Radiative properties of model gases for applications in radiative energy transfer

An approximate analysis of the radiative properties of gases is presented for use in problems of fluid mechanics involving radiative transfer of energy. The analytical expressions obtained are presented in a non-dimensional form which clarifies their meaning and gives insight into the numerical magnitudes of significant radiative properties.Results are presented for line and continuum spectral absorption coefficients as functions of frequency and temperature. The corresponding emission coefficients are integrated to obtain Planck mean absorption co-efficients. It is found, for example, that for monatomic gases in the temperature range considered, T < 30 000°K, the Planck mean for atomic lines always exceeds that for the continuum. Although the absorption coefficients for continuum radiation in this temperature range are greatest for frequencies above the ground state ionization frequency, the major contribution to the Planck mean absorption coefficient comes from frequencies below the ionization frequency.Comparison of the photon mean free paths with the particle mean free paths, shows that the Planck photon mfp is much longer than the particle mfp but that the photon mfp corresponding to the peak line absorption coefficient is much shorter than the particle mfp.