Laminar mixed convection in a vertical flat channel with a constant wall heat flux

An analytical solution to a system of momentum and energy equations was obtained for a fully developed laminar flow and heat transfer in a vertical flat channel with a constant wall heat flux under the effect of buoyancy force. The velocity and temperature profiles and the Nusselt numbers for the downward and upward flows are compared. The behavior of these parameters under the effect of the buoyancy force is explained. The predicted Nusselt numbers are compared with the available data for round pipes. All components of the hydraulic resistance coefficient encountered in the upward and downward flows are analyzed.