Study On The Effects Of Cooling Rate And Additives On Supercooling Degrees Of Hydrated Salts

With the rapid development of economy and the constant growth of population, the demand for energy sources is on the increase each year. Beause of the limited traditional energy workable reserves, renewable energy sourses such as solar energy will replace the traditional energy gradually. The solar radiation changes along with the different area and times, so it is always difficult to keep the balance of the demand and supply of solar energy. In order to use the solar energy more wisely, it is necessary to store it. Due to their advantages such as appropriate phase-transition temperature, larger phase change latent heat and higher heat storage density, the inorganic hydrated salts have become the most common heat storage materials in the solar utilization system. The supercooling phenomenon of the hydrated salts materials are easy to occur during use, and the supercooling can impact on material’s heat storage performance.The effects of cooling rate,nucleating agents’adding mass and crystal structure on the supercooling degrees of inorganic hydrated salts CH3COONa-3H2O and Na2HPO4·12H2O were investigated with gradually cooling method. And the supercooling performances of the eutectic mixtures were researched. This kind of mixtures were made by adding another hydrated salt to CH3COONa·3H2O and Na2HPO4·12H2O respectively.The way of changing the cooling rate of hydrated salts system was to change one of the constant temperature and the cooling environment temperature and keep the other unchanged in the experiment. The results show that, the lower cooling environment temperature made the cooling rate greater when the constant temperature stayed the same. At the same time, the supercooling degrees of pure CH3COONa·3H2O sample and nucleating agents-CH3COONa·3H2O composites became bigger. When there was no change of the cooling environment temperature, only the pure CH3COONa·3H2O sample that its constant temperature was65℃appeared crystallization phenomenon in the process of cooling to20℃.Four different kinds of nucleating agents were added to Na2HPO4·12H2O and CH3COONa·3H2O, and the adding mass of every nucleating agent respectively were0.05g,0.10g,0.15g,0.20g,0.30g and0.40g. The results prove that:the adding mass is an appropriate range in order to improve supercooling effectively. Four kinds of nucleating agents have different levels of improvement effect to reduce the supercooling phenomenon of Na2HPO4·V12H2O and CH3COONa·3H2O. The kind of nucleating agent is better at reducing the supercooling than others in several selected nucleating agents, if one of its lattice parameters was much closer to hydrated salts’.The mixtures were prepared by mixing Na2HPO4·12H2O or CH3COONa·3H2O with another hydrated salt in various mass ratio.The mixtures were conducted melting-solidification experiment. The experimental results show that:if the mixture crystallized during the cooling process, its phase change temperature was lower than the two original hydrated salt materials’melting points, and its supercooling degrees also reduced.