Evaluation of the gray gas model to compute radiative transfer in non-isothermal, non-homogeneous participating medium containing CO2, H2O and soot

Abstract

Thermal radiation is usually the dominant heat transfer mode in combustion processes due to the presence of participating gases and soot at high temperatures. However, gases and soot present quite distinct spectral behavior in participating gases, the spectrum can be formed by millions of spectral lines, while in soot, the absorption coefficient varies linearly with the wavenumber. Therefore, when soot radiation is dominant, one can attempt to use simpler approaches, such as the gray gas (GG) model, instead of the sophisticate gas models that are required in gas-dominant radiation. This paper analyses the conditions in which the GG model can be used to provide reasonably accurate computations of radiation in soot–gaseous mixtures. Results are obtained for a one-dimensional slabs formed by a mixture of CO2, H2O and soot, and then compared with the benchmark line-by-line integration. This study shows that, even for relatively moderate concentrations of soot, the GG model can provide sufficiently accurate estimations. In addition, this paper presents newly obtained GG correlations for soot, based on empirical equations, and for CO2 and H2O, based on HITEMP2010 database.