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Assistance needed

Posted 25 juin 2020, 05:52 UTC−4 Heat Transfer & Phase Change, Battery Design, Equation-Based Modeling 2 Replies

Kevin Ngangoum Wanche
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good morning,

I have been trying to simulate the thermal runaway effect of a li-ion battery and i have been trying to input the equation governing the heat release during such thermal runaway reaction.

i keep receiving the message ''unexpected unit of input'' after entering the equation HimiAiexp(-Ea/(RT))alpha^ni1(1-alpha)^ni2 into the heat source field. i will like to know what could be the problem.

Regards

2 Replies Last Post 25 juin 2020, 10:38 UTC−4
Alexis Prel
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Posted: 4 years ago 25 juin 2020, 07:39 UTC−4

Hi Kevin,

The problem is that somewhere inside your expression, units are not what they should from COMSOL point of view.

The expression should be highlighted in red or yellow when you enter it.

To solve your problem, you should apply a divide and conquer strategy : remove some parts of your equation until the message disappears. Then you know that the problem came from something you deleted.

Once you have identified where the unit is wrong. Check the unit of your input parameters : are they all correct? If yes, check the expression itself and try to work the units by hand.

Things to remember :

  • the input of all usual functions exp, log, sin, cos, etc. should have no dimension
  • when using a^b, a may have a dimension but b must be dimensionless
  • you can not add or subtract quantities that do not have the same dimension
  • the unit of a product is the product of the factors' units

Cheers, Alexis

Hi Kevin, The problem is that somewhere inside your expression, units are not what they should from COMSOL point of view. The expression should be highlighted in red or yellow when you enter it. To solve your problem, you should apply a divide and conquer strategy : remove some parts of your equation until the message disappears. Then you know that the problem came from something you deleted. Once you have identified where the unit is wrong. Check the unit of your input parameters : are they all correct? If yes, check the expression itself and try to work the units by hand. Things to remember : * the input of all usual functions exp, log, sin, cos, etc. should have no dimension * when using `a^b`, `a` may have a dimension but `b` must be dimensionless * you can not add or subtract quantities that do not have the same dimension * the unit of a product is the product of the factors' units Cheers, Alexis
Kevin Ngangoum Wanche
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Posted: 4 years ago 25 juin 2020, 10:38 UTC−4

Hi Alexis,

Thanks for your reply. it was very usefull to me

Hi Alexis, Thanks for your reply. it was very usefull to me

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