Preparation And Properties Of SiO₂/SIC Composite Film For Radiation Refrigeration

With the increase of global demand for refrigeration system,the proportion of carbon emissions in greenhouse gases also increases.Space radiation cooling is to radiate heat to space cold source through"atmosphere window"(8-13 μm band),so as to reduce the temperature of objects.As a passive and non-consuming cooling method,the application research and potential value of radiation cooling have an impact on the construction of energy conservation and environmental protection society.Based on the research and analysis of the radiation characteristics,processing properties,mechanics and temperature resistance of the materials,this subject selects the polyethylene terephthalate(PET)with good radiation characteristics and temperature resistance mechanical properties as the base material of the radiation cooling film.And to improve the emissivity of the film by adding silicon dioxide,silicon carbide and other materials.And the reflective layer of radiation cooling film is prepared by electron beam evaporation.In this paper,the research and development and preparation of radiation cooling film are as follows:(1)FDTD solutions is used to model and simulate the radiation cooling film,and the emissivity of the film is analyzed and calculated.The volume fraction of silicon dioxide,the volume fraction of silicon carbide and the thickness of the film are controlled as single variables by the control variable method.The influence of different factors on the emissivity of the radiation cooling film is explored,and the law of the influence of the added materials and the thickness of the film on the emissivity is obtained.When the volume fraction of SiO2 and SiC is 8%and 1%respectively,and the film thickness is 60～90 μm,the emissivity of radiation cooling film is more than 0.9.(2)The radiation cooling film was prepared by biaxial stretching and electron beam evaporation.By changing the processing parameters and the volume fraction of the added materials,the effects of the processing parameters and the proportion of the added materials on the processing technology and the emissivity of the film were explored.Single factor experiment was designed by changing the factors such as silicon dioxide content,silicon carbide content and film thickness to explore and verify the influence trend of different factors on the emissivity of radiation cooling film,and the simulation results are verified.Through orthogonal experiment,the importance order of the factors on emissivity was obtained:film thickness>silicon carbide content>silicon dioxide content.The effect of heat setting temperature on the mechanical properties of the film was studied by studying the heat setting temperature after biaxial stretching,and the optimum mechanical properties can be obtained under the heat setting temperature of 120℃.By changing the thickness of the reflective layer of the radiation cooling film,the influence of the thickness of the reflective layer on the emissivity of the film is studied,and when the thickness of the reflective Ag layer is more than 200 nm,the average reflectivity is more than 90%.(3)In this paper,through the calculation of radiation cooling power in different environments,the influence of different non-radiation cooling coefficient,solar radiation and emissivity on radiation cooling power is explored,and conditions of the test are determined.The experimental results show that compared with pure PET film,the radiation cooling film reduces about 5℃ in the daytime and more than 10℃ at night.