2D sketch of situation - ring main loopDear fellow engineers,

I have a question regarding a fluid dynamic problem which I have sketched out. The initial fluid velocity is 1.5 m/s at 1.5 bar and the fluid is water. The pipe line has a constant diameter. In the sketch, the fluid starts flowing through a horizontal pipe. At the end of the pipe there is a ring main with a branch and a valve. I have drawn the flow direction of the fluid with green arrows. However, I am a bit in doubt if the fluid will split upon opening of the valve where the direction of fluid will continue around the ring main and part will go through the valve. Or will the fluid only flow in the direction indicated by the green arrows.[![enter image description here][2]][2]


1 Answer 1


Flow only flows towards lower pressure, and all flow of a non-compressible fluid (which means pretty much all liquids we would use in normal practice) in a length of pipe must have the same flow rate. The pressure will always be highest right where the blue pipe enters the red one, so we can't have flow go past the valve.

Static pressure drops in a pipe from inlet to exit, known to most mechanical engineers as "head loss." This is due to friction from the pipe's walls taking away energy from the stream while the stream's mass flow rate remains constant.

That means there is no way for flow to go to the right from the valve. We might come up with flow rates through the valve that result in zero flow through the top pipe, but we will never have counter clockwise flow through it.

  • $\begingroup$ Ok, if I understand your answer you mean to say that upon opening the valve, the flow will be directed down towards the perpendicular pipe and will not go pass the valve along the loop iniicated by the two black arrows? Green arrows indicate what I believe the flow pattern will be $\endgroup$
    – Dfhaa_DK
    Oct 7, 2023 at 12:31
  • $\begingroup$ I updated the picture where green arrows is what I think the flow pattern/direction will be and black arrows is what I am not entirely certain if this will be the pattern $\endgroup$
    – Dfhaa_DK
    Oct 7, 2023 at 13:27
  • $\begingroup$ green is correct. You cannot have flow in a pipe in 2 directions $\endgroup$
    – Tiger Guy
    Oct 10, 2023 at 5:47
  • $\begingroup$ But you will naturally have a split in flow so Qtotal before the split and Q1 and Q2 around in the two directions. $\endgroup$
    – Dfhaa_DK
    Oct 10, 2023 at 12:39

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