Preparation And Properties Of Polyether Based Composite Phase Change Materials With Enhanced Thermal Conductivity

Thermal conductivity enhancement of composite phase change energy storage materials have been prepared by the sol-gel method in this thesis. Inorganic SiO2 and PEG with high phase change enthalpy were used as support materials and phase transition component, respectively. The form-stable phase change materials had good phase change property, high thermal conductivity because of addition of various materials, such as Ti4O7 carbon fibre and metal form Ni.Ti4O7/PEG/SiO2 form-stable phase change materials were prepared by acid-base sol-gel method and in-situ doping Ti4O7. The structure and performance characterization of composite PCMs were studied by SEM、FT-IR、XRD、DSC、TG、coefficient of thermal conductivity and thermal conversion test, and heat storage capacity test. Results indicated that it was physical mixture among each material. PEG chains bounded in three dimensional network structure of SiO2, on account of amorphous phase transformation performance the composite materials had no leakage phenomenon in the process of phase transition. Because of the addition of Ti4O7 with excellent performance of thermal conductivity, its coefficient of thermal conductivity improved, the rate of store heat and release heat were accelerated. Ti4O7 in ultraviolet-visible area had a strong ability of light absorption and transformation, which can be used for the capture and utilization of ultraviolet-visible high-energy light, which was 45% of the solar radiation energy, so as to improved utilization efficiency of solar energy. When Ti4O7 content reached 3% in the composite PCMs, the phase transition enthalpy value reached up to 145.0 J/g, coefficient of thermal conductivity was 0.45 W/(m·K). When the temperature was below 360 ℃, composite PCMs had a good thermal stability.By acid and alkali catalytic sol-gel method in-situ doping carbon fiber (CF), CF/PEG/SiO2 form-stable phase change materials were prepared. CF had strong performance of thermal conductivity and light absorption capability. Compared with the pure PEG, heat accumulation rate and heat release rate of CF/PEG/SiO2 composite PCMs were faster. And solar-thermal conversion performance of PCMs was better than pure PEG. SEM results showed that the porous structure of SiO2 of composite materials was fully populated by PEG and CF. IR analysis showed that there was no new material generated in the composite materials, and XRD analysis indicated that crystallinity of PEG decreased. When the mass fraction of CF was 2%, Phase change enthalpy value was 159.1 J/g, coefficient of thermal conductivity was 0.44 W/(m-K), thermal conductivity enhancement rate was 69.2%. Composite materials had a very good stability under 340 ℃.PEG/SiO2-Ni composite PCMs was prepared by acid and alkali catalytic sol-gel method and vacuum impregnation method. Metal foam had good thermal conductivity and adsorption capacity because of its uniform porous structure. A mixture of silica sol and PEG was adsorped, and the gel was formed gradually while heating. Due to PEG was propected by inorganic SiO2 and metal foam skeleton, when composite PCMs reached phase change temperature, there was no liquid leakage. XRD analysis showed that PEG crystallinity was restricted. DSC, TG results showed that composite PCMs had high phase change enthalpy and good thermal stability under 340 ℃. Compared with PEG/SiO2 composite PCMs, thermal conductivity increased at a rate of 57.7%. Besides, the heating/cooling curves measurements showed that the rate of store/release heat of PCMs was increased significantly.