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Old   February 3, 2012, 14:55
Default Help: "Ions-Transport"
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Hello guys; first, sorry for my bad english .
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

Last edited by CrisCFD; February 4, 2012 at 07:32.
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Old   February 4, 2012, 11:34
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Maybe I didn't explain well...
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Old   February 5, 2012, 18:18
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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.
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Old   February 6, 2012, 04:47
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Quote:
Originally Posted by ghorrocks View Post
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.
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Old   February 6, 2012, 20:06
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But again, you said A=C so the expression evaluates to zero.
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Old   February 7, 2012, 04:27
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Quote:
Originally Posted by ghorrocks View Post
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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