# Looking for suggestions about how to set up a boundary condition

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 February 25, 2010, 18:08 Looking for suggestions about how to set up a boundary condition #1 New Member   Pete Launie Join Date: Feb 2010 Posts: 10 Rep Power: 7 I would like to model a multi-component gas flowing over a membrane which allows one of the components to diffuse through it. Not sure how to set up the problem in star ccm. can I define a boundary with a negative mass flow based on a field function which looks at the local mass fraction of that gas component? Is this asking for trouble or does anyone have other ideas about how to set it up? Thanks for your help.

 February 28, 2010, 14:14 #2 Member   Naimish Harpal (MS Aerospace Engr) Join Date: Jul 2009 Location: Long Beach, CA Posts: 50 Rep Power: 8 Regrading your membrane BC, to diffuse multi-component gas, you can define that boundary as 'Pressure Outlet'. Then define pressure and the mass-fraction (between 0 and 1 w.r.t to total mass-fraction) of particular gas to be sucked out. You may calculate the pressure in terms of velocity and mass flow rate using simple Bernoulli' equation. I hope that this may help you.

March 23, 2010, 16:12
#3
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Pete Launie
Join Date: Feb 2010
Posts: 10
Rep Power: 7
Quote:
 Originally Posted by naimishharpal Regrading your membrane BC, to diffuse multi-component gas, you can define that boundary as 'Pressure Outlet'. Then define pressure and the mass-fraction (between 0 and 1 w.r.t to total mass-fraction) of particular gas to be sucked out. You may calculate the pressure in terms of velocity and mass flow rate using simple Bernoulli' equation. I hope that this may help you.
On a pressure outlet boundary, doesn't the mass fraction (species specification) only apply when there is backflow?

 April 6, 2010, 13:08 Update #4 New Member   Pete Launie Join Date: Feb 2010 Posts: 10 Rep Power: 7 CD-adapco said there is no way to specify a per species boundary condition and trying to come up with a work-around.

 Tags boundary conditions, star ccm+

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