Hi How do we draw the system cur

[Kadongo]

Hi

How do we draw the system curve for a pipeline of tap offs, for example a pipline with a 2 tapoffs with a flow rate of 200,000 m3/d I need to draw the system cure in case of on tap off flow rate is 25000 and other case that two tap offs is on with 50000 in total

Thanks

 

[GBTorpenhow]

The system curve is no more and no less than the system total resistance plotted as a parabola, head = C * flow^2. Determine the total piping system resistance factor then solve for C and plot the curve. Rinse and repeat.

 

[Snickster]

I would calculate the system pressure drop for each flow path under the different flowrates to see which one gives the highest pressure drop and then base the system curve on this highest pressure drop flow path in order to size the system pump.

The flow paths would be one from the beginning to the end of the pipeline, one from the beginning of the pipeline to the end of the first take off, and one from the beginning of the pipeline to the end of the second take off. You would size your pump on the highest pressure drop. To maintain the actual required flow you would likely need to install flow control valves at the take offs so pressure drop calcs would need to include pressure loss across control valves.

If there is very little pressure drop in the main pipeline you may need to install a back pressure regulator in the pipline to keep enough back pressure available at the take off to produce the flow you need in the takeoffs even with control valves at the take offs.

 

[1503-44]

A system curve for a flat profile pipeline can de developed from pressure drop calculations.
You can use the pressure drop calculator at h2xengineering.com (addressed in the picture).
You run the calculator for a number of different flow rates and connect the dots to get the system curve.

This system curve is for a flat profile pipeline with one pipe diameter.
If you have two or more pipe diameters, you can run the calculator for each diameter at the same flow rate, then add the results together.

If you have an outlet higher than the inlet, then the curve starts above the origin by the amount of the elevation rise (converted to pressure, if you are making a pressure system curve diagram, rather than a head diagram.) If your outlet is lower than your inlet, you would start the curve below the origin. Generally it is better to make diagrams using head, in feet, or meters, rather than pressure, although you can choose whatever way suits your requirements.

Note that n in Q^n is closer to n=1.82 rather than 2.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[GBTorpenhow]

Note that n in Q^n is closer to n=1.82 rather than 2.

An implicit assumption when using the resistance coefficient method (K factor) is complete turbulence in a 'rough' pipe, i.e. constant friction factor, in which case head loss is proportional to flow squared.

With modern computing it is trivial to do the three or so iterations required to solve for the friction factor, there is little reason to use Hazen-Williams over Darcy-Weisbach. OP hasn't even stated that the fluid is water.

 

[pierreick]

Hi,
Using an excel sheet with a solver, having the proper set of equations (Bernoulli, Darcy Weisbach, Colebrook and continuity), altimetry, minor losses, pipe dimension, fluid properties to describe the network, this will be my way to tackle the problem.
No point to use approximation.
My view.
Pierre

 

[1503-44]

H2x calculator says it uses DArcy-W
Graph values were calculated by H2x.
HW equation is only there for comparison of exponent.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

A lot depends on how this system actually works and what you are trying to do with the system curve.

A curve gives you head vs flow for a variety of flows, not a fixed one. So what range are you working to?

Is there a min main flow before the tap offs flow?

You end up with three curves.

One for main line only, one for main line plus one with flow at 25000 m3/day, one with two taps at 50,000.

How are the tap offs controlled? To a certain flow rate or something else?
If the taps are close to the start you will see a big impact, less so towards the far end.


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

 

[1503-44]

Right. Great point. The mainline system curve changes depending on the flow rate and pipe diameter of each segment of the mainline and the pressure required to deliver each active tape's flow rate at its delivery point.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."