[dumpstermonkey]

Hi Folks,

Could anyone recommend a concise reference book of dive calculations ? I'm looking for calculations with regard to Pressure's/cylinder volume's/nitox pp02 top up's,
Cheers

Dumpstermonkey

 

[mala]

vance harlow.

oxygen hacker's companion.

 

[soggybottoms]

Mr Hewitt's got all sorts of calcs on his site. Why not have a gander?

Nigel Hewitt base server

 

[barrygoss]

Hi Folks,

Could anyone recommend a concise reference book of dive calculations ? I'm looking for calculations with regard to Pressure's/cylinder volume's/nitox pp02 top up's,
Cheers

Dumpstermonkey

Sounds harsh, but learn and understand the physics. It'll cost you less in the long run, and really it's simple
P1V1/T1=P2V2/T2 pretty much covers everything you'll need to know.
Where P Is the pp of the gas multiplied by the pressure.
That way you'll be able to do nitrox top offs with a phones calculator and tell the fill monkey what nitrox mix will be in the tank after he's filled it to 232 bar.
B

 

[dumpstermonkey]

Thanks for all your help folks its appreciated.
dumpstermonkey.

 

[A. Berk]

Sounds harsh, but learn and understand the physics. It'll cost you less in the long run, and really it's simple
P1V1/T1=P2V2/T2 pretty much covers everything you'll need to know.
Where P Is the pp of the gas multiplied by the pressure.
That way you'll be able to do nitrox top offs with a phones calculator and tell the fill monkey what nitrox mix will be in the tank after he's filled it to 232 bar.
B

Er, sorry but that don't make no sense what-so-ever-not-nothing-no-way-ever. You are mixing gas laws and getting Chaltons Law or summat :redface:. As a rule of thumb its best to get your own sh!t in order before advising someone else... sounds harsh but it'll cost you less in the long run!

Broke

 

[EBT]

Erm, actually it does make sense. The only bugbear is you need to be working in SI units (ie temp is in kelvin). You can ignore the temp part if you want a rough n ready calc (eg for gas cascading).

 

[barrygoss]

Ok,
Making it simple for you.
Ignore temp (T) as we'll assume for our rough and ready calc the temperatures aren't really going to change.
So you've got a 12L with 100bar of 50% and you're going to air top it. What mix will you get?
You've got P = 100bar (50bar O2, 50bar N2 as it's 50%) and V=12L - Remember its Partial pressures that go to make the whole P
So you've got 50 x 12L of O2 = 600L of O2.
Now you're going to top off with air to 232bar.
Thats 232-100 = 132bar of 21/0/79 or 132 x .21 x 12 = 332.64L of O2.
So my final mix is 600L add 332.64L (932.64L) of O2 out of 12 x 232bar (2784L)
932.64/2784 = 33.5% O2.
Can you see all we've done there is P1V1+P2V2 = PV
He is just as simple you just run through with three gasses.
You can work it backwards to work out what O2 you need to put in a tank to mix your own Nitrox and it can all be done on a phones calculator, or if you can, your head.
The nice thing with doing all that in your head is, if the mix comes out high, you know he's not filled the tank to 232bar and if low, you've got an overfill.
Hope I've got my sh!t in order
B

 

[mala]

Er, sorry but that don't make no sense what-so-ever-not-nothing-no-way-ever. You are mixing gas laws and getting Chaltons Law or summat :redface:. As a rule of thumb its best to get your own sh!t in order before advising someone else... sounds harsh but it'll cost you less in the long run!

Broke

not mixing them--combining all 3 of them.

its called the combined gas law.

 

[A. Berk]

I've been mixing all manner of gaseous sh!t for a living for 39 years and that's why I question the statement; "Where P Is the pp of the gas multiplied by the pressure" after showing a General Gas Law formula which has never had any reference to PP in it before - that was summat Mr Dalton spouted off about weren't it - or is that Boylton Lusac's Law of Partial Volume Temperatures? :redface:


There should not be any ambiguity when explaining or teaching this stuff as there's too much at stake - '100% exact' is only just good enough :teeth:.

