| Inorganic salt hydrates are typical inorganic phase change materials, especially suitable for the temperature range of0-150℃, with such characteristics as abundant resource, easy to obtain, inexpensive price and higher energy storage capacity etc, but due to the disadvantages of supercooling and phase segregation during the process of their utilization, their stability and service life of thermal energy storage are affected. Moreover, in the use of inorganic salt hydrates as phase change materials, since their phase transition temperature usually doesn’t exactly match with the operation temperature of latent heat storage system, it is necessary to be adjusted and controlled, therefore the investigation on the stability and performance of thermal energy storage as well as phase transition temperature adjustment of inorganic salt hydrates has more important practical value.In allusion to the disadvantages of the use of inorganic salt hydrate-Mg(NO3)2·6H2O as a phase change material, by means of the experimental method of measuring with the thermocouples installed in the test tubes, DH3816Temperature Testing Analytical System and the computer with the related software, the comparatively systemic investigation on the stability and performance of thermal energy storage of inorganic salt hydrate-Mg(NO3)2·6H2O was carried out, and the experimental research on phase transition temperature adjustment of inorganic salt hydrate-Mg(NO3)2·6H2O was made by adding excess water. The main contents of the whole investigation are as follows:1. Testing of the main thermophysical property parameters of inorganic salt hydrate-Mg(NO3)2·6H2O sample. By the melting-solidification experiments of Mg(NO3)2·6H2O sample, it was obtained that its phase transition temperature and latent heat capacity are respectively88.67℃and149.99kJ/kg, and its supercooling degree is10.17℃.2. Selection of the additives. Based on the selection method of the additives, MgCl2, MgCl2·6H2O and Ca(NO3)2·4H2O were initially selected as the additives of Mg(NO3)2·6H2O, the investigation on the improvement situation for the supercooling degree of Mg(NO3)2·6H2O made by the different addition quantity of the three additives, as well as the influence on phase transition temperature and latent heat capacity of Mg(NO3)2·6H2O was carried out, the research results showed that, adding the three additives could reduce supercooling degree, since the additive MgCl2·6H2O could not only make the supercooling of Mg(NO3)2·6H2O reduced effectively, but also the influence on its latent heat capacity was less, MgCl2·6H2O was ultimately selected as the additive of Mg(NO3)2·6H2O, its addition range of the suitable mass fraction is4%-20%, its most suitable addition mass fraction is6%.3. Research on the influence of MgCl2·6H2O for the stability and performance of thermal energy storage of Mg(NO3)2·6H2O. By selecting MgCl2·6H2O as the additive of Mg(NO3)2·6H2O, Mg(NO3)2·6H2O with different mass fractions of MgCl2·6H2O was prepared, afterwards its500cycle melting-solidification experiment was carried out. The research results showed that, for Mg(NO3)2·6H2O added the additive of MgCl2·6H2O with different mass fractions, the supercooling degree and latent heat capacity didn’t change large along with the increase of the circulation cycle number, at the same time the evident phase segregation phenomenon in Mg(NO3)2·6H2O didn’t appear during the whole experiment process, consequently the stability and performance of thermal energy storage of Mg(NO3)2·6H2O with the additive of MgCl2·6H2O were verified.4. Research on phase transition temperature adjustment by adding excess water. Mg(NO3)2·6H2O with the additive of6%MgCl2·6H2O was prepared by adding excess water of different mass fractions, afterwards its phase transition temperatures were measured and its500cycle melting-solidification experiment was carried out. The research results showed that, the method of adding excess water could achieve the purpose of phase transition temperature adjustment of Mg(NO3)2·6H2O, its suitable addition range of the mass fraction of excess water is0-10%, its suitable adjustment range of phase transition temperature is73.29℃-83.15℃.The research work and achievements in this paper can effectively solve the problem of the use of inorganic salt hydrate-Mg(NO3)2·6H2O as a phase change material, which will provide a comparatively reliable experiment evidence and technical foundations for the utilization in the recovery engineering of various industrial afterheat or waste heat. |
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