Discussion Forum

Hi

I suppose you are in v3.5a then,
it looks like (from the little you show) you have defined a contat case but that the equations are not fully connected up.

really try first one physics, then add the next one, its easier like that

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Good luck
Ivar

Hello,
Yes I am using v3.5a.

I've attached an example of the problem that I'm having with simple geometries. When I run the model I get the same error, regarding comsol being unable to evaluate variable contact_cp1.
Are there any other details that may help?

I cannot find an example anywhere which includes thermal contact resistances. Does one exist? Or if not, then is it mentioned within any of the manuals?

Thanks,
Joe

Hi

I do not have 3.5a here, but I loaded your model into 4.1. I'tzs slightly tougher to understand but I believe I have found one issue:
As you have no structural physics, and for me contact is more for mechanical contact, I believe that is why you have some errors.

Try an identity pair instead, then solve and make a cut line from Z= -1 to +1 along the x=0, y=0 axis poition and plot the temperature. If you lower further the heat flux in your thin film layer you will see a larger step.

Constacs are really for mechanical pressure estimations requiring the ST physics module. Important for you if your thermal resitance is also depending on the contact pressure. In such a case you must could run a contact pair on the ST physics and a identity on the HT, but using the calculated contact pressure to modulate the heat transfer

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Good luck
Ivar

Thank you Ivar, that has sorted the problem.

If anyone is interested (this is the bit I got wrong previous), here's how you add the thermal interface resistance correctly:
1 - Create your geometry
2 - Draw --> Create pairs
3 - Choose the appropriate objects/boundaries and create an identity pair (NOT CONTACT PAIR! - thanks Ivar!)
4 - Boundary settings --> Pairs tab --> Choose boundary condition of thin thermally resistive layer

I might be interested in modelling the pressure effects in the future, but we'll leave that for another day I think!

Hey, I am using thermal indentical resistance layer as well.
but when I choose the boundaries, it shows: not applicable after the boundarier number. Do you know why? Thank you

Regards,
Siqi

Hi

check carefully the doc, the use of thin layer physics has evolved with the latest v4 versions, to make them easier to use, in latest patch often one need not to make an assembly and pairs, COMSOL looks after this

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Good luck
Ivar

Hi where is this create Pair Options in geometry ( for 4.3 version ) ?

Thank you Ivar, that has sorted the problem.

If anyone is interested (this is the bit I got wrong previous), here's how you add the thermal interface resistance correctly:
1 - Create your geometry
2 - Draw --> Create pairs
3 - Choose the appropriate objects/boundaries and create an identity pair (NOT CONTACT PAIR! - thanks Ivar!)
4 - Boundary settings --> Pairs tab --> Choose a boundary condition of thin thermally resistive layer

I might be interested in modelling the pressure effects in the future, but we'll leave that for another day I think!

--
ishant.jain@tatasteel.com

Hi where is this create Pair Options in geometry ( for 4.3 version ) ?

Thank you Ivar, that has sorted the problem.

If anyone is interested (this is the bit I got wrong previous), here's how you add the thermal interface resistance correctly:
1 - Create your geometry
2 - Draw --> Create pairs
3 - Choose the appropriate objects/boundaries and create an identity pair (NOT CONTACT PAIR! - thanks Ivar!)
4 - Boundary settings --> Pairs tab --> Choose a boundary condition of thin thermally resistive layer

I might be interested in modelling the pressure effects in the future, but we'll leave that for another day I think!

--
ishant.jain@tatasteel.com

Hi

this has changed in the V4, no these identity pairs appear under "Model Definitions" noe.
But first of all often, if you are not using contact physics, you can add many "thin boundary" physics directly without using the assembly and identity pair technique, in the latest 4.x versions.
But if you have contacts that might open or close, then OK you need assembly geometry mode too (except if you also model the air inbetween, but then you need to keep some material in the gap (with a contact offset) to avoid any topology changes

--
Good luck
Ivar

Hi there. I am also trying to include a thermal interface between two surfaces. My model has a hot prismatic surface which is being cooled by a minichannel through which water is flowing. I tried following the same steps you suggested, but the boundary selection in the "pair thin thermally resistive layer" says that the boundaries selected are not applicable. I use 4.4