Study On Preparation And Performance Of Composite Solid-Solid Phase Change Materials

Some energy sources and energy utilization systems, such as solar energy, geothermal energy, distributed energy,refrigeration and air conditioning and et al, suffer from intermittent supply or instability due to the variable load of energy supply or energy consumption. The operating stability, reliability and economy of energy system can be improved by employing energy storage technology to store and release heat. Therefore, it is of great importance to study energy storage technology and the performance of thermal energy storage materials. And how to improve the properties of thermal energy storage materials is one of the most critical problems. Among so many varieties of phase change materials (PCMs), solid-solid PCMs have obvious priority of non flowing compared to the solid-liquid PCMs. However, there are still some shortages that obstruct their applications. Hence, this thesis focuses on the preparation and properties investigation of composite solid-solid PCMs.The contents of this thesis are as follows:Firstly, a kind of solid solid phase change material pentaerythritol (PE), with phase change temperature of 181℃, is chosen to be studied. For the reason of low crystallization rate and heat releasing rate, different composites are proposed and prepared with additives of graphite powders and nano-particles. The phase change temperature, latent heat and thermal conductivity of different composites are measured. The structure and morphology of the crystal are investigated by Fourier infrared spectrum analyzer, X-ray diffraction and scanning electron microscope. Meanwhile, based on the DSC curves of heat flux versus temperature at different cooling rates, Avrami and Mo method are confirmed to be suitable for the non-isothermal crystallization kinetic analysis for PE and its composites, and the results reveal that appropriate additives can be helpful to accelerate the crystallization rate of PE and reduce the supercooling degree.Secondly, a novel solid solid phase change latent functionally thermal fluid(LFTF) is proposed and prepared by directly mixing the micronized polyols particles into heat transfer oil without special packaging. Compared to traditional LFTF with microencapsulated solid-liquid PCMs, this LFTF takes advantages of easy preparation and risk free of breakage during application. In this study, the heat storage capacity is investigated. The phase change temperature, latent heat and apparent specific heat of the novel LFTF with various amounts of solid solid PCMs are measured by DSC. Results show that the values of apparent specific heat of the proposed LFTF are higher than that of the heat transfer oil. It also can be used as heat transfer fluid with better property and heat storage ability.Finally, Crosslinked high density polyethylene (XLPE) is obtained through cobalt ray irradiation and Soxhlet extraction method. There are some superiorities of this method:high crosslinked bond energy, good stability, no chemical pollution of agent which isn’t needed in this preparation process. The solid solid phase change property of XLPE is verified through testing the melting fluid index. The physical structures, chemical structures, phase change temperatures, latent heats and specific heats of high density polyethylene and XLPE are all investigated, which are the important thermophysical properties for applications as a solid solid PCM.