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Hello,

I created a simplified model which just simulates the flow of heated air through a pipe, heating up a small piece of the pipe-wall.

It´s completley symmetric, so I decided to use the symmetrie line in the center. For the further application of the Model, I cant reduce the problem to a 2D-Axiasymmetric model.

The transferred heat from the gas to the pipe wall seemed to be way to low. My Calculations showed that the energy which is lost by the hot air is several times bigger than the energy which heated up the pipe.

Checking the heat fluxes of the system revealed that energy goes through the symmetry and "disappears".

Removing the cut-line and simulating with the whole cross-section gives a correct result ( less than 3% difference between theory and simulation).

Are there any wrong boundary conditions? Why do those heat-fluxes out of the System appear? Or is it a problem in Comsol?

About the Simulation:

Run Study 2 (solves the flow)

Enable the 3 Multiphysics (Flow does not converge while those physics are enabled, though they are deactivated in the solver for this solution is not activated)

Run Study 4 (solves the temperature for 20 sec, pipe should be heated to around 22 degC)

Changes done in full cylinder: - Disabling workplane 1, Partition Domain 1, Delete Entities 1 - Adding the new Boundaries to the Boundary Layer Mesh

Same procedure to run like the first model. Now the pipe heats up to nearly 27 degC.

Thanks for any help!

If you have any further remarks or suggestions about the model, feel free to answer :-)