Investigation On The Preparation And Thermal Storage Performance Of The Shape-stabilized Organic-Inorganic Phase Change Composites

The heat energy storage and release using phase change materials (PCMs) are realized by the phase change latent heat of the phase change materials which absorb and release heat during phase transformation process. Most of the organic PCMs (such as stearic acid and paraffin) have high energy storage density, good heat resistance, low volume expansibility, no corrosivity and toxicity, environmental friendly character, ect., and their phase change processes occur under almost constant temperature, which can be used in solar thermal storage, building energy efficiency, electronic equipment cooling, textiles and aerospace fields. However, two distinct shortcomings present in these organic PCMs, namely, low thermal conductivity and the leakage during freezing-melting process. Therefore, the shape-stabilized organic-inorganic phase change composites were designed and prepared in our work using the organic PCMs as working substances and the porous magnesium oxide (MgO) or carbon nanotubes (CNTs) as supporting materials by the simple impregnation method. The microstructures and thermal storage performance of the as-obtained composites were characterized, and the results indicated that the organic-inorganic composites not only solved the problems of the low thermal conductivity and leakage, but also realized controlling the thermal storage performance of the PCMs. The research results in this dissertation are listed as follows:1. The PEG/MgO shape-stabilized phase change composites were prepared by an impregnation method, in which the polyethylene glycol (PEG-1000) as working medium was imbedded into the support materials of porous magnesium oxide (MgO) with super high surface area. The structure and morphology of MgO and the composite are discussed and summarized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and specific surface area (BET), ect. The phase change temperature, phase change latent heat, thermal stability properties and shape stability of the composites were measured by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and leakage test. The physical and chemical reaction between the supporting material and the working medium were analyzed by Fourier Transform infrared spectroscopy (FT-IR). The results show that honeycomb porous structure of MgO with specific surface area as much as596.16m2/g, and PEG was dispersed into the porous structure of MgO, and there was no obvious chemical reactions between the two components of composite. The composite has a larger phase change latent heat (96.4J/g). The thermal performance changed little after several phase change cycles, and no obvious seepage was observed when the composite was kept above the melting point of PEG-1000.2. A series of stearic acid/carbon-nanotubes (SA/CNTs) shape-stabilized phase change composites with different mass ratios of SA/CNTswere prepared through the impregnation method by using the stearic acid(SA) as a working substance and the carbon nanotubes (CNTs) as a supporting material. The structure, morphology and thermal properties of the composites were investigated by SEM, TEM, XRD, FT IR, DSC, ect. The results show that the SA molecules were effectively fixed into the porous structure of the CNTs by the surface tension and capillary force. With the increase of SA content, the phase change latent heat (as much as111.75J/g) of the composite increased gradually. The stability and thermal conductivity of the composites were significantly improved.3. In order to demonstrate the application of the shape-stabilized phase change composites, a novel composite cotton with temperature control performance was obtained by the impregnation method using the paraffin and stearic acid as a working substance, respectively. The cotton has a high adsorptivity to the organic PCMs, and a highadsorption rate was achieved as much as90wt%. No obvious leakage was observed in the composite cotton under the constant condition temperature of80℃. The phase change latent heat of the composites increased gradually with increasing content of organic PCMs. The phase change latent heat of paraffin/cotton of and the SA/cotton composite reaches112.9J/g and172.7J/g, respectively.