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yansongdi October 3, 2009 10:59

"reaction" threshold
 
Please, can you suggest which solvers I can combine to model the transport in pipes of dissolutions close to the solubility limit?

My plan is to have passive transport of a component X as long as it is below the solubility Xmax. Where X>Xmax, it should precipitate as a solid Xs, settle to the bottom of the pipe, and remain there until some fluid parcel with X<Xs dissolves the precipitate again.

I would define two scalar fields X and Xs which describe the dissolved concentration and the precipitated amount (VOF-method).

The question is, how to describe the precipitation process. I would define
dX/dt=-k(X+Xs-Xmax)
dXs/dt=-dX/dt
where X>Xmax or Xsol>0 and dX/dt=dXs/dt=0 elsewhere. The rate k would be adjusted to about 1e3/runTime.deltaT() to force near-equilibirum conditions.

Can I use the chemistrySolver and the ODEchemistryModel to model "reactions" which are only activated above a solubility limit Xmax? If yes, please provide a few lines of code to show the essential steps or point me to some useful documentation.
Another question is, whether the combination of transport and reaction as it is implemented in reactingFoam is still valid, if the reaction time scale is much faster than the transport time scales?
As I understand reactingFoam, it solves first the chemical ODE and then the transport step. The disadvantage is that fast kinetics are frozen during the transport step. Does some solver exist which solves the chemical reaction implicitly during the transport step?

Additional processes, like temperature dependent solubility, heat release or volume change during dissolution or precipitation, will also be important at a later time. But for the moment I only need to find a way how to model the precipitation.

Sincerly,
YAN


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