| With the development of social economy and the advancement of urbanization,the energy consumption of buildings is increasing.At present,the country has accelerated the adjustment of energy structure,which the latent heat storage dominated by phase change storage in renewable energy has made a huge breakthrough in the field of building energy conservation.However,the fluidity and low thermal conductivity of phase change materials(PCMs)during phase change and how to combine with building walls to maximum the thermal storage need to be further analyzed and explored.Above all,the effects of different thermal conductivity reinforcement materials and the addition of stability materials on the thermophysical properties of fatty acid PCMs were studied.Phase change gypsum board was prepared by combining phase change materials with gypsum powder by direct mixing method and interlayer method,and its thermal performance of heat storage/retrieval was investigated by systematic experiment and numerical simulation.The theoretical melting temperature and value of latent heat of fatty acids were predicted by the Schroeder formula.The high latent heat value is the key to choosing the superiority of PCMs in the suitable range of phase change temperatures,so lauric-myristic-stearic acid(LA-MA-SA)with a phase change temperature of 29.74 ℃ and a latent heat value of 151.64 k J/kg was chosen as the PCM.PCMs with high thermal conductivity can quickly meet the requirements of human for indoor thermal comfort in a short time.Expanded graphite(EG)with dense long heat conduction chain and large specific surface area was selected as the thermal conductivity reinforcing material.Diatomite(DE)rich in porous structure was added to effectively prevent the leakage of PCMs.EG and DE based ternary fatty acid stability composite PCMs were prepared by direct melt impregnation method.The morphology of the composite PCMs was characterized.LA-MA-SA in LA-MA-SA/10 wt.%EG/10 wt.% DE was basically adsorbed into the pores by DE and EG through capillary action,and the surface was smoother and flatter.The leakage test found that there were no traces of leakage on the surface of the filter paper.Differential scanning calorimetry(DSC)test showed that the latent heat decreases with the increase of the amount of carrier material added.The value of latent heat of the stability composite PCM with 10 wt.% EG and 10 wt.% DE was 117.06 k J/kg,which was 22.8%lower than that of the pure ternary fatty acid LA-MA-SA.The thermal conductive experiments of steady-state method showed that EG effectively improves the thermal conductivity of PCMs.After adding EG with mass fraction of 1～10%,the thermal conductivity of PCMs increased by29.7～708.2%.The thermal conductivity of LA-MA-SA/10 wt.% EG/10 wt.% DE material was4.5072 W/(m·K).TGA and FTIR analysis showed that it has good thermal and chemical stability in the scope of building use.Through DSC cycle stability test,it was found that the change of phase change temperature and latent heat of composite PCMs are less than 1% after 100 cycles,showing good cycle stability.Phase change gypsum board was prepared by direct mixing method and interlayer method.Through the water tank heat storage/retrieval experiment,it showed that the phase change gypsum board prepared by different-positions interlayer method is better than that prepared by direct mixing method.For the phase change board in different positions,placing the phase change board close to the indoor side can play a greater role of PCM.Under different heating/cooling conditions,the average relative thermal comfort duration of indoor side interlayer phase change gypsum board was increased by 495% and 189% respectively compared with pure gypsum board and direct mixed phase change gypsum board.Through the experimental study of thermal response of radiant,it showed that,similarly,because the phase change board melts and absorbs heat near the phase change temperature,the heating rate of the indoor side is slowed down,the temperature curves are smoother and have a smaller temperature fluctuation range.The interlayer phase change gypsum board on the indoor side is less affected by the outdoor temperature,and the phase change board is in the phase change temperature range for a long time,so it has a relatively longer duration of thermal comfort.The relative duration of thermal comfort of indoor interlayer phase change gypsum board was increased by 61.1%、172.4%,143% and 205.4% respectively compared with pure gypsum board at the temperatures of 37 ℃,40 ℃,45 ℃ and 50 ℃.Finally,the experiment of heat storage/retrieval in water tank was numerically simulated.Comparing the numerical simulation and experimental results under different heating/cooling conditions,the temperature curves were in good agreement,and the curves inflection point and flat interval within the phase change temperature range were also in good agreement.Therefore,the accuracy of the model was also verified.Through the analysis of temperature profile,it was found that in the process of heat storage/retrieval,the density stratification of water in the water tank leads to inconsistent temperature distribution at the upper/lower parts,resulting in asynchronous temperature delay at the upper and lower parts of gypsum board.When the area of gypsum board is larger,this phenomenon will be more obvious.Therefore,for daily sunlight exposure,due to a certain exposure angle,for hot climate areas,more phase change materials can be added to the upper part of the wall to ensure longer indoor thermal comfort;For the cold climate area,relatively more phase change materials should be added to the lower part of the wall. |
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