The only option to add term to a transport equation without affecting how other terms being calculated is a source term.nSo, I don't think you have other options. I know in multiphase flow, to get all these properties for different phase, you need to recall different domains and threads for every cell which is difficult to program and more difficult to optimise. Also I am not sure if this applies to species model or not.nSearch the forum, I remember there was few posts by the same person and he was defining sources for species. And actually was helping him. That is why I tagged him. n