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This study analyses the effects of nongray gas radiation on double diffusive convection, in a square differentially heated cavity filled with air-CO 2 mixtures, when the buoyancy forces (thermal and mass) are cooperating or opposing. The radiative source term in the energy equation is evaluated by the discrete ordinate method (solving the radiative transfer equation) and the SLW spectral model (accounting for real radiative properties of absorbing species). Here, gas absorption varies with the local temperature and concentration of pollutant, which induces a strong direct coupling between the concentration and thermal fields that would not exist with gray gas. Simulations are performed at different concentrations of CO 2 corresponding to different flow regimes (thermal, transitional, and mass). Results show the following: (i) in cooperating flow, radiation modifies essentially the heat transfer and the characteristics of temperature and concentration fields; (ii) in opposing flow, radiation effects are more important and depend on the nature of the flow regime.

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A three-dimensional (3D) numerical study has been performed to investigate the effects of non-gray gas radiation on double-diffusive natural convection in a cubic enclosure filled with either air-H 2 O or air-CO 2 mixtures in cooperating situations. Gas radiation was taken into account by the discrete ordinates method (DOM) associated with the spectral line weighted-sum-ofgray-gases (SLW) spectral model. Results obtained for two average concentrations of H 2 O and CO 2 (10% and 20%) show that radiation modifies the temperature and concentration structures by creating oblique stratifications. The heat transfer rate is decreased, whereas mass transfer is not much modified. In addition, a comparison between 2D and 3D results is presented. ARTICLE HISTORY

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