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sanjib
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Join Date: Jan 2009
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Compressed Air Discharge in Water

01/20/2009 2:25 AM

How to clculate compressed air discharge (CFM) in normal water through a line of 1 inch dia at 6 bar gauge pressure?

Plzzz.... suggest.....!

Regards,

Sanjib
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ducon
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#1

Re: Compressed air discharge in water

01/20/2009 3:57 AM

Install an Air Flow meter and read the CFM reading.

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Beej50
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#2

Re: Compressed Air Discharge in Water

01/21/2009 1:49 AM

If you want to Calculate (as opposed to comment at #1) there is a standard formula (for a discharge into air), however, into water will require a modification and the first thing we need to know is:- at what depth.

At around 60 meters depth (gauge), it will be zero!

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sanjib
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#3
In reply to #2

Re: Compressed Air Discharge in Water

01/21/2009 3:11 AM

Thank U Beej50, This is what is actually showing me the way. Plz suggest the same for a depth of 1 Mtr. as wel as the calculation procedure. Regrds, Sanjib
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Beej50
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#4
In reply to #3

Re: Compressed Air Discharge in Water

01/21/2009 4:18 AM
To determine air flow through an orifice:- V=CK√P Q=AV VP=(V/K)²
Where:
V = Velocity in feet per minute (fpm)
C = Orifice Coefficient
K = Constant = 14,786 when P is expressed in In. Hg
21,094 when P is expressed in PSIG
4,005 when P is expressed in In. of Water
(Above constants are based on an air density of 0.075 lbs/ft )
P = Pressure differential across the orifice
Q = Flow rate in cubic feet per minute (CFM)
A = Total orifice area expressed in square feet

VP = Velocity pressure (units are those of pressure)

Now I suspect that all you have to do is modify the atmospheric pressure (K) to that of 1 meter of water BUT, I am not a mathamatician and only use these formula verbatum! Also, I've never needed to work this problem out before!

Your best option is to wait until someone else jumps in here! A mans just gotta know his limitations!

I hope this helps a bit!

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Beej50
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#5
In reply to #3

Re: Compressed Air Discharge in Water

01/21/2009 4:29 AM

You will also need this:-

Coefficent C for orifices under vacuum or pressure flow:-

Bugger! It just dosent want to paste into this field!

I will email to your postbox!

Good luck with it!

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ndt-tom
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#6

Re: Compressed Air Discharge in Water

01/21/2009 3:28 PM

Further-to Beej50's posts ... in the Commercial Diving industry, for underwater grit blasting, we calculate "Pressure-at-the-nozzle" including the figure 0.45psi per foot of water depth. So Beej50 was spot-on for 60 meters...

For anyone interested: It really DOES require appropriate training to operate such equipment ... underwater as well as topside, or you can end-up with disastrous results...! <click link

[I'm waitin' to hear more about that nozzle coefficient factor...]
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ducon
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#7

Re: Compressed Air Discharge in Water

01/21/2009 3:50 PM

FLOW OF AIR SCFM , SIZE ORIFICE 1" AT 80 PSIG = 1177 SCFM, 90 PSIG = 1305,

100 PSIG = 1433.

SOURCE : http:/www.trident.on.ca/orifice-air-flow.htm

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babybear
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#8

Re: Compressed Air Discharge in Water

01/21/2009 7:45 PM

Hello sanjib:

Can you tell me what the ID of the hose is please?

Take care.................

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#9
In reply to #8

Re: Compressed Air Discharge in Water

01/22/2009 2:36 AM

Hi, babibear, The ID is 25.26mm as measured. Waitn 4 ur reply. Thanks... Sanjib
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babybear
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#10
In reply to #9

Re: Compressed Air Discharge in Water

01/22/2009 1:44 PM

Hello Guest........

OK. Am busy trying to sort it.

Take care............

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U V
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#11

Re: Compressed Air Discharge in Water

01/23/2009 1:44 AM

You may wish to actually physically test this. That much CFM will displace the water above it and cause surging. The weight of the water will keep trying to fill the hole and gravity will force the air up. The pressure will go from maximum to minimum as the air displaces the water above it. Pressure drops and the water rushes back in.

or not, a meter may be deep enough to stop it at that volume but my vote is- it is not.

Brad

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Anonymous Poster (1); babybear (2); Beej50 (3); ducon (2); ndt-tom (1); sanjib (1); U V (1)

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