Local configuration factors for radiant interchange between cylindrical surfaces in rod bundle geometry

The aim of this study is to obtain configuration factor expressions for the diffuse interchange of radiant energy between two parallel cylindrical rods by contour integral technique. The contour integral approach for diffuse configuration factors has been derived by Sparrow (1963). It replaces the usual area integrals by more tractable contour (i.e., line) integrals, which simplifies analytical calculation of configuration factors. The advantages of this representation are associated with the reduced order of the integrals (i.e., double reduced to single, quadruple reduced to double) which must be evaluated to calculate the angle factor. For the numerical or analytical evaluation of configuration factors, the reduction in the order of the integrals has a great practical utility. In the literature, contour integral technique has been stated to appreciably be the more precise method than the area integration method. ses studied are for elemental ring areas of (i) two cylindrical rods/tubes, (ii) two cylindrical rods with interference from a third rod and (iii) cylindrical rod within a cylindrical enclosure. The results of present configuration factor expressions meant for the ring elements of finite length geometries have been compared with values using exact algebraic expressions available in the literature for infinite length, analytical configuration factor expressions for equal finite lengths and with numerical results available in the literature. Contour integral technique has been observed to be a simple method that yields realistic results. This study has application in the analysis of fin-tube radiators, boiler tubes, nuclear fuel rod bundle, etc.