Emissivity Calculations for Diatomic Gases

An approximate method for estimating radiant-heat transfer from gaseous emitters has been developed. An average absorption coefficient is used for an effective width of an entire vibration-rotation band. The procedure for determining an average absorption coefficient in terms of integrated absorption can be justified, approximately, for very large total pressures where the spectral half-width is no longer small compared with the rotational spacing. Because of this limitation, it is to be expected that the procedure proposed here will be particularly useful only in estimating gaseous emissivities for emitters in high-pressure combustion chambers. Nevertheless, it appears that the simplified procedure yields reasonable results even at relatively low total pressures. Thus a comparison of calculated and observed emissivities for CO at atmospheric pressure shows satisfactory agreement, especially at large optical densities. Representative emissivity calculations over a wide temperature range are described. Emissivity calculations on CO, NO, HF, HCl, HBr, and HI can be carried out very rapidly by the use of recently published data on these gases.