Combined gas radiation and laminar mixed convection in vertical circular tubes

A numerical study of the interaction between thermal radiation and laminar mixed convection for ascending flows of emitting and absorbing gases in vertical tubes is presented. The radiative properties of the flowing gases, H2O, CO2 and H2O–CO2 mixtures are modeled by using the global absorption distribution function model. The temperature-dependent thermophysical properties are considered when solving the flow field and energy balance equations. Results are presented in terms of velocity and temperature fields, and of evolution of centerline velocity, friction factor and heat fluxes. The effects of radiation on the regime of reverse flow occurrence are also examined. It is shown that, for heated gases, radiation tends to reduce the velocity distortion effect of buoyancy. Radiative transfer delays then significantly the occurrence of reverse flow for heated gases while, for cooled gases, the flow regime is practically not affected.