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Heat transfer in solid-Soild domain

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Old   May 9, 2010, 20:55
Default Heat transfer in solid-Soild domain
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Hello,

I wonder how to achieve the successful heat transfer (conduction) betweeen two solid domains (aluminum and steel).
I set conservation target and RMS as 0.01 and 1e-4 respectively (for convergence criteria).
RMS and imbanace are O.K after the simulation.

Aluminum is set 204C initially and is cooled down by heat conduction to the steel. And the intial temp. of steel is 25C.

The temp. of steel near aluminum reaches 80C within 1.6 sec (from 25C) and then is decreased to 26C at the end of transient simulation (87sec).
It does not look normal because the steel temp. is increased to its maximum in a very short time (1.6 sec) and immediately after that, is dropped very quickly with big change (80-26=54C) only in 87sec under condition that the steel has natural convection with air,25C.
Also the aluminum is cooled down from 204C to 27C in 87sec. (It's not realistic!)
I cannot explain properly about these results.

To get good heat conduction between solids domains, aluminum of initial temp. (204C) should last constantly at least a few seconds?
If addtional setup in cfx-pre are required for heat transfer only in solid-soild domain, please let me know.
Thank you very much.

Jaho
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Old   May 10, 2010, 08:26
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Glenn Horrocks
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Lots of things could be wrong.
1) Have you done a mesh size sensitivity check?
2) Have you done a time step size sensitivity check?
3) Have you done a convergence tolerance sensitivity check?
4) Is your convective boundary condition accurate?
5) Are your material properties correct?

Point 5 is a doozy - Aluminium probably undergoes a phase change in the temperature range you quote. Depending on the steel alloy you are using then steel might also. If the metal undergoes a phase change then it gets a lot more complicated - often the phase change releases heat and can temporarily heat up the bar. And modelling it is not easy at all.
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Old   May 11, 2010, 07:28
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Luis Filipe Fabiani
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Jaho,

Is it a 2D or a 3D simulation?

As ghorrocks mentioned, check your mesh near the contact boundary (on each size), it should be fine enough to catch the conduction heat transfer correctly. I would say that elements with less than 1mm for about 50 mm should do it, but as ghorrocks also mentioned, you must do a mesh size sensitivity check.

It is reasonable to assume that a thin portion of the steel will get very hot very soon (have you ever touched a really hot sourface? it burns almost instantaneously...)

Regarding the time it takes to cool down, check the natural convection boundary. How are you setting it?

Best regards

Luis Filipe
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