Brain fade/idiot moment - simple question about pipe flows

AI Thread Summary
The discussion revolves around the placement of a butterfly valve in a pipe system involving a fan and various pipe configurations. It is noted that the positioning of the valve—either upstream or downstream of the fan—can affect system performance, particularly in terms of backpressure control. A common practice among process engineers is to place the valve downstream to manage backpressure effectively. The original poster seeks clarity on the expected outcomes of different configurations before investing time in a more complex 3D model. Ultimately, the correct placement depends on the specific operational goals of the fan within the system.
alpha754293
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Stupid question:

I have the following pipe configuration:

Working fluid = ambient air

Pipe1 = 6 inch ID x 24 inch length
Expansion1 = 2 inch length
Pipe2 = 8 inch ID x 2 inch length
Fan1 = assume 200 CFM @ 2860 rpm, 0.05 inH2O
Contraction1 = 2 inch length
Pipe3 = 6 inch ID x 12 inch length
Butterfly valve, 50% open
Pipe4 = 6 inch ID x 12 inch length

Question:

Does it matter whether the butterfly valve is downstream of the fan or upstream of the fan?

(e.g. Pipe1 --> Expansion1 --> Pipe2 --> Fan1 --> Contraction1 --> Pipe3 --> Butterfly valve --> Pipe4

Or

Pipe1 --> Butterfly valve --> Expansion1 --> Pipe2 --> Fan1 --> Contraction1 --> Pipe3 --> Pipe4)

Discuss/prove your work/answer please.

(I tried modelling it with a 1D pipe flow program and I don't know if I am doing it right. And before I go and spend a significantly longer amount of time building the 3D model, I would like to know what the expected value should be for a problem like this. Thanks.)
 
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alpha754293 said:
Discuss/prove your work/answer please.
This looks like schoolwork. Should I move it to the schoolwork forums for you?
 
berkeman said:
This looks like schoolwork. Should I move it to the schoolwork forums for you?

It looks like it's schoolwork, but it actually isn't.

It's professional work.

(Background: I'm doing CFD with turbomachinery and we are having some problems with the test results so I wanted to quickly model it with 1D pipe flow program and failed to do so, and I wanted to see if there was a way to quickly come up with the answer before I go spending a lot of time building the 3D CFD model to test for the same thing.)

Thanks.

Like I said - idiot/brain fade.
 
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It is impossible to give a 'correct' answer without knowing what the purpose of the fan is in the context of the wider system. That said, from my experience (process engineer) it is far more common to control rotating equipment such as fans with backpressure (i.e. valve downstream) rather than on the suction side.
 

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