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Dealing with multiple outlets and mass fractions

Question asked by Matthew Paone on Jul 2, 2013
Latest reply on Jul 8, 2013 by Jared Conway

Hi all!


I am attempting to model a simple air flow channel. In my application, oxygen diffuses out through the roof of the channel. I want to observe the change in mass fraction of oxygen down the length of the channel.


I have set this up in the following way:


Inlet face: mass flow rate inlet, Oxygen and Nitrogen with substance concentration set to 0.22 Oxygen and 0.78 Nitrogen volume fractions.

Roof: mass flow rate outlet, Oxygen only (using substance concentrations of 1 Oxygen and 0 Nitrogen)

Outlet face: static pressure opening, set to atmospheric pressure.


When I run the model, using a cut plot along the length of the channel there is no change in the mass fraction of Oxygen or Nitrogen, regardless of the inlet/outlet mass flow rates.


Does anyone have any suggestions as to why I am not observing a gradient in the mass fraction of Oxygen along the length of the channel?