Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.
Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Definition of species within the Nernst-Planck application in Chem Eng module
Posted 15.10.2009, 23:07 GMT-4 Version 3.5a 1 Reply
Please login with a confirmed email address before reporting spam
When using the Nernst-Planck (with electro-neutrality) option in the Chemical Engineering module, ensure the first species (which has its concentration calculated by COMSOL based on electro-neutrality) is one with a higher initial concentration, e.g. either Na+ or Cl- ions in a seawater droplet, rather than the H+ or OH- ions that are present in trace amounts.
Otherwise, rounding off errors will result in the calculated concentrations of dilute species (e.g. H+ or OH-) to reach un-physical values, including negative concentrations, even if the relative and absolute errors are defined to be extremely small. In a time-marching scheme, these errors progressively get blown out.
This thread also is related to Solution No. 952 in the knowledge base related to negative concentrations .
Hello Dayalan Gunasegaram
Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.
If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.
Please login with a confirmed email address before reporting spam
Do you know by any chance why in this same module the defined species have in the subdomain settings different equations? You can see that the nomenclature is not the same.
And why the second specie has only the option of artificial diffusion?
Thanks