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diffusion with a specialized boundary condition

Posted 05.06.2012, 23:01 GMT-4 Chemical Reaction Engineering, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.2 3 Replies

Scott Hertel
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Hi! I think my question is fairly straightforward, I just can't seem to figure it out...

I am trying to model diffusion of particles from one region into another region. The two regions are separated by a boundary with two characteristics:
1) flux is fixed at zero in one direction
2) in the other direction, flux is defined in terms of a transmission probability. (for a given incoming particle, the particle has a specified probability of passing through, and a specified probability of bouncing back)

I understand how to describe the physics of each each region using a coefficient form PDE. Is a boundary such as described above a type of "weak constraint"? It seems like a simple situation, but I haven't yet found a way to implement this....

Thanks a lot for your help!

-scott
3 Replies Last Post 15.06.2012, 11:40 GMT-4
Scott Hertel
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Posted: 1 decade ago 14.06.2012, 17:26 GMT-4
Hmm... this should be pretty simple, but I still haven't figured it out... can anyone help? How can I set up a boundary that allows diffusion in only one direction? Thanks a lot!

-scott
Hmm... this should be pretty simple, but I still haven't figured it out... can anyone help? How can I set up a boundary that allows diffusion in only one direction? Thanks a lot! -scott
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 15.06.2012, 00:59 GMT-4
Hi

often 1 line of text can translate into a few pages of math ;)
Unfortunately I cannot help like that, but have you tried to ask "support", here we are only users ...

--
Good luck
Ivar
Hi often 1 line of text can translate into a few pages of math ;) Unfortunately I cannot help like that, but have you tried to ask "support", here we are only users ... -- Good luck Ivar
Dao Trinh (COMSOL)
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Posted: 1 decade ago 15.06.2012, 11:40 GMT-4

Hmm... this should be pretty simple, but I still haven't figured it out... can anyone help? How can I set up a boundary that allows diffusion in only one direction? Thanks a lot!

-scott


The diffusion coefficient can be set to vector. So just change the value of the direction that you dont want the diffusion occurs to be zero 0.

Cheers,
Dao
[QUOTE] Hmm... this should be pretty simple, but I still haven't figured it out... can anyone help? How can I set up a boundary that allows diffusion in only one direction? Thanks a lot! -scott [/QUOTE] The diffusion coefficient can be set to vector. So just change the value of the direction that you dont want the diffusion occurs to be zero 0. Cheers, Dao

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