Preparation Of Composite Phase Change Materials And Its Application To Gypsum-based Products

As the consumption of fossil energy and increasingly severe of greenhouse effect, building energy conservation received more and more attention, and thermal energy storage gain an unprecedented rapid development. Phase change materials(PCM) is a low-carbon environmental way for energy saving. The key problems for phase change buildings are the preparation of high performance PCM and its combination with building matrix. Organic PCMs have been widely studied on account of their advantages of high thermal density and low price. But extant organic PCM have unsolved problems, such as low thermal conductivity and leakage of PCM in liquid phase, which are obstacles for the common application of PCM in many fields involved. Therefore, this paper aims at saving the problems. Composite paraffin was selected as PCM, preparation of phase change building material(PCBM) and its application in gypsum-based products were studied, The main works and conclusions are presented as follows:(1) Paraffin wax(PW) and liquid paraffin(LP) were mixed together by melting and mixed method to prepare PCBM, phase change temperature and latent heat of PCM were tested by step cooling curves and differential scanning calorimeter(DSC). The results showed that PW and LP could form a eutectic mixture, and the 5:5 mass ratio of PW-LP has the phase change temperature of 28.6℃ and latent heat of 87.2 J/g, which regulated the phase change temperature to a suitable scope for building use.(2) Based on negative pressure adsorption method, expanded perlite(EP) and ceramsite(C) were selected as porous carriers, EP/Paraffin and C/Paraffin composite PCMs were made. Thermal cycling test showed that it has 0.08% mass loss rate after 50 times thermal cycling of the 3:10 mass ratio of EP: Paraffin. Gypsum/Emulsifier Paraffin(G/EP) Shape-Stabilized Phase Change Material(SSPCM) was made by mixing gypsum paste and melting paraffin. Compressive strength and mass loss rate of G/EP was 3.49 MPa and 0.54% respectively with 4% emulsifier and 30% paraffin. The density, specific heat, thermal conductivity and latent heat of PCM were tested. The results showed that thermal conductivity of paraffin and G/EP was 0.17W·m-1·K-1and 0.38W·m-1·K-1, respectively. The heat transfer performance of paraffin was elevated by gypsum.(3) Phase change gypsum board were prepared by sandwich method and direct admixing method, the effect of different ways and different PCMs on the compressive strength and thermal expansion of phase change gypsum board were studied. Modeling thermal performance test, thermal conductivity performance of phase change gypsum board was tested. The results showed that coefficient of linear expansion and compressive strength of phase change gypsum board with 40% of SSPCM was 16.5×10-6/℃ and 6.29 MPa, respectively. The indoor temperature was reduced 4.5℃ by SSPCM in sandwich method.(4) ANSYS finite element method was used for analyzing the thermal transfer process of PCM and phase change gypsum board. The change process of temperature field was showed by temperature distribution. Simulation results showed that the thermal inertia of gypsum board was elevated by addition of PCM. Moreover, the cooling side temperature was decreased and the temperature rise rate was also delayed. The effect of temperature delay of gypsum board was the best when the thickness of PCM was about 15 mm. When the phase change temperature was over environment temperature a little, the energy-saving efficiency was better.