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Cylinder and Vessel @ different pressure

Cylinder and Vessel @ different pressure

Cylinder and Vessel @ different pressure

(OP)
Hello everybody,

hope you can help me in attached issues, since past post are not much helpful - or I haven't been able to find these information -.


I have got some cylinders containing Nitrogen.
Their volume is 45 l and the pressure of N2 is 2800 PSI.
I want to utilize this N2 for leak testing a vessel @ 2366 PSI..


Question 1: which is the law that links pressure into the bottle and volume ?
Does the old perfect gases low works fine (P1V1 = P2V2) ?
The key issue is: when N2 starts to move from cylinder to vessel, pressure into the cylinder is reduced.
Please, I'd need to know
1.1 - how much is reduced when I transfer a certain quantity of N2 into the vessel.
This quantity is equal to the vessel volume.
I would suppose that both pressure would stabilize around 2366 PSI.
1.2 - which is the quantity of N2 remaining into the cylinder (I suppose initial volume less the volume of the vessel).


Question 2 - which is the low that lets me know the volume of N2 @2366 PSI if I know the volume @ 2800 PSI ?
Again Perfect gases low ?

I would suppose this is a standard problem in fluid dynamics.

Please note that each calculation is made according to engineering criteria !



Many thanks

RE: Cylinder and Vessel @ different pressure

You also need the volume of the vessel.

If considering a nonideal gas, you need to find the compressibility factors for N2 at the initial and final pressures.  You don't know the final pressure right now to find zf, so an iterative solution is required.


Pi*Vi/zi = Pf*Vf/zf
i subscript is initial condition
f subscript is final condition
Vi = 45 L
Vs = vessel volume
Vf = Vs + Vi

Pf = 2800 * 45 * zf /zi /(Vs + 45)
get the final pressure, first assuming zf = 1,
get the actual compressibility factor for the resulting pressure, recalculate the final pressure and if it changes much, get another value for zf and continue until you get a convergence of Pf.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/

RE: Cylinder and Vessel @ different pressure

As shown in good detail above, the perfect gas law will get you close, then - if more exact predictions are important, keep iterating.

You will have a bank of small N2 cylinders - Check with your vender: you will likely be able to receive gas at higher pressure than 2800 psig.    Your system will never be able to exceed the ratio between the final volume (bottles + tank) compared to the initial volume (bottles alone)

You vent through the N2 regulator to the tank, ignore the small volume in the gas lines, and then isolate the tank once it gets high enough in pressure for the test - how much N2 gas are you allowing to waste to purge the tank?  Or will you press up with the original air left in the tank?     

RE: Cylinder and Vessel @ different pressure

Are you sure you have to test with a pressurized gas?  

A high pressure water test is much safer since there is many thousand times less stored energy in event of a catastrophic failure - or a small failure that leads to to a catastrophic failure.

RE: Cylinder and Vessel @ different pressure

I second racooke1978's concern!

If the convenience of the N2 being a high pressure source is the driver, fill the vessel 95% or more with water and apply the N2 pressure on top of that.

Good luck,
Latexman

RE: Cylinder and Vessel @ different pressure

N2 is commonly available in US cylinders up to 5000 psig

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/

RE: Cylinder and Vessel @ different pressure

Standard 300CF cylinders are generally filled to 2500-3000psi from gas distributors.  The high pressure cylinders that you are talking about are larger, heavier, hard to find and cost a whole lot more than the 300cf variety.  However, you can get up to 6k psi in the larger tanks.

It doesn't sound like the OP is pressure-testing tanks.  Sounds as if they are doing a simple leak check, hopefully at operational pressures.  Pressure rating cylinders is a dangerous task especially if you don't know what calcs and standards to use.

Dan

www.eltronresearch.com
Dan's Blog

RE: Cylinder and Vessel @ different pressure

(OP)
Many thanks to all of you for your interesting answers.

To Mr. Eltron.
Correct, we are making a leak test

To Mr. racookpe1978  and Mr.Latexman
Unfortunately we cannot use water or liquids for this test.

 

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