Air Flow - calculation challenge.

**Blknight.aus** · 17th May 2019, 07:13 PM

For this calculation the shape of the vessel is more or less immaterial.

we know that it has 90M3 behind it. and its going to be a 4 inch hole.

lets make a couple of other assumptions...

1. its coming out laminar (it wont be)
2. the valve opens instantly
3. its dumping directly to atmosphere with nothing after the valve
4. we are only interested in the split second after the air gets moving on the way out and the interial delay can be ignored
5. its plain dry compressed air

if we're working with absolute pressure the first 101.3 KPA of your 120 KPa is taken up by the external atmospheric pressure so you really only have 18.7kpa to work with, thats about 2.7psi...

if thats the situation then your air velocity will be in the order of 958l/s with a velocity of 1.2m/s and with a flow mass of around 1.17kg/s

IF youre working in gauge....... it get a little more energetic about things as youve got the full 17.4psi of head pressure

you have the air coming out at 2403l/s with a velocity of 3.04m/s with a flow mass of nearly 3kg/sec

****edit*****

forgot you wanted CFM, multiply by 2.12 to go l/s-cfm

so 2030CFM if your pressure is absolute

and

5095 if its in gauge

now I've done the fun bit...

what the hell is it for, those pressures and volumes sound sussly like a decompression chamber

**W&KO** · 17th May 2019, 07:31 PM

Needing some numbers to back up my case with the OEM on damage to its dust collector.

**Blknight.aus** · 17th May 2019, 07:35 PM

IF you're talking about damage caused by the discharge through the 4 inch hole then I suspect that you're likely to be more interested in the mass flow numbers rather than the flow velocity.

you have my curiosity.

Whats such a large pressure vessel for with such a low pressure?

**austastar** · 17th May 2019, 08:20 PM

Hyperbaric chamber??
Cheers

**ramblingboy42** · 18th May 2019, 08:33 AM

if it was a recompression chamber, you would or should already have all that information.

I'm with you Dave.

**Old Farang** · 18th May 2019, 11:45 AM

IF youre working in gauge....... it get a little more energetic about things as youve got the full 17.4psi of head pressure

you have the air coming out at 2403l/s with a velocity of 3.04m/s with a flow mass of nearly 3kg/sec

Blknight.aus : The numbers that you have come up with may have a bit more credibility if you were to show at least some of the factors used to arrive at them.

Why confuse the question by asking if it is absolute or gauge pressure? The shape of the vessel may be "more or less immaterial", but in fact the volume is
closer to 96.5 cu metres than 90. In view of later comments made by the OP it appears that he may be involved in some form of legal dispute, where by quoting even accurate numbers without proof could lead to more problems. There are too many unknown variables to arrive at even an estimated number.

OP: do yourself a favour and go and buy a cheap anemometer, more so if you are in dispute over equipment.

https://www.amazon.com/General-Tools.../dp/B002OGVUF2

**W&KO** · 18th May 2019, 11:58 AM

No legal dispute, more about me getting a better understanding so I can engage in the conversations.

Just trying to get the set up right. We are somewhat limited on the weight of the ancillary equipment.

The vessels official capacity is 90m3 as registered with Queensland WHS, the measurements were from memory.

No biggie....I’ll get it sorted.

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