Pipe sizeing problem
Pipe sizeing problem
(OP)
Hello...
I am struggling with calculating the pipe size diameter for real life problem, suppose I want to supply water to a premises from munsipality main line and the data I have:
Water demand= 90 cubic meter/day
Avilable pressure at tie-in = 1 bar
Distance from tie-in point to the premises ground water tank = 20 meter
the pipe line runs horizontally on the ground and goes vertically about 3 meter to the tank.
The equations I am working on are Energy and Darcy equations, but I am not sure how to fit the scenario I have described above into those equations, also I am comparing my result with Pipe Flow Wizard software but with no success!
Any help would be appreciated
Thank you.
I am struggling with calculating the pipe size diameter for real life problem, suppose I want to supply water to a premises from munsipality main line and the data I have:
Water demand= 90 cubic meter/day
Avilable pressure at tie-in = 1 bar
Distance from tie-in point to the premises ground water tank = 20 meter
the pipe line runs horizontally on the ground and goes vertically about 3 meter to the tank.
The equations I am working on are Energy and Darcy equations, but I am not sure how to fit the scenario I have described above into those equations, also I am comparing my result with Pipe Flow Wizard software but with no success!
Any help would be appreciated
Thank you.





RE: Pipe sizeing problem
RE: Pipe sizeing problem
Qark is of course right.
90m3 a day is however not much. If you do a rough calculation, even putting in considerable less pressure drop to overcome any unforeseen factors, you will probably have more than sufficient capacity with a one inch pipeline.
Please check necessary peaks as stated by Quark.
Any dimension below one inch have to be more exact calculated. Going up or down in piping size is more a question of what is normally done or required (also by any regulations and demands, also including considerations for, if any, firewater demand) in the area, and what is best suited and economical over time.
RE: Pipe sizeing problem
You should be getting something like a 2" or 2.5" diameter pipe, which will lose somewhere around 150mm of head in the 20 meters.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pipe sizeing problem
Quark and Gerhard thank you for your response
Just want to correct one thing!
The total demand is 2160m3/day = 90m3/h, and we are going to fill the tank within 8 hours; therefore the flow rate would be 270m3/h.
My most concerned is how to do the calculation rather than logic.
RE: Pipe sizeing problem
Logic. Use outlet pressure = max tank fluid level
Use flowrate = 270 m3/h
Assume pipe diameter
calculate inlet pressure (online pipe flow calc)
If inlet pressure is greater than available,
increase pipe size
or add pump
Return
Else
Reduce pipe diameter
End
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pipe sizeing problem
For Darcy use length = 23 m, pressure available = 0.7 bar (= 1 bar - 0.3 bar). I would add in a K value of about 10 to cover valves, bends, entrance and exit losses.
My software says you need an 8" pipe for 270 m3/h.
If you are still having problems with the calculation you will have to be more specific about exactly what is troubling you.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pipe sizeing problem
Harvey,
What are your assumptions?
RE: Pipe sizeing problem
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pipe sizeing problem
RE: Pipe sizeing problem
applying "Energy equation" and "Darcy equation"
assuming p1=1 bar, p2= 0.5,Z1=0, Z2=3m,Vsqr.1=Vsqr.2(removed from both side of Equation)
solve for hf,=2.1m
Darcy Equ.
D=(8(fL/hf)(Qsqr/PisqrXg))1/5
assume f=0.001, given: L=20, Q= 0.075m3/s and hf=2.1
Therefor, D= 85mm
using Moody Diagram,
Ks/D----assume Ks=0.001
we get Resistanse coeff., f=0.0095
Therefor,D =133mm=5in, so I can go with the next commercial pipe size avilable wich is 6in
"Pipe Flow Wizard" software gives me almost the same result, also same as Quark result :)
RE: Pipe sizeing problem
You cannot ignore the velocity change. Effectively V1 is 0 m/s and all of V2 is lost in the target tank. You have also ignored any valves and bends. There must be at least one valve because you need to control the flow, and there will probably be an isolation valve at the municipal tie-in.
How did you calculate your friction factor? My calcs make it 0.016. Can you upload a screen shot of the Pipe Flow Wizard input data and results - I would be most surprised if commercial software confirmed this answer.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pipe sizeing problem
RE: Pipe sizeing problem
I see you are using copper pipe. Under these circumstances copper will give about 30% less friction loss than commercial steel pipe because copper is smoother than steel. That explains my query about the friction factor. Copper pipe is more expensive than steel, and I am not sure how easily it is available in this size.
The screenshot confirms that you have ignored the fittings, valves, entrance and exit losses. Pipe Flow Wizard seems to have a reasonable selection of fittings and valves, but I cannot find any allowance for entrance and exit losses. This will lead to real errors, especially if you are trying to use a velocity of 8 m/s. This is a much higher velocity than what would typically be used.
I still do not see how you got to 2.1m for the allowable friction loss.
My impression of this job is that you need more help than what is available via Eng-Tips. Eng-Tips is not intended as a replacement for sound engineering help and I would advise you to engage a local professional engineer to do this design. At the very least run your intended design past the municipal engineers who will probably have a wealth of practical knowledge that cannot be given in a forum like this.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pipe sizeing problem
I believe it won't make big deferent if you choose a deferent pipe material or adding fittings and valves, in term of pipe size selection, calculations and software confirm that. I have chosen copper just as an example; otherwise I can go with HDPE or MDPE.
Regarding head loss,hf=2.1m I got that from Energy Equation:
P1/ρg+V2/2g+Z1=P2/ρg+V2/2g+Z2+hf
P1=100KPa/m2,---------->(100KPa= 1bar)
Assume P2=50Kpa/m2(minimum factor that we can expect from system to be in the safe way! And we may use it in the software as available pressure )
V1=V2 since the pipe sectional area is same at all the pipe line system, and since it is energy equation the total energy in the left side will be equal to the right side, so V's cancel each other.
Z1= 0, because the entry pipe line is running on the ground, and Z2 =3m (targeted tank height).
Ρg=9.81x1000
Solving for hf, hf = 2.1
What do you think?