Predicted effects of inlet turbulent intensity on mixed convection in vertical tubes with uniform wall heat flux

Simultaneously developing upward mixed convection of air in vertical tubes with uniform wall heat flux was studied numerically using the three-dimensional elliptic conservation equations. The coupled hydrodynamic and thermal fields were predicted using both laminar and turbulent formulations (the latter was based on the Launder and Sharma low Reynolds number k–ɛ turbulence model) for Re=1000 and three different values of the inlet turbulent intensity over a wide range of Grashof numbers (Gr⩽108). The turbulent formulation is more versatile since it can predict turbulent as well as laminar fully-developed flow fields. The effects of inlet turbulent intensity on the axial evolution of the hydrodynamic and thermal fields as well as on the developed velocity and temperature profiles are presented. It is also shown that the increase of the inlet turbulent intensity causes a significant decrease of the wall temperature and of the skin friction coefficient at certain Re–Gr combinations.