Hydrated Salt Storage Material Properties

Phase change materials (PCMs) can store energy and discharge energy by phase transition of PCMs, which is called latent heat storage. So latent heat storage can overcome the mismatch between energy demand and energy supply. PCMs have the advantages of higher storage density, and smaller temperature difference between storing and releasing heat,and easly controlled, etc.Hydrated salts usually have phase transition temperature range in middle-term period usage. They are attractive materials for use in thermal energy storage due to their high volumetric storage density, relatively high thermal conductivity and moderate costs. They have become a main topic in recent 20 years research, and about 45 commercially available PCMs have been applied in the field of solar energy storage,building heating,commodity and so on. But most of hydrated salts have ploblems of phase segregation and supercooling, decline in the stability of thermal cycling. Hence, adding thickening agents and nucleating in hydrated salts are efficient to minish phase segregation and supercooling, and they are also economical methods.Nucleating tests of ammonium alum were studied in this paper. 1.75wt% CaF₂ and 0.25wt% carbon is the most efficientive nucleating agents ,which can reduce the supercooling of ammonium alum nearly to 7-10℃.The latent heat and melting point of ammonium alum were determined by differential scanning calorimetry (DSC) technique after repeated thermal cycles. The components and microstructure of ammonium alum are researched in detail by X-ray powder diffraction examination. Crystalline water content of ammonium alum was determined by EDTA (back) titration of the aluminum ion contents. Several reasons for the reduction in thermal stability were analysed.Container of ammonium alum is necessary as heat storing and discharge of ammonium alum are provided through solid-liquid phase transition. Corrosion resistance of four common metals and two plastics which are on contact with two kinds of molten ammonium alum had been studied. Immersion corrosion tests have...