Thermal Property And Building Envelope Application Research Of Self-healing Polymer-based Form-stable Phase Change Materials

Energy consumption of China is increasing,non-renewable resources are gradually scarce,renewable energy development and phase change energy storage has become research hotspots.The latent heat storage technology based on phase change material can realize thermal energy storage in application scenarios by characteristic of continuous endothermic or exothermic at melting point temperature and constant temperature.At present,the composite phase change materials are faced with the problems of complex preparation process,easy damage of materials and unrepairable after damage while solving the leakage problem caused by the solid-liquid conversion of phase change materials.In view of the existing problems,self-healing polymer-based phase change materials were prepared by one-step plate vulcanization method and applied to practical scenarios in this paper.At present,the energy consumption of China's construction at the operation stage accounts for about 21.7 % of the total energy consumption of the country,which accounts for a relatively high proportion.The combination of phase change energy storage and building envelope can reduce building energy consumption and achieve effect of building energy saving.In this subject,the preparation of phase change envelope for building energy saving is studied as the main application.The main research contents are as follows:(1)Polymer-based form-stable phase change materials were prepared by one-step plate vulcanization method,and the physical crosslinking mechanism between hydrogenated styrene-ethylene/butene-styrene triblock copolymer(SEBS)and paraffin was explored.Both solid and liquid paraffins can be physically cross-linked with SEBS at room temperature.In this paper,paraffins with phase change temperature of 9-10 °C,50-52 °C and 22-24 °C were explored.The DSC test results of the composite phase change material prepared by SEBS and paraffin show that it has high energy storage density.The maximum adsorption capacity of SEBS for paraffin is 85wt% and the latent heat values of composite phase change materialsthe phase change temperature at 9-10 °C,50-52 °C and 22-24 °C were 137.6 J·g-1,188.1 J·g-1and 205.6 J·g-1,respectively.The thermal stability test results showed that the pyrolysis temperature was delayed to 200 °C after the combination of paraffin and SEBS,and there was no leakage of paraffin after 50 cycles,indicating that it had good thermal stability.The mechanical property test results show that the maximum elongation is as high as 1160 %,and it has good elastic properties.The energy storage test results show that it can maintain a certain period of temperature platform,indicating that its good thermal storage performance.(2)The self-healing mechanism of composite phase change materials prepared by SEBS and paraffin was proved by self-healing property experiment,and the best self-healing conditions were proved.The experiment on heat and mass transfer rate characteristics determined that the self-healing rate was affected by the mass fraction of paraffin,self-healing temperature and thermal conductivity.Different influencing factors were explored by designing self-healing experiments,and the optimal conditions corresponding to the highest self-healing rate were obtained.The experimental results showed that the optimal self-healing conditions were as follows: self-healing temperature is 130°C,paraffin mass fraction is85wt%,and mass fraction of spherical Al2O3 particles is 10%,self-healing takes 25 min.The results of stress-strain test showed that the maximum elongation of the composite was still as high as 1160 %,means that the self-healing did not affect the mechanical properties of the material.(3)Through the combination of experimental test and numerical simulation,the phase change enclosure structure was made by using the polymer-based materials prepared by paraffin at the phase change temperature of 22-24 °C,which was applied to the small mobile plate house model.The internal temperature of the model was monitored within 6 hours at38 °C.The experimental results show that the maximum temperature of the internal center of the model is 28.32 °C after adding the composite phase change material,which is lower than the ambient temperature 9.68 °C.The duration of the internal center maintenance temperature in the range of 22-24 °C is 5.0 h.The internal center temperature of the model without adding composite phase change material reaches the maximum temperature of 38 °C within 5.3 h,which indicates that the addition of composite phase change material can effectively control the internal temperature and reduce the temperature fluctuation.The test process was repeated through numerical simulation,and the results were consistent.The central temperature inside the model was calculated by changing the thickness of composite phase change materials through numerical simulation.The results show that when the thickness increases from 0.5 cm to 1 cm,the maximum temperature inside the model decreases from 27.9 °C to 25.0 °C within6 h.When the thickness is 1 cm,the temperature plateau period inside the model is constant between 22 °C and 26.5 °C within 10 h.When the thickness changed from 1 cm to 1.5 cm,the maximum temperature inside the model decreased from 25.0 °C to 24.7 °C within 6 h.When the thickness was 1.5 cm,the temperature plateau period inside the model was constant between 22 °C and 25.1 °C within 10 h.This shows that when the thickness of composite phase change material increases from 0.5 cm to 1 cm,the temperature control effect is most obvious.