Abstract
The big challenge of utilizing intermittent renewable energy sources is the time lag between the energy source and energy demand. The storage of energy forms a suitable solution for this challenge. The phase change materials (PCMs) can be used effectively to store a large amount of latent heat during the phase-change process. However, these PCMs suffer from their low thermal conductivity. The augmentation of the effective thermal conductivity of PCMs by introducing thermal conductivity enhancers is considered a promising tool for obtaining a more efficient thermal energy storage system during melting and solidification processes. The present paper introduced a review of the experimental, computational and analytical studies related to the solidification of nano-enhanced phase change materials (NePCM) in various common containers utilized for thermal energy storage like planar, spherical, annular and cylindrical enclosures. The influences of dispersed nanoparticles concentration and geometrical and operating conditions such as wall waviness, thermal radiation, magnetic field, temperature, and flow rate of heat transfer fluid (HTF) are assessed. Dispersing the nanoparticles in PCM promotes the rate of transmitted heat from the NePCM into the heat sink. Therefore, the NePCM has a higher solidification rate and lower freezing time than that of pure PCM. On the other hand, the introduction of nanoparticles decreases the stored energy within NePCM. In addition, applying waviness on the container's wall, reducing the HTF temperature and increasing the HTF flow rate enhance the freezing characteristics. Moreover, it is recommended to disperse nanoparticles in small concentrations to compromise the enhancement in thermal conductivity and solidification performance of NePCM in hand, and the decrease in energy storage capacity and the possibility of nanoparticle sedimentation on the other hand.