Study On The Preparation And Properties Of Passive Radiative Cooling Films

Radiative cooling can send heat energy of terrestrial objects to the outer space in the form of electromagnetic waves,which indicates its wide application prospect.The nocturnal radiative cooling has been studied for decades,and in 2014,diurnal radiative cooling has gained a breakthrough.However,for the current reported radiative coolers,their cooling performance is limited.Therefore,improving the cooling performance of the coolers has become a research hotspot in the field of radiative cooling.Based on reducing the influence of external environment on the radiative cooler,we proposed three methods to improve the radiative cooling performance,including preparing radiative coolers with thermal insulation function,fabricating multi-layer cooler structure and using passive evaporative cooling to assist the radiative cooling.(1)A radiative cooler with the function of thermal insulation ability was prepared by hot pressing micron-sized silica particles and nano-sized silica particles to the substrate.On the one hand,this kind of cooler can emit heat radiation to the outer space,and scatter solar radiation back to the surrounding environment.On the other hand,it can also restrain the heat conduction from the upper surface to the lower surface of the cooler.In the three hours(11:20-14:20)with strong solar radiation during daytime,this cooler has successfully cooled the water to about 6.1? lower than the air temperature.(2)We designed a multi-layer structure to reduce the temperature of cooler's nonradiative heat diffusion environment.In this design,the atmospheric air temperature and the air temperature around the radiative cooler are treated separately.Through experiment and simulation,we have confirmed the the cooling performance of the multi-layer structure cooler can be improved at night.The theoretical calculation results show that when the air temperature around the cooler is reduced by 20 K,the cooling effect of the cooler will be increased by 25 times.(3)We also made three combined cooling devices based on passive evaporation and passive radiation to achieve radiative cooling effect throughout the day under the condition of haze.Evaporation can take away heat energy,reduce the cold loss caused by heat exchange and improve the radiative cooling performance.Based on the application mode of cold source,the devices can be divided into indirect method device and direct method device.We used the two kinds of devices to conduct outdoor cooling experiment.The experimental result shows the coolers in both devices can cool down throughout the day,the average temperature of the coolers in the indirect method device was 6.2? lower than the air temperature,and the average temperature of the cooler in the direct method device was 6.1? lower than the air temperature.