Maximum flow through pipe

[RJ08]

Hi all,

If a pipe has a 1" inside diameter and has a 40bar pressure at one end and 3bar pressure at the other what would be the maximum flow through that pipe?

The fluid has water properties and the pipe length is unknown.

Thanks

 

[nouanda]

what is the source of the pressure drop? friction? elevation? tanks, vessels?

 

[RJ08]

sorry it is tanks

 

[quark]

Theoretically, it corresponds to a pressure drop of 37 bar.

 

[zdas04]

Somewhere between not very much and a lot. With an unknown pipe length, unknown elevation change, unknown pipe roughness there is no way to quantify the maximum flow rate in a 1-inch pipe. There is one trivial solution, if the outlet is 1219 ft higher than the inlet then the maximum flow is zero.

I am curious though, when you say the "source of the pressure drop" is "tanks", what the heck does that mean? The question was about a 1-inch pipe that has a 37 bar dP over some unspecified length. Where do the tanks come in?

David

 

[BigInch]

The best you can do with all those unknowns is to figure the flowrate at a velocity of around 60 ft/sec. Any more than that and the cost of power is going to bust your wallet, or your pipe won't last too long.

If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?" - Seymour Cray (1925-1996), father of supercomputing
***************

http://virtualpipeline.spaces.live.com/

 

[zdas04]

Water at 60 ft/sec? Errosional velocity is 6 ft/sec.

David

 

[JimCasey]

>>Water at 60 ft/sec? Errosional velocity is 6 ft/sec.

David <<<

Never have I seen an erosion limit of pipe at 6fps, but that's immaterial. THe question asks for the maximum flowrate if you put a lot of pressure in one end and not a lot in the other. Still, my references allow up to 30fps in CS pipe and 50 in SS.

I'm with BigInch on this one. If there's nothing but a straight shot of pipe with a large DP, the velocity will get really high, and 60 fps is a reasonable estimate. High enough velocity will possibly even cause cavitation. Can't evaluate for cavitation because the vapor pressure of the fluid is not known

 

[katmar]

If the pipe is very short, then the frictional loss is negligible and the only losses are the entrance and exit (i.e. acceleration) losses. My software says that under these circumstances the flowrate is 562.2 USGPM and the velocity is 230 ft/s. In real life you can only get less than this.

If the line is 300 ft long then the velocity drops to 30 ft/s and the flow to 73.5 USGPM. And so on.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[SeanB]

I just want to say that I don't even know why people are arguing numbers in here seeing as the original question posted was nonsense. Without a length of pipe the answer can be anything - which is probably the point the people responding are making.

 

[BigInch]

Strange isn't it. Usually if you know anything, its how far you want to go!

If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?" - Seymour Cray (1925-1996), father of supercomputing
***************

http://virtualpipeline.spaces.live.com/

 

[JimCasey]

>>If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?" <<

Well, the chicken trick WOULD get you some notoriety......

 

[JimCasey]

Sorry, I can't let go of this....

PULL IT!, Pullet!

 

[BigInch]

Notoriety is the one thing I have too much of already.

If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?" - Seymour Cray (1925-1996), father of supercomputing
***************

http://virtualpipeline.spaces.live.com/

 

[ChemEng84]

please someone tell me if what i'll suggest now is reasonable or just nonesense:
why can't we use bearnoulli's equation:we have the dP and i think we could have the inlet veocity, the density so we can get the outlet velocity.
we have the diameter i.e the area and velocity so we have the flow rate.

 

[zdas04]

Pretty much nonsense. What makes you think that the problem as stated includes an inlet velocity?

David

 

[ChemEng84]

Sorry, my bad.

 

[katmar]

ChemEng84, what you suggest is basically what my software has modelled. In the original Bernoulli equation friction was ignored (i.e. my "short" pipe) and only the acceleration term (often called exit loss) is applicable here. There is no change in height, no shaft work, no volume change etc. So you can use Bernoulli to calculate a theoretical frictionless velocity if you know the pressure difference and the physical properties of the fluid.

The form of Bernoulli that we all use now incorprates the Darcy equation to deal with the friction. I included an inlet loss as well in my "short pipe" model. Unfortunately RJ08 has not explained what he is actually trying to calculate, so it is all just mental gymnastics really.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[gerhardl]

After reading all above (''I am still not chicken enough '') to let go of the original question, and ask for more information on the actual problem.

Why are you trying to obtain a figure for the maximum flow? In real life you will have some force (pump or elevation or pressure in a tank) to give the starting pressure.

After this you have your 1" pipe and tanks, all of undetermined length, layout and size, all giving an unknown contribution to an internal pressure loss, and you end up with 3 bars (measured or back pressure?)at the other end.

Three ways out:

a. Calculate with known layout the loss for the components step by step.

b. Measure the flow at the end.

c. Limit the flow to a sensible flow for the liquid and type of tanks and pipelines by regulating valves, or boost by pumping to a sensible flow value.

For c: The sensible limit for pipelines, tanks and valves an other pipeline components could perhaps be normally conservatively used 2-4 m/s for watery fluids( about 7 to 14 ft/s), or up to perhaps the double (8m/s - 30 ft/s).

Above this you would start to loose control if you do not know exactly what you are doing.

 

[zdas04]

gerhardl,
I think we are casting pearls before swine. He hasn't logged on since his September 23 post and I don't think any more information will be forthcoming. So I guess we can make up any answers to our questions that make us feel good.

David