Heat Transfer in Absorbing Emitting Hot Gaseous Mixtures Flowing inside Circular Ducts.

In this work numerical calculations are performed to study thermal radiation effects on heat transfer for combustion products (H₂O-CO₂-N₂) flowing inside circular ducts. Combined heat transfer, by thermal radiation and forced convection is presented in some cases of practical situations such as combustion of natural gas, propane and heavy fuel. Special attention was paid to the treatment of real gaseous mixture thermal radiation, with its spectral nature, and their effects on evolution of radiative, convective and conductive fluxes for a steady laminar flow. The infrared radiative properties of the flowing H₂O-CO₂-N₂ gas mixtures are taken into account in this analysis by using the global Absorption Distribution Function model. Some differences between non gray radiative behaviors of these combustion products, due to different structures of their spectra, are put in evidence through the evolution of the volumetric radiative power. The flow and energy balance equations are solved simultaneously with temperature dependent fluid properties. The approximations of a boundary layer flow are made, except for radiative transfer. The results are presented for typical conditions of combustion products flows. It is shown that radiative transfer affects significantly the different heat fluxes exchanged, and thus the Nusselt number and bulk temperatures. [ABSTRACT FROM AUTHOR]