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Comparing Transport of Dilute Species to Coefficient form PDE

Posted Oct 13, 2015, 3:53 p.m. EDT Modeling Tools & Definitions Version 4.2a 2 Replies

Robert LeSuer
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I am trying to learn more about the Coefficient Form PDE application node. To do so, I'm using a system with which I am familiar, namely simulating the steady state behavior of a microelectrode. A model file is attached. The current predicted by the Transport of Dilute Species node is consistent with the analytical solution; however the Coefficient form PDE returns an electrode current that is low by a factor of about 2.5. Looking at the concentration profiles, the PDE appears to have more spherical symmetry and extends farther out from the electrode than anticipated. I suspect I have not set the boundary conditions correctly; however I am not sure where I have gone wrong. The only thing I can think of is that there is no explicit way to set axial symmetry in the PDE form (set by default?). Any help is appreciated.
2 Replies Last Post Oct 13, 2015, 10:12 p.m. EDT
Jeff Hiller COMSOL Employee

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Posted: 9 years ago Oct 13, 2015, 4:39 p.m. EDT
Indeed, you are not solving the same equation in the Coefficient Form physics as you are in the Transport of Diluted Species physics, for the reason that you mention: your selection of coefficients needs to reflect the symmetry.
An example of setting up a spherically symmetric model in 1D is included in the Application Library (Its title is "Spherically Symmetric Transport") and can be used for inspiration.
Best,
Jeff
Indeed, you are not solving the same equation in the Coefficient Form physics as you are in the Transport of Diluted Species physics, for the reason that you mention: your selection of coefficients needs to reflect the symmetry. An example of setting up a spherically symmetric model in 1D is included in the Application Library (Its title is "Spherically Symmetric Transport") and can be used for inspiration. Best, Jeff
Robert LeSuer
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Posted: 9 years ago Oct 13, 2015, 10:12 p.m. EDT
That did the trick, thank you.
That did the trick, thank you.

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