Turbulent Combined Heat Transfer in a Vertical Square Duct under Variable Thermophysical Properties and Non-Boussinesq Condition

Abstract

The objective of the present article is to investigate the effects of thermal radiation on turbulent mixed convection in a vertical square duct under variable thermophysical properties and the non-Boussinesq condition. Both right and left walls are kept at constant temperatures whilst back and front ones are insulated. Participating medium is considered as gray, absorbing and scattering. Dynamic viscosity and thermal conductivity vary with temperature using the power law. Density variation is based on the perfect gas equation of state and it is regarded as the non-Boussinesq condition. Results are presented for both entrance and thermally and hydrodynamically fully developed regions. Numerical simulations are carried out by developing a solver in OpenFOAM and the finite volume method is employed to solve governing equations. RANS based model is used to simulate turbulence. With a rise in radiation effects by decreasing single scattering albedo, due to reduction in buoyancy effects, the temperature profiles become flattened. As single scattering albedo decreases, mean velocity, temperature, turbulence kinetic energy and mean Nusselt number on both aiding and opposing sides increase significantly. Near the hot wall (aiding side), mean Nusselt number and friction factor for Boussinesq approximation are more than the non-Boussinesq condition. Whilst, near cold wall (opposing side) the non-Boussinesq condition results in greater mean Nusselt number and friction factor.