| The development of human society fairly depends on the energy,and the gradual depletion of energy forces people to explore and use renewable energy.At the same time of "open source","throttling" is also a good way.Energy storage technology is an important way of throttling.This paper focuses on the field of latent heat storage.Latent heat energy storage is to store heat energy through phase change materials,which has the characteristics of flexibility,temperature stability and large heat storage.However,leakage and low thermal conductivity are also problems that need to be solved.In order to solve the problem of leakage and enhance the thermal conductivity of materials,three different composite methods of phase change materials were used to prepare microencapsulated phase change energy storage materials and form-stable phase change energy storage materials.The first chapter introduces the development background and research progress of energy storage technology,including the principle,material type,composite method and selection rules of phase change energy storage.In the second chapter,the preparation process and properties of microcapsulted composite phase change materials with silica as shell and octadecanol as phase change material are presented.The third chapter describes the preparation and properties of two other form-stable phase change materials with different supporting materials.One uses lauric acid as phase change material,graphite foam as the base material and graphite nanosheets as composite material.The other one uses stearic acid as phase change material and high density polyethylene as the base matrix to add carbon fiber.1.Synthesis and properties of microencapsulated phase change materials for thermal energy storageThe investigation on microencapsulated phase change materials has greatly promoted thermal energy storage development.In this work,microencapsulated phase change materials with SAL as the core material and silica as the shell material were successfully prepared by sol–gel method.The chemical structure and crystal phase of SAL,silica and MPCM were measured by FT–IR and XRD.These results indicated that only physical interactions have taken place between SAL and silica.The images of the MPCM observed by SEM demonstrated that the MPCM has a complete spherical and compact shell.The DSC results showed that the best microencapsulated phase change materials is MPCM1.Its melting temperature and latent heat are 55.89 ? and 229.73 k J/kg,respectively.The encapsulation rate reaches up to 90%.The latent heat becomes larger when the proportion of SAL in the MPCM increases.The results of TGA and DTG confirmed that MPCM has good thermal stability over their working range.After 100 thermal cycles,the latent heat and melting temperature of the MPCM1 hardly changed.The thermal conductivity of the MPCM1 during melting state was measured to be 0.1508 W/m.K.Therefore,MPCM1 is found to be a promising candidate for applying in thermal energy storage.2.Synthesis and properties of form-stable phase change materials for thermal energy storageThe composite PCM with GNP have smaller impregnation ratio compared with the composite PCM without GNP.Among the three pore density,the size of 70 PPI has the best impregnation.XRD and FT–IR experiments verified that LA was physically absorbed into the metal foam composites without chemical interaction.The images of the CPCM observed by SEM demonstrated that the additives are well immersed in the iron foam.Among these CPCM,the CPCM1 has the highest solidifying latent heat of 177.82 k J/kg.The solidifying temperature of CPCM1 is 42.39 °C.During the melting process,the S–S phase change has a latent heat of 4.78 k J/kg at 38.63 °C while S–L phase change has a latent heat of 177.88 k J/kg at44.36 °C.Compared with the LA,the melting temperature of the CPCM has a slight increase,and the solidifying temperature of the CPCM has also a slight increase.In addition,the greater the pore size of the iron foam,the greater latent heat of the CPCM.The results of TGA and DTG confirmed that the CPCM maintain good thermal stability.The thermal conductivity of the CPCM has an obvious enhancement.The smaller pore size can lead to higher thermal conductivity.The GNP can also improve thermal conductivity effectively.The thermal conductivity of CPCM6 can reach 1.227 W/(m·k),which is increased by 10.67 times compared to that of the LA.In this investigation,the SA/HDPE/CF composites were synthesized as composite phase change materials for heat storage.The SA played a role of phase change material in the CPCM,which absorbs and releases latent heat.The HDPE was performed as matrix materials to reduce leakage of the PCM.The addition of the CF made the structure of the CPCM closer to keep the SA away from separating with the CPCM and improved thermal conductivity of the CPCM.From the results of FT–IR,XRD and SEM,it can be found that the SA has no chemical interaction with the HDPE which was uniformly embedded in the HDPE.The hybrid of the SA,HDPE and CF was combined physically and the crystal structure of the CPCM kept constant.According to the data of DSC,the CPCM6 melts at 68.48 ? and the latent heat is 140.17 k J/kg,and solidifies at 66.95 ? and the latent heat is 141.09 k J/kg.The DTG and TGA curves showed that the CPCM has two decomposition processes and attains better thermal stability at the operating temperature.Thermal conductivity of the CPCM6 is 0.4043 W/m?K,and its value is 2.22 times higher than that of the SA.The HDPE can prevent leakage of the SA in the CPCM,and the CF can effectively enhance thermal conductivity of the CPCM.Therefore,the CPCM6 possesses good thermal properties and is potential in heat storage fields. |
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