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Thermal Runaway Modeling negative temperature

Hello everyone,

I am building a model to investigate the thermal runaway propagation behavior in a battery module. I am currently facing a problem where I keep getting negative temperatures between the cells that are next to propagate. The propagation also happens way too fast (within a minute for 11 cells) so I am wondering if those negative temperatures might be the reason. It might be important to add that the negative temperatures keep appearing in the battery holders which are placed at the bottom part of the batteries. When I delete them, the negative temperatures disappear.

Do you have any idea why this might be happening? Any advice is welcome, thank you!

6 Replies Last Post Jun 17, 2024, 12:09 p.m. EDT

Posted: 1 month ago
Updated: 1 month ago

Hello MAC,

It is very hard to say much without seeing your mph file.

If I were to venture a guess:

Sometimes you can get negative values within a single finite element although the nodal values are all positive - that could be what's happening in your model. In 1D, imagine a 3-node element with its nodes at x=-1,0 and 1, and set the values at these nodes to be 1, 0 and 0 respectively. Then the field defined by those three nodal values will be equal to -1/8 at x=.5 (because the shape function corresponding to the node at x=-1 is x*(x-1)/2 ).

To figure if this is what's going on with your model, switch to linear elements instead of quadratic ones (BTW: If you are already using linear elements, then my guess is wrong) and see if the negative values disappear. If they do disappear, then you need to use a finer mesh in those areas to avoid the undershoot.

To repeat myself, this is just one of many possibilities. While I hope I am lucky with this guess, the odds are that readers of this forum will need to look at your model in detail to provide more help.

Jeff

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Jeff Hiller

Posted: 1 month ago

Here are the screenshots

Posted: 1 month ago
Updated: 1 month ago

Hello Jeff,

thanks for your reply. I have attached some screenshots which might help with visualising the problem at hand. If you need any further screenshots to identify the problem let me know. The red arrow indicates the area where the negative temperatures appear (within the holder). Also note how the negative temeperature "jumps" within the holder when the fire propagates from one cell to another. Also interesting to note might be the fact that the picture shows a mesh that I have built with minor tweaks to the physically constructed mesh. I have so far used the physically constructed mesh and the minor changed one. I doubt that might be the reason for the negative temperatures but I thought I would mention this.

I have been trying to create a new post or reply with the screenshots for the last few days but I keep getting an error saying "This forum post cannot be viewed." I have no idea why this happens and it is really frustrating that posting something is so hard. Do you know why this might be happening?

Posted: 1 month ago

Hello MAC,

Please post your mph file (after clearing the mesh and solution, as always, to keep it under the 5MB limit). Screenshots are not really helpful.

Best,

Jeff

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Jeff Hiller

Posted: 1 month ago
Updated: 1 week ago

Hello Jeff,

attached you find the .mph file

Posted: 1 month ago

Thank you very much for your patience and help!

I have no idea as to why I get negative temperatures in the holders and why the propagation is happening as fast as it is (within one minute). This has been following me for weeks, so I would be really happy if you can find the reason for it.