Theoretical And Experimental Study Of Radiation Cooling Film Based On Silica Emission

With the development of industry and the advancement of technology,human beings are increasingly demanding energy.The energy sources currently used such as coal,oil and natural gas are non-renewable resources.In addition,the massive burning of these resources will cause air pollution and greenhouses.Environmental issues such as effects.Radiation cooling phenomenon is widely existed in nature.Radiation cooling utilizes the special spectral properties of the atmosphere to radiate heat from the ground to outer space by means of thermal radiation.The whole process is pollution-free and energy-free.However,the radiation cooling effect of most materials is not obvious.In order to improve the radiation cooling efficiency of materials and reduce the production and application cost of radiation cooling materials,this paper proposes a polymer base with good radiation cooling effect,silicon dioxide(SiO2).The filled radiant cooling film adopts an aluminum layer as a metal reflective layer,and the preparation process is simple and the cost is low.The main contents of this paper are as follows:(1)Based on the electromagnetic time-domain difference finite algorithm,combined with the optical design software FDTD Solutions,the effects of particle size,volume fraction and film thickness of micron-sized SiO2 particles on the emissivity of radiation-cooled films were investigated.The results show that the emissivity of the radiant cooling film increases with the SiO2 filling volume fraction and the film thickness.When the SiO2 particle size is 4?m,the emissivity of the radiant cooling film is the best;the thickness of the metal reflective layer is optimized.The thickness of the metal layer is not less than 150 nm.(2)The effect of particle size,volume fraction and film thickness of SiO2 particles on the infrared emissivity of the composite film was investigated by orthogonal experiment.Through the range analysis,the results show that the degree of influence of the three factors is:volume fraction>particle size>film thickness,which has certain guiding significance for obtaining high emissivity composite film.(3)The emission layer of the radiation-cooled film was prepared by the processing method of the cast film,and the reflective aluminum layer and the emission layer were hot-pressed to obtain a radiation-cooled film.The infrared emissivity of the radiant cooling film in the 8?14?m band was measured.The radiant cooling film with a SiO2 particle size of 4p?m a filling volume fraction of 12%and a thickness of 200?m had an infrared emissivity of 0.93.The radiant cooling film was tested in sunlight.The reflectivity of the band has an optimum reflectance of 0.92.(4)Theoretically calculated the nighttime and daytime radiant cooling flux of the radiant cooling film,and analyzed the influence of ambient temperature and non-radiative heat transfer coefficient on the radiation cooling effect.A radiant cooling device was built to test the cooling effect of the radiant cooling film at night and during the day.The results show that the composite film with SiO2 volume content of 12%is 14.50 C lower than the ambient temperature at night and 4.3? lower than the ambient temperature during the day.The composite film showing that the volume content of SiO2 is 12%has certain radiation cooling performance at night and during the day.