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timeint cannot evaluate expression

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I'm using "transport of solute species in porous media" module to find out how the concentration change. I have a term called retention which desribes how much particles deposit inside the porous media. It equals to the time integration of (velocity*(inlet concentration-outlet concentration)/length), where velocity, length and inlet concentration are constant values. So in Results>Derived values, I want to use timeint( ) to integrate my variable c (concentration), however, it said "undefined variable".

I don't know why it says "undefined variable" since I did define it. And how to fix it?

Thank you in advance if you can help me out.



0 Replies Last Post May 13, 2021, 2:17 p.m. EDT
COMSOL Moderator

Hello Xuejia Du

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