Abstract: The coupled radiation and convection heat transfer in high temperature heated/cooled tubes with inside participating medium flowing is investigated by numerical simulation.The laminar flow is developed with a Poiseuille velocity distribution but thermal status is developing.By the discrete ordinate method,the nonlinear integrodifferential radiative transfer equation in cylindrical coordinate system is solved to obtain the radiative source term in the energy equation.And the energy equation for the coupled heat transfer is discretized by the finite difference approximation.The local Nusselt number and wall heat flux for convection and the total wall heat flux for coupled heat transfer are used to evaluate the influence of radiation on convection.The effects of the medium thermal conductivity,scattering albedo and phase function as well as the wall emissivity are discussed based on the calculated results.The analysis shows that the effect of radiation weakens convection heat transfer,but compared with the simplex convection,the coupled heat transfer accelerates the development of temperature field and significantly shortens the tube length with obvious heated/cooled effect.Difference appears between the two cases of coupled heat transfer in heated/cooled tubes even though the medium property parameters keep constant.The wall emissivity,the medium thermal conductivity and scattering albedo have great influences on the coupled heat transfer,while the effect of the medium scattering phase function is small.