duration of Nitrogen output from a canister. 2

[angelil6]

Hello.
I am trying to estimate the duration of Nitrogen output from a canister.
Last time I needed to calculate this was about 30 years ago…
Can someone please look at my numbers.

Link for an image with my calculations:

https://i.postimg.cc/L5tN7LDH/2021-10-04-at-13-40-22.jpg

The canister is 40 L with 200 bar of Nitrogen.
The output is 6 bar ,with a flow rate of 4 liter / minute.

Came out to about 5.5 hours of flow from a 40 liter tank.
Thanks

 

[MortenA]

Does you bottle come with a constant flow vale?

If not then flow will drop somewhat as the pressure in the bottle drops,

I assume all pressure are in gauge? In this case you should use 7 bara instead of 6 (and 201 but not so big an impact)

Best regards, Morten

--- Best regards, Morten Andersen

 

[angelil6]

Hi, thank you for replaying.
The pressure is in Bar.
There is a constant flow valve.
Not on the bottle itself, somewhere along the line.
So is my time estimation of 5.5 hours is correct ?

 

[1503-44]

Yes. I get 5.23h at a 200 and 7 Bar absolute pressures

 

[LittleInch]

You need to be careful about units and pressures.

Also "cannister" sounds like an aerosol can you use to spray paint with. "Cylinder" is a much better word...

It's much easier if you just convert everything to standard conditions. And always work in absolute pressure. makes very little difference at 200 bar, but a lot at 6 barg

So you have 40 litres at 200 barg., So approximately 0.04m3 x 201 = 8.04 sm3 or 8040 standard litres.

However you will have residual N2 at 6 bar so subtract 0.04* 7 = 7760 Standard litres.

Now the big question - at what pressure is your 4 litres/minute? - Standard conditions? or at 6 barg? You don't say.

At 6 bar this makes a factor of 6 difference in your time calculation.
If it's 4l/min at 6 barg (7bara), that's 28 s litres so 7760/28 = 4.612 hours
Hence why you always better to state the pressure so either scm or acm (actual cubic metres ( or litres) at a stated pressure.

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

 

[angelil6]

Thank you for the detailed explanation.
it has been awhile seen the last time I had to calculate one of these.

the 4 L/min is at 6 bar.
I needed an estimate in order to apprise how many such cylinders I will need.
so now I have my answer

Thank you

 

[LittleInch]

Don't forget that your regulator may have a minimum pressure to be able to deliver 4l/min at 6 bar, so I wouldn't reckon on it working well much below 10 barg.

SO somewhere between 4 1/2 to maybe 5 hours. I can't remember what the z factor is for nitrogen, but I would always err on the side of caution.

And also make sure everyone is on the same page about what pressure your 4 l/min is at....

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