Which is the correct Physics?
 

Hello All,

I have an interesting and may be a simple question on fluid flow.

Let us assume, case 1 we have cylindrical pipe where the flow enters at inlet pressure P1 and exits at outlet pressure P2 for given length (P1>P2). In case 2, we have same cylindrical pipe with some blockage in middle of the pipe. The only difference is blockage within the pipe.

Now, the question is pressure P1 in both case 1 & case 2 will it still remain the same if the pressure P2 is same in both cases. If Yes/No, kindly explain the physics scenario.

Might be my question look silly. But I'm looking for proper explanation.

That's not the ONLY difference because you haven't considered that there is a flow and this flow interacts with the blockage. In general the difference between P1 and P2 (the pressure drop) is a function of the flow field and vice versa.

You can have the same P2 and find a flow for Case 1 that yields a P1 and a different flow for Case 2 that yields the same P1. Alternatively, if you have nominally the same flowrate and you hold P2 the same for both, then P1 should change to whatever it needs to be to satisfy the flowrate.

Thanks LuckyTran for your explanation. This is what i had in mind.

One more question for better understanding. So, for same P1 and P2 in both cases which one will have higher flow. I hope case 1 will have more flow with lesser resistance. Correct me if I am wrong.

Considering the characteristic theory for compressible Subsonic flows, the inflow will be influenced by the internal flow