Reduction of the supercooling of Ca(NO3)2•4H2O using electric field and nucleating agent effects

Abstract The performance of thermal energy storage systems with Ca(NO3)2•4H2O (abbreviated as CaNT) as a phase change material is limited by its complex thermal properties and relatively large degree of supercooling. In this study, we demonstrate active and passive methods to reduce the degree of supercooling via the addition of electrical energy and nucleating agents. The degree of supercooling decreases almost linearly with an increase in the electric field intensity, whereas the crystallisation period shows the opposite trend. Twelve types of nucleating agents were chosen based on the Edisonian method, and the effectiveness of each agent was tested by adding 1 wt% of nucleating agent to CaNT. The effect of the nucleating agent is clearly observed in the variation in the freezing temperature. We found that carbonate anions and earth alkali cations were the most suitable, and the best results were obtained for the BaCO3 nucleating agent. It showed the smallest degree of supercooling and standard deviation value. The TG/DTA curves indicate that careful heat treatment is essential for the nucleation of CaNTs. Both the electric field and nucleating agent contribute to heterogeneous nucleation, and in this case, the application of an electric field leads to a flow of current and the formation of complex compounds. The analysis of the FT-IR spectra revealed different roles and the mechanisms of the electric field and nucleating agent in inducing the nucleation of CaNTs.