H. Kim, R. Garcia-Mendez, T. Thompson, J. Sakamoto, A. Lenert. Nanoporous Thermal Filters for High-Performance Sub-Ambient Radiative Cooling. Materials Research Society Fall Meeting, Boston, MA, November 26-December 1, 2017.
A. Lenert, Enhanced Energy Conversion by Shaping the Spectrum of Thermal Radiation, Gordon Research Conference: Pathways for Solar Energy Conversion and Storage: Electricity, Thermal and Fuel, Hong Kong, June 17-22, 2018.
H. Kim, A. Lenert. Optical and thermal filtering nanoporous materials for sub-ambient radiative cooling. Journal of Optics, 20 (8), p. 084002, 2018. https://doi.org/10.1088/2040-8986/aacaa1
Materials that reject heat into Space by selectively radiating through the atmospheric 8-13 mm transparency band show promise in passive cooling applications such as peak electrical load reduction and dry cooling for arid climates. Being able to emit in the 8-13 mm “atmospheric window” while simultaneously preventing solar radiation from reaching the cold emitter is important to the performance of the device. We investigate an approach where selective emission is enabled by a selectively transparent cover on top of a broadband emitter. A theoretical study is conducted on the effects of volume fraction and material composition on the radiative properties of the cover. By tailoring the porosity and composition of the solid structure we observe a spectral region of transmittance surrounded by regions of short-wavelength scattering and long-wavelength absorption. Unlike conventional white paints that primarily reflect sunlight, a selectively transparent porous cover may enable passive cooling at temperatures lower than the surroundings.
KEY WORDS: nanostructured materials, thermal radiation, radiative cooling, spectral selectivity
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