Cold thermal energy storage by encapsulated phase change materials system using hybrid nanofluids as the heat transfer fluid

Abstract

The comprehensive study of the cascaded latent heat thermal energy storage (LHTES) systems and usage of phase change materials (PCM) are of great interest in the literature. Experimental and numerical measurements have been performed to analyze the performance of LHTES systems employing different PCMs. Overcharging is a known obstacle in the way of deploying a cascaded energy storage system that reduces the stored energy quality and amount. Furthermore, the complicated character of the phase transition of materials conjures up the importance of an accurate model. In the current study, the effects of overcharging a three-stage cascaded cold LHTES through a concentric dispersion model had been analyzed. Three nanoparticles, Al2O3, CuO, and Fe3O4, in the ethylene glycol and water (EG/W) mixture selected as the heat transfer fluid. Also, three eutectic and hydrated salt solutions were chosen as three PCM materials, encapsulated in spherical high density polyethylene shells, and arranged in three stages, namely, PCM-1, PCM-2, and PCM-3, storing high grade, medium grade, and low grade thermal energy, respectively. To overcome the overcharging issue of the system, two different scenarios were introduced. Results indicate that Al2O3, CuO, and Fe3O4 nanoparticles in the EG/W mixture reach their highest charging efficiency at 74.8%, 69.1%, and 75.1%, respectively. Results also revealed that to reach a shorter overcharging time utilizing Al2O3 and CuO nanoparticles, the optimized ratio of the PCM-2 to PCM-1 and PCM-3 to PCM-1 capacity were both 0.55. The optimized ratio of the PCM-2 to PCM-1 and PCM-3 to PCM-1 capacity utilizing Fe3O4 nanoparticles were 0.68 and 0.61, respectively. To maintain the highest charging thermal efficiency, the optimized ratio of the PCM-2 to PCM-1 and PCM-3 to PCM-1 heat capacity was 0.55 for all the three nanofluids.