I run my model and it works. However, I obtain negative concentration values. It is a model related to the hydrogenation-dehydrogenation of a hydride bed. I have experimetal thermodynamic parameters and an semi-empirical kinetic model. At the time to run the model just with the application of Transport of diluted species, applying the semi-empirical kinetic model, the model works properly and the concentrations are ok. Howevere, when I add the transport of species in a porous bed (hydride bed), applying Darcy's law, the model provide negative values of the concentration. I tried with a finer mesch, but it does not improve the model.
Anybody had an idea what could it be?
Thanks!!