Abstract
Mixed convection in the entrance region of a horizontal steel tube insulated over its bottom half and subject to a uniform heat flux over its top half, has been studied numerically. The effects of circumferential conduction in the wall are evaluated by comparing the hydrodynamic and thermal fields in water for the conjugate problem with corresponding results calculated by applying the thermal boundary condition to the fluid-solid interface. In the former case, an intense secondary flow induced by natural convection extends over the entire cross-section while the second case results in thermal stratification. Far from the entrance, the axial velocity profiles as well as the circumferential distribution of the local Nusselt number and the wall shear stress are quite different for these two cases.