Preparation And Properties Of Inorganic Phase Change Material Microcapsules

With the continuous development of science and technology,the growing demand for energy in human society has led to the energy crisis and environmental pollution problems,and people pay more and more attention to the efficient use of energy.In this background,phase change energy storage technology has been developed rapidly.The center of phase change energy storage technology is the phase change material,which can absorb or release large amount of latent heat through phase change process.The discontinuous and unstable heat can be fully utilized with this heat storage property of phase change materials.By using phase change materials as core materials to make phase change material microcapsules through microencapsulation technology,it can overcome the problems of easy leakage,poor compatibility and corrosiveness of phase change materials in the process of using them alone.The ideal phase change material microcapsules should have the advantages of high energy storage density,good heat transfer performance and stable performance.This thesis is devoted to the preparation of high heat storage and stable phase change material microcapsules by an easy-tooperate and environment-friendly method.The main research contents are as follows.1.In this paper,two binary eutectic hydrated salts(EHS)were prepared and their microscopic morphology,chemical structure and thermal storage properties were investigated by SEM,XRD,step-cooling experimental device and differential scanning calorimetric analysis.The optimum mass ratio of Na2SO4·10H2O to Na2HPO4·12H2O was 2.5:7.5,and the step-cooling curve showed that the phase transition temperature was 29.3℃ and the subcooling degree was about 3℃.The latent heat of phase transition was 218.58 J/g measured by DSC.The best mass ratio of Na2CO3·10H2O to Na2HPO4·12H2O is 4:6,and the step-cooling curve shows a phase transition temperature of 21.3℃ and the subcooling degree of about 9℃.The latent heat of phase transition is 214.26 J/g measured by DSC.SEM and XRD results display that the eutectic salt is obtained by physically mixing of two hydrated salts without chemical reaction.2.The phase change material microcapsules with eutectic salt(Na2SO4·10H2ONa2HPO4·12H2O)as the core material were prepared by organic phase separation method using ABS and EC as composite shell materials and dimethyl silicone oil(PDMS)to trigger the phase separation of shell materials in dichloromethane.Most of the organic reagents in the preparation process were also recycled and reused,and the principles of the preparation of phase change material microcapsules were investigated.The microstructure,chemical composition,phase change properties and thermal stability of the microcapsules were characterized by SEM and its electronic energy spectroscopy(EDS),FT-IR,DSC and freeze-thaw cycle tests.The phase transition enthalpy of the microcapsules prepared by this method was 182.36 J/g and the phase transition temperature was 29.7℃.The SEM results showed that the microcapsules were nearly spherical and the shell material formed a dense film on the surface of the eutectic salt with a typical core-shell structure.3.Microcapsules with eutectic salts(Na2CO3·10H2O-Na2HPO4·12H2O)as core materials were successfully prepared by an improved organic phase separation method using ABS and EC as composite shell materials.The microstructure,chemical composition,phase transition properties and thermal stability of the microcapsules were characterized by SEM and its electronic energy spectroscopy(EDS),FT-IR,DSC and freeze-thaw cycle tests.The effects of different types of surfactants,surfactant dosage and core-to-shell mass ratio on the particle size and microstructure of microcapsules were investigated.4.The heat transfer mode of the phase change material was analyzed based on the principle of heat transfer,and the temperature field and phase change inside the microcapsules were numerically simulated by using ANSYS Workbench 2020 to build a finite element model.Finally,a model of the wall was established to simulate the effect of the microcapsules of the phase change material on the indoor temperature after they were dispersed in the wall.The results show that the phase change material inside the microcapsules rapidly completes the phase transition after the temperature reaches the phase change temperature,so there is no need to add substances to enhance the thermal conductivity of the phase change material;moreover,if the phase change material microcapsules are used in the building field,the relatively low thermal conductivity is beneficial to the equilibrium of the indoor temperature.