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turbosonix
Posts: 2
Registered: ‎03-27-2013

Back Pressure

155 Views, 5 Replies
03-27-2013 12:12 PM

I am modeling a flow meter. My outlet boundary condition is 4.35psi which represents the meters back pressure. I specify a volumetric flow rate at the inlet of the flow meter. When I run the model it calculates the pressure at the outlet to be 19 psi, does anyone know what my issue could be? The model is fairly simple - just a flow tube.

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OmkarJ
Posts: 437
Registered: ‎10-02-2012

Re: Back Pressure

03-27-2013 02:21 PM in reply to: turbosonix

It is a bit confusing. You mention you have already specified a outlet boundary condition. From what I understand solution of pressure should propogate from outlet to inside of the domain. It is physically not possible to have a different pressure at outlet than what you specified as a boundary condition.

 

Either you didn't specify the outlet pressure as 4.35 psi, or you didn't measure the outlet pressure rightly. Also,  check if you have given two inlet boundary conditions, mass flow rate and inlet pressure. 

 

OJ

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Product Support
wildej
Posts: 927
Registered: ‎08-25-2011

Re: Back Pressure

03-27-2013 04:11 PM in reply to: OmkarJ

I think for the first time ever I have to disagree with Omkar.

 

You are at risk of overconstraining the model if you have pressure on both inlet and outlet and a flow rate at the inlet.


Please could you list all of the boundary conditions you are applying here?

How long are your extensions at the inlet and outlet - could you provide a marked up screenshot?



Jon Wilde
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OmkarJ
Posts: 437
Registered: ‎10-02-2012

Re: Back Pressure

03-28-2013 02:13 AM in reply to: wildej

Jon, 

 

With due respect, among many possibilities, I did mention the overcosntraining issue in my last sentece - indicating that inlet may have been specified with pressure as well as mass/volume flow rate.

 

If I am not missing something, aren't we on the same side? :smileyhappy:

 

OJ

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Product Support
wildej
Posts: 927
Registered: ‎08-25-2011

Re: Back Pressure

03-28-2013 02:20 AM in reply to: OmkarJ

Ah yes, I see what you meany by that sentence now.

 

As far as I know, all 3 of us are on the same team :smileyhappy:



Jon Wilde
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New Member
turbosonix
Posts: 2
Registered: ‎03-27-2013

Re: Back Pressure

03-28-2013 05:01 AM in reply to: turbosonix

I have Q = 35 gal/min specified for the inlet boundary condition and P = 4.35psi as the outlet boundary condition. There are inlet and outlet pipes on the model and each are 7.5 inches long. The flow tube itself is 4 inches long with a 3/4" opening on each end. I am measuring the pressure using a static pressure  x-y plot in the plane result mode. I will upload a picture later today. Thanks for your help!

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