Preparation And Properties Of Phase Change Materials With Enhanced Thermal Conductivity

The form-stable phase change materials (PCMs) with enhanced thermal conductivity were synthesized in this thesis. Polyethyleneglycol (PEG) was acted as oganic phase change component to realize the storage and release of energy, SiO2was used as inorganic supporting material to realize form-stable effect. The form-stable PCMs with high latent enthalpy and good thermal conductivity were prepared through in-stu thermal conductivity enhanced agents (such as Al2O3, Cu and MCNT) doping.PEG/SiO2-Al2O3form-stable composite PCMs were prepared through ultrasound assisted sol-gel method. The influence of preparation method and phase change component to the form-stable effect and phase change properties of the PCMs were researched. Aluminium isopropoxide and aluminium nitrate were used to prepare the form-stable composite PCMs with different content of Al2O3. The structure and properties of the PCMs were studied by FTIR, XRD, DSC, TGA and the thermal conductivity instrument. The results showed that PEG and SiO2-Al2O3combined physically, the latent heats were a little decrease because the crystallization of PEG were limited by the inorganic network. When the PCM prepared by aluminium isopropoxide included3.3%of Al2O3, the latent heat was102.3J/g, the thermal conductivity was0.414W/(m·K), the thermal conductivity enhancement was15%. While the PCM prepared by aluminium nitrat included3.3%of Al2O3, the latent heat was126.2J/g, the thermal conductivity was0.398W/(m·K), the thermal conductivity enhancement was10.6%. The results of cooling curves were corresponded with the thermal conductivities. The composite PCMs were stable below290℃.A novel type of PEG/Cu/SiO2hybrid form-stable PCM with high thermal conductivity was obtained by in situ reduction of CUSO4solution through ultrasound-assisted sol-gel method. The XPS result of this material showed that the valence state of copper was mainly zero. The FTIR demonstrated that there was no new chemical bond between Cu, PEG6000and SiO2. The SEM images showed that SiO2network in the composites was filled with PEG and Cu additives. The phase change enthalpy of Cu/PEG/SiO2PCM reached up to114.6J/g, and the thermal conductivity was0.414W/(m·K) for2.1wt%Cu in PEG/SiO2, which was enhanced by13.9%compared with PEG/SiO2. The PEG/Cu/SiO2hybrid material had excellent thermal stability below260℃. To achieve the same temperature of48℃, the freezing time of the form-stable PEG/Cu/SiO2(2.1wt%) composite PCM was reduced by699%compared with that of pure PEG.PEG/MCNT/SiO2composite forma-stable PCMs were synthesized through in-situ doping multi-walled carbon nanotube (MCNT) by ultrasound assisted sol-gel method. We introduced MCNT, which has broad absorbance of UV-Vis light and good light-thermal conversion capability, into PCMs system to store solar thermal energy. The results showed the SiO2network in the composites were filled with additives, which confirm the quasi-uniform distribution of the additives in the shape-stabilized PCMs. When the PCMs were heated over the melting point of the phase change component, there was no liquid leakeage. The FTIR ananlysis proved that there was no chemical bond between MCNT, SiO2net and PEG. When the mass fraction of MCNT was1%in the PCM, the phase change enthalpy was116J/g, the thermal conductivity was0.421W/(m·K), the thermal conductivity enhancement was16.9%. The composite PCM had a good stability below340℃, the light-thermal efficiency reached0.918.