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problem understanding interaction between ambient pressure and inlet pressure

Question asked by Michael Oswald on Nov 1, 2013
Latest reply on Nov 3, 2013 by Michael Oswald

I'm sure this is a stupid question and maybe it's due to lack of enough coffee, but I'm having a problem defining the pressure in a flow simulation. We're trying to simulate a portion of a vacuum chamber.  Just a tube, .093" diameter x 2" long.  On inside face of the lid at one end of the tube I set the inlet static pressure to 1 Torr (that's what we measure on the real system) and I have a 12 lpm outlet flow on the inside face of the lid at the other end.  When my environmental pressure is set to 1 Torr (in General Settings > Initial Conditions > Thermodynamic Parameters) everything is fine.  If I set that to 760 Torr, the flow goes backwards and the pressure increases to 340 Torr at the inlet.

 

I thought that by defining the pressure at the inlet, I'm forcing it to use 1 Torr.  But apparently Solidworks assumes that my inlet is open to atmosphere, and completely ignores my 1 Torr boundary condition?  Why even have a boundary condition on the inlet then?  And what pressure is it assuming at the exit?  I'm just confused in how to set up a model that isn't open to atmosphere.

 

Any help would be appreciated.  Thanks a lot.

 

Michael

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