Ansys Employee
Have you performed a mesh convergence study? The mesh might not be fine enough to give an accurate result. Theflange also seems to be made of lots of intricate parts. You might want to simplify the geometry (use a simple rectangular block instead ) and try remeshing with a much finer mesh. On the top pipe you have used only one element over the thickness of the pipe and 2 different boundary conditions on each face, meaning there is heat transfer in the direction perpendicular to the thickness. You will need more elements across the thickness to get accurate results.
Regards Ishan.