Abstract
The effective hemispherical absorptivity of a window in a cavity with Lambertian walls of absorptivity α is determined by considering the cavity to be at a uniform temperature and calculating the radiant energy escaping from the aperture when multiple internal reflections are considered. The window has an angularly independent transmissivity τ. The effective hemispherical absorptivity is found to be αeff = τα/{1 − τA1/(A2 − A1)] + τA1/(A2 − A)}, where A1, the aperture area, is small compared with A2, the area of the cavity including the aperture. The results can be used for determining the acceptance of solar radiation by direct-gain passive solar rooms.
© 1980 Optical Society of America
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