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Radiation View Factor for Co-Axial and Unequal Rectangles in Parallel Planes

ABSTRACT A closed-form and easy-to-use analytical expression is derived for calculating the radiation view factor between a pair of dissimilar rectangular surfaces facing each other from two different parallel planes. The alignment of the rectangles is such that: (i) a line joining their centers would be normal to both surfaces, and (ii) observed in a plan view in the direction of this shared axis, the rectangles are not turned by an angle relative to each other. Strangely enough, a simple formula for finding view factors for this configuration is not available at present in well-known references on this topic. The usefulness of the proposed expression, for quick calculations of view factors, is demonstrated with examples. It is shown that this generalized expression can be readily specialized to a few well-documented view factor formulae. It can be easily extended for view factor calculations involving pairs of unequal and non-aligned parallel rectangular surfaces, making it a flexible and handy result for heat transfer pedagogy.