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Latent heat thermal energy storage (LHTES) systems and their applications have been very substantive for the developments in energy science and engineering. The efficiency of LHTES systems largely depends on the thermal conductivity of the phase change materials (PCMs) and the heat transfer mechanisms in them. This review focuses on the methods employed to enhance heat transfer in LHTES systems which accordingly improve their storage performance. This includes the possible geometrical configurations of LHTES systems and the effects of their design parameters. The various methods adopted for enhancing LHTES systems' performance through either applying nanomaterials additives, using cascaded or encapsulated PCMs, or employing extended surfaces, such as fins, are discussed in detail. Additionally, various designs of PCM based heat exchangers with active and passive heat transfer techniques were highlighted. These systems are critically analyzed to help selecting reliable techniques and compatible materials for effective designs in order to achieve more efficient LHTES systems. This review would be helpful for the researchers to further develop heat transfer intensification mechanisms in LHTES systems.

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This study presents the numerical investigation of the performance improvement of Metal Hydride (MH) bed equipped with nano-enhanced phase change material (NePCM) jacket for heat reaction recovery via U-tube heat exchanger using Nanofluid. In this study, Mg 2 NiH 6 is used as an MH bed, sodium nitrate (NaNO₃) as heat storage medium (PCM), and sodium-potassium nitrate (60% NaNO₃-40% KNO₃) as a heat transfer fluid (HTF). A computational model for this system is developed and validated. Furthermore, the hydriding of the MH bed, the melting of NePCM, and the overall heat transfer characteristics are simulated. With this model, the effect of a few types of nanoparticle additives on the hydriding process is investigated. The nanoparticles of iron oxide (Fe 2 O 3) and copper oxide (CuO) are dispersed at various concentrations (to a range of 0-1.5 wt.%) in the HTF. Further, CuO and graphene nanoparticles are added to the PCM to a range of 0 to 5 wt.%. The simulation shows that a reduction of hydriding process time by 33.5% is possible by using this MH-Nanofluid-NePCM system in comparison with a conventional MH bed system. The use of nanoparticles in the HTF, at an optimum flow rate, did not show a significant effect on the enhancement of the hydriding process. Also, the results show that CuO-PCM composite has a greater impact in decreasing the time of complete hydriding relative to graphene-PCM composite.