Design And Fabrication Of Selective Radiation Refrigeration Devices With Non-Tapered Array Structure

Radiative cooling is a method of passive cooling that does not consume energy by adjusting the emissivity/absorptivity of the structure to match the wavelength of atmospheric transparency window.Nocturnal radiative cooling has been known for centuries,but for many years,due to the low emissivity of natural materials in the atmospheric window and the limited reflectivity of the solar spectrum,most radiant cooling structures are unable to reach sub-ambient temperatures in the sun.Therefore,it is still a challenge to achieve radiative cooling during the day.The high emissivity/absorptivity characteristics of the structure are necessary for radiative cooling.In recent years,advances in nanofabrication technology have made it possible to fabricate structures with specific radiation properties,but radiation-cooling devices have so far been difficult to large-area fabrication.This greatly hinders the practical application of radiative cooling devices.Therefore,this paper proposes a non-tapered metamaterial emitter method.Compared with the traditional tapered metamaterials,the band diameter of the structure absorption spectrum is no longer controlled by the ratio of the top to bottom diameter of the array.And the effective dielectric constant of the non-tapered metamaterial is only depending on the diameter of the vertical columns and the thicknesses of the dielectric layers.The optical and cooling properties of Al-Ge-MgF₂multilayer films are analyzed by Finite Element Method.The main research content of this article is as follows:The first chapter mainly introduces the development and research status of radiative cooling devices,also briefly introduces the development and application of nighttime and daytime radiative refrigeration.The second chapter discusses the basic theoretical knowledge of radiative cooling,including atmospheric radiation,solar irradiance,non-radiative heat transfer and heat transfer balance.In third chapter,the theoretical analysis of the non-tapered structure is carried out,and the sensitivity of the emission spectrum characteristics of the non-tapered metamaterial emitter to the slant of the side wall is studied.The average emissivity of the emitter in the atmospheric window is0.8,and the wavelength is 8-13μm.In the absence of parasitic heat,the temperature can be reduced by 55 K.The fourth chapter mainly introduces the preparation process of the non-tapered emitter,and the sample is analyzed by SEM/microscopy and bench analyzer.In fifth chapter,the above work is summarized,and the performance of non-radiative metamaterial emitter is described in a general way.At the same time,the deficiencies in the experiment are also proposed,which paves the way for the follow-up research work.