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Commentator

Join Date: Apr 2007
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Pipe Network-Arriving System Curve

02/09/2012 12:54 AM

Hi, I have a doubt with Hardy Cross Method.

For one assumed flow at inlet, I've found flow divided into each tank with satisfying the conditions of Hardy Cross Method through iterations. Similarly for 2nd, 3rd, etc, assumed flow also I found flow divided into each tank. But to plot the System curve between total flow Vs Total pressure at inlet, how to find Total pressure at inlet of system for a particular assumed flow?

Can I do it like this? With known pressure loss for the corresponding flow in each pipe Total pressure at inlet of system = 1) Pressure loss at pipe 1 + Pressure loss at pipe 2 + Pressure loss at pipe 6 or 2) Pressure loss at pipe 1 + Pressure loss at pipe 3 + Pressure loss at pipe 5 + Pressure loss at pipe 6 or 3) Pressure loss at pipe 1 + Pressure loss at pipe 3 + Pressure loss at pipe 4. or all three cases will be same sir? Please correct me sir. Though softwares are there, before using them, I would like to understand how they work at back end.

Please guide me,

Thank you

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#1

Re: Pipe network-arriving system curve

02/09/2012 1:14 AM

I think we've seen this before. What does line 2 do that 3/5 do not?

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#2
In reply to #1

Re: Pipe network-arriving system curve

02/09/2012 2:58 AM

Yes sir, I've posted earlier about same system with graphical method solution and i got an option of trying through Hardy cross method, which i've tried and posted my doubt in that here.

There is one more line tapping from line 2 to 3rd tank which i've not mentioned here for simplicity.

Thank you.

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#3
In reply to #2

Re: Pipe network-arriving system curve

02/09/2012 7:39 AM

What else have you not mentioned, "for simplicity"?

How can we do your work for you if you don't know what you are doing?

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#4

Re: Pipe Network-Arriving System Curve

02/09/2012 11:00 PM

Well, I'll give you a "P" for persistance, but that's all...

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#5

Re: Pipe Network-Arriving System Curve

02/10/2012 3:48 AM

1. Scenario 1 and 2 are approaching the right understanding except that you need to add elevation into the equation

2. The pressure drop 1+2+6 is the same as 1+3+5+6. The difference is the flowrate in each section but they are related by mass balance

3. The flow through 2 is not the same as that in 3 and flow in 3 is not the same as in 5.

4. Hope the above gives you some food of thought.

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#6
In reply to #5

Re: Pipe Network-Arriving System Curve

02/10/2012 6:53 AM

Thank u sir,

I understood, if the case, in which all sumps opened to atmosphere, pressure difference between Pump outlet and sumps(tanks) inlets will be same & in that case pressure drop 1+2+6, 1+3+5+6 & 1+3+4 will be same. But here case is different and the pressure drop values will be different. please correct me, if i'm wrong.

Can u give some point on plotting system curve for this case.

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Guru

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#8
In reply to #6

Re: Pipe Network-Arriving System Curve

02/10/2012 6:16 PM

You understand correctly, If

1. There is no change in elevation

2. The final calculated flows are in the same direction as shown in your diagram and all pressure differences are positive. (If the calculated flow is opposite an arrow, you would subtract the pressure difference.)

Remember that this is an approximate method, and depending on the final error you accepted, the 3 totals will not be exactly the same. How much difference are you calculating? What pressure difference did you calculate for each section?

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#7

Re: Pipe Network-Arriving System Curve

02/10/2012 12:14 PM

Obvious homework problem. And yes, he/she is persistent to say the least.

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#9

Re: Pipe Network-Arriving System Curve

02/13/2012 6:37 AM

hola todos, en primer lugar nosotros necesitamos clarifique la información

1-hight bombas, TKs y conducto

2-Diam 1-2-3-4-y 6 y largo de cañería

3-elbos, tee....

cuando nosotros tendremos esa información, empieza el cálculo

- aplique a modelo de matemática

- aplique el software

Galindo, Alberto

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