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Does the "Thin material" Interface model include thermal mass?

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Old   May 3, 2012, 18:42
Default Does the "Thin material" Interface model include thermal mass?
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Erik
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Greetings, I've searched the modeling and theory guides and have yet to find a definitive answer.

Does the "Thin material" Interface model for a fluid-solid interface include thermal mass? Meaning would it be appropriate to use this for a transient simulation that would involve the thin material cooling down and absorbing energy?
Or is it only applying the thermal resistance of the material?
If so it would only be valid for steady state problems but not transient.

I'm trying to look at cooling down a large insulated tank with a 1mm thick steel membrane on the inside. This membrane is what I would like to model using the "thin material" as 1mm is much smaller than the rest of the mesh.

Thanks in advance
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Old   May 3, 2012, 19:37
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That is correct, the thin material option just evaluates a thermal resistance and does not include a mass/thermal inertia component. This does not mean it is not applicable to transient flows - transient flows there the time scale of the interface is much smaller than the fluid thermal time scale will still work OK.

If you have a large tank with a 1mm steel wall I suspect that the thermal inertia of the walls are not important in your case as well and therefore the thin surface model will work fine. But if you want to include thermal inertia the easiest way is to model the 1mm thick wall as a CHT body and give it the correct conductivity, density and specific heat properties.
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Old   May 4, 2012, 12:36
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Thank for the reply Glenn,

I have to include the steel membrane as its transient temperature is the main concern of the analysis, and everything is cooling from the inside of the membrane, its actually 2 mm thick, I was mistaken before.

I was afraid I'd have to model it, but the small size is going to be hard to mesh as it is much thinner than the mesh around it (2.5cm). Perhaps I'll try to see if I can use similitude to make it thicker but behave the same way thermally. Decrease density, increase conductivity, increase thickness, hopefully this doesn't cause problems of its own. I'll play with it a little, Thanks for the advice.
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Old   May 5, 2012, 07:30
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It should not be too hard to mesh. Define the inner surface as a named selection (or a part if in ICEM) and the outer surface as a different named selection/part. The they are easy to find in CFX-Pre. Also Workbench has lots of shell meshing stuff for FEA and that might be useful here.
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