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system curve

system curve

(OP)
i want to get the system curve of a pipeline , i ask about the method,i calculate th loss for fixed flow rated and i use the formula : PDC = a * (Qv^2)to get the curve.
with
PDC is the losshead in the system
Qv is the volume flow rate

when can i use yhis formula ?
is there any other method ?

RE: system curve

I would suggest you take the time to type "calculate head loss in pipes" into google or similar, you might be surprised to see over 800,000 links.

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: system curve

(OP)
Artisi:thx for your reply but i'm already calculted the total head loss in the pipeline for a fixed flow rate. i'm asking about the system's curve.

RE: system curve

you calculate for various flowrates below and above the fixed flowrate, and then plot the curve from this data.
Did you actually look at any of the links to see how its done - guess not?
There are even online calculators to make your life easy.

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: system curve

I use this spreadsheet I made. It uses basic equations you can find in any fluids book. I'll sell you a copy for $1,000,000.

RE: system curve

That's a bargain.
Send me 10.

RE: system curve

how much for a metric version or is that included in the $1M?

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: system curve

I can do metric for an extra $1.12.

RE: system curve

Busted! Gentlemen promotion and sales are not allowed on the Eng-Tips website.

smile

Technology is stealing American jobs. Stop visas for robots.

RE: system curve

Keep it quiet and I'll give you a .001% kick back on the sale.

RE: system curve

Hey. I know when I'm getting the shi# end of the pipeline.

Technology is stealing American jobs. Stop visas for robots.

RE: system curve

In simplistic terms

PDC = Hl + ( a * Qv^2)

Where Hl is the static head loss at zero flow or any sort of static pressure at your end point converted to head.

Also whilst pressure drop is proportional to flowrate ^2, it is not a precise curve as Re no changes.

In the example given above , Hl is about 34ft.

In low head systems something like the difference in liquid level in a tank at the end point can change your system curve enough to make a difference.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: system curve

Pipe to the top of the tank. Or.... we could do it with a VFD.

Technology is stealing American jobs. Stop visas for robots.

RE: system curve

when can i use this formula ?

This formula is used with full pipe flow. Plot the system curve on a graph with the pump performance curve. See the example to balance the pump curve and system curve:

www.ce.utexas.edu/prof/maidment/ce356Fall04/docs/P...


is there any other method?

Yes, but this is the easiest method for day to day tasks.

RE: system curve

Ouahmed,

You can convert your single calculated point to a curve using the following formula:

H = [(PCD - StaticHead)/(Qv^2)] x F^2 + StaticHead

Where

H is head of fluid as a function of F
F is flow
StaticHead is your lift and/or tank pressure
PCD is head at your single calculated point
Qv is flow at your single calculated point

You can find your operating head (H) for any value of F by curve-fitting the pump curve to a 2nd order polynomial and setting the two formulas equal to each other then finding zero. Then use the quadratic equation to solve for F. Plug F back into the equation above to find the corresponding H.

I used to count sand. Now I don't count at all.

RE: system curve

Well, repeat the calculation for another fixed flow rate, and keep doing it until you can make a nice graph, from which you can estimate your coefficients.



Mike Halloran
Pembroke Pines, FL, USA

RE: system curve

Using Mike's method, you only need 3 points because it will be a second order polynomial. You only need to calculate 2 points because they can be mirrored about the head axis.

I used to count sand. Now I don't count at all.

RE: system curve

MFJewel,
Is there a discount for multiple copies? I presume the software comes with full QA and Certificate of conformity? Do you need excel or is it a self-contained software package?

RE: system curve

Ask nicely and I'll let you make all the copies that you can carry away in one day from the one I bought.

Richard Feynman's Problem Solving Algorithm
1. Write down the problem.
2. Think very hard.
3. Write down the answer.

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