title: Effective absorptivity of a Lambertian cavity with a dielectric window.
abstract: The effective hemispherical absorptivity of a window in a cavity with Lambertian walls of absorptivity alpha 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 tau. The effective hemispherical absorptivity is found to be alpha(eff) = taualpha/{alpha[l - tau A(1)/(A(2) - A(1))] + tauA(1)/(A(2) - A)}, where A(1), the aperture area, is small compared with A(2), 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.
authors.forename: J F
authors.initials: JF
authors.lastname: Burkhart
authors.forename: R E
authors.initials: RE
authors.lastname: Jones