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-   -   Looking for suggestions about how to set up a boundary condition (http://www.cfd-online.com/Forums/star-ccm/73075-looking-suggestions-about-how-set-up-boundary-condition.html)

 plaunie February 25, 2010 18:08

Looking for suggestions about how to set up a boundary condition

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.

 naimishharpal February 28, 2010 14:14

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.

 plaunie March 23, 2010 16:12

Quote:
 Originally Posted by naimishharpal (Post 247801) 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?

 plaunie April 6, 2010 13:08

Update

CD-adapco said there is no way to specify a per species boundary condition and trying to come up with a work-around.

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