Thread: Air Flow - calculation challenge.

Good luck. We only deal with leaks here, the oily type.

Originally Posted by W&KO

I’m struggling to work out the air flow out of a pressure vessel.

90m3 vessel @ 120kpa

4” outlet, fully opened

How do I work out the rate of air flow out of the vessel (to atmosphere) in either m3/min or CFM.

Good luck with that!

Gas Discharge Rate Atmosphere From a Pressure Vessel | Engineers Edge | www.engineersedge.com

I don't think you can.

Quite a few years ago an engineer where I was working tried to measure the open flow rate of steam on I think an 8" line.

he fired up the boilers and got full head of steam and then opened a v/v with a flow meter some 12" or so in front of the open v/v.

all that happened was that within minutes all the boilers ......and there were a number of them....were at full burn , the stacks were belching black , the Weir pumps were working like jumping jacks , huge amount of vapour going into the sky and we nearly all fell around laughing.

btw , this was Australia's largest cotton textile plant, so there was serious boiler power.

Originally Posted by W&KO

I’m struggling to work out the air flow out of a pressure vessel.

90m3 vessel @ 120kpa

4” outlet, fully opened

How do I work out the rate of air flow out of the vessel (to atmosphere) in either m3/min or CFM.

Absolute or gauge?

Originally Posted by Blknight.aus

Absolute or gauge?

Er more info

Compressor is turned off

De-pressurizing

Need to know max air flow leaving vessel.

Originally Posted by W&KO

Er more info

Compressor is turned off

De-pressurizing

Need to know max air flow leaving vessel.

Err, I am inclined to think that I can probably fart more than what you are asking. 120 Kpa is 17.4 psi. Through the size outlet you are quoting the pressure will equalise within a few seconds, that is if you can fully open the orifice instantly.

If you neglect viscosity, Bernoulli's equation (just Navier-Stokes without frictional or stress terms) will get you into the ballpark:

Pg+12ρgv2g=PaPg+12ρgvg2=Pa

fluid dynamics - Calculate flow rate of air through a pressurized hole - Physics Stack Exchange

Originally Posted by Old Farang

Err, I am inclined to think that I can probably fart more than what you are asking. 120 Kpa is 17.4 psi. Through the size outlet you are quoting the pressure will equalise within a few seconds, that is if you can fully open the orifice instantly.

If you neglect viscosity, Bernoulli's equation (just Navier-Stokes without frictional or stress terms) will get you into the ballpark:

Pg+12ρgv2g=PaPg+12ρgvg2=Pa

fluid dynamics - Calculate flow rate of air through a pressurized hole - Physics Stack Exchange

Keep in mind it’s a 90m3 vessel, 40 foot long by 3.2 meters round. It probably takes 10min to de-pressurize. For the first few minutes the airflow comes out at a rate of knots and I need to clean the air. The current systems are undersized, while limiting how much we open the valve this increases de-pressurize time.

Kinda hoped there would be a simple calculation.

Originally Posted by W&KO

Keep in mind it’s a 90m3 vessel, 40 foot long by 3.2 meters round. It probably takes 10min to de-pressurize. For the first few minutes the airflow comes out at a rate of knots and I need to clean the air. The current systems are undersized, while limiting how much we open the valve this increases de-pressurize time.

Kinda hoped there would be a simple calculation.

Cannot be a simple calculation as the pressure is continually falling.

What is "3.2 metres round"? Is it circumference, diameter or what? You also need to use the same units to even calculate the volume of air in it.