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-   -   Help: "Ions-Transport" (https://www.cfd-online.com/Forums/cfx/96887-help-ions-transport.html)

 CrisCFD February 3, 2012 14:55

Help: "Ions-Transport"

Hello guys; first, sorry for my bad english :D.
I have to simulate a single-phase system, with anions and cations diffuse in an aqueous solution. Ions and cations are obviously scalars.
How can I insert the effects due to electrical interactions?
How can I insert the condition: C = A in each element (electroneutrality)?
where A and C are the concentrations of anions and cations, respectively

thanks

 CrisCFD February 4, 2012 11:34

Maybe I didn't explain well...

 ghorrocks February 5, 2012 18:18

If A=C then why model two concentrations? Just model one and the other will be the same. This is easily done with a additional variable.

But I do not know what electrical interactions you wish to include.

 CrisCFD February 6, 2012 04:47

Quote:
 Originally Posted by ghorrocks (Post 342843) If A=C then why model two concentrations? Just model one and the other will be the same. This is easily done with a additional variable. But I do not know what electrical interactions you wish to include.
I'm modelling a reverse electrodialysis system...so I have Na+ (cations) and Cl- (anions).
I have to consider the electrical interactions in the transport equation as an additional term, as a source term.
I just found an expression like this: S+ = - σ / ε * (C-A)
and
S- = σ / ε * (C-A)

But the very low value of the costant "ε " (dielectric constant = 2,21 E-10) is a problem for the solver, a numerical problem, I think.

 ghorrocks February 6, 2012 20:06

But again, you said A=C so the expression evaluates to zero.

 CrisCFD February 7, 2012 04:27

Quote:
 Originally Posted by ghorrocks (Post 343007) But again, you said A=C so the expression evaluates to zero.
I have deleted this condition (A = C) from the model and I have considered the source term S

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