Best way to mesh closed pipe-loop
 

Hey everyone,
I am modelling a rectangular(with branching at top and bottom) natural circulation loop with isothermal heat source and heat sink and the rest of the surfaces are adiabatic.
I am unable to mesh the closed loop properly.If I use the default mesh generate
option,I am getting 1 million cells.I also need to redefine mesh near the wall for the boundary layer.
Out of the many meshing methods available in ansys mesher,
which one would be suitable for this?
Also how can i convert tetrahedral(triangular) mesh to quad mesh?
I am attaching a pic of the geometry.One pic is of the whole geometry.
2nd pic is of upper-right zoomed-in section of the geometry showing tetrahedral cells.
Any help is appreciated.Thnx

hello sir,do you know how to mesh a close loop-pipe now? I have the same question as you were,could you please help me