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Temperature-Dependent Material Property & Time-Dependent Study

Posted Mar 23, 2022, 3:26 p.m. EDT Heat Transfer, Parameters, Variables, & Functions, Structural Mechanics 6 Replies

Dan OBrien
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Hi all! I'm having an issue with a Joule Heating model of mine. I am modeling joule heating in a gold resistor and wanted to incorporate gold's temperature-dependent conductivity into the model.

I was able to get the model to run for a stationary state study, but it freezes when starting calculations under time-dependent study. Any thoughts or leads as to why this would occur would be so deeply appreciated!

6 Replies Last Post Mar 25, 2022, 10:12 a.m. EDT
Jeff Hiller COMSOL Employee

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Posted: 3 years ago Mar 23, 2022, 3:56 p.m. EDT
Updated: 3 years ago Mar 23, 2022, 4:13 p.m. EDT

Hi Dan,

I would suspect an inconsistency between boundary conditions, initial conditions, and material properties.

Can you upload your mph file (with mesh or solution cleared to keep it small)? Without it, you'll only get conjecture like mine.

Jeff

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Jeff Hiller
Hi Dan, I would suspect an inconsistency between boundary conditions, initial conditions, and material properties. Can you upload your mph file (with mesh or solution cleared to keep it small)? Without it, you'll only get conjecture like mine. Jeff
Dan OBrien
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Posted: 3 years ago Mar 24, 2022, 9:35 a.m. EDT

Thank you, Jeff! Your advice is so appreciated.

I've uploaded my mph file so you can have a look. Let me know if I can provide further information. (Note: the electrical conductivity of Au is the only material property changed)

Thank you, Jeff! Your advice is so appreciated. I've uploaded my mph file so you can have a look. Let me know if I can provide further information. (Note: the electrical conductivity of Au is the only material property changed)

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Jeff Hiller COMSOL Employee

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Posted: 3 years ago Mar 24, 2022, 10:03 a.m. EDT
Updated: 3 years ago Mar 24, 2022, 10:13 a.m. EDT

Hi Dan,

1/ Looking at your model confirms the suspicion I expressed earlier: at t=0, you have a voltage drop applied across the device, which means that there's a current flowing through it, which means heat is generated, which means it can't be at the uniform temperature you specified. Hence the initial conditions are inconsistent with the boundary conditions. You can resolve that by ramping up U2 from zero over a short time.

2/ Unless I had a very good reason to model the gold trace as a 3D object, I wouldn't: I'd replace it with a shell approximation as is done in this model of a very similar electric heater. This approach would save you computational time and memory.

3/ Looks like you are using a bit of an antique version of our software :) I can't remember when we introduced the shell formulations for heat transfer and electric currents that I mentioned above. It's been a while, but they may not be available in your 4.2 installation (It also depends on which modules your license carries).

Best,

Jeff

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Jeff Hiller
Hi Dan, 1/ Looking at your model confirms the suspicion I expressed earlier: at t=0, you have a voltage drop applied across the device, which means that there's a current flowing through it, which means heat is generated, which means it can't be at the uniform temperature you specified. Hence the initial conditions are inconsistent with the boundary conditions. You can resolve that by ramping up U2 from zero over a short time. 2/ Unless I had a very good reason to model the gold trace as a 3D object, I wouldn't: I'd replace it with a shell approximation as is done in [this model](https://www.comsol.com/model/heating-circuit-465) of a very similar electric heater. This approach would save you computational time and memory. 3/ Looks like you are using a bit of an antique version of our software :) I can't remember when we introduced the shell formulations for heat transfer and electric currents that I mentioned above. It's been a while, but they may not be available in your 4.2 installation (It also depends on which modules your license carries). Best, Jeff
Dan OBrien
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Posted: 3 years ago Mar 24, 2022, 10:41 a.m. EDT

Ah yes, that makes sense. Can't have T_0=273 && T_0>273.

I'm a new user so pardon the perhaps simple question: in order to execute this change, I have defined a function (rm1) that ramps from 0 to a cutoff at U2, then called this function as the electric potential applied at the terminal V_0 = rm1.

Is this the correct approach?

Ah yes, that makes sense. Can't have T_0=273 && T_0>273. I'm a new user so pardon the perhaps simple question: in order to execute this change, I have defined a function (rm1) that ramps from 0 to a cutoff at U2, then called this function as the electric potential applied at the terminal V_0 = rm1. Is this the correct approach?
Jeff Hiller COMSOL Employee

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Posted: 3 years ago Mar 24, 2022, 10:48 a.m. EDT

If the argument for a function rm1 is time, you call it by rm1(t).

Jeff

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Jeff Hiller
If the argument for a function rm1 is time, you call it by rm1(t). Jeff
Dan OBrien
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Posted: 3 years ago Mar 25, 2022, 10:12 a.m. EDT

Yes -- perfect. Thank you again for your help, Jeff.

I'll take a look at the shell approximation and see if I can get that to run on this archaic software version!

Yes -- perfect. Thank you again for your help, Jeff. I'll take a look at the shell approximation and see if I can get that to run on this archaic software version!

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