NON-KIRCHHOFF SURFACE USING MEDIA WITH DIRECTIONALLY VARYING ABSORPTION EFFICIENCY

A unique radiation trapping surface is proposed in which the effective monochromatic absorptivity-to-emissivity ratio is much greater than o ne (a non-Kirchhoff surface), The surface is comprised of a plane-para llel layer of a disperse suspension of compound particles, Each partic le has a small absorber sphere embedded eccentricly in a larger lens s phere, resulting in an absorption coefficient for the medium that is h ighly dependent on direction, In combination with an opaque, specularl y reflecting boundary opposite tile incident flux side of the medium, such a device acts as a planar radiation trap. Computational results s how that an effective monochromatic absorptivity-to-emissivity ratio o f up to 70 can be achieved, along with a through-flux that is superior to that of an opaque surface that obeys Kirchhoff's law. The effects of optical thickness, incidence angle, particle orientation error, and suspending substrate conductivity are investigated.