Discussion Forum

In Comsol 4.0a, when using
- Species transport in porous media
- Darcy's Law
Comsol solves for all the concentrations, i.e. all species are dependent variables (instead of N-1 species when using Transport of concentrated species for example). With the concentrations, the gas phase density and pressure could be readily calculated with the ideal gas law. Therefore, the continuity equation associated with the Darcy's Law becomes useless, the pressure being the dependent variable of the continuity equation. The problem is over defined! We could just calculate the average gas velocity from the Darcy's law without the help of the continuity equation, because we got the pressure from the ideal gas law. But I'm not sure this is a good way to solve the problem.

When I use Species transport in porous media + Darcy's Law, I get incoherent results such has gas density ridiculously high, mass fractions higher than 1, negative mass fractions, etc. Something is obviously wrong.

Does Comsol is confident that their formulation of the Gas species conservation equation in porous media coupled with Darcy's Law is coherent???

I would appreciate some help with the formulation of the Gas species conservation equation in molar form, for all species, coupled with the Darcy's Law.

It's very weird that Comsol solves for all species instead of N-1 species, Comsol lets us over define problems?

Thanks