Preparation And Evaluation Of Temperature-responsive Transmission Switch Film With Phase Change Material

Building energy consumption accounts for approximately 31% of global final energy consumption and 40% of global primary energy consumption.Radiative cooling technologies have become a hot topic in building energy conservation research in recent years due to their no additional energy consumption required.However,current radiative cooling systems are static and can increase heating energy consumption when cooling is no longer needed during the winter.To address this problem,there is an urgent need to develop a temperature-adaptive radiative cooling system that can cool when the ambient temperature is above a critical temperature and automatically shut off radiative cooling when the temperature drops below the critical temperature.Paraffin has a transmittance of 2-5.4% in the visible and near-infrared spectra when in a solid state,while its transmittance is over 91% when in a liquid state.This makes paraffin a potential material for transmission switch films with a transmissive function and when combined with radiative cooling devices,can form a temperature-adaptive radiative cooling system.Based on this,a series of research studies have been carried out as follows:(1)Preparation and performance testing of temperature-responsive transmission switch films(TRTSF): Leakage problems were found in TRTSF samples with phase change material(PCM)content of over 30% through phase change cycle leakage analysis.Therefore,samples with 10-30% PCM content were selected for DSC and TG analysis.The calculated PCM content in the sample was close to the results obtained from DSC and TG,and the phase change temperature of TRTSF was close to that of PCM.Optical characterization and microstructure analysis of TRTSF samples showed that the switch effect before and after the solid-liquid phase transition was obvious.Additionally,the TRTSF samples tested showed high emissivity characteristics at 8-13 μm in the liquid phase state,which can close radiative cooling,while the samples showed Mie scattering in the solid phase state,which can block the internal and external conduction of visible and mid-infrared waves and theoretically turn off radiative cooling.(2)Experimental study of temperature-adaptive daytime radiative cooler(TADRCer): To verify the feasibility of replacing the radiative cooling device emission layer with TRTSF to achieve temperature adaptation,a multilayer temperature-adaptive radiative cooler TADRCer was prepared.A structured daytime radiative cooler(DRCer)was also prepared as a reference.Both devices were monitored for temperature changes during summer and winter,and the working effect of the temperature-adaptive radiative cooler with a fixed-phase change material emission layer was validated.Outdoor experimental results showed that both devices achieved radiative cooling function at night and under weak sunlight during the summer.In winter,DRCer still performed radiative cooling,while the PCM in TADRCer in the solid state which demonstrating its insulation effect state could close radiative cooling in the case of Mie scattering,resulting in an average surface temperature higher than the ambient temperature at night.(3)Model validation: A CFD simulation model was established and the simulation results were compared with the outdoor experimental results,which were found to be basically consistent,validating the reliability of the TADRCer simulation model and laying the foundation for scaling up and predicting the temperature-adaptive effect of TADRCer.