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Phase change not working, warning inverted element

Posted 24 avr. 2016, 16:49 UTC−4 Heat Transfer & Phase Change, Mesh, Studies & Solvers Version 5.1 6 Replies

Radhika Rajaram
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I am trying to simulate the heating and phase change of a low melting point metal. In the mph file that I've uploaded to Google drive (drive.google.com/file/d/0B3QaD21DDcpNeFdlYjJwNWE4Rzg), you can see the innermost helical heating coil, surrounded by a helical silicone tube. A small air gap exists between these two domains. The silicone tube is immersed in the low-melting point metal which is in turn contained by two concentric cylinders of silicone.

When solving, I get a warning (Inverted element near ~0,0,0). This cannot be, there is no material near the origin.

The solution shows that the model is being heated but I cannot find any evidence of phase change in the Field’s metal (you can see this by plotting out Table 1 in results section). As far as I can see, I have set the Physics options correctly. Can you please give me a clue as to what I might be doing wrong?

When I improved mesh quality, warning disappeared, but solver hung as soon as it was time for phase change (at melting point) and seemed to stay there forever. I tried to improve convergence by changing fully-coupled settings (max no.of iterations- 25 and tolerance - 1e-3), but this did not work either.

6 Replies Last Post 25 avr. 2016, 13:44 UTC−4
Parth Swaroop
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Posted: 9 years ago 25 avr. 2016, 03:02 UTC−4
The file size is quite large.

You can check this blog post on how comsol's solver works and achieve better convergence :

www.comsol.nl/blogs/improving-convergence-multiphysics-problems/

In essence it is recommended to use "auxiliary sweep" so as to improve initial guess for the solver. i hope this works.
According to my understanding, larger the number of iterations , poorer would be the framework for achieve solution.

Regards
Parth
The file size is quite large. You can check this blog post on how comsol's solver works and achieve better convergence : https://www.comsol.nl/blogs/improving-convergence-multiphysics-problems/ In essence it is recommended to use "auxiliary sweep" so as to improve initial guess for the solver. i hope this works. According to my understanding, larger the number of iterations , poorer would be the framework for achieve solution. Regards Parth
Radhika Rajaram
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Posted: 9 years ago 25 avr. 2016, 07:10 UTC−4
Thank you! I suppose I should run an auxiliary sweep for temperature variable and set a range around the melting point?

Is this the right approach?

I am not able to find many details about auxiliary sweeps within the user guide/reference manual about auxiliary sweeps. Any link to some material/ someone's own implementation etc. would be appreciated.
Thank you! I suppose I should run an auxiliary sweep for temperature variable and set a range around the melting point? Is this the right approach? I am not able to find many details about auxiliary sweeps within the user guide/reference manual about auxiliary sweeps. Any link to some material/ someone's own implementation etc. would be appreciated.
Parth Swaroop
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Posted: 9 years ago 25 avr. 2016, 08:31 UTC−4
Ideally you would want to create a sweep for external perturbations or variables that change the equilibrium of the situation.

i think, auxiliary sweep with respect to power source would make sense. You can create a parameter for the power input and then assign it your heat source. In study step -> study extension -> choose parameter and choose a range.

Do you know how the solution will look like?

You can search for a relevant example here : www.comsol.nl/models
Ideally you would want to create a sweep for external perturbations or variables that change the equilibrium of the situation. i think, auxiliary sweep with respect to power source would make sense. You can create a parameter for the power input and then assign it your heat source. In study step -> study extension -> choose parameter and choose a range. Do you know how the solution will look like? You can search for a relevant example here : https://www.comsol.nl/models
Radhika Rajaram
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Posted: 9 years ago 25 avr. 2016, 08:43 UTC−4
Oh, thanks a lot! I will implement that.

Yes- I know the output from experiment. The plot of temperature vs time at any point in the model should more or less follow the trend of a phase change of a simple pure metal subject to nearly uniform heating with a constant power heat source.
Oh, thanks a lot! I will implement that. Yes- I know the output from experiment. The plot of temperature vs time at any point in the model should more or less follow the trend of a phase change of a simple pure metal subject to nearly uniform heating with a constant power heat source.
Parth Swaroop
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Posted: 9 years ago 25 avr. 2016, 11:03 UTC−4
That seems like a good approximation to start with. why do you need a complicated helical heat source?
That seems like a good approximation to start with. why do you need a complicated helical heat source?
Radhika Rajaram
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Posted: 9 years ago 25 avr. 2016, 13:44 UTC−4
The heating source used in the experiment is helical. We require this model to be flexible as well. So we use a spring-like heating coil.

Just for the purpose of phase change study (not structural study) is there a simpler approximation of a helical coil that I can use? A series of closely packed rings stacked on each other, for instance?
The heating source used in the experiment is helical. We require this model to be flexible as well. So we use a spring-like heating coil. Just for the purpose of phase change study (not structural study) is there a simpler approximation of a helical coil that I can use? A series of closely packed rings stacked on each other, for instance?

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