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wrong values in thermal analysis

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Old   December 7, 2009, 05:41
Default wrong values in thermal analysis
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Hi to all people!

I'm contacting you for this reason:

I have built a model that refers to a pipe that is covered by insulating material, I have used bidimensional surfaces to model isulation.

I have made 3 simulation tests :

-The first : with insulating surface at distance of 10 mm from heating source ( exaust pipe) where i assigned only emissivity (aluminium ) insulating surface

-the second :where I moved surface to 5 mm from heating source and added thermal resistance (relative to Glass Fiber)

- The third : only changed thermal resistance of insulating material changing it to a value that is 2 times greater than the material I used in the second test.

My problem is that , in the first two simulations, I have obtained correct values in post processing relative to avarage and maximum temperature. But in the last one I have obtained a peak in some cells that are really out of range, so this influences my average and maximum temperatures, bring my simulation to totally wrong values.

My model use about 800000 polyhedral cell.
I used surface to surface radiation model , coupled flow for convection.

Could It be a meshing problem? Maybe due to thermal resistance raised value?

Anybody can help me ?

Thank you guys...

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