Preparation And Property Study Of Expanded Graphite-based Hydrated Salt Phase Change Energy Storage Materials

In this paper,the eutectic points of the two hydrated salts of Na2CO3·10H2O and Na2HPO4·12H2O have been explored,and the phase change materials of binary eutectic hydrated salt compounds have been prepared,and the heat storage performance has been studied.For the leakage problem in the process,expanded graphite was encapsulated,and the heat storage performance of the encapsulated composite phase change material and the mechanism of the effect of expanded graphite pore structure on the binary eutectic hydrated salt were studied,and the research was carried out on a laboratory scale.The expanded graphite was modified,and the metal organic framework materials ZIF-67 and ZIF-8 were grown in situ on the surface of the expanded graphite.The modified expanded graphite-based composite phase change energy storage material was prepared and its thermal properties were studied.The eutectic binary hydrated salt phase change energy storage material is prepared by the melt-blending method.The binary hydrated salt is obtained by mixing Na2CO3·10H2O and Na2HPO4·12H2O with different mass ratios.The experimental test results show that only when the mass ratio of Na2CO3·10H2O and Na2HPO4·12H2O is 4:6,and it is a transparent liquid state in the molten state,the DSC test result of the binary hydrated salt shows an endothermic peak,indicating that the eutectic point is reached at this time.The eutectic binary hydrated salt phase change energy storage [1] material SD has no phase separation phenomenon.The latent heat of SD is as high as239.4J/g,the phase change temperature is 24.2°C,and the degree of subcooling is 5.7°C.Compared with a single hydrated salt,SD has no phase separation phenomenon,and the degree of subcooling is much lower than that of the two single hydrated salts.The experimental results prove that this eutectic hydrated salt SD has excellent performance and is very useful and practical in life application.The expanded graphite-based binary eutectic hydrated salt composite phase change energy storage materials with different encapsulation ratios were prepared by physical steeping.The shape stability test found that the maximum encapsulated volume of expanded graphite was 85%.The SD/E material has good shape stability and can effectively solve the leakage problem of the hydrated salt during the phase change process.The latent heat of phase transition of SD/E is196.2J/g,the phase transition temperature is 23.5°C,the supercooling degree of the binary eutectic hydrated salt is reduced from 5.7°C to 0.8°C.EG provides more nucleation sites for the hydrated salt,which greatly increases the nucleation rate,thereby reducing the degree of supercooling.The excellent gain performance of expanded graphite improves the thermal conductivity from 0.82W/(m·K)to 2.37 W/(m·K).This shows that the stereotyped composite phase change energy storage material we prepared has excellent heat storage performance.The expanded graphitebased binary eutectic hydrated salt phase change material is pressed into a plate shape,and a layer of magnesium cement slurry is wrapped on the outside.After the slurry is dry,a plank with a "sandwich" structure is obtained.The experimental test results show that when the temperature raised,the indoor temperature with a phase change material cement interlayer is 2.1°C lower than that of pure cement,and when the temperature reduced,the indoor temperature of a phase change material interlayer is 1.5° higher than that of pure cement.This shows that the phase change material can reduce the influence of the external environment on the indoor temperature through the transformation of the thermal energy,so as to achieve the effect of heat insulation.The metal-organic framework ZIF-67 and ZIF-8 were loaded on the surface of EG in situ,respectively,and expanded graphite was modified to obtain ZIF-67@EG and ZIF-8@EG,which packaged SD binary eutectic hydrated salt compound.The chemical composition test results show that the metal organic framework materials ZIF-67 and ZIF-8 have successfully grown in situ on the surface of the pore structure of EG.The phase transition temperature of SD/ZIF-67@EG and SD/ZIF-8 @EG composite phase change energy storage materials are respectively,the latent heat of phase change is respectively,and the encapsulation rate is respectively.This shows that the metal organic framework covers a certain pore space.-67 and ZIF-8 can further increase the thermal conductivity of composite phase change materials,the conversion of SD/ZIF-67@ EG,and the increase rate of SD/ZIF-8@EG.The chemical composition analysis shows that SD/ZIF-67@EG and SD/ZIF-8@EG composite phase change energy storage materials have better chemical stability.