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Roman January 13, 2003 09:37

semipermeable membrane
Dear all!

I want to simulate a module with a semipermeable membrane in CFX 5.5.1. I thought about using a thin surface but that is not porous/permeable. Ideally it should be fluid on the one side and gas on the other side. The membrane is permeable for two component of a tree component mixture. Has anybody an idea?

Thanks, Roman

Mads Bang January 13, 2003 10:27

Re: semipermeable membrane
To hinder passage of one fluid (scala equation) you simply set the a-coefficients to zero at the given boundary.

E.g. if you define your membrane domain as porous and at the interface to the free flow domain set the a-coefficients to zero (in fortran routine "userfds" in CFX4.3) I dont know how to access them in CFX 5.5. But at least you now got the principle.

Cheers, Mads

Roman January 14, 2003 09:44

Re: semipermeable membrane
Tanks, Mads

I fear the a-coefficients and the userfds don't exist in CFX 5.5.1. Anyway I don't know it and I can't find it. The user fortran subroutines which there are in CFX 4.3 don't exist in CFX 5.5. I suppose because of the many changes of the structure of CFX. Now the user can set all parameters in CFX Build or in the CCL-file so that own fortran subroutines are unusual.

Do you have a other idea?

Bye, Roman

Mads Bang January 14, 2003 10:38

Re: semipermeable membrane
Ok, if the a-coefficients are not accessible for the user (I certainly find that stupid!) then another option is to set the diffusivity of the specie to a very low value.

Generally speaking this is the most physical thing to do for many problems since there will nearly always be some crossover of your separated fluid.

However it will possible take longer to get a converged solution with this approach.

Cheers, Mads

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