Preparation And Properties Of High Transmittance/Emission For Atmospheric Window Band On Radiative Cooling Performance

Radiation refrigeration means radiating heat from an object to a cold source through an atmospheric transparent window in the form of electromagnetic waves without consuming other forms of energy.In order to achieve refrigeration effect,materials must have high transmission to emit heat in the atmospheric window band,or high emission to radiate heat and reflect visible light.In this paper,a composite film material was prepared,which takes the macromolecule as matrix and inorganic as additive,and the results are as follows:1.Dense composite radiation refrigeration film was prepared by coating method,which uses polystyrene?PS?and polyethylene?PE?as polymer matrix,and CaF₂,ZnO and ZnS as inorganic additives.We use a FTIR spectrometer to test the infrared transmissibility of the inorganic materials and the prepared thin films.The thickness of the film was measured using an optical microscope.The radiation refrigeration performance of the film was investigated through a lab-assembled temperature measuring device.The results show that with the increase of the content of inorganic additives,the permeability and refrigeration performance of the composite film materials are improved.When the content and type of inorganic additives are identical,the refrigeration performance of the composite film of PE series is better than that of the PS series.The transmission of the PE composite film with 4 wt% CaF₂ is as high as 95% in the spectral range of 8?m to 13?m,and the corresponding equilibrium temperature is 34.0?.Compared to the film without the additives,this PE composite film has a lower equilibrium temperature of 3.1?and the best refrigeration performance.The equilibrium temperature can be kept around 34.5? when the thickness of the 4 wt% CaF₂/PE composite film is controlled to be 30?m.CaF₂ as additive has the best potential of application.2.Radiation refrigeration film was prepared through electrospinning by using acrylic resin,PVC and PMMA as polymer matrix and adding inorganic additives such as TiO₂,ZnO and ZrO₂.The pore size of the film was controlled by adjusting the spinning voltage,and the microstructure of spinning film was characterized by SEM.Furthermore,the reflectivity and emissivity of the material are measured by Fourier transform infrared spectrometer.The radiation cooling performance of the material was tested on a lab-made device.The results indicate that the acrylic resin films with small pore size have higher reflectivity in the 0.2-2.5?m wave band and higher emissivity in atmospheric window band than those with large pore size.For different polymer matrix,the acrylic resin system and PMMA system have high reflectivity in the 0.2-2.5?m wave band when they have same pore size.The acrylic resin films with 2 wt% TiO₂ have the highest reflectivity of about 89%.The reflectivity of PMMA composite spun film at 0.2-2.5?m band increased with the increase of inorganic additive content.The reflectivities of the 6 wt% TiO₂/PMMA and 6 wt% ZnO/PMMA composite films are as high as 89% without obvious effect on the emissivity of atmospheric window.Under the illumination of a solar simulator,the acrylic resin films with 2 wt% TiO₂show the lowest the equilibrium temperature of 32.1?.The 6% wt TiO₂/PMMA and ZnO/PMMA composite films have equilibrium temperatures of 32.8? and 33.0?respectively.The TiO₂/acrylic resin system has high reflectivity in the solar spectrum and high emissivity in the atmospheric window,and therefore has promising prospect of application.