Manifold design
Manifold design
(OP)
I've been reading a lot of threads of manifold design but it is still confusing to me. Here is my problem:
I've a 4 inch inlet pipe which will bring in about 300-500 gpm of water from a pump. I need to design a manifold of about 7 ft length. We are going to drill holes into the 7 ft pipe to create orifices. I have to figure out the spacing and size of these orifices to get uniform flow rate from all the orifices. The pipe thickness would be 4 inches and the manifold will be used in vertical direction. Any help is greatly appreciate. Thank you
I've a 4 inch inlet pipe which will bring in about 300-500 gpm of water from a pump. I need to design a manifold of about 7 ft length. We are going to drill holes into the 7 ft pipe to create orifices. I have to figure out the spacing and size of these orifices to get uniform flow rate from all the orifices. The pipe thickness would be 4 inches and the manifold will be used in vertical direction. Any help is greatly appreciate. Thank you





RE: Manifold design
Good luck,
Latexman
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Manifold design
Diameter of the pipe: 4 inches
Inlet flowrate: 300-500 gpm
Output flowrate: Uniform flow through all the orifices
The idea is that we have pump that is going to pump water into a tank. We want to design a manifold so that the water is distributed uniformly along the depth into the tank. The tank depth is about 7 ft. Hope this makes sense?
RE: Manifold design
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Manifold design
RE: Manifold design
RE: Manifold design
If the manifold just has to be vertical, then I would enter it from the bottom and gradate the hole size (so that the first hole the water sees is the smallest hole at the highest pressure, and so forth until the top is the biggest hole at the lowest pressure).
You could do equal hole sizes if you could turn your manifold horizontal, but you would still get more flow from the hole(s) closest to the source.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Manifold design
best to make the manifold pipe larger (than 4 inches) and make the orifices larger and then the headloss in the manifold will be reduced to negligble.
RE: Manifold design
1) select an orifice size at the bottom of the tank.
2) select an arbitrary pressure on this orifice.
3) calculate the flow from the orifice
4) calculate the pressure loss in the segment of pipe between the bottom orifice and the next orifice.
5) the pressure the next orifice "sees" is the sum of the pressure loss in the segment of pipe and pressure selected in step 2.
6) repeat 3-6
Do this for several values of pressure from step 2 and draw a system curve.
RE: Manifold design
@tkall: I was doing something similar and I thought there must be something much more easier. Also, it should be assumed that the tank is full of water. The height of water will probably up to the top of the tank at all times.
@zdas04: Kind of uniform is acceptable. We want to reduce unwanted eddies due to the difference in velocities when submerged in water. Can I vary the spacing instead of the diameter? It would be easier to use one size drill hole.
RE: Manifold design
Have you looked into "jet mixing"? That will be easier, IMO.
Use Search (undet the thread title, between Forum and FAQs) on distributor or maldistribution and you will find some useful threads.
Good luck,
Latexman
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Manifold design
Other option is: can I move the inlet into the center for a better pressure distribution in the manifold? I guess this means more bends and more minor losses.
RE: Manifold design
However, can't see how this is such a critical problem, the flow rate isn't even nailed down as yet, 300-500 gpm is quite a range and the pipe is about 7ft, staying with this same near enough spec. "X" number of drilled orifices should give approx the same flow rate.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Manifold design
For a variable flow a fixed orifice system will provide variable distribution but for a equal resistance system it should stay more or less the same.
Go for a diam and number of hoses which gives a similar total internal area to your incoming pipe.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Manifold design
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Manifold design
Good luck,
Latexman
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Manifold design
What controls the flow from a short manifold is the resistance to flow through each outlet, which is primarily controlled by the square root of the differential pressure across each outlet, Q = K dH^2. The square root of the difference between all manifold outlet differential pressures in a 7 foot length, even if vertical and immersed in water (3 psi) will not make a hill of beans difference to the flow across each orifice, as long as the pressure inside the manifold is somewhat high relative to the 3 psi, all flows will be nearly the same, high being only 20 psi. That should produce outflows that vary by no more than +/- 15%. A 10 psig manifold pressure would have around a +/- 25% rate of equality. at 50 psig, +/- 5%
Independent events are seldomly independent.
RE: Manifold design
If you size the orifices for an orifice pressure drop equal to approx 3 times the manifold's inlet velocity head, then you would likely meet the +/- 10% variation at the design flowrate. Alternately, if the total flowrate is relatively constant , then you can drill each of the 4 orifices differently , to account for the varying velocity head in the manifold as the gross fluid flowrate decreasses from 4 to 3 to 2 to 1 downstream flowpaths. Or, you can reduce the manifold diameter followign each orifice so that the velocity head upstream of each orifice is a constant value.
"Nobody expects the Spanish Inquisition! "
RE: Manifold design
Independent events are seldomly independent.
RE: Manifold design
If the manifold is designed for a velocity of 6 ft/s at a flow of 500 gpm then you get a 6" pipe and the friction pressure drop over 7 ft would be less than 0.1 psi. If the pump can deliver (say) 15 psi at the top of the manifold then the friction loss is negligible and the static pressure changes offset each other. The result is that an orifice at the top of the manifold "sees" exactly the same available pressure drop as the bottom orifice. Even if you continue the 4" pipe as the manifold the friction drop will be less than 0.4 psi and is probably still negligible.
You can safely space the orifices evenly over the length of the manifold. If they are spaced every 4 inches you will have about 20 orifices. Size each orifice for 25 gpm (= 500/20) at a pressure drop of 15 psi and you will have a simple manifold with 20 identical orifices that gives a very close to uniform flow over its length.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Manifold design
Independent events are seldomly independent.
RE: Manifold design
In a full tank you are exactly right. I was seeing it as an empty tank, and the dP would change over the length into an empty tank.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"