日间辐射制冷材料研究进展

Research Progress of Daytime Radiative Cooling Materials

辐射制冷是一种备受关注的新型降温方式,该方式利用大气透明窗口(ATW)向外太空辐射传热,实现被动降温。一般日间辐射制冷材料应在8~13μm波段内具有高发射率,在太阳光谱波段吸收率低于5%。辐射制冷研究可以绿色低耗的方式为建筑节能、服饰降温、冷藏冷凝、电池降温等提供方案,有着广阔的应用前景。如何使辐射材料较好地匹配理想辐射光谱是目前最主要的问题。近年来研究者多从辐射材料结构入手,在提高8~13μm窗口波段发射率的同时,通过构建具备光子带隙或发生Mie散射的结构等方式,减少太阳辐射吸收,并取得了显著成果。通过高聚物掺杂纳米粒子、不同折射率材料堆叠等结构设计,使辐射制冷材料的红外选择性得到了显著提升。一些高聚物在8~13μm波段内具有高发射率,同时可有效隔绝体系外的热量输入。将高聚物与发射光谱互补的掺杂纳米粒子相结合,可覆盖整个目标波段,提高其制冷性能。层堆叠模式参考了光子晶体阻断特定波长电磁波传播的特性,设计了不同折射率层交替排列,在不影响高发射层向外辐射红外能量的同时降低了材料对太阳光的吸收。本文主要综述了近年日间辐射制冷材料的研究进展,按其结构形态,将前沿辐射制冷材料分为薄膜类、涂层类、织物类和块材类,并阐述了辐射制冷器在建筑、电池降温等方面的实际应用。

Radiative cooling is a new type of cooling method that has attracted much attention.In this way,it could transfer energy in the form of heat radiation to outer space through the atmospheric transmittance window(ATW)by the materials,thus realizing passive cooling.Generally,the materials suitable for daytime radiative cooling should be highly emissive within the wavelength range from 8 to 13μm,and its absorption in the solar spectrum should be less than 5%.Radiative cooling technology has broad application prospects which could provide green and low-consumption solutions to building energy efficiency,cooling costume,refrigerated condensation,battery cooling and other problems.Currently,the cooling power of radiative cooling technology indeed can not achieve the expected objectives,and the key reason lies in the mismatch of spectral curve between radiator and ideal radiative coolers.Hence,many conventional materials with new-designed structures have been put forward to promote this technology.Those newly developed radiative cooling materials simultaneously possess high reflectivity in the solar spectrum and high emissivity in the ATW by constructing radiators with photonic band gaps or Mie scattering structures.With structural design,such as polymer doped nanoparticles and stacking of materials with different refractive indices,radiative cooling materials are more consistent with the ideal radiative coolers spectral characteristics.Some polymers have a high emissivity in the ATW,and meanwhile,effectively reduce the heat input from heat conduction and heat convection.It has been suggested by some research results that the combination of complementary doped nanoparticles with polymer could cover the whole target band and greatly enhance the cooling power.Some research brought in photonic crystals to block the propagation of an electromagnetic wave with specific wavelength.By alternately arranging of different refractive index layers,the overall absorption of sunlight can be reduced without affecting the infrared radiation of the emissive layer.This paper mainly reviews recent advancement of daytime radiative cooling materials,which are,according to their structure,divided into thin films,coatings,fabrics and bulks,and also summarizes the applications of radiative coolers in buildings and battery cooling.