Help: "Ions-Transport"

CrisCFD · February 3, 2012, 13:55

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

CrisCFD · February 4, 2012, 10:34

Maybe I didn't explain well...

ghorrocks · February 5, 2012, 17:18

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, 03:47

Quote:

Originally Posted by ghorrocks

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, 19:06

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

CrisCFD · February 7, 2012, 03:27

Quote:

Originally Posted by ghorrocks

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

February 3, 2012, 13:55	Help: "Ions-Transport"	#1
CrisCFD New Member Join Date: Feb 2012 Posts: 10 Rep Power: 14	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 06:32.

February 4, 2012, 10:34		#2
CrisCFD New Member Join Date: Feb 2012 Posts: 10 Rep Power: 14	Maybe I didn't explain well...

February 5, 2012, 17:18		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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.

February 6, 2012, 19:06		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	But again, you said A=C so the expression evaluates to zero.