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October 11, 2012 6:18pm UTC

Modelling different time scale processes

Hello, I m trying to simulate an EKR process, I have flow of ions and need to model the water equilibrium for minimaly realistic results. I want to model water equilibrium as fast (instantaneus) equilibrim, I think I can do it writing expresions for the time derivatives of the H+ and OH- concentrations and resolve at the end of each step of the electromigration solver, but I can´t do it, ¿Is there anyway of say to comsol to solve migration, then equilibrium, the migration etc?.
I dont want to introduce the equilibrium condition togheter with migration cause I would nedd to introduce a great reaction rate and possibly use a small time step, whereas migration is a slow process.
I have read topics in this forum about reaction equilibrium questions that was not answered.
I know how to implement segregated solver and multistep solution procedure but still can't find the way or have encountered in the internet an example of how to do what I want, Im pretty desperated.
Any help of how to introduce water equilibrium in my simulation??
Also I have read about add a algebraic constraint to the concentrations, but Im not totally sure that this really captures the schtochiometry of the water equilibrium

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