I created a tutorial demonstrates the simulation of forced convection in a pipe: Turbulent Forced Convection
The physical problem to solve is that of a circular-cross section pipe with a heated section where a constant heat flux is added and with ambient air flowing into the pipe from the left with a uniform velocity.
The pipe geometry is
Length: 6.045m
Radius: 0.0294m
The mathematical model used to solve this problem is a boundary value problem.
The domain (or the geometry of the region of interest) is governed by a set of equations, namely conservation of mass, conservation of momentum, and conservation of energy, as well as the ideal gas law, k-conservation, and 
-conservation that need to be solved. Since there is heating in the pipe, the density is variable. Note from the governing equations that the flow is also turbulent. These two additions further complicate the governing equations. The model used to solve the governing equations is the k-epsilon turbulence model.
The boundary conditions are defined at the edges of the domain. For this problem, the boundary conditions are outlined below:
