Critical crystallisation issue in sodium acetate-based latent heat accumulation substance

The phenomenon of self-crystallisation is scarcely discussed in the context of phase-change materials. However, energy accumulation in supercooled substances can play a significant role and negatively impact long-term energy storage. This paper shows a spontaneous self-crystallisation without external initiation of the sodium acetate trihydrate water solution in several temperature environments (–24 to +21 °C) and different added water contents (0 to 14 %wt.). The tabilised composition of the phase change solution was determined for each observed temperature environment, and the crystallisation rate was defined. Moreover, a novel approach for determining the density function of such a crystalline structure was successfully investigated for this metastable material. It was found that even the substances with 6 %wt. of water, generally considered stable, crystallises at room temperature if the initiation-free heating cycles are performed several times, which has not been observed before. The crystalline layer characteristics and density varied significantly in different temperature environments. These findings will help design and evaluate future thermal energy storage systems based on SAT with respect to the self-crystallisation phenomenon, providing new knowledge to the state- of- the- art.