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ion concentration/concentration gradient
Posted Aug 17, 2015, 10:47 a.m. EDT Electromagnetics, Fluid & Heat, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.0 1 Reply
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Hello
I am working in the PDE model and I have a 1D geometry consisting of 2 intervals.
by flowing current through the system, I would like to show that one interval represents an ion selective zone while the other one does not. so how can I define this behavior which causes concentration gradient?
actually I dont know how to define this concentration gradient in COMSOL.
Regards
I am working in the PDE model and I have a 1D geometry consisting of 2 intervals.
by flowing current through the system, I would like to show that one interval represents an ion selective zone while the other one does not. so how can I define this behavior which causes concentration gradient?
actually I dont know how to define this concentration gradient in COMSOL.
Regards
1 Reply Last Post Aug 18, 2015, 1:22 a.m. EDT
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Posted:
9 years ago
Hi
I have also tried to find out how to simulate an ion-exchange membrane but so far failed to do that. The essence is the existence of immobile fixed charge density. Contrary to what you wrote, there is hardly no concentration gradient within an ion-exchange membrane, and ion transport takes place solely by migration. In a moderately charged porous material concentration gradients exist, but I am not quite sure why you want to define it since it comes as a result of the simulation. But of course, if you need to define a concentration gradient, use a linear profile like
c = c1 - (c1 - c2)*x/L
where c(0) = c1 and c(L) = c2, and L is the length of the ion-selective domain.
The problem of simulating an ion-exchange membrane is that I cannot set zero as the diffusion coefficient of the fixed charges. In the Poisson-Boltzmann equation charges can be set in a domain, but that would be incorrect since the membrane is electroneutral and Donnan equilibrium sets the potential in the membrane.
If anybody has an idea how to do this, I would be most grateful.
BR
Lasse
I have also tried to find out how to simulate an ion-exchange membrane but so far failed to do that. The essence is the existence of immobile fixed charge density. Contrary to what you wrote, there is hardly no concentration gradient within an ion-exchange membrane, and ion transport takes place solely by migration. In a moderately charged porous material concentration gradients exist, but I am not quite sure why you want to define it since it comes as a result of the simulation. But of course, if you need to define a concentration gradient, use a linear profile like
c = c1 - (c1 - c2)*x/L
where c(0) = c1 and c(L) = c2, and L is the length of the ion-selective domain.
The problem of simulating an ion-exchange membrane is that I cannot set zero as the diffusion coefficient of the fixed charges. In the Poisson-Boltzmann equation charges can be set in a domain, but that would be incorrect since the membrane is electroneutral and Donnan equilibrium sets the potential in the membrane.
If anybody has an idea how to do this, I would be most grateful.
BR
Lasse