Long-term supercooled thermal energy storage (thermophysical properties of disodium hydrogenphosphate 12H2O)

This work aims at developing long-term latent heat storage using supercooling. Compared with conventional thermal energy storage systems, supercooled thermal energy storage (Super-TES) can store thermal energy at rather lower temperatures, below the melting point of the phase change material, so that Super-TES can reduce heat loss from the storage system. Although the supercooling degree depends not only on the material itself but also on such conditions of the material as volume, there is not enough information on the supercooling phenomenon, except for distilled water. In this paper, as one of the promising materials for Super-TES, the thermophysical properties of disodium hydrogenphosphate 12H₂O are investigated in detail. Density, specific heat, thermal conductivity, and coefficient of viscosity of this hydrate are shown as a function of temperature. Density and viscosity in the liquid phase decreases monotonously as the temperature of the hydrate rises. Specific heat in the liquid phase and thermal conductivity in the solid phase were observed twice as large as the values in literature references. The results reveal the hydrate is more useful not only to use latent heat of the hydrate but also to use sensible heat effectively, to reduce the heat loss from the storage material, and to exchange heat between the hydrate and heat source efficiently