Phase-Transition Efficacy and Material Compatibility with Thermal Cycling of Lithium Nitrate Trihydrate as a Phase-Change Material

Abstract

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.