CORRELATED-K FICTITIOUS GAS-MODEL FOR H2O INFRARED RADIATION IN THE VOIGT REGIME

The ability of the correlated-k fictitious gas (ckfg) approach to accurately predict radiative transfer in strongly nonhomogeneous media is studied for the case of water vapor absorption lines with Voigt profiles. In the ckfg approach, the real gas is considered as a mixture of fictitious gases, each one characterized by absorption lines with similar transition lower level energies. The correlated-k approach is then applied to each gas and the spectra of different gases are assumed to be uncorrelated. The model is studied for a range of temperatures (180-2500 K) and pressures (10(-2) atm). In addition, the model takes into account the nonlorentzian behavior of the far wings. The model parameters are obtained from line-by-line calculations based on approximate spectroscopic data suitable for high temperature and low spectral resolution applications. The choice of the quadrature for spectral integrations and of the lower level energy E '' ranges is discussed. ckfg results are compared to the reference line-by-line calculations and to the results from the correlated-k (ck) approach, and from available statistical narrow-band (SNB) models in the Voigt regime. It is shown that a 10 point quadrature may be sufficiently accurate, even for very small line widths. ckfg results agree well with line-by-line calculations while ck and SNB models may strongly underestimate the intensity of radiation emitted by a hot gaseous column and transmitted through a long cold column.