Heat storage medium of moistened Na.sub.2 HPO.sub.4.12H.sub.2 0 and method of a preparation thereof

摘要

Na.sub.2 HPO.sub.4.12H.sub.2 O is prevented from deteriorating as a heat storage medium after repeated cycles of heat storage and heat withdrawal resulting from precipitation of dehydrated forms of the salt by mixing thoroughly into the dodecahydrate material a small water content up to 5% of the mixture by weight, after which the material is heated above the melting point of the dodecahydrate and then cooled in a gas-tight container. Between 0.1 and 2% by weight of urea, and most preferably about 0.7% by weight thereof, may also be incorporated into the mixture, as by first dissolving the urea into the water to be added, in order to reduce the thermal expansion coefficient of the heat storage medium. Unlike disodium hydrogen phosphate dodecahydrate with stoichiometric hydration, the heat storage medium with the above- mentioned additions fully retains its phase reversibility after many heat cycles and makes available the highly suitable temperature of phase change and large magnitude of latent heat of the material for practical solar heating, heat pump, and air-conditioning systems.