Mixed convection heat transfer in the entrance region of horizontal annuli

The present study deals with a numerical investigation of steady laminar mixed convection heat transfer in a horizontal concentric annulus using air and water as the working fluid. Special attention has been paid to the entrance region effect. The thermal boundary condition chosen is that of uniform heat flux at the inner wall and an adiabatic outer wall. The basic numerical procedure used is the SIMPLE algorithm [Int. J. Heat Mass Transfer 15 (1972) 1787] which uses the finite difference method for solving the momentum and energy equations. The investigations reveal that the Nusselt numbers for air are considerably greater than the corresponding values for fully developed mixed convection values over a significant portion of the annular duct. The numerical results were supplemented with some experimentally obtained data.