Preparation And Properties Of Lauric Acid/Stearic Acid-Based Composite Phase Change Materials

China’s construction speed and the number of existing buildings in recent years are the highest in the world,and building energy consumption accounts for a large proportion of energy consumption,and is increasing year by year.The construction industry is facing the double pressure of environment and resources,so it is urgent to develop "green building" and reduce energy consumption.Phase change materials have the property of storing and releasing latent heat by changing their own material state under the condition of constant temperature.Compounding them into building materials can play the role of building temperature regulation,waste heat recovery,auxiliary heat storage and solar energy storage,which can not only fully and reasonably utilize energy,but also reduce energy consumption due to indoor temperature fluctuations to a certain extent.Most of the current research on phase change materials focuses on the performance of single-phase change materials or binary mixtures,and further research is still needed on the effect of phase change materials on temperature control in building interiors.In this paper,LA-SA/EP,LA-SA/EV,and LA-SA/EG composite phase change materials were prepared by vacuum adsorption method using expanded perlite(EP),expanded vermiculite(EV)and expanded graphite(EG)as carrier materials for the summer climate in the middle and lower reaches of Yangtze River.The compositions,microstructures,and thermal properties of the three composite phase change materials were analyzed and studied by FT-IR,ESEM,DSC,TGA and other methods.On this basis,the test chambers with composite phase change materials partition walls were set up to test the temperature regulation effect of the three composite phase change materials respectively,and the temperature regulation effect was compared and analyzed with that of the control chambers to provide a theoretical and practical basis for the practical application of phase change materials in buildings.The main research contents and conclusions are as follows:(1)Based on the second law of thermodynamics and the lowest eutectic theory,the predicted lowest eutectic point of LA-SA binary phase change material was calculated;the phase change curves of binary phase change materials with different LA:SA ratios were measured and obtained by DSC method,that is,the correspondence between eutectic fatty acid and phase change temperature.The results showed that when the required phase change temperature was 37°C,the LA-SA binary fatty acid low eutectic mixture mass ratio was 76:24,and the latent heat of phase change of the material was 155.8 J/g.The experiments showed that the measured DSC results were like the theoretical prediction.(2)Lauric acid/stearic acid-based composite phase change materials were prepared by vacuum adsorption method.The optimum loading amount of LA-SA by expanded perlite(EP),expanded vermiculite(EV)and expanded graphite(EG),as well as the morphology,structure,thermal properties,thermal cycle test and other characterization analysis of composite phase change materials were studied.The results show that the maximum loading of EP,EV and EG on LA-SA is 40%,45% and 90%,respectively.When the three carriers are loaded with LA-SA phase change materials,the components are well compatible,only physical changes occur,and there is no obvious leakage problem;The onset phase change temperature and latent heat of the three composite phase change materials LA-SA/EP,LA-SA/EV and LA-SA/EG are34.80℃ and 60.14 J/g,32.1℃ and 67.57 J/g,33.0℃ and 134.47 J/g respectively;After100 cycles of 20℃-70℃-20℃,the change of phase change temperature and latent heat of the three composite phase change materials is small,and the stability is good.(3)The thermal conductivity of the composite phase change materials was measured separately by Hot Disk,and the results showed that the thermal conductivity of LA-SA/EP,LA-SA/EV,and LA-SA/EG were 0.185 W/(m·K),0.151 W/(m·K)and1.562 W/(m·K),respectively,which means that the thermal conductivity of the LASA/EG material is nearly 10 times larger than those of the other two materials and have excellent thermal responsiveness.(4)The temperature regulation effects of LA-SA/EP,LA-SA/EV and LA-SA/EG composite phase change materials were tested and analyzed separately using small chamber tests,and the results showed that LA-SA/EG partition wall can hold more heat,the maximum temperature inside the partition wall is the lowest,and the time required to reach the maximum temperature is the longest,that is,LA-SA/EG material not only has the best thermal The LA-SA/EG material not only has a fast response,but also has the best temperature control effect on the small chamber test area and the best overall performance.