Expanion rate of air and CO2... is it constant?

[FallNAngel]

Basically, the title has the question. Does the rate that air expands to ambient temperature depandant on the pressure it's under, or is it a constant? For example, assume you have two containers, one filled to 100psi and the other filled to 10psi. Now imagine you open a valve and let the air out at once. Will the air expand to ambient temperature at the same rate or will one take longer. Same question on CO2. I've been searching on this for a while and haven't found the answer. Any help would be appreciated.

[the electrician]

hmm... well, air at 1000 psig can flow faster, through the same size orfice, than air at 10 psig. but there is more air, alot more in the container with 1000 psig, than the one with 10 psig. so the one with only 10 psig will, of course, be done expanding before the other one, but it's flow rate is slower.

don't know if that helped?

[FallNAngel]

Hmm... let me try asking it like this:

you have two containers the size and pressure of each are the inverse of the other. So you have one 68ci/4500 and one 4500ci/68... both are full. If the air in each is released at the same time, will they reach ambient pressure at the same time?

[the electrician]

well there again, are you sure that's what you really mean?

a 68/4500 holds 11 cu ft of air while a 4500/68 would hold about 15 cu ft of air. so if they are both exhausting out of the same size orfice, then the 68/4500 would exhaust faster just by volume alone, not to mention 4500 psi air moves at a higher velocity than 68 psi air.

let's say the amount of air in the two cylinders is the same, and still the exhaust orfice is the same for both cylinders, the one with the higher pressure will exhaust faster, because the air is moving faster through the orfice.

how about that? is that what you mean?

[Wat]

It also depends on the orafice the gas is expanding out of. If the orafice is small enough, and the pressure differential accross it large enough, you get a necking effect. Essentially, the gas reaches its top speed (the speed of sound in the medium) through the orafice and cannot go any faster. Its a physical speed limit. Once you reach this point, it doesn't matter if its 4500psi or 10,000 psi, it can only go through the orafice so fast.

[the electrician]

oh yeah, that's a good point wat.


so if the hole was really small, it could possibly limit the speed enough to make the higher pressure come out at the same velocity as the lower pressure.

I imagine co2 and air flow at different rates. which one would be faster wat?

[Wat]

Not 100% sure which would go faster, I would guess CO2. The physical speed limit is the speed of sound. Since CO2 is denser than HPA, that should mean that the speed of sound in CO2 is higher than HPA, so the speed limit is faster.

So the question is, are you hitting the speed limit? If you are not hitting the speed limit, then i think your right that HPA would have the higher velocity since it generally has the higher pressure than CO2. If you are hitting the speed limit, CO2 has a higher limit than HPA so CO2 would be faster.

It really would depend on the size and geometry of the orafice

If only real world engineering were as simple as freshman physics...

[BAMFSK]

The Answer to this question is NO if have two tanks filled one to 3500psi the other to 4500psi barring regulaters lets say the both blew up the 4500 and the 3500 would expand at there respective psi

[elprup]

As I stated in another thread: I have not read in full nor researched this topic, but I happened to come across this page while searching for something else.

http://www.warpig.com/paintball/technical/gasses/co2dynamics.shtml

Disect it all you want. I hope it helps give some answers.