Molecular Gas Radiation in the Thermal Entrance Region of a Duct

The effect of molecular gas radiation upon the thermal development downstream from a step change in wall temperature is examined for both laminar and turbulent flow in a black-walled flat-plate duct. The exponential-tailed band model is used to represent spectral variations in gas absorption and emission. Values of total and radiative Nusselt numbers, cold-wall-layer transmission factors, and dimensionless bulk temperatures are reported for several dimensionless axial locations and for various sets of the dimension-less controlling parameters. Even in the entrance region, self absorption by wall layer gas blocks significantly the radiation exchange between the gas core and wall. An approximate correlation is proposed for both plane-duct and pipe turbulent entrance flows.