[Nighmare] seawater level and impact on the head loss 2

[setasena]

Dear all,
I truly need your support on this nightmare.
I just had a huge argument with my boss, about something we are doubting so far.

Our client is currently asking for our support to determine the diameter of our pipe that is sufficient enough to have a total of flowrate of 86.4 m3/s.
So the pipe will be under the sea, conecting from the sea (which is in the right side) to a basin/ reservoid (left side). Because our pipe is just like a communicating vessel, the sea level between the sea itself and the reservoir will always remain the same. And from the reservoir it will be connected to a pump that will suck 86.4 m3/s water to the system. The client is requesting that the head loss due to friction shall always remain not bigger than 1.1 meter k =0.6

So the client is asking us to provide 4 lines (2 lines which is bigger than the 2 other lines), so that it can reduce the transportation cost by nesting it (putting the smaller diameter into the bigger one).


Now this is the funniest thing.
each line has different of length.
Line A 1616 meter
Line B 1604 meter
Line C 1601 meter
Line D 1613 meter.

Both me and my boss do a calculation comes up with 2 different result:

My boss argument is that:
- The head loss shall always be the same as the sea level of the reservoir and the sea intake are the same, which is 1.1 meter. (Does the head loss has anyting to do with the sea level??????)
- when the pump is activated to take the water from the reservoir, the velocity from each pipe can be different due to the length of the pipe (is this true??? I cannot imagine how the pump is possible to arrange different of velocity for each line).
and this is his calculation

he ends up having a combination of 4000 mm and 3500 mm diameter

My argument is:
The head loss cannot be the same as the length are also different. at the end the client is requesting that the head loss shall be smaller or equal than 1.1 meter. not all of them suppose to be 1.1 meter.
The velocity is the main criteria and shall always remain the same. . Is my argument correct?

I end up having a combination of 4000 mm and 3600 diameter.

What is the best argument for me to inform my boss about this?

Any idea??

Thank you so much for your full support. I add the excel sheet that my boss had done, and I made some adjustment.

Please review.

 

[setasena]

The file for your reference.

 

[SlideRuleEra]

Your boss's assumption that head loss is equal for all four pipes is correct. The velocity will vary in each pipe. The way I understand the problem, each pipe supplies water to the reservoir. The pump suction is in the reservoir and is not connected to any off the four reservoir supply pipes - velocity in each pipe will not affect the pump suction velocity. Pump suction velocity is probably different from any of the four reservoir supply pipes.

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[LittleInch]

From what I can figure out you're both not correct.

The reservoir at the left hand end will need to reduce in level to generate flow. This can be a MAXIMUM of 1.1m

For parallel pipes the only fixed item between them all is the head difference. That's all.

The length difference is very small and shouldn't make a difference, but the number of bends might become significant.

It becomes an iteration between the pipes to adjust the flow and velocity in each pipe to match an identical head loss and total up the flow to your 86.4m3/sec.

Your bosses calculation is close, but then screws up on the last pipe. Why would this pipe suddenly have a lower head loss?? It won't, so he needs to adjust the head loss figures to be identical, but less than 1.1m

Your calculation is not correct. Velocity is determined by head loss in this case as there is no other driving force.

I think your client is mad. You can probably do this with three 4.2m pipes. Any saving on transport by nesting won't pay for a forth pipe

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

 

[SlideRuleEra]

Don't blame the boss. The OP copied the boss's numbers for "Line 4" incorrectly. On the boss's attached spreadsheet the results for "Line 4 are almost identical to "Line 3", as they should be.

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[setasena]

Dear all,
thank you so much for your answer.

yes you are right.
dont blame the boss.. It was my fault for not inputting the right head loss of the boss. all should be identical to 1.1 meter


"I think your client is mad. You can probably do this with three 4.2m pipes. Any saving on transport by nesting won't pay for a forth pipe"
Our standard product is only limited to 4.0 meter. therefore we agreed to give them a combination of 4000 mm and 3500 mm.

Dear SlideRuleEra,
yes you are understanding correctly:
"The way I understand the problem, each pipe supplies water to the reservoir. The pump suction is in the reservoir and is not connected to any off the four reservoir supply pipes"

Dear Littleinch,
What is still hard for me to understand is the fact about what is the relation between the head loss (which is friction) and your statement saying that the reservoir at the left hand end will need to reduce in level to generate flow. This can be a MAXIMUM of 1.1m"
What I always understand is that head loss is pressure loss due to friction.

I thought that if you have a pump already sucking the water from the reservoir, this will automatically suck the water from the pipe water intake without having impact on the level of the reservoir?
Please correct me if I am wrong.

 

[LittleInch]

setasena,

You're wrong. In this instance the level in the reservoir the pump is pumping from is part of a system which includes a set of pipes coming from the sea. How else are you generating a head difference to let the water flow into your open pit??

Head loss is head loss. In this case where there is atmospheric pressure on both ends of the system, this heads loss translates into a physical head loss, i.e. if the level of the sea is say 0.00masl, then the water level in your LH open pit chamber will need to be lower than 0.00 in order to generate any head difference and hence flow. NO head difference between the ends of a pipe - no flow.

In your case this has been limited by the client to 1.1m, i.e. a liquid level of -1.1masl.

In many case head loss is translated into pressure loss as the fluid is contained inside a pipe, but here you have two open ends with only atmospheric pressure on each end.

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