Growth rate of crystallization in disodium hydrogenphosphate dodecahydrate

The solidification process of disodium hydrogenphosphate dodecahydrate was investigated to develop long-term latent heat storage that uses supercooling. Supercooled thermal energy storage (Super-TES) stores thermal energy at temperatures lower than the melting point of the phase-change material (PCM), thus reducing the heat loss from the storage system. During nucleation and solidification, the temperature of PCM is not constant in Super-TES. The solidification process in Super-TES, therefore, influences the performance of the storage system because thermal properties of PCM, strongly depend on the temperature and phase of the material. The results show that the growth rate of the hydrate increased with increasing degree of supercooling and that this growth rate was slow compared with that of metals. When the degree of supercooling was less than about 10 K, the crystal of the hydrate grew like a single crystal, and the growth rate was approximately proportional to the third power of the degree of supercooling. Because the viscosity of the hydrate in the liquid, phase below the melting point increased drastically, when the degree of supercooling exceeded about 10 K, the crystal grew like a dendritic crystal, and the increase in the growth rate with increasing degree of supercooling, decreased.