Pieter:
Thanks for the help. Your suggestion led me to examine the velocity field more closely.
I believe that the Darcy velocity is solving correctly. If I impose BCs of no flow at the anode, atmospheric pressure and outflow at the (open) end of the porous cathode, the outflow velocity corresponds exactly to the deposition rate.
However, the ion concentrations in the electrolyte are rising. This is unphysical because the anion is not involved in any reaction, so its integrated concentration must be constant, and therefore the cation also by neutrality. (These are dilute species in the tertiary current node.)
I find that the increase in concentration corresponds exactly to the loss of volume in the cathode, so the ions are not "flowing" with the electrolyte, although I am coupling Darcy flow (dl.u) to the convection field in the electrolyte. Clearly, I do not fully understand the equations, and must somehow compensate for the loss in electrolyte volume.
After a short time the solver stops converging and reports a possible singularity that I have not yet identified.
I will keep working on it, but would welcome any suggestions.
Campbell
Thanks for the help. Your suggestion led me to examine the velocity field more closely.
I believe that the Darcy velocity is solving correctly. If I impose BCs of no flow at the anode, atmospheric pressure and outflow at the (open) end of the porous cathode, the outflow velocity corresponds exactly to the deposition rate.
However, the ion concentrations in the electrolyte are rising. This is unphysical because the anion is not involved in any reaction, so its integrated concentration must be constant, and therefore the cation also by neutrality. (These are dilute species in the tertiary current node.)
I find that the increase in concentration corresponds exactly to the loss of volume in the cathode, so the ions are not "flowing" with the electrolyte, although I am coupling Darcy flow (dl.u) to the convection field in the electrolyte. Clearly, I do not fully understand the equations, and must somehow compensate for the loss in electrolyte volume.
After a short time the solver stops converging and reports a possible singularity that I have not yet identified.
I will keep working on it, but would welcome any suggestions.
Campbell