Experimental results for phase transition during extended thermal cycling of the salt hydrate LiNO 3 •3H 2 O in both heterogeneous nucleation and self-seeding as well as material compatibility are presented. Controlled samples of this phasechange material (PCM) are heated and cooled between 20 and 40 °C. This was carried out for 1000 thermal cycles to ascertain the long-term suppression of subcooling without degradation in latent heat (h sf ). In heterogeneous nucleation, two additives were considered, Zn 3 OH 4 (NO 3 ) 2 , and Zn(NO 3 ) 2 •6H 2 O, whereas the self-seeding was induced by less than complete (90%) melting. The two nucleating agents were selected by the minimal latticemismatch method for salt crystals. Self-seeding was found to completely suppress subcooling without any loss in the latent heat of fusion, whereas heterogeneous nucleation with additives resulted in a subcooling of ΔT s > 3 °C and an up to 8−52% loss in latent heat after 1000 thermal cycles. Additionally, the material compatibility test was conducted with Al 3003, Al 1100, and SS 304 for 4000 heating−cooling cycles. The corrosion rates observed without nucleating agents were insignificant and less than typically observed in similar metals exposed to marine conditions.

Salt hydrate based Phase-Change Materials (PCM) typically store and discharge large quantities of heat during their phase transition process. However, the repeated use of these PCM, especially when they are completely dehydrated and superheated in a cyclic process, is impeded by certain irreversible behavior. These include (1) phase segregation: where the PCM degrades to forms a lower hydrate during phase transition while losing its storage capacity, and (2) subcooling: when crystallization and rehydration from the liquid PCM state occurs at a temperature lower than their phase transition point. Higher degrees of subcooling (ΔTs), which is how much the PCM has to be super cooled below its phase transition temperature for crystallization to begin, adversely affects its performance and in some cases renders it ineffective. Lithium Nitrate Trihydrate [(LNT) LiNO3.3H2O] is one of the more promising candidate among these inorganic salt hydrate PCMs because of its rather stable phase change behavior and relatively very high latent heat capacity (282kJ/kg). Nevertheless, when completely in superheated liquid phase, it requires a high degree of subcooling (ΔTs > 20°C), which limits its utility. This study reports a novel nucleating agent — Zinc Nitrate Hexahydrate (ZNH) that reduces the subcooling to below 5°C (1000 Cycles). However, the latent heat capacity reduced to half the initial value after the cycling.