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ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
PROPOSITION OF A NEW METHODOLOGY FOR GENERATING THE COEFFICIENTS OF THE WEIGHTED-SUM-OF-GRAY-GASES MODEL IN MIXTURES OF PARTICIPATING GASES
Submission Author:
William Hellwig , RS
Co-Authors:
William Hellwig, Roberta Juliana Collet da Fonseca, Fatmir Asllanaj, Francis França
Presenter: William Hellwig
doi://10.26678/ABCM.ENCIT2022.CIT22-0513
Abstract
In combustion problems, which occur at elevated temperatures due to the chemical reactions and the presence of soot and participating gases, the thermal radiation tends to be the main mechanism of heat transfer. Thus, correctly describing the radiative heat transfer involved in the burning of fossil fuels is of fundamental importance to reduce the emission of pollutants into the atmosphere. However, the accurate calculation of the thermal radiation requires the solution of the radiative transfer equation (RTE), in which it is necessary to account for the hundreds of thousands of spectral lines that compose the absorption coefficient of the gases. Although the line-by-line (LBL) integration is the most accurate among the known methods, in some cases its use is unfeasible, due to the high computational cost required. As an alternative to overcome this difficulty, the development of the global spectral models, such as the weighted-sum-of-gray-gases (WSGG), has received much attention in the radiation field. In this method, the highly irregular behavior of the absorption coefficient of a gas is replaced by some equivalent gray gases with uniform absorption coefficients and the transparent window. So, in this framework, the present study proposes a new methodology for the generation of the coefficients of the WSGG model for mixtures of water vapor and carbon dioxide – two typical products of the combustion of methane in air. This new approach aims to improve the solution of the standard WSGG model by implementing new considerations on the computation of the coefficients, in which the function that determines the weighting factors is composed of terms associated with positive and negative exponents. A molar ratio of 2/1 between the participating species will be used. The generation of the coefficients will be based on the HITEMP2010 database and the temperature range will vary between 400K and 2500K. These new coefficients will be applied for computing the radiative heat flux and radiative heat source and compared with results provided by the LBL benchmark solution. It is expected that these correlations improve the accuracy of the solution and demonstrate a satisfactory agreement with the LBL integration, in addition to being a competitive method in comparison with the existing modern models.
Keywords
thermal radiation, participating gases, weighted-sum-of-gray-gases model, line-by-line integration
