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How can I define a porous wall in comsol?

Posted 20.05.2014, 04:45 GMT-4 Computational Fluid Dynamics (CFD) Version 4.4 6 Replies

Xiaoxu Yan
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Hi everyone, I'm now modeling a membrane filtration process.
it a very simple 2D rectangle domain,
one boudary is inlet, one boudary is outlet, one is no slip wall, the rest is a wall with porous structure(considered as membrane).
So the problem is how can I treat the wall as a porous wall, because it is very thin and we don't have to built its real porous structure
Many thanks!
6 Replies Last Post 22.05.2014, 11:35 GMT-4
Pieter Westerik
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Posted: 1 decade ago 20.05.2014, 10:59 GMT-4
So is one domain boundary porous or is the whole domain a porous medium?
So is one domain boundary porous or is the whole domain a porous medium?
Xiaoxu Yan
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Posted: 1 decade ago 20.05.2014, 11:23 GMT-4
Just one boudary of the domain, not the whole domain
Just one boudary of the domain, not the whole domain
Pieter Westerik
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Posted: 1 decade ago 20.05.2014, 11:39 GMT-4
Ok and what is on the other side of your membrane (so outside your domain)? What physics do you use for your domain? Transport of diluted species? Is there a flow of your solvent across the membrane, or just of the sollute(s)?
Ok and what is on the other side of your membrane (so outside your domain)? What physics do you use for your domain? Transport of diluted species? Is there a flow of your solvent across the membrane, or just of the sollute(s)?
Xiaoxu Yan
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Posted: 1 decade ago 20.05.2014, 11:51 GMT-4
Many thanks for you patient help Pieter !
Actually right now there is no computational domain outside the membrane, the permeate side of the membrane is not considered yet, but will be taken into consideration in the future after this problem is solved.

Also I'm not sure would there be any different whether the permeated side is considered in computational domain or not...

The computational domain is a two phase fluid domain. The continous phase is water and dispersed phase is solid particles. Only water is allow to pass through the membrane

Thanks again for your generous help ^_^
Many thanks for you patient help Pieter ! Actually right now there is no computational domain outside the membrane, the permeate side of the membrane is not considered yet, but will be taken into consideration in the future after this problem is solved. Also I'm not sure would there be any different whether the permeated side is considered in computational domain or not... The computational domain is a two phase fluid domain. The continous phase is water and dispersed phase is solid particles. Only water is allow to pass through the membrane Thanks again for your generous help ^_^
Pieter Westerik
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Posted: 1 decade ago 21.05.2014, 03:20 GMT-4
Hi Xiaoxu,

I hope I am actually helping you, because I do not have experience with such a problem. If you have constant pressure in the permeate region I do not think you have to include it in your model. I would think that your membrane has a certain flow resistance: the water flux through the membrane at any point on the membrane would be proportional to the local pressure difference over the membrane. For the particles you would impose a no flux boundary at the location of the membrane I would think.
Hi Xiaoxu, I hope I am actually helping you, because I do not have experience with such a problem. If you have constant pressure in the permeate region I do not think you have to include it in your model. I would think that your membrane has a certain flow resistance: the water flux through the membrane at any point on the membrane would be proportional to the local pressure difference over the membrane. For the particles you would impose a no flux boundary at the location of the membrane I would think.
Sri Puranam
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Posted: 1 decade ago 22.05.2014, 11:35 GMT-4
Xiaoxu,

Pieter's method is good idea. If you want to try something else, try this. The filter has a finite thickness in real life. You could make a thin porous domain equal to the thickness of the filter on the filter boundary of the rectangle. You don't have to specifcy the BC between the two domain, COMSOL will apply continuity directly and figure it out. For the outlet side of the filter, I would have a outflow BC.

Sri Puranam
Xiaoxu, Pieter's method is good idea. If you want to try something else, try this. The filter has a finite thickness in real life. You could make a thin porous domain equal to the thickness of the filter on the filter boundary of the rectangle. You don't have to specifcy the BC between the two domain, COMSOL will apply continuity directly and figure it out. For the outlet side of the filter, I would have a outflow BC. Sri Puranam

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