Numerical Simulation of Laminar Mixed Convection of Air Flow Through Uniformly Heated Vertical Tubes

This paper discusses laminar mixed convection of air flow through vertical tubes. Calculations were performed by solving the Navier-Stokes and energy equations for a number of heating lengths. The Reynolds number based on the fluid bulk velocity and diameter of the tube is Re = 500 and Grashof number based on wall heat flux is Gr = 10⁶. The numerical results have been obtained using a finite-volume code which solves the governing equations in axi-symmetric coordinate system. The pressure field is obtained with the SIMPLE algorithm. The HYBRID scheme is used for the convective terms. The computer code was validated by comparing its predictions with the reported analytical, numerical and experimental results. For various heating lengths the values of Nusselt number and friction coefficient are presented and the effects of heating length on these parameters are studied. It was found that for the buoyancy-aided convection, the velocity in the vicinity of the wall increases while decreases in the core region. These result in an enhancement of wall heat transfer coefficient.