Accurate modeling of radiative heat transfer through combustion gases has received considerable attention in recent years. The spectral line weighted-sum-of-gray-gases (SLW) model was developed based on detailed line-by-line spectral data of gases. A critical element of the SLW model is the absorption line blackbody distribution function (ALBDF). This function was designed to utilize the spectral properties of gases in an efficient and compact manner. However, there are several limitations of the ALBDF in its original form. First, the valid ranges of temperature and pressure are not large enough to include important applications, such as oxy-combustion, where temperatures can exceed 2500 K, and pressurized combustion, where non-atmospheric pressures are expected. In addition, since the original ALBDF correlation was developed, new spectral data have become available which extend the accuracy of the previous work. Finally, it is desirable to be able to represent the ALBDF of CO in addition to H2O and CO2. Improving the SLW model in this manner will make it more generally applicable and ensure greater confidence in its accuracy. Line-by-line absorption cross-section data were generated carefully using a recently released spectroscopic database, HITEMP 2010. The Voigt line profile was implemented, and line wings were included in regions where they maintain a significant contribution. Line-by-line calculation of the ALBDF, total emissivity, and radiative transfer were also performed in order to provide benchmark data and to explore the influence of variable total pressure. It was found that increasing total pressure causes the ALBDF to shift to lower values at a given absorption cross-section, although this change is weaker at increasing temperature. Total emissivity is strongly affected by total pressure changes, although the change is modest if the product of partial pressure and path length is held constant. Increasing total pressure in a layer of gas increases the radiative flux exiting the gas layer; this was also found to be true for both the case of constant layer length and constant mass of radiating material. Efficient representations of the ALBDF were generated. The hyperbolic tangent correlation of Denison and Webb was updated to reflect improved spectroscopic data and to cover a wider range of temperature (400 K = T = 3000 K) and pressure (0.1 atm = p = 50 atm). The correlation was also extended to CO, which had not been correlated previously. Using tabulated line-by-line data directly was also explored, and these data have been made available for H2O, CO2, and CO. Finally, these efficient representations of the ALBDF were successfully validated by comparison with line-by-line calculations and experimental data for both total emissivity and radiative transfer. The latter included comparisons with intensity measurements and a comprehensive combustion simulation implementing the SLW model.

A radiation code based on method of lines (MOL) solution of discrete ordinates method (DOM) for the prediction of radiative heat transfer in nongray absorbing-emitting media was developed by incorporation of two different gas spectral radiative property models, namely wide band correlated-k (WBCK) and spectral line-based weighted sum of gray gases (SLW) models. Predictive accuracy and computational efficiency of the developed code were assessed by applying it to the predictions of source term distributions and net wall radiative heat fluxes in several one- and two-dimensional test problems including isothermal/non-isothermal and homogeneous/non-homogeneous media of water vapor, carbon dioxide or mixture of both, and benchmarking its steady-state predictions against line-by-line (LBL) solutions and measurements available in the literature. In order to demonstrate the improvements brought about by these two spectral models over and above the ones obtained by gray gas approximation, predictions obtained by these spectral models were also compared with those of gray gas model. Comparisons reveal that MOL solution of DOM with SLW model produces the most accurate results for radiative heat fluxes and source terms at the expense of computation time when compared with MOL solution of DOM with WBCK and gray gas models. In an attempt to gain an insight into the conditions under which the source term predictions obtained with gray gas model produce acceptable accuracy for engineering applications when compared with those of gas spectral radiative property models, a parametric study was also performed. Comparisons reveal reasonable agreement for problems containing low concentration of absorbing-emitting media at low temperatures. Overall evaluation of the performance of the radiation code developed in this study points out that it provides accurate solutions with SLW model and can be used with confidence in conjunction with computational fluid dynamics (CFD) codes based on the same approach.