Equilibrium temperatures of ideal spectrally selective surfaces

Abstract

Abstract Spectrally selective surfaces were assumed for which the monochromatic emissivity changed abruptly at specific wavelengths. These surfaces could be completely characterized by two parameters: the height of the step change in emissivity, and the wavelength of the change. This characterization is more general than the widely used a e ratio. Equilibrium temperatures were calculated for such surfaces when exposed to both focused and unfocused solar radiation at the earth's orbit distance. Varying step heights at wavelengths between 0.3 and 20 microns were assumed. With unfocused radiation, temperatures as low as 40 K were found for surfaces for which the emissivity increased from zero to unity at long wavelengths, and temperatures as high as 2400 K when the change was from unity to zero at short wave-lengths. For focused radiation, much higher temperatures were found. Such surfaces may find application in power-generation cycles or in the storage of cryogenic propellants in space.