Theoretical And Experimental Study On Room-temperature Phase Change Materials Using Hydrated Salts As Agents

The demand of people about the energy sources is increasing with the development of the society and the improvement of standard of living. But at the same time, the ratio of making use of the energy sources is not so high and the provision of the energy sources is more and more difficult, as well as the protection of the environment. Studying and then exploiting the energy sources which can make full use of the heat resources in the low temperature, in the recent time, become the crucial approach to resolve the problem of provision intension of the energy sources. As a kind of quite important material of building which can saving energy effectively, the advantages of phase change materials of energy storage in the room-temperature include the full use of the heat resources and the heat energy in the low temperature, the large density of energy storage, the high enthalpy of phase change, the low cost and etc. Whereas, the inorganic phase change materials of energy storage whose melting point are between 15℃-25℃, which have been discovered presently, are rare and costly. So, whether the exploiture of the lower cost, safer (no hidden trouble) and more excellent phase change materials of energy storage which are in the room-temperature is possible, become the key of the process in which the phase change materials of energy storage in the room-temperature are applied in practice. The existing"prescription"(adding reagents step by step) model used as a method of finding energy storage materials, however, is so expending time and pelf that it is barely applied in practice. Therefore, in our study, the calculation about the phase diagram of multi-component salt-water system whose cost is low and density of energy storage is also large, is carried out with the thermodynamics model to find the new phase change materials of energy storage in the room-temperature whose phase change temperature are between 15℃-25℃. The central work as follows:1) The current situation of thermodynamic model in research and application fields is evaluated, and a reliable thermodynamic model——BET model is selected to predict room-temperature phase change materials in theory, then this model is assumed and deducted theoretically again and its scope of application is also expanded.2) According to the results of theoretical research about the model, we compile the program which is used to simulate the parameters and predict the phase diagram. 3) By combining the simulated model parameters of NH₄NO₃ with the known model parameters of LiNO₃,Mg(NO₃)₂ and NaNO₃, the poly-thermal solubility phase diagram of ternary LiNO₃-NH₄NO₃-H₂O, LiNO₃-Mg(NO₃)₂-H₂O, LiNO₃- NaNO₃-H₂O systems and quaternary LiNO₃-Mg(NO₃)₂-NaNO₃-H₂O system is predicted, and the eutectic points whose phase change temperature is between 15℃-25℃, which may exist in those above systems, is discovered.4) The properties of hydrated salts materials, whose predicted phase change temperature is between 15℃-25℃, is tested according to the results of theory prediction. The cooling curve, heating curve and other curves of these materials is also tested.By the phase diagram prediction with the BET model about multi-component salt-water system which includes the lithium salt or magnesium salt, a eutectic point, whose phase change temperature is 16℃, is found out exist in the ternary LiNO₃-NH₄NO₃-H₂O system, and its composing is: LiNO₃·3H₂O: 66.17 wt.%, NH₄NO₃: 33.83 wt.%. A eutectic point whose phase change temperature is 24.25℃is also found out exist in the quaternary LiNO₃-Mg(NO₃)₂-NaNO₃-H₂O system and its composing is: LiNO₃·3H₂O: 67.4 wt.%, Mg(NO₃)₂·6H₂O: 26.9 wt.%, NaNO₃: 5.7 wt.%. By properties test about the above two materials, we can say, the eutectic point in this percentage of each species can fit the requirements of phase change materials of energy storage in the room-temperature. And by the experimental research, two phase change materials of energy storage in the room-temperature are found in the LiNO₃-KNO₃-H₂O and LiNO₃-Mg(NO₃)₂-KNO₃-H₂O systems.In this paper, by the theoretical prediction and experimental validation, four new phase change materials of energy storage in the room-temperature, which are never been reported by any literature in the world and which possess independent intellectual property rights in our country, are obtained successfully.