Optimization And Application Of Sodium Acetate Trihydrate And Disodium Hydrogen Phosphate Dodecahydrate Based Composites

Solar energy has a series of advantages such as being green,pollution-free,inexhaustible,and easily available,but it also has problems such as discontinuities and low utilization due to weather changes.Therefore,in this paper,through research and improvement of inorganic hydrated salt phase change heat storage materials,solar energy is stored and reused in the form of thermal energy in order to improve the utilization rate of solar energy.Aiming at the problems of subcooling and phase separation of hydrated salt phase change materials,this paper uses melting method to obtain disodium hydrogen phosphate dodecahydrate-based composite phase change heat storage materials in order to solve the problems of subcooling and phase separation.And the disodium hydrogen phosphate dodeca-based composite phase change thermal storage material was applied to solar hot water system,and the solar energy was stored in the form of thermal energy to study the thermal conversion efficiency of phase change thermal storage material on solar hot water system effect.The main findings are as follows:1. Solve the problems of subcooling and phase separation in pure CH₃COONa·3H₂O. In this paper,Na₂HPO₄·12H₂O is mixed with CH₃COONa·3H₂O,and the phase characteristics under different mass ratios are studied.The optimal phase ratio B₃（CH₃COONa·3H₂O:Na₂HPO₄·12H₂O=1.5:8.5）composite phase change thermal storage material is obtained.The supercooling degree of B₃composite phase change heat storage material is 0.3℃,the heat release platform lasts 1220s,the heat release process is stable,and the endothermic value is 1357.1k J/kg.2. Analysis of cold-heat cycle stability of B₃composite phase change thermal storage material.Aiming at the problem of the increase of the subcooling degree after the B₃composite phase change heat storage material undergoes 150 cold-heat cycles,different mass proportions of Na₂Si O₃·5H₂O,Na₄P₂O₇·10H₂O,Na₂B₄O₇·10H₂O were added to the B₃composite phase change heat storage material after 150 cycles for improvement.The experimental results show that the B₃composite phase change heat storage material has the best improvement by adding1.5%nucleating agent Na₂Si O₃·5H₂O,which is called C material.The subcooling temperature is 0.5℃,the heat release temperature of the platform is about 51.2℃,and the heat release can reach 1130s.After the C composite heat storage material is circulated 200times,the material solidifies-melts stably,the degree of subcooling is controlled within 1.2℃,and the maximum exothermic temperature is about 51℃,which is maintained for about1100s.3. Application test of phase change heat storage material.The Na₂HPO₄·12H₂O-Na₂SO₄·10H₂O composite phase change thermal storage material is applied and tested in a solar hot water system.When the average ambient temperature is below zero,the water temperature of the water tank in the solar hot water system can meet the phase change thermal storage material phase.The melting temperature requirements require more than 90%of the thermal storage material to melt.The intensity of solar radiation is the determining factor for the increase in water temperature.The higher the intensity of solar radiation,the shorter the delay time between the water of the water tank and the collector outlet water,and the faster the temperature increase.Increasing the thermal storage material in the solar hot water system can improve the light-to-heat conversion efficiency of the solar hot-water system.The light-to-heat conversion efficiency in Yijun area reaches about 66.4%.