“…Instances of these processes are nuclear reactor engineering and in heating or cooling of heat exchangers for viscous liquids, heat exchangers for gas flows, electronic cooling, compact heat exchangers, and the cooling of rotating parts such as rotor blades of gas turbine also the pipe lines used for transporting oil. Raisee and Shahraeeni [1], (2007), made numerical simulation on vertical tubes that uniformly heated with laminar mixed convection air flow. For a bit of heating lengths, the Navier-Stokes and energy equations were solved using a finite-volume code which solves the governing equations in axisymmetric coordinate system, with Reynolds number Re=500 which depends on the fluid bulk velocity and diameter of the pipe, and Grashof number Gr=10 6 which depends on wall heat flux.it was resolved that the velocity near the wall increases for the buoyancy-aided convection, and decreases in the center area.…”