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Joule heating of 2D metal bar

Posted 25.07.2012, 16:53 GMT-4 Heat Transfer & Phase Change Version 4.3 5 Replies

dnh37
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Hi,

I've tried searching the model library and there is a Joule Heating example but I don't believe it is directly applicable here.

I am trying to do the simple task of drawing a 2D metal rectangle embedded in some dielectric, pass a current through, and plot the temperature distribution due to heating (which will be hottest where the bar is narrowest).

I have attached a file with a 2D metal bar between. I am getting the error "Singular matrix. There are 1806 void equations (empty rows in matrix) for the variable mod1.V...."\

Not sure why I'm getting this.

One other thing: I set the relative permittivity for the metal equal to 1 because I'm looking for the electrical solution at DC, to find the thermal solution at DC. This may not be correct as, as I understand it, electric permittivity of a metal at DC is 1 + (large imaginary number), however I'm just following Ivar's suggestion here: www.comsol.com/community/forums/general/thread/6809/

Any ideas?

Thanks

Attachments:

5 Replies Last Post 27.07.2012, 13:24 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 25.07.2012, 17:12 GMT-4
Hi

are you using MEF physics ? and have you given some conductivity for all domains ? Else you might get these kinds of errors, but it might be something else too (I'm not by my COMOSL WS for several days so I cannot have a look ;)

--
Good luck
Ivar
Hi are you using MEF physics ? and have you given some conductivity for all domains ? Else you might get these kinds of errors, but it might be something else too (I'm not by my COMOSL WS for several days so I cannot have a look ;) -- Good luck Ivar
dnh37
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Posted: 1 decade ago 26.07.2012, 11:39 GMT-4

Hi

are you using MEF physics ? and have you given some conductivity for all domains ? Else you might get these kinds of errors, but it might be something else too (I'm not by my COMOSL WS for several days so I cannot have a look ;)

--
Good luck
Ivar


Hi Ivar,

What is MEF physics? I did a google search but it's not clear to me what that means.

Conductivity for all domains was given through the Material Browser (where I got the materials). The only thing Material Browser didn't give me was "relative permittivity" for Al.

I thought it might be helpful to attach an image of what I'm trying to simulate. It is really a simple structure, just trying to find What is the temperature distribution in a thin Al sheet sandwiched between SiO2 and air, in a 2D (cross-sectional) format.

Thanks.
[QUOTE] Hi are you using MEF physics ? and have you given some conductivity for all domains ? Else you might get these kinds of errors, but it might be something else too (I'm not by my COMOSL WS for several days so I cannot have a look ;) -- Good luck Ivar [/QUOTE] Hi Ivar, What is MEF physics? I did a google search but it's not clear to me what that means. Conductivity for all domains was given through the Material Browser (where I got the materials). The only thing Material Browser didn't give me was "relative permittivity" for Al. I thought it might be helpful to attach an image of what I'm trying to simulate. It is really a simple structure, just trying to find What is the temperature distribution in a thin Al sheet sandwiched between SiO2 and air, in a 2D (cross-sectional) format. Thanks.

Attachments:

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 26.07.2012, 17:05 GMT-4
Hi

ES (electro statics) EC (electric current) MF (magnetif field) and MEF (magnetic and electric field) are the "tag" names for the COMSOL physics, you should rather run a search on the COMSOl doc, or the Forum, you will get a better hit rate I expect ;)

I prefer to specify these tag names, as this tell us, out here, at least which dependent variables are in play, as ACDC can mean many things ;)

for the materials, the material data base might give you values, but these do not mean they are "correct" for a given physics. If you are solving for the Voltage V (i.e. MEF physics) you must have some NON-zero conductivity, even if the default of the material is "0". So if you have some "air" or water, try to set a conductivity of 1 S/m

--
Good luck
Ivar
Hi ES (electro statics) EC (electric current) MF (magnetif field) and MEF (magnetic and electric field) are the "tag" names for the COMSOL physics, you should rather run a search on the COMSOl doc, or the Forum, you will get a better hit rate I expect ;) I prefer to specify these tag names, as this tell us, out here, at least which dependent variables are in play, as ACDC can mean many things ;) for the materials, the material data base might give you values, but these do not mean they are "correct" for a given physics. If you are solving for the Voltage V (i.e. MEF physics) you must have some NON-zero conductivity, even if the default of the material is "0". So if you have some "air" or water, try to set a conductivity of 1 S/m -- Good luck Ivar
dnh37
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Posted: 1 decade ago 27.07.2012, 11:38 GMT-4

If you are solving for the Voltage V (i.e. MEF physics) you must have some NON-zero conductivity, even if the default of the material is "0". So if you have some "air" or water, try to set a conductivity of 1 S/m


That did it! Thanks! Would be good to have a more helpful error message which would see if you set conductivity to zero and just warn you.

Thanks
[QUOTE] If you are solving for the Voltage V (i.e. MEF physics) you must have some NON-zero conductivity, even if the default of the material is "0". So if you have some "air" or water, try to set a conductivity of 1 S/m [/QUOTE] That did it! Thanks! Would be good to have a more helpful error message which would see if you set conductivity to zero and just warn you. Thanks
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27.07.2012, 13:24 GMT-4
Hi

I agree partially, but on the other side you need to undersand the physics too, and solving for V in this case requires some conductivity to get a current flow and a voltage distribution, if you take the time to study closer the equations set up

--
Good luck
Ivar
Hi I agree partially, but on the other side you need to undersand the physics too, and solving for V in this case requires some conductivity to get a current flow and a voltage distribution, if you take the time to study closer the equations set up -- Good luck Ivar

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