Reordering the Absorption Coefficient Within the Wide Band for Predicting Gaseous Radiant Exchange

Abstract

The “exact” calculation of the radiant transfer in gaseous enclosures has remained impractical for design; the highly complex nature of the absorption spectrum of the gases has meant that an inordinately large computational effort is required to effect an exact answer. In this paper we show how the complex absorption distribution for an isothermal gas can be replaced by a set of smooth curves. This procedure can be visualized as one of actually reordering the full complex absorption distribution within each vibration-rotation band, and then replacing it by a smooth curve. Such a smooth curve can then be readily approximated by a stepwise function, and radiant exchange calculations can be carried out at each step and then summed over all the steps to get the total exchange. This paper explains how the reordered curve can be obtained and gives some sample plots of the reordered absorption coefficient curve. Fitted functions for the rearranged curves have been provided, and some solutions to the radiant exchange problems are given and compared to line-by-line solutions. About 50 to 200 steps in the stepwise curve are found to be adequate in order to obtain an answer within a few percent of the exact answer.