Analysis of spectral radiative entropy generation in a non-gray planar participating medium at radiative equilibrium with two different boundary conditions

Abstract

In the present study, spectral radiative entropy generation analysis is presented for radiative heat transfer between two parallel plates containing non-gray absorbing and emitting medium at radiative equilibrium. In order to evaluate the effect of boundary condition (BC) on the entropy generation, two configurations of BC are considered. In the first configuration, two bounding walls are assumed to be at prescribed temperatures. In the second configuration, one wall is assumed to be at a prescribed temperature and the other wall is assumed to have prescribed heat flux BC. The discrete ordinates method and the finite volume method are respectively used for the angular and spatial discretization of the radiative transfer equation and radiative entropy generation equations. While the correlated-k (CK) non-gray model is used to evaluate spectral radiative properties. Five cases are considered, including two homogeneous cases and two non-homogeneous cases with a single participating gas (i.e. H2O or CO2) and one homogeneous case with a mixture of H2O, CO2 and soot particles. Spectral, volumetric and total radiative entropy generations are calculated for each BC configuration and case. Also, the effects of the concentration of participating gas, wall emissivity and total gas pressure on radiative entropy generation are attentively analyzed. The results show that irreversible radiative transfer at the wall with lower temperature is the main source of radiative entropy generation in the system. Soot particles increase radiative entropy generation due to absorption and emission process but decrease radiative entropy generation due to walls radiation. The radiative entropy generation is approximately constant when the concentration of participating gas varies for both BC’s. Total radiative entropy generation for the system with the prescribed temperature at walls significantly increases with the increase of wall emissivity; conversely, for the system with mixed BC, total radiative entropy generation linearly decreases. Furthermore, for the system with the prescribed temperature at the walls, radiative entropy generation slightly decreases when medium total pressure increases; while for the problems with mixed BC, increasing medium total pressure does not significantly effect on radiative entropy generation. Finally, results demonstrate that the wall emissivity has a considerable effect on the radiative entropy generation for radiative heat transfer in the non-gray medium in radiative equilibrium.