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OBJECTIVES:
Prediction of radiative transfer in high temperature gases is very difficult due to the strong spectral variation of the absorption spectrum. Past approaches have employed wide or narrow band averaging. However, these approaches prescribe the gas emissivity or transmissivity as the basic radiative property. Contemporary techniques for predicting radiative transfer in volumetrically participating systems solve the Radiative Transfer Equation (RTE), in which the absorption coefficient is specified locally as the fundamental radiative property. Thus, band averaging approaches in modeling high temperature gas radiative effects are incompatible with the best available methods for predicting the radiative transfer. The objective of the effort summarized here is the development of a model which specifies the absorption coefficient as the fundamental property, and which can be used in arbitrary solution method for the RTE. Specifically, the SLW model is a radiative property model for H2O-CO2 mixtures developed to account for the non-gray radiative transfer in gases in an efficient manner, while retaining the physical basis of the spectral line information of the infrared-participating gases.

DESCRIPTION:
The SLW model for the prediction of radiation transfer in high temperature gases has been developed to provide an engineering prediction tool for the calculation of radiative transfer in high temperature gas systems with accuracy approaching that of much more costly line-by-line techniques. The SLW model may be applied using any arbitrary solution method for the RTE (e.g., spherical harmonics, discrete ordinates, moment methods, discrete transfer, etc.) which requires a locally defined absorption coefficient. Further, the model may be used in multidimensional situations, irregular geometries, and where scattering must be accounted for. Drawing from the classical Weighted-Sum-of-Gray-Gases (WSGG) model for high tempera-ture gas radiative properties, the SLW approach incorporates the detailed line structure of the partici-pating gases. The parameters in the model are obtained directly from the line-by-line spectra of the primary radiating species in combustion environments, H2O and CO2. The model is based on a novel absorption-line blackbody distribution function, which is generated and fitted empirically from detailed spectral line data. High temperature lines are generated using approximate theory to extend the current gas spectral absorption data base to combustion temperatures.

The SLW model has been formulated for applications of increasing complexity including isothermal/homogeneous media, non-isothermal/non-homogeneous media, binary gas mixtures, and non-gray boundaries and particulates. Extensions to high pressure have been recently added. The SLW model has been extensively tested by comparison with computationally intensive line-by-line integrations of the RTE for a broad range of one-dimensional, and some limited two-dimensional geometries. The accuracy of model predictions compares very favorably with spectral line-by-line bench-marks, at a small fraction of the computational effort. The SLW model has also been implemented in comprehensive calculations to demonstrate its use in a coupled situation as well.

ACKNOWLEDGMENTS:
The SLW model was developed by Prof. Brent W. Webb and Martin K. Denison, a former doctoral student at BYU. The financial support of ACERC is gratefully acknowledged. The Center is supported by the National Science Foundation, U.S. Department of Energy, the State of Utah, and a number of industrial companies.

REFERENCES:
Denison, M.K. and Webb, B.W. "A Spectral Line-Based Weighted-Sum-of-Gray-Gases Model for Arbitrary RTE Solvers," ASME J. Heat Transfer, Vol. 115, 1993, pp. 1004-1012.

Denison, M.K. and Webb, B.W. "An Absorption-line Blackbody Distribution Function for Efficient Calculation of Gas Radiative Transfer," J. Quant. Spectr. Rad. Transfer, Vol. 50, 1993, pp. 499-510.

Butler, B.W.; Denison, M.K. and Webb, B.W. "Radiation Heat Transfer in a Laboratory-Scale, Pulverized Coal-Fired Reactor: Experiment and Analysis," Exp. Thermal Fluid Sci., Vol. 9, 1994, pp. 69-79.

Denison, M.K. and Webb, B.W. "k-Distributions and Weighted-Sum-of-Gray-Gases--A Hybrid Model," Heat Transfer - 1994, Vol. 2, 1994, pp. 19-24.

Denison, M.K. and Webb, B.W. "Development and Application of an Absorption-Line Blackbody Distribution Function for CO2," Int. J. Heat Mass Transfer, Vol. 38, 1995, pp. 1813-1821.

Denison, M.K. and Webb, B.W. "The Spectral Line-Based Weighted-Sum-of-Gray-Gases Model in Non-Isothermal Non-Homogeneous Media," ASME J. Heat Transfer, Vol. 117, 1995, pp. 359-365.

Denison, M.K. and Webb, B.W. "The Spectral-Line Weighted-Sum-of-Gray-Gases Model for H2O/CO2 Mixtures," ASME J. Heat Transfer (in press).

Denison, M.K. and Webb, B.W. "The Spectral Line Weighted-Sum-of-Gray-Gases Model--A Review," in Proceedings First International Symposium on Radiative Heat Transfer (in press).

Denison, M.K. and Webb, B.W. "The Absorption-Line Blackbody Distribution Function at Elevated Pressure," in Proceedings First International Symposium on Radiative Heat Transfer (in press).