Abstract
Phase change materials (PCM), especially salt hydrates possess high volumetric energy storage capacity in their transition temperature range. These materials are used in applications where it is necessary to store thermal energy due to temporary load shift between demand and availability. Thus, possible applications are HVAC, recovery of waste heat, and defense thermal management. In spite of salt hydrates potential, the practical feasibility of latent heat storage with salt hydrates is limited due to low power rating, supercooling, phase segregation, and long- term stability. Its low power rating and long-term stability limits its application in most applications. This work experimentally validates, the stability and thermal performance of a compact heat exchanger charged with salt hydrate during melting and freezing. The compact heat exchanger was designed with fins on both the Heat Transfer Fluid (HTF) and salt hydrate PCM side. The thermal performance of the Latent Heat Thermal Energy Storage System (LHTESS) were evaluated for various operating conditions. The results show that LHTESS could achieve an average heat transfer coefficient of 124 and 87 W/m2 - K during melting and solidification respectively. The stability of the system in suppressing supercooling were validated over 800 cycles with nucleating agent and active homogenous nucleation techniques. The supercooling was reduced to 3 °C with zinc hydroxyl nitrate as nucleating agent and less than 1 °C with active homogenous nucleation technique. The LHTESS showed less than 5% degradation in energy storage capacity over 800 cycles.