Research On The Structure And Properties Of Porous Matrix Composite Phase Change Materials

With the serious global energy consumption,energy conservation and environmental protection have become the general trend of the whole society,especially in the field of industrial development.If the waste heat in the industry can be reused,it will greatly reduce the loss of fuel.Similarly,if the heat of solar energy can be applied to people’s daily life,it will greatly protect the environment.In this regard,the porous matrix composite phase change material can meet the requirements.In this thesis,a composite phase change material with excellent properties was prepared by using expanded graphite（EG）as a matrix and filling it with fatty acids or crystalline hydrated salts with high latent heat value.The specific research contents are as follows:1.Using the method of melt blending,the pure substances PA,MA,SA,PW are heated and melted,and mixed according to a certain proportion to prepare the multi-component composite phase change material.Firstly,the proportions of multi-component composite phase change materials were calculated and predicted by the multi-element eutectic theory,and verified each other through experiments.Secondly,the mixture phase was analyzed by DSC,FT-IR,XRD,step cooling curve experiment,heat storage and release cycle experiment and other research methods.The change characteristics and thermal stability were analyzed,and finally the optimal ratio of PA-MA-SA was 3:5:2.At the optimal ratio,the melting point was 42.31°C,the latent heat of fusion was 170.65J/g;the solidification temperature was 41.52℃,the latent heat of solidification is 168.6 J/g;the degree of supercooling is 0.79℃.2.According to the characteristics of high latent heat of phase transition of hydrated salts,the phase transition materials Na₂SO₄·10H₂O and Na₂HPO₄·12H₂O with relatively close phase transition temperatures are used as the basic phase change materials.Through the mixing ratio of different masses,according to the mass ratio of 1:9,2:8,3:7,4:6,5:5,6:4,7:3,8:2,9:1,10:0 The phase transition temperature,latent heat of phase transition and subcooling degree of binary eutectic hydrated salt were measured and analyzed by differential scanning calorimetry（DSC）.At 20%,the latent heat of fusion value is the highest,and the phase transition temperature is also in line with our application range.However,the degree of supercooling is a bit high.The eutectic hydrated salt EHS is further optimized by the three-dimensional surface method.When the proportion of Na₂Si O₃·9H₂O is 5%,the content of nucleating agent Si O₂is 3%,and the content of refrigerant Li Br is 5%.,the minimum subcooling degree is 1.06℃,the latent heat of fusion is 238.36 J/g,and the latent heat of solidification is 225.75 J/g.The composite phase change material after 3D surface optimization has a good effect.3.Using the pore absorption capacity of expanded graphite EG,PA-MA-SA/EG composite phase change materials and EHS/EG composite phase change materials were prepared.Firstly,the optimal mass ratio of PA-MA-SA and EG is 12:1,and the optimal mass ratio of EHS and EG is 14:1 through experimental analysis.Finally,the analysis and characterization shows that the addition of EG improves the thermal conductivity of the composite phase change material.