Design And Study Of Daytime Radiation Cooling Based On Optical Thin Film Structure

The rapid development of human society has led to a huge increase in global energy demand.The consumption of fossil energy has accounted for about 85%of the world’s total annual energy consumption.At the same time,the burning of fossil fuel has also brought a large number of greenhouse gas emissions,thus aggravating the problem of global warming.Developing new energy sources and increasing the consumption of non-fossil fuels has become one of the hot topics in today’s society,with the development of technology and manufacturing processes,the concept of daytime radiation cooling proposed in recent years is expected to break through the traditional high-energy-consuming cooling methods,and has received wide attention.Radiation cooling is a passive and efficient refrigeration method.The novelty of radiation cooling is that it can achieve temperature reduction without requiring any additional energy input.It radiates heat to outer space by using the transparent window of the atmosphere.It saves energy and has no pollution,which is in line with today’s sustainable development trend.The daytime radiation cooling further breaks through the limitation that traditional coolers can only be installed and used at night,and can achieve passive cooling under the sunlight during the day,which is conducive to our response to the problems caused by global climate change.This thesis takes daytime radiation cooling as the research object,and gives a detailed introduction to the related research progress,physical mechanism and energy flow relationship of radiation cooling.We design and study the daytime radiation cooler based on the multilayer optical film structure.And on that basis,in view of the color requirements of the external installation of the cooler,we make a further design of the colored daytime radiation cooling structure.An optical structure of multilayer dielectric thin film is proposed,which has high reflectivity in the solar band and high emissivity in the mid-infrared band(especially in the atmospheric transparent window area).Through numerical simulation,the net cooling power of 151.63 W/m2 can be achieved when the cooler reaches the equilibrium state.The simulation results also show that the structure is insensitive to the polarization of incident light when the incident angle is lower than 60°,and can work under oblique incident conditions.For functional and aesthetic reasons,the outdoor installation of the daytime radiation cooler needs to be able to display a variety of colors visually.On this basis,through the combination of the above-mentioned structure and the selective narrow-band absorber realized by the MIM(metal-medium-metal)structure,a daytime radiation cooling structure which can realize the color rendering needs is proposed.This structure can cover the full color range by changing the thickness of the color-developing part of the medium layer.Compared with the previous structure,this structure achieves a different color display on the surface of the cooler by reducing the net cooling power by about 27.8%on average.It not only realizes the need of daytime radiation cooling,but also broadens the application range of the cooler.The simulation results also prove that the structure can work under the condition of oblique incidence and has the characteristic of insensitive angle.