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Flowrate behind orifice2

Flowrate behind orifice

(OP)
Hello all!

I have 8-bar pressurized clean water system with 50 mm ID pipework and a hydrant. On this hydrant I want to install orifice plate and connect 50 mm hose. However I am limited by a maximum flowrate behind orifice which can't be higher than 5 m/s.

The equation everyone is familiar with uses Cd*srqt(2*g*H) where typical Cd is probably about 0.62.

From these using continuity equation A=Q/V I could obtain orifice diameter.

Could you please tell me whether this approach is suitable? As a pressure (head) difference would you use 8 bar - 1 bar (atmospheric)= 7 so 70 m? Is there any way to estimate whether Cd will be closer to 0.6 or 0.7?

Jed

RE: Flowrate behind orifice

Try something like this ?

http://www.tlv.com/global/TI/calculator/water-flow...

Also do you mean velcoity of 5m/sec? If so what is pipe size so you can work out flowrate.

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

RE: Flowrate behind orifice

You have to work the problem in four steps.
1. Figure out the flow rate in the hose that matches your desired velocity.
2. Then use Darcy-Weisbach to figure the pressure downstream of the orifice (upstream pressure in the hose).
3. Then use Darcy again to get the dP in the pipe to find the upstream pressure for the orifice (downstream pressure in the pipe).
4. Now you have upstream and downstream pressure for the orifice. Then go to the link that LittleInch provided and put in these values and adjust the orifice size until the flowrate matches the two segments.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Flowrate behind orifice

(OP)
Thank you both for your input.

I meant volumetric flowrate of 5 m3/s is the maximum I can't exceed behind the orifice (actually at the end of the hose).

To be completely sure I got it right:

1. From vol. flowrate I can obtain velocity and then using Bernoulli and Darcy-Weisbach for losses in the hose I can obtain total head that will be needed to discharge 5 m3/s at the end of the hose. My total head here would consist of velocity head and frictional head loss
2. Knowing that upstream to orifice I have 8 bars of pressure I don't need to use Darcy to calculate losses here.
3. My pressure drop is 8 bars minus the value I got from point 1.

Did I get it right or made mistakes?

RE: Flowrate behind orifice

You didn't say where the 8 barg was at. If that is the pressure at the orifice location then you have it right. If the known pressure is some distance of 50 DN hard-pipe upstream then you have to calculate the friction drop in the 50 DN hard-pipe.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Flowrate behind orifice

5 m3/s in a 50 mm hose? I don't think so.

RE: Flowrate behind orifice

I hope it's 5m3/hr.... or is actually 5m/s velocity.

A jet velocity of 2,500m/sec would be some fire hose alright...

Or maybe it's something like this... https://www.youtube.com/watch?v=pn-CVQh62Eo

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

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