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Capacity of O2 gas in a cylinder

thread1036-416222

Capacity of O2 gas in a cylinder

Capacity of O2 gas in a cylinder

(OP)
Hello,

I want to know how can I calculate the volume capacity of O2 gas in a cylinder when the gas is in 2524 psi with a room temperatura (70°F).


thanks in advance

RE: Capacity of O2 gas in a cylinder

Boyle's Law is a pretty good start as long as you're happy with an answer that's there or thereabouts and you're going to take the oxygen out reasonably slowly (or at least let it recover to 70F before you attempt to measure its volume. Otherwise:

Oxygen isn't quite an ideal gas so, at 2524 psi and 70F, you'll find you can get nearly 6% more of it into a cylinder than Boyle's law would lead you to expect (the sweet spot is at about 2200 psi - after that it slowly starts getting closer to the ideal). Other gases behave differently (so with air at that pressure, a cylinder holds one or two percent less than Boyle's Law predicts)

If you expand the oxygen quickly, it will come out cold and take up quite a bit less volume than you might otherwise expect until it warms back up again.

A.

RE: Capacity of O2 gas in a cylinder

(OP)
Thanks guys, yes I remenbered the boyle law but I have other question. If I want to get a closer value what other procedure can help me ? I mean what other kind of analisys, law or equation I could help me to be closer with the reality?

RE: Capacity of O2 gas in a cylinder

Since O2 is an non polar gas, try one or more of these EOS and see which one suits you :
a) The Redlich Kwong equation
b) The Benedict Webb Rubin equation

Methods for these can be found in 6th edition of Perry Chem Engg Handbook in the section on physical properties estimation - a lot of this material (especially the BWRS EOS) is excluded in the 7th edition. Since O2 is paramagnetic, would suspect it deviates more than say nitrogen from z=1 at high pressures.

RE: Capacity of O2 gas in a cylinder

ie. Consider the compressibility factor for O2

RE: Capacity of O2 gas in a cylinder

Refprop.exe from NIST says that the compressibility factor is 0.93759 at your conditions (about 6% off ideal like zeusfaber said)

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: Capacity of O2 gas in a cylinder

Yes, true, but he didn't say the key words "compressibility" and "factor".

RE: Capacity of O2 gas in a cylinder

There's also the question of what volume or "standard" volume conditions you're expressing this in. Makes a difference as well.

There is sadly no universal "standard" conditions to which you reference back to. This has been debated a LOT on these pages so I won't start it up again now.

Seems to be a very precise pressure reading....

Also depends on what is your end pressure if you're trying to work out usable volume

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

RE: Capacity of O2 gas in a cylinder

(OP)
Again , thanks guys. Finally I am using the boyle law with the compresibility factor "z". Also I will do a spreadsheet to run the Redlich kwong equation to have a closer value.
Just to know in what source Can I get the z values for different kinds of gases, like N2,Ar, Helium, Air in different pressures?

RE: Capacity of O2 gas in a cylinder

Try the attached spreadsheet from ChE Forums - it calculates Z based on several cubic equations of state (EOS). You need to provide fluid-specific properties (critical pressure, critical temperature, acentric factor, molecular weight - you can get all these in textbooks or online) and operating conditions (pressure, temperature).

You can also build your own spreadsheet because the EOS' are not that complex.

Dejan IVANOVIC
Process Engineer, MSChE

RE: Capacity of O2 gas in a cylinder

Quote (LittleInch)

Seems to be a very precise pressure reading....

It's a much rounder number when you convert it to bar (same as people are always asking me why our systems run at 276 bar).

By the way, can I be really nosy and ask BigInch - LittleInch: Any relation?

A.

RE: Capacity of O2 gas in a cylinder

Typically O2 from a cryo column will contain a small amount of Ar (less than 1% v/v from memory), so you'll need to apply the mixing rules suggested in Perry to get to mix values for the critical props for the RK / SRK method if you want better accuracy.

RE: Capacity of O2 gas in a cylinder

Zeus. Not nosy, We know each other quite well and he introduced me to this forum. In honour of the many posts I hadread before I knew who he was and a lack of imagination I kind of adapted his handle. We generally agree on technical issues so isn't too confusing. I like the name now.

I hate it when nominal figures get converted exactly and not rounded.

No one bit on the standard volume question though....

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

RE: Capacity of O2 gas in a cylinder

I took the name from the Big Inch Pipeline, which also had a Little Inch Pipeline (actually some 200 miles longer) built to transport oil along the US east coast in order to avoid risks of German U-boat activity during WWII.

https://en.wikipedia.org/wiki/Big_Inch

RE: Capacity of O2 gas in a cylinder

I took the BigInch name from the Big Inch pipeline built along the US east coast during WWII to avoid attacks from German U-Boats on the ocean shipping route from Texas to New Jersey. Coincidently ... it also had a Little Inch counterpart pipeline, which was actually 200 some miles longer.

We usually agree on everything ... eventually. Well ... except for the spelling of certain words.

RE: Capacity of O2 gas in a cylinder

Fascinating bit of industrial history I hadn't heard before. Thanks for that.

A.

RE: Capacity of O2 gas in a cylinder

Never knew that. Thought big inch was just general slang for large diameter long distance pipeline, esp in the US.

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

RE: Capacity of O2 gas in a cylinder

Family history.
... And you thought we wern't related.

RE: Capacity of O2 gas in a cylinder

@little inch, most gas pipelines in the Danish sector of the north sea has a design pressure of 138 barg (and its stated in barg) - try to covert that to psig smile

Best regards, Morten

RE: Capacity of O2 gas in a cylinder

138 barg = +/- 2000 psig
Why do we want to know?

276 barg = +/- 4000 psig

RE: Capacity of O2 gas in a cylinder

To get back to the original point - the cylinder pressure is clearly a nominal barg number ( I get 174, ) which may actually be 175??, a bit odd as most seem to be 250 barg.

So pretending to have a pressure accurate to 1psi is a non starter to begin with.

Charts like this already tell you how much you get out of a cylinder....

https://www.praxairdirect.com/Industrial-Gas-and-W...

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

RE: Capacity of O2 gas in a cylinder

it was the talk about round numbers in one unit system being converted into another unit where its not round and then kept with decimals (almost). If the first designer had not been heavily influenced by ASME (i think it must be) then most likely they would have chosen say 150 barg i would think (but then again im not a pipeline designer)

RE: Capacity of O2 gas in a cylinder

Not sure in this case, because the topic is gas in a "cylinder", which I took to mean a bottle-type cylinder. Those often have maximum pressures (in psig) of 2500, 4000 and 5000 psig which don't correspond to piping class pressures, only the material that the cylinders are made from, aluminum in some cases.

RE: Capacity of O2 gas in a cylinder

And sometimes it looks like it's the test pressure rather than the working pressure that ends up being a nice round number - which must be why the divers always seem to want to fill their bottles to 232 bar.

A.

RE: Capacity of O2 gas in a cylinder

Right, that's 3500 psi, I used to fill N2 cylinders to 3500, or the HP cylinders to 5000 psig.

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