Menu

Discussion Forum

New Discussion
Filtrer

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Dilute species transport concentration condition

Posted 16 nov. 2012, 16:21 UTC−5 Chemical Reaction Engineering Version 4.3a 3 Replies

Martin Hediger
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi
I wonder why the "Concentration" condition in the dilute species transport model is of type "boundary" and not "domain", since its unit is in "Mole/Volume". Why does this make sense? How should this be regarded?

Thanks for any input on this.
3 Replies Last Post 19 nov. 2012, 02:10 UTC−5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 17 nov. 2012, 05:12 UTC−5
Hi

I agree a concentration density on a boundary seems strange (I'm not by ma COMSOL WS so I cannot check) but my first thoughts would e that on boundaries we defne fluxes or constant values.

Now it happens that a flux is ((myvalue/distance)/surface) which happens to give the same units as a (myvalue/volume) but it is in fact a flux per surface variable

Could tha explain your issue ?

--
Good luck
Ivar
Hi I agree a concentration density on a boundary seems strange (I'm not by ma COMSOL WS so I cannot check) but my first thoughts would e that on boundaries we defne fluxes or constant values. Now it happens that a flux is ((myvalue/distance)/surface) which happens to give the same units as a (myvalue/volume) but it is in fact a flux per surface variable Could tha explain your issue ? -- Good luck Ivar
Martin Hediger
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 18 nov. 2012, 14:10 UTC−5
Ok, so instead of thinking of what concentration to assign to that boundary, i should rather consider the flux at the boundary?
Ok, so instead of thinking of what concentration to assign to that boundary, i should rather consider the flux at the boundary?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 19 nov. 2012, 02:10 UTC−5
Hi

Now back on my WS and checking the help file, I understand it not as a constant flux (the per second is missing to), but a infinite reservoir of given concentration, this applies for inflow, as for open boundary

if you check the boundary equations: inflow fixed the concentration on the boundary to the one of a fictitious reservoir on the external side. Outflow, defines a normal flux, but does not fix it in absolute, while open boundary allows for a normal concentration to leave, but a constant concentration to enter

The Flux BC set a flux per sec

--
Good luck
Ivar
Hi Now back on my WS and checking the help file, I understand it not as a constant flux (the per second is missing to), but a infinite reservoir of given concentration, this applies for inflow, as for open boundary if you check the boundary equations: inflow fixed the concentration on the boundary to the one of a fictitious reservoir on the external side. Outflow, defines a normal flux, but does not fix it in absolute, while open boundary allows for a normal concentration to leave, but a constant concentration to enter The Flux BC set a flux per sec -- Good luck Ivar

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content