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Problem with transport of diluted species mass conservation

Posted Jul 23, 2014, 1:33 p.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Electrochemistry Version 4.3, Version 4.4, Version 5.0 7 Replies

Kramer
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Dear Comsol Community,

My model is a 2d axisymmetric geometry, composed by one fluid layer and many porous layers.

I'm modeling both laminar flow and transport of diluted species. This chemical species flows with the solvent into the fluid layer, then, by both convection and diffusion, passes through the porous layers, in radial direction.

My problem is that the concentration in the fluid layer remains uniform. This is quite strange, because:

1) physically, the concentration should increases a little bit, near the boundary between the fluid region and the first porous layer,
2) the mass decreases: this should imply that the species concentration increases, but this is not happening

Does anyone of you have suggestions for this? I'm not familiar with Transport of diluted species

Thank you for your attention,

Kramer

7 Replies Last Post Jun 8, 2015, 1:41 a.m. EDT
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Hello Kramer

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Tobias K
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Posted: 10 years ago Mar 9, 2015, 7:16 a.m. EDT
Dear Kramer,

this is interesting. Did you find an answer to your problem? Could you post an example clarifying what you mean?

Best regards,
Tobias
Dear Kramer, this is interesting. Did you find an answer to your problem? Could you post an example clarifying what you mean? Best regards, Tobias
Lasse Murtomäki
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Posted: 10 years ago Mar 10, 2015, 6:19 a.m. EDT
I had the problem of mass balance before I used a rather dense mesh in the domains of convective diffusion. Also, close to domain (phase) boundaries nonuniform meshing (geometric/arithmetic distribution) helps a lot.

Lasse
I had the problem of mass balance before I used a rather dense mesh in the domains of convective diffusion. Also, close to domain (phase) boundaries nonuniform meshing (geometric/arithmetic distribution) helps a lot. Lasse
Tobias K
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Posted: 10 years ago Mar 10, 2015, 6:42 a.m. EDT
Dear Lasse,

thank you for you post. I see. Up to now I just refined the boundaries while sticking to the free triangular meshing for the domain.
Is there an advantage over that using your technique?

Best,
Tobias
Dear Lasse, thank you for you post. I see. Up to now I just refined the boundaries while sticking to the free triangular meshing for the domain. Is there an advantage over that using your technique? Best, Tobias
Lasse Murtomäki
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Posted: 10 years ago Mar 12, 2015, 3:47 a.m. EDT
I have no definite answers, try different meshes and you'll see which one keeps the mass balance the best. In thin channels I have used mapped (2D) or swept (3d) meshes with sweep distribution.

br
Lasse
I have no definite answers, try different meshes and you'll see which one keeps the mass balance the best. In thin channels I have used mapped (2D) or swept (3d) meshes with sweep distribution. br Lasse
Tobias K
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Posted: 10 years ago Mar 12, 2015, 4:24 a.m. EDT
Thank you, Lasse!
I will give that a try.

Best,
Tobias
Thank you, Lasse! I will give that a try. Best, Tobias
Kramer
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Posted: 10 years ago Jun 7, 2015, 7:01 a.m. EDT
Dear Tobias and Lasse,

Thanks for your answers.

I still didn't fix it at all. Physically, my model didn't simulate the solute accumulation at the free flow/porous membrane interface. I attach an image to clarify what I mean.

I was thinking that probabily i need to manually impose boundary conditions (with form assembly) between the free flow/porous membrane layers, but I'm not sure at all. Probabily it is a mesh issue, but my mesh is very dense. Any suggestions?

Regards,
Kramer
Dear Tobias and Lasse, Thanks for your answers. I still didn't fix it at all. Physically, my model didn't simulate the solute accumulation at the free flow/porous membrane interface. I attach an image to clarify what I mean. I was thinking that probabily i need to manually impose boundary conditions (with form assembly) between the free flow/porous membrane layers, but I'm not sure at all. Probabily it is a mesh issue, but my mesh is very dense. Any suggestions? Regards, Kramer

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Lasse Murtomäki
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Posted: 10 years ago Jun 8, 2015, 1:41 a.m. EDT
Hi

It is rather impossible to comment without seeing your model. Naturally you need to have, for example, a Brinkman equation in the porous membrane and define boundary conditions for the mass transfer across the mebrane boundaries. But if you attach your model I can comment afresh.

br
Lasse
Hi It is rather impossible to comment without seeing your model. Naturally you need to have, for example, a Brinkman equation in the porous membrane and define boundary conditions for the mass transfer across the mebrane boundaries. But if you attach your model I can comment afresh. br Lasse

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