Effect of Wall Heat Flux Distribution on Laminar Mixed Convection in the Entrance Region of a Horizontal Rectangular Duct

Using a vectorized, finite-difference marching technique, the steady-state continuity, momentum, and energy equations are solved numerically to evaluate the effects of buoyancy on forced flow in a horizontal duct of aspect ratio A = 2. The thermal boundary conditions consist of eight distinct heating configurations for which selective duct surfaces are either adiabatic or uniformly heated, with identical conditions applied to the side walls. Heating from the sides and/or from above results in a single pair of counterrotating circulation cells. However, with heating from below, multiple pairs of counterrotating circulation cells develop. For each heating condition, the developing cross-stream morphology of the buoyancy-driven secondary flow is presented and used to interpret the longitudinal Nusselt number distribution.