Research On The Spatial Properties Of Radiative Thermal Management Devices

In recent years,great progress has been made in the field of radiative thermal management.Radiative thermal management includes radiative cooling and radiative insulation.In this paper,the spatial properties of radiation thermal management devices were studied.For the study of the spatial properties of radiative cooling devices,this paper first introduced the principle of radiative cooling,and illustrated the general calculation method of radiative cooling by calculating the cooling effect of an actual radiative cooling device.Then,this paper analyzed the three spatial angle terms that affect the cooling performance,namely the solar height angle,the absorption critical angle,and the heat mirror aperture angle.Theoretical research shows that as the solar altitude angle increases,the radiative cooling effect becomes worse;while the larger the critical angle of the absorption rate,the radiative cooling effect becomes better.This paper also studied the relationship between the full-angle absorptivity and cooling performance of radiative cooling devices.The results show that the greater the mid-infrared hemispheric emissivity of the device,the better its radiative cooling performance,the experimental result verified this well.Three kinds of materials with hemispheric emissivity of 0.89,0.8 and 0.04 in the 8 to 14 microns waveband were used in the experiment.When the ambient temperature was 281 K,the first two materials respectively achieved low-temperature radiative cooling effects below the average ambient temperature of 4.2 K and 3.9 K.The copper plate with hemispheric emissivity of 0.04 did not achieve low-temperature radiative cooling.The experimental results verified the results of theoretical research.Finally,this paper shows that the introduction of the heat mirror structure does improve the radiative cooling performance of the device.Compared with selective spectral radiative cooling devices,the heat mirror structure improves the cooling performance of broadband spectral radiative cooling devices even more.For the study of the spatial properties of radiative insulation devices,this paper analyzed the influence of the hemispheric emissivity of the material on the performance of radiative insulation based on the principle of radiation insulation.The result shows that in order to achieve radiative insulation,the material needs to have the lowest outer surface hemispheric emissivity in the human radiation band.The result of theoretical analysis was verified by experiments.The first step of the experiment was preparing a radiative insulation device with low hemispheric emissivity.The second step of the experiment was testing the radiative insulation performance of different hemispheric emissivity materials.Three kinds of radiative insulation materials with hemispheric emissivity of 0.03,0.65 and 0.8 in the 8 to 14 microns waveband were used in the experiment.When the ambient temperature was 300 K and the input heat generation power density was 100 W/m2,the material with a 0.03 hemisphere emissivity achieved an average 2 K and 4 K radiative thermal insulation improvement compared to the latter two thermal insulation materials.The experimental results verified the conclusion of the theoretical research.