Buoyancy-assisted flow reversal and combined mixed convection–radiation heat transfer in symmetrically heated vertical parallel plates: Influence of two radiative parameters

The present article encompasses the laminar ascending flow and combined mixed (free and forced) convective-radiative heat transfer within symmetrically heated vertical parallel plates. Radiative heat transfer between two opposite walls is considered and the gas is assumed as gray, absorbing, emitting and scattering. Elliptic governing equations for the case of buoyancy assisted flow are solved numerically employing a home-made CFD code based on the finite volume method. The radiative transfer equation is solved using the discrete ordinates method, adopting its S6S6 quadrature scheme. The influence of two important radiative parameters, namely, wall emissivity and scattering albedo, while the extinction coefficient is either constant or not, on the occurrence of flow reversal, fanning friction coefficient, flow and thermal fields, is investigated. Present results show that the occurrence of reversed flow enhances both heat transfer and the fanning friction coefficient, and the radiation mode amplifies heat transfer, while reducing the fanning friction coefficient. As wall emissivity increases from 0 to 1, effects of radiation on flow and thermal fields rise. However, there is no linear relationship for the whole range of εε. As scattering albedo varies between 0 and 0.75, radiation effects on flow and thermal fields for the constant and variable extinction coefficient are entirely opposite.