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Thermal contact resistance

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Hello,
I'm trying to model a thermal sensor in contact with a solid. To do this, I need to embed a heat source in one material and then see the heat flow into a second material. I also need to account for the thermal contact resistance between the two solids.
I understand that I can create a 'contact pair' and then set this to have a boundary condition of 'thin thermally resistive layer'. However, I am struggling beyond this as I get an error message:
Error: 6170
Failed to evaluate variable
Variable contact_cp1

I am unsure about using contact pairs and I'm obviously missing a step out. Does anyone know of an example for using contact pairs, or can offer advice on modelling thermal contact resistance in comsol?


Thanks,
Joe

10 Replies Last Post 03.12.2016, 16:49 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 22.11.2010, 10:17 GMT-5
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

--
Good luck
Ivar
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 -- Good luck Ivar

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Posted: 1 decade ago 22.11.2010, 10:38 GMT-5
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
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


Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 22.11.2010, 15:01 GMT-5
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

--
Good luck
Ivar
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 -- Good luck Ivar

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Posted: 1 decade ago 23.11.2010, 03:54 GMT-5
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!
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!

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Posted: 1 decade ago 27.08.2012, 04:59 GMT-4
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
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

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 27.08.2012, 16:10 GMT-4
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

--
Good luck
Ivar
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 -- Good luck Ivar

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Posted: 1 decade ago 16.01.2013, 01:31 GMT-5
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 ) ? [QUOTE] 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! [/QUOTE] -- ishant.jain@tatasteel.com

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Posted: 1 decade ago 16.01.2013, 01:31 GMT-5
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 ) ? [QUOTE] 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! [/QUOTE] -- ishant.jain@tatasteel.com

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 16.01.2013, 14:28 GMT-5
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 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

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Posted: 8 years ago 03.12.2016, 16:49 GMT-5
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
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

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