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2D TRANSIENT Heat Transfer Problem

Posted Apr 26, 2013, 3:05 a.m. EDT Fluid & Heat, Heat Transfer & Phase Change, Mesh, Studies & Solvers Version 4.2 2 Replies

Gary Yu
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Hi everyone,

I am encountering an error in the time dependent situation - Failed to find consistent initial values, last time steps not converged.

I have specified 'initial values' and the required boundary conditions, also I used the finest mesh available in the model already. The error still comes out.

Please find attached my model for details.

I have previously done a Stationary scenario for the same model, there was no problem, and gave a very logical solution. Once I changed it to Time Dependent, I have this problem.

It would be greatly appreciated if someone can advise or assist.

Thank you in advance.

Kind regards,

Gary Yu
2 Replies Last Post Oct 29, 2014, 3:23 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 26, 2013, 3:19 a.m. EDT
Hi

first of all, for long thin pipes the best results are with the pipe flow module, it's specifically set up for that. In full NITF you are wasting Gb of RAm and time solving the full NS for nothing in reality ;)

Then I'm not sure you initial conditions are that good. What about the absolute pressure, the gauge pressure and the pressure drop in such a long tube ? use at least an initial velocity flow of parabolic type and a pressure drop of Poiseuille type, then run a stationary solver to get a constant fluid flow, there after run a time dependent sovler with the temperature defined.

Often its simpler to start with a straight 1m long tube, get the physics to match, be sure one masters all the settigns, and then do a more complex case as this one ;)

--
Good luck
Ivar
Hi first of all, for long thin pipes the best results are with the pipe flow module, it's specifically set up for that. In full NITF you are wasting Gb of RAm and time solving the full NS for nothing in reality ;) Then I'm not sure you initial conditions are that good. What about the absolute pressure, the gauge pressure and the pressure drop in such a long tube ? use at least an initial velocity flow of parabolic type and a pressure drop of Poiseuille type, then run a stationary solver to get a constant fluid flow, there after run a time dependent sovler with the temperature defined. Often its simpler to start with a straight 1m long tube, get the physics to match, be sure one masters all the settigns, and then do a more complex case as this one ;) -- Good luck Ivar
Myungwu Woo
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Posted: 1 decade ago Oct 29, 2014, 3:23 p.m. EDT
Hi,
I revised your .mph file to get a transient solution. Please see attached file.
I am not sure you like or not I changed. But I hope this helps to your work.

Regards,
Hi, I revised your .mph file to get a transient solution. Please see attached file. I am not sure you like or not I changed. But I hope this helps to your work. Regards,

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