Preparations And Physicochemical Properties Of The Middle Temperature Aluminum-based Phase Change Materials

Phase change materials (PCMs) absorb or release thermal energy in the process of phase change and the temperature of the process of crystallizing nearly constant. Hence, PCMs can resolve the imbalance of energy supply and consumption in the time and space. Middle temperature PCMs (60～80℃) were widely used in practical application but the properties of development value of the middle temperature PCMs are few at present. Hence, it’s important to research and develop the middle temperature PCMs.The main purpose of this thesis is to develop1-2kinds of solar energy storage insulation materials with good performance, practical value, appropriate phase change temperature (60～80℃), high volumetric storage density and thermal conductivity etc. SAL and NAL have large heat fusion, low-costs and high melting temperature. According to the selective principle of solar energy storage insulation materials, we selected SAL and NAL as major raw materials, and adding improver to modulate the melting point. We analyzed and studied the phase change temperature, latent heat, supercooling and thermal stability, and the diagrams of step cooling, DSC and thermal stability were also given.Using sulfate (magnesium sulfate and ammonium sulfate) and distilled water to decrease the phase change temperature of SAL, maintaining molar ratio of SAL and magnesium sulfate was1:1to prepare a series of mixture samples with different ratios of ammonium sulfate, and distilled water. Based on the experimental results, the sample had the best thermal storage properties when the percentage of ammonium sulfate and water was16.8%and15.9%. The physicochemical properties of the phase change temperature, supercooling degree and latent heat of this PCM without the phenomenon of phase separation were69℃,2-4℃and206.2J/g. The maximum deviation of the freezing point and the latent heat of the composite were21.5%and 2.1%, respectively, and the most freezing point temperature was between68.5℃and71℃through50times of melting-crystallizing heat recycle tests.Using aluminum sulfate and distilled water to decrease the phase change temperature of SAL, preparing a series of mixture samples with different ratios of aluminum sulfate, NAL and distilled water. Based on the experimental results, the sample had the best thermal storage properties when the percentage of aluminum sulfate and water were18.2%and9.1%, respectively. Phase change temperature and latent heat of the PCM synthesised without phenomenon of phase separation and supercooling were70℃and213.6J/g, respectively. The maximum deviation of the freezing point and the latent heat of the composite were2.8%and5.2%,respectively, and most freezing point temperature was between69℃and71℃, through50times of melting-crystallizing heat recycle tests.