermal efficiency of solar systems, herein, the heat storage performance of nano PCM (nPCM) was numerically scrutinized. For this purpose, a vertical double-tube heat exchanger containing paraffin and five different nanoparticles was simulated. By originating scientific results, 31 radial fins were considered on the tube side of the heat exchanger. RT35 paraffin wax as PCM includes a melting point close to the ambient temperature, making it easy to investigate domestic usage's charging and discharging processes. It was found that nanoparticles be able to decrease the duration of melting and solidification processes. Adding 5 vol% of Cu, CuO, TiO2, Carbon nanotube (CNT), and Graphene nanoplatelet (GNP) to the PCM caused 6.6%, 10.2%, 10.7%, 33.4%, and 56.4% of the melting time reduction, while time reductions of 20.3%, 13.4%, 13.2%, 43.1%, and 69.7% for solidification were observed, respectively. The results showed that thermal conductivity, density, and heat capacity properties affect the melting process, whereas thermal conductivity was the most critical parameter in the solidification process. Thus, despite the better performance of CuO and TiO2 compared to Cu in the melting process, it diminished the solidification time greater than the others. Also, the presence of nanoparticles was more significant in the solidification process. Moreover, the heat transfer coefficient of GNP-PCM was the highest among others (66.63 W/m2.K for 5 vol%), while it was 24.68 W/m2.K for 5 vol% of Cu-PCM. This comprehensive study yielded beneficial results for preparing more efficient thermal energy storage systems.