Abstract
The mass and cooling-rate dependences of degree of supercooling was evaluated for disodium hydrogenphosphate dodecahydrate, which is used in long-term, supercooled thermal energy storage (Super-TES). Super-TES stores thermal energy at temperatures lower than the melting point of the phase-change material, which reduces heat loss from the storage system. From the theoretical analysis for homoge-neous nucleation, the degree of supercooling is dependent on the mass of the material and independent of the cooling rate of the material. From the results of the experi-ments, we found that the degree of supercooling of the hydrate decreases monotonically with increasing mass. The measured degree of supercooling is about one half of that calculated by the homogeneous theory, which indicates that the crystallization of the hydrate in Super-TES is initiated not by homogeneous nucleation but by heterogeneous one. We also found that the degree of supercooling increases monotonically with increasing cooling rate of the hydrate because of the time lag of heat transfer in the hydrate. For practical condition in Super-TES, however, the influence of the cooling rate is negligible.
