Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
EVALUATION OF THE WSGG MODEL FOR COUPLED CALCULATIONS OF LAMINAR FLAMES
Submission Author:
Pedro Wink Guaragna , RS
Co-Authors:
Pedro Wink Guaragna, Guilherme Crivelli Fraga, Francis França
Presenter: Pedro Wink Guaragna
doi://10.26678/ABCM.ENCIT2022.CIT22-0167
Abstract
The radiative heat transfer process in participating media is a subject of great importance, especially for the energy generation industry, as in combustion processes thermal radiation is generally the main heat transfer mode. However its reliable computation still is challenging. The radiative properties of absorbing-emitting species have a complex behavior as these are not regularly distributed regarding the wavelength, but rather in specified intervals, called bands, inside which they strongly oscillate. Moreover, radiation in participating media is a volumetric phenomenon, instead of a surface phenomenon, so changes in the temperature and species concentration of the gases throughout space must also be accounted for. Compromise between accuracy and computational costs must be accounted for when modelling the gas radiation in the combustion process. Among the models that represent this dependence that are available in the literature, the weighted-sum-of-gray-gas (WSGG) stands out for such compromise. The WSGG model represents the spectrum with a few gray gases that occupy certain portions of the spectrum plus a transparent window, and various recent studies have shown that the model is capable of fully accurate predictions of the radiative heat flux and heat source. However, most studies have assessed the WSGG model for decoupled radiative transfer calculations, i.e., where the radiation field is computed from predetermined fields of pressure, temperature and species concentration. In practical applications, though, radiation is coupled to all other physical processes, and it is known that inaccuracies in the prediction of the radiation field can lead to errors in other scalars, such as the temperature and the rate of species formation. In the framework of combustion processes, this can be particularly important, since it is critical to accurately capture formation of some species (e.g., CO). Therefore, this study carries out an evaluation of different formulations of the WSGG model for coupled radiation-combustion calculations of a set of one-dimensional, laminar diffusion flames. The calculations are performed in the CHEM1D code, on which the WSGG model has been implemented. Results for the fields of temperature and species concentrations, as well as the radiation field, will be analyzed and compared to both experimental cases (when available in literature) as well with the line-by-line integration (which stands out as the benchmark for spectral models). The cases were for a counterflow methane-air combustion with and without dilution in the fuel side of carbon dioxide.
Keywords
Radiation heat transfer, weighted-sum-of-gray-gases model, Combustion, numerical heat transfer
