Figuring out EaN Percentages

[daviking]

Hello all! I am unsure as to where this would go... But if this isn't where it belongs, please feel free to aid me in getting it there. I'm new to scuba board.

So, I am creating a diving app for computers, phones and a discord bot. One of the functions I want to add, os figuring the theoretical FINAL percentage of Oxygen in a tank. Here's the deets:
1) I have a tank that is at 500 psi, and contains EaN36.

2) I want to fill this tank with air to 3,000psi.

Armed with this information, I want to know what the Oxygen concentration is after I fill the tank with 2,500 psi of air.

What is the/a formula I can use to figure out the theoretical end percentage after filling a tank regardless of the starting pressure of the tank?

 

[kaylee_ann]

My idea was convert the percentage of O2 and nitrogen to PSI
For 500 PSI: 180PSI O2, 500PSI nitrogen
The remaining 2500: 525, 1975
Add both together- 705 PSI O2, 2295 PSI nitrogen
Divide by total PSI of 3000
23.5% O2 76.5% nitrogen
Idk how gas mixing works, if you can have the oxygen percentage be 24% and nitrogen 76%. That’s what I got when trying to figure this out- I feel there’s still a flaw in it. What’s the right way?

 

[MaxBottomtime]

Technical Diving and Recreational - Nitrox Calculator

nitrox calculator.

www.divelasvegas.com

 

[Blackcrusader]

Armed with this information, I want to know what the Oxygen concentration is after I fill the tank with 2,500 psi of air.

Me I just test with an analyzer and take the reading off that.

 

[dberry]

@kaylee_ann got it right and it can be described more simply with an equation.
Assuming ideality (ignoring compressibility of gasses), it's just a weighted average:

(500*0.36 + 2500*0.21)/3000 = 0.235 (23.5% O2)

 

[broncobowsher]

That is the simple answer. And it works.

Compressibility doesn't really play enough in the normal scuba pressures.
The accuracy of the gauge is another factor.
And the initial nitrox measurment, that analyzer has a bit of error to it as well.
And the temperature rise of the fill, that changes the pressures. Let it cool, did you overfill it enough to hit the target pressure once it cools off?
Oh the endless list of variables. You could over-complicate things to they never work. Or just use the above, and analyze in the end like you really should.

 

[daviking]

Me I just test with an analyzer and take the reading off that.

Well, of course, we will analyze the tank before diving. Wouldn't be smart not to. The idea is purely theoretical for informational purposes, due to the variability of... Well... The variables. For example, my wife and I will go diving soon (in real life). We will be using EaN36 for the first dives, then refilling our tanks with air from 500 psi. I was curious in theory, what our gas mix would be after we got a refill, because I know that we would still be breathing nitrox, but didn't know the percentage. Lol

 

[daviking]

That is the simple answer. And it works.

Compressibility doesn't really play enough in the normal scuba pressures.
The accuracy of the gauge is another factor.
And the initial nitrox measurment, that analyzer has a bit of error to it as well.
And the temperature rise of the fill, that changes the pressures. Let it cool, did you overfill it enough to hit the target pressure once it cools off?
Oh the endless list of variables. You could over-complicate things to they never work. Or just use the above, and analyze in the end like you really should.

Indeed, the list lol. Actually, my calculator will only be for constants. It doesn't account for variabilities. I'm a beginner in the coding world, and figuring out stuff lile that and making it functional is proving to be difficult.

 

[daviking]

No, the pe

My idea was convert the percentage of O2 and nitrogen to PSI
For 500 PSI: 180PSI O2, 500PSI nitrogen
The remaining 2500: 525, 1975
Add both together- 705 PSI O2, 2295 PSI nitrogen
Divide by total PSI of 3000
23.5% O2 76.5% nitrogen
Idk how gas mixing works, if you can have the oxygen percentage be 24% and nitrogen 76%. That’s what I got when trying to figure this out- I feel there’s still a flaw in it. What’s the right way?

Nope, the percentages HAVE to equal 100%. So if you round 23.5 up to 24, you must likewise round 76.5 up to 77.

 

[Searcaigh]

What’s the right way?

Use Bar