| With the advancement of science and technology and the continuous improvement of the industrial level,the consumption of energy is increasing.As a result,the problems,such as environmental pollution,greenhouse effect and so on,become increasingly prominent.In the new era of economic transformation and energy development,people's awareness and ideas of environmental protection,as well as material demand,have been gradually raised.It is urgent to optimize the energy structure and seek new energy sources,which are green,efficient,environmentally friendly and low energy consumption.Phase change heat storage technology is the storage and release of heat with the absorption and release of latent heat during the process of material state change.It can solve the supply and demand contradiction of thermal energy in time and space effectively,and relieve the pressure of energy shortage.It is a new and efficient green energy technology to meet the needs of the development of the times.The crystalline hydrated salt is a kind of representative medium and low temperature phase change heat storage material.It has the advantages of high latent heat of fusion,high density of energy storage,stable performance and low price.Compared with organic phase change heat storage materials,it has higher thermal conductivity and nonflammabilityThis article takes phase change material?PCM?ammonium aluminum sulfate dodecahydrate?NH4Al?SO4?2·12H2O?as the object of study.It is a stable crystalline hydrated salt,namely,the melting process is the same element melting,and there is no phase separation phenomenon.It can be widely used in industrial waste heat recovery,industrial and agricultural thermal utilization,building wall fireproof material and other fields.It is an ideal phase change heat storage material with great value for development and application.At present,there are few studies on NH4Al?SO4?2·12H2O phase change material,some of the basic application problems have not been solved,which hinders the application development of it.On the basis of experiments and combined with application requirements,this article mainly researches the thermal conductivity and undercooling of NH4Al?SO4?2·12H2O.Firstly,the basic heat storage performance of NH4Al?SO4?2·12H2O is tested.The thermal conductivity of pure NH4Al?SO4?2·12H2O is 0.599 W/m·k.By the heating-cooling cycle experiment,the phase change storage time of pure NH4Al?SO4?2·12H2O is 2573 s,and the undercooling degree is 42.7?.The differential scanning calorimetry?DSC?measurements show that the phase transition point of NH4Al?SO4?2·12H2O is 93.7?and the latent heat is269.49 J/g,which is consistent with the description in the literature.On this basis,the effects of different materials on the thermal conductivity and undercooling of NH4Al?SO4?2·12H2O are compared.It is concluded that graphene nanoplatelets and CaCl2·2H2O are the excellent materials to improve the thermal conductivity and undercooling of NH4Al?SO4?2·12H2O.The microstructure of NH4Al?SO4?2·12H2O composite phase change materials was analyzed by scanning electron microscope?SEM?and Micro Raman spectrometer.The results show that graphene nanoplatelets and CaCl2·2H2O can tightly combined with NH4Al?SO4?2·12H2O matrix and have good dispersibility.X-ray diffractometry?XRD?analysis shows that graphene nanoplatelets and CaCl2·2H2O can promote the heterogeneous nucleation of NH4Al?SO4?2·12H2O,and the crystal structure of NH4Al?SO4?2·12H2O before and after compositing is almost unchanged.They are just simple physical compounds,and do not affect the phase transition process of NH4Al?SO4?2·12H2O.After many groups of heating-cooling cycle experiments and comparing test results,it is finally determined that NH4Al?SO4?2·12H2O+1 wt%CaCl2·2H2O+2.5 wt%graphene nanoplatelets are the best compound formulas.It has the best heat conduction effect.The phase change storage time is stable at about 1892 s,which is 26.4%higher than that of pure NH4Al?SO4?2·12H2O.The undercooling degree is stable at about 24.43?,which is 42.7%lower than that of pure NH4Al?SO4?2·12H2O.The thermal conductivity and undercooling of the modified NH4Al?SO4?2·12H2O phase change materials have been greatly improved.It is of great significance for its further application research and popularization of production. |
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