Combined convection and radiation heat transfer in non-gray participating media in a differentially heated square cavity

Natural convection and radiation in a non-gray participating gas mixture in a differentially heated square enclosure is studied numerically. The commercial package ANSYS Fluent 14.5 is used to solve the equations governing flow and energy by the finite volume method. The volumetric radiation source term in the energy equation is governed by the radiative transfer equation (RTE) and it is solved using the discrete ordinates method (DOM). The non-gray behavior of the gas mixture is modeled by the spectral line weighted sum of gray gases (SLW) approach. For an emitting and absorbing medium, the spectral absorption coefficient is modeled alternatively as a gray-SLW temperature dependent quantity, evaluated using the SLW model. User defined functions have been developed to incorporate the radiation source term in the heat transfer equation, while solving the governing equations using Fluent software. The effect of gas mixture mole fraction variation (CO2, H2O, and N2), wall emissivity, Rayleigh number, and convection-radiation interaction are studied. The presence of non-gray gas radiation substantially changes the temperature and flow patterns in the cavity. The results show an augmentation in total Nusselt number and reduction in convective Nusselt number. Comprehensive correlations for total Nusselt number by convection and radiation heat transfer modes are developed which provide insight into the physics associated with the problem.