Diffusion simulations with multiple species involved in reactions

[jgostick]

We need to come up with a way to do reactive transport with multiple species in the mixture, so we can have the following source term: r = kC_{A}C_{B} where both species A and B are diffusing.

[ma-sadeghi]

Indeed. I think we also need to unify/integrate mixtures with phases in parallel. I don't exactly know how mixtures work and they relate to our phases.