adjusting pressure drops to ensure equal flows
adjusting pressure drops to ensure equal flows
(OP)
Hi,
I have a pipe system as in this picture:

The water flows in with flow rate of V1 [m3/s].
I have to adjust diameter of openings in flanges (d1 and d2) so water flows with the same speed through each small hole (diameter d3).
There are n1 holes in section I and n2 holes in section 2.
How to calculate d1 and d2?
All dimensions of, fluid properties, pressure etc. are known.
Thanks for any help,
Paul
PS.
My idea is to calculate flow rates in section I and II:
(V.I=n1/(n1+n2)*V1, V.II=n2/(n1+n2)*V1), and then then:
1. adjust d1 and d2
2. calculate pressure drops (for example from inlet to section I and from inlet to section II)
3. repeat 1 & 2 until I get the same delta P for section I and II.
Is it worth trying or am I totally wrong?
I have a pipe system as in this picture:

The water flows in with flow rate of V1 [m3/s].
I have to adjust diameter of openings in flanges (d1 and d2) so water flows with the same speed through each small hole (diameter d3).
There are n1 holes in section I and n2 holes in section 2.
How to calculate d1 and d2?
All dimensions of, fluid properties, pressure etc. are known.
Thanks for any help,
Paul
PS.
My idea is to calculate flow rates in section I and II:
(V.I=n1/(n1+n2)*V1, V.II=n2/(n1+n2)*V1), and then then:
1. adjust d1 and d2
2. calculate pressure drops (for example from inlet to section I and from inlet to section II)
3. repeat 1 & 2 until I get the same delta P for section I and II.
Is it worth trying or am I totally wrong?





RE: adjusting pressure drops to ensure equal flows
RE: adjusting pressure drops to ensure equal flows
If V1 does not need to be any specific value then there are infinite solutions. You may specify d1 at any value, and calculate d2. In fact if your objective is only to have the same velocity through each d3 hole, then why have a restriction at d1 and d2 at all? If the pressure in I and II are line pressure, then the flowrate through all the d3 holes will be the same. This will be possible without restriction d1 and d2, if the cross-section of (n1+n2)*d3^2*(pi/4) is << cross-section at V1.
If you must control the total flow at some value why not just put a single restriction in the common line, or resize the d3 holes so as to give that design flow without additional restrictions (if either option is possible).
best wishes,
sshep
RE: adjusting pressure drops to ensure equal flows
...<< If the pressure in I and II are line pressure, then the flowrate through all the d3 holes will be the same .... If you must control the total flow at some value why not just put a single restriction in the common line....>>
...
What is your actual target? Within 'normal' viscosity range and full pipeline all d3's will give the same output, as sshep says.
Sizing of d3's (with good approximation) by outlet from one d3 at given size and pressure, multiplied by total number of d3s.
Regulating: either regulating valve in main pipeline if excess pressure or variable pump for boosting and regulating if too low.
If open to atmosphere and natural fall, you could even regulate the flow somewhat by having a higher placed common feeding vessel and maintaining a certain level (or levels) in this.
If closed to atmosphere you have the possibility to regulate pressure by topping the vessel with regulated air or gas pressure (open or bag enclosed gas in the vessel).
RE: adjusting pressure drops to ensure equal flows
RE: adjusting pressure drops to ensure equal flows
I'm afraid Bernoulli won't do you a very good job and you'll have to get out the Flower manual before you'll even be able to start looking at that seriously.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: adjusting pressure drops to ensure equal flows
Thanks for replies
Sorry if something was unclear.
First, so called "section I and II" are not chambers, but pipes, each with many holes (more than 20).
V1 and inlet pressure are known and constant, as well as all pipe system dimensions and arrangement.
What I have to do is to, by adjusting orifices (without changing anything else), ensure that flow rate into each "section" is about the same (for simplification I can omit in calculations pipes "I" and "II").
I just want to know if I can solve this by calculating pressure drops (friction factors for pipes, K-factor for bends, tees and orifices, etc.) and adjusting orifices, so that pressure drops (from inlet to "I" and from inlet to "II") are the same.
RE: adjusting pressure drops to ensure equal flows
Of course the flowrates into pipe "I" and "II" shouldn't be the same, but proportional to number of d3 holes in each pipe.
Sorry for confusion.
RE: adjusting pressure drops to ensure equal flows
RE: adjusting pressure drops to ensure equal flows
Thanks.
RE: adjusting pressure drops to ensure equal flows
I've written exact instructions for posting diagrams in this thread,
thread378-184348: "Parallel" Pump Head Calculation: "Parallel" Pump Head Calculation
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: adjusting pressure drops to ensure equal flows
Thanks
RE: adjusting pressure drops to ensure equal flows
OK, I just opened Word and made a few stick figures with the drawing tools. I selected the result, copied it, then opened up MS Paint and pasted it there. I saved it as a JPG, so now I'm sure that it (should) work like I told you above.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: adjusting pressure drops to ensure equal flows
There's a FAQ which addresses image posting. Might be easier to just point to it than having to re-write the information each time.
FAQ559-1100: How Can I Show An Image In A Post
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Sometimes I only open my mouth to swap feet...
RE: adjusting pressure drops to ensure equal flows
Doug