I'm trying to make a biofuel cell model in COMSOL where the anode and cathode have Michaelis Menten kinetics. When I enter those rate equations (multiplied by # electrons transferred and Faraday constant) for the local current density in place of the default Butler-Volmer kinetics, my model does not converge. Has anyone encountered this issue?
Dear Russell,
I have not studied biofuel cells, but generally there can be various reason why your model does not convergence. Is your model stationary or time-dependent?
First of all, check what is the error message that COMSOL gives (should be under your Study node), that can (even though not always very clear for me at least :) ) tell you more what the problem is.
Generally, some ideas to check:
1) check that you have build the model correctly: all domains and boundaries are correctly defined, you have meshed the whole model (e.g. not so that some domain unmeshed) and the quality is "good enough" (well, not always so easy to be sure)
2) If you have some sudden changes like steps (time-dependent problems) --> try to make "smooth" steps, so ramp up (/down) change instead of "real step" --> this should help numerical calculations
3) If you have some values near zero (e.g. concentrations/#electrons/...), it might be better to use some close approximation instead of zero (e.g. eps function in COMSOL), because sometimes numerical approximation could calculate e.g. concentration to unrealistic negative value.
Hope these helps.
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