 

[A. Berk]

I have been asked to clarify things, so here goes; All of this stuff below from barrygoss needs no 'volumes' at all to work it out as its a Dalton's Law problem;

"So you've got a 12L with 100bar of 50% and you're going to air top it. What mix will you get?
You've got P = 100bar (50bar O2, 50bar N2 as it's 50%) and V=12L - Remember its Partial pressures that go to make the whole P
So you've got 50 x 12L of O2 = 600L of O2.
Now you're going to top off with air to 232bar.
Thats 232-100 = 132bar of 21/0/79 or 132 x .21 x 12 = 332.64L of O2.
So my final mix is 600L add 332.64L (932.64L) of O2 out of 12 x 232bar (2784L)
932.64/2784 = 33.5% O2.
Can you see all we've done there is P1V1+P2V2 = PV"

No, we can see you've got your Dalton's and Boyle's in a twist though. Its that sort of confusion between gas laws that leads to mistakes so I reckon you don't have it together yet. Your problem is to find what you have after topping 100b of 50/50 with air to 232b?

You have 132b of air to add so; 132 x .21 (% O2 in air) = 27.72 which is the ppO2 that comes with the air. Add this to the 50b ppO2 in your original mix 27.72 + 50 = 77.27 (ppO2 in final mix). Multiply this by 100 and divide by the final pressure to find your final O2%; 77.72 x 100/ 232 = 33.5% - there you go, not one unit of volume required!

Berko

 

[barrygoss]

I have been asked to clarify things, so here goes; All of this stuff below from barrygoss needs no 'volumes' at all to work it out as its a Dalton's Law problem;

"So you've got a 12L with 100bar of 50% and you're going to air top it. What mix will you get?
You've got P = 100bar (50bar O2, 50bar N2 as it's 50%) and V=12L - Remember its Partial pressures that go to make the whole P
So you've got 50 x 12L of O2 = 600L of O2.
Now you're going to top off with air to 232bar.
Thats 232-100 = 132bar of 21/0/79 or 132 x .21 x 12 = 332.64L of O2.
So my final mix is 600L add 332.64L (932.64L) of O2 out of 12 x 232bar (2784L)
932.64/2784 = 33.5% O2.
Can you see all we've done there is P1V1+P2V2 = PV"

No, we can see you've got your Dalton's and Boyle's in a twist though. Its that sort of confusion between gas laws that leads to mistakes so I reckon you don't have it together yet. Your problem is to find what you have after topping 100b of 50/50 with air to 232b?

You have 132b of air to add so; 132 x .21 (% O2 in air) = 27.72 which is the ppO2 that comes with the air. Add this to the 50b ppO2 in your original mix 27.72 + 50 = 77.27 (ppO2 in final mix). Multiply this by 100 and divide by the final pressure to find your final O2%; 77.72 x 100/ 232 = 33.5% - there you go, not one unit of volume required!

Berko

You've used exactly the same method, just bar (Pressure) is L/V where L is litres of the gas and V is volume of the tank, you've eliminated that step.

Combined gas law - Wikipedia, the free encyclopedia shows you how all the gas laws can be combined, it's school Physics.

Now use your method to calculate the mix if I've got 50% in my 12 @ 100bar and a 15L of air with 232bar in it and I'm going to decant on the dive boat. What mix have I got and what pressure?

We'll both do it exactly the same way, it's physics. I'll work it out using litres (and you will too to find out the final pressure) then you'll jump to using bar and 1 bar in a 12litre tank is 12L of gas. (whatever the PP of each gas in that mix are)

 

[A. Berk]

Combined gas law - Wikipedia, the free encyclopedia ... yes, an interesting combination of gas laws - strangely short of anything by Dalton

Berko :teeth: