Radiation Cooling Performance Of Expanded Polyterafluoroethylene

In recent years,people's requirements for the comfort of indoor environment have been further improved,and the use of air conditioners and refrigerators has become more and more widespread,resulting in an annual increase in building energy consumption.Radiation cooling has a low cost,simple installation structure.Therefore,it is crucial to develop new cooling and cooling technologies to reduce building energy consumption.At present,photonic crystals or metamaterials used for radiation cooling are difficult to be applied in a wide range due to their complex fabrication process,high price and high cost.For practical application in the radiation cooling outdoor materials,the influence of the environment of dust'll let radiation characteristics on the surface of the material change,material hard to ensure cleanliness,confined to most of the laboratory is generally put forward a new method,new materials,confirms the feasibility of radiation cooling in theory,and the actual large-scale application in the study of building energy saving is a long process.Studies have shown that polytetrafluoroethylene has ideal radiation properties and can achieve radiation cooling.Expanded polytetrafluoroethylene is more hydrophobic than polytetrafluoroethylene,and its self-cleaning property is further improved to achieve better radiation cooling.Besides,the density of expanded polytetrafluoroethylene is lower,and the total mass can be further reduced.The radiation characteristics of expanded polytetrafluoroethylene were studied in this paper.The reflectivity of expanded polytetrafluoroethylene was measured by integrating sphere and spectrograph.The measured reflectivity was integrated to explore the influence of thickness and density on the reflectivity.Based on the measured reflectivity of expanded polytetrafluoroethylene,the radiant cooling power and temperature drop realized by radiation refrigerator were calculated.Based on the calculated temperature drop,the influence of factors such as material thickness,material density,ambient wind speed and atmospheric transmittance on the temperature drop of radiation refrigerator was investigated.The 24-hour ambient temperature on a day in spring and summer in Harbin was selected as the reference to study the temperature drop in spring and summer for radiometer of different specifications.The results show that the larger the thickness is,the larger the reflectivity is,but the reflectivity remains unchanged after the thickness increases to a certain value.In daytime,the reflectivity effect and refrigeration effect of expanded polytetrafluoroethylene with a density of 0.7 g/cm~3 are relatively ideal.At night,the reflectivity and refrigeration effect of expanded polytetrafluoroethylene with a density of about 1.6 g/cm~3 are relatively ideal.The larger the visible distance is,the higher the atmospheric mass is and the better the refrigeration effect will be.The higher the wind speed is,the worse the refrigeration effect will be.When the wind speed reaches a certain value,convective heat transfer dominates,and radiation refrigeration cannot be realized.In spring,the radiator can achieve a temperature drop of 13 K,In summer,the radiator can achieve a temperature drop of 17 K.