Optical Design of Silica Aerogels for On‐Demand Thermal Management

Abstract

Silica aerogels, a type of porous material featuring extra low density and thermal conductivity, have drawn increasing interest from both academia and industry owing to their excellent thermal insulation performance. However, thermal insulation is always the single consideration when silica aerogels are used for thermal management. In this study, the on‐demand thermal management (ODTM) of silica aerogel with either passive thermal insulation, passive heating, or passive cooling in different environments is revealed. The ODTM behavior of silica aerogels can be simply fulfilled through their optical property variations such as solar light transparency and infrared emissivity, which are controllable via the microstructures of the building blocks and surface composition design. Robust solar heating of 25 °C higher than the ambient in the daytime and sub‐ambient cooling of 7 °C at night is achieved with the traditional transparent silica aerogel. Interestingly, sub‐ambient cooling of 5 °C in the daytime and a warmer state on cold nights is achieved by modifying its solar transmittance and infrared emissivity. This study guides a comprehensive understanding of the thermal management behavior of silica aerogels and leads to ODTM applications of silica aerogels by tailoring their optical and thermal conductivity properties.

Highly Optically Selective and Thermally Insulating Porous Calcium Silicate Composite SiO2 Aerogel Coating for Daytime Radiative Cooling

“…In the mid-infrared band, because the coating thickness is much larger than the infrared wavelength, usually 400 μm, it is difficult for electromagnetic waves in the infrared band to exchange heat through the coating. Therefore, the infrared transmittance exhibited by the radiative cooling coating is 0 . According to Kirchhoff’s law of thermal radiation and thermal equilibrium, the absorption rate A for a material at a specific wavelength equals its emissivity E . , The emissivity and solar reflectivity of ideal radiative cooling materials are depicted in Figure b.…”

“…Therefore, the infrared transmittance exhibited by the radiative cooling coating is 0. 54 According to Kirchhoff's law of thermal radiation and thermal equilibrium, the absorption rate A for a material at a specific wavelength equals its emissivity E. 55,56 The emissivity and solar reflectivity of ideal radiative cooling materials are depicted in Figure 1b. Therefore, the key to achieving optimal performance in radiative cooling materials lies in effectively reflecting sunlight energy (0.3−2.5 μm) to minimize heat absorption caused by solar radiation, while simultaneously possessing a 100% emissivity within the atmospheric window band (8−13 μm), and efficiently reflecting nonatmospheric window band near-infrared energy (2.5−8 μm, 14−20 μm) to reduce radiative heat transfer to the surrounding environment.…”

Synthesis of graphene oxide-mediated high-porosity Ni/C aerogels through topological MOF deformation for enhanced electromagnetic absorption and thermal management

“…Generally speaking, the thermal insulation performance of a medium is mainly determined by its intrinsic properties and microstructure. 65 From NCCA to NCGCA-3, the carbon content is incremental and the relative graphitization degree is reinforced. Thus, the intrinsic thermal conductivity will be gradually enhanced.…”

Conformal Structured Ceramic Textiles with Passive and Active Heating Functionality

“…The high IR emissivity of the PPy@Al 2 O 3 ceramic fiber fabrics indicated potential passive radiative cooling, combining their high-temperature resistance up to 1300 °C, which may find specific application in ultrahigh temperature protection. Nevertheless, the effect of RC should be avoided on sunny nights. − …”