| Building energy consumption accounts for about 20% of the total energy consumption of the whole society, in building energy consumption, the part which is used to regulate the temperature of the building is one of the largest part. Today, the energy shortage becomes more and more serious, and reducing building energy consumption becomes a worldwide problem which must be solved at present. Periodic solar radiation leads to the diurnal temperature fluctuation of building, using phase change materials (PCMs) to store the heat which the building absorb during the daytime and release them slowly at night, can buffer the peak temperature of construction and reducing the energy consumption of the building. The phase change mediums which have the phase change temperature near body temperature are composition of organic usually, when they absorb the heat and give rise to the phase change of melt, it will flowing deformation, the original shape is difficult to keep, thus bring much of inconvenience for the application. So the phase change medium must be blended with porous materials in order to solve this problem. The diatomite, which is natural porous material, has the characteristics of high specific surface area, high temperature resistant and high corrosion resistant, so it is a good matrix of form stable phase change materials (FS-PCMs). In this paper, the matrix material diatomite was processed and modified to improve the adsorption capacity of the phase change medium; the mixing paraffin with low phase-transition temperature was prepared by blending method, and was used as the phase change medium; the 2 materials above was blended together by vacuum impregnation method to prepare the FS-PCMs, and the thermal properties of FS-PCMs was studied. The results of research are as follows:1. The diatomite was processed by NaBH4/PVP mixed solution or 1mol/L NaOH solution, or modified by trimethyl chlorosilane, in order to improve the pore structure and modify its surface. The change of pore structure was studied by SEM and static nitrogen adsorption instrument. It was found that the processe of NaOH solution under 75℃ can rise the diameter of the pore structure, and there is a linear relationship between the rise of diameter and the extent of process time. When the reaction time is 8 h, the diameter increases from 0.359μm to 0.924 μm. The adsorption towards castor oil in castor oil/water mixture of the diatomite which was modified by trimethyl chlorosilane for 32 h rises about 10 times than the adsorption of the unmodified diatomite, which reaches 169.7%.2. The mixing paraffin with low phase-transition temperature was prepared through the blending of liquid paraffin and sliced paraffin, which has good thermal stability. When the mass fraction of sliced paraffin in the mixing paraffin is 60%, the phase change temperature of the mixing paraffin was 34.71℃, and the phase transition enthalpy was 171.53 J/g.3. The FS-PCMs were prepared by vacuum impregnation method, and the loading effect of diatomite before and after the expansion processing or organic modification towards mixing paraffin with low phase-transition temperature was studied, as well as the thermal properties of FS-PCMs. When the FS-PCM is prepared by the diatomite which is processed by NaOH solution at 75℃ for 8 h, the mass fraction of mixing paraffin in FS-PCM can reach 64% without give rise to leakage. TG analysis shows that the FS-PCM has good thermal stability, and the DSC analysis result shows its phase-transition temperature is 34.73℃, and the enthalpy was 109.34 J/g. |
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