About Transferring Gases to other Containers

[oldflounder]

I have some questions for those of you out there that are good in math and physics. Consider 2 pretend scenarios:

1. I go on vacation to Aruba. I will rent tanks there but I want to take my 13 cuft pony with me on the plane as carry-on. I need to remove the valve to get past security in the airports. I will be taking along a transfer whip [I think that's what you call it] to refill the pony later.I rent a few tanks and use one to refill the pony. Let's say the Al80's I rent are filled to 3200psi. How much can I fill the pony and how much will be left in the 80???

2. I have a slow leak in my tire. I come out of the house one morning and my tire is flat. I have a partially used tank of air handy and in my save-a-dive kit I have one of those tire inflators that attach to the low pressure hose on my bc. The tire is a 205/60 R16 rated to 50 psi max and the tank is a steel 100. At least how much air needs to be in the tank to fill the tire to 50psi ? What does the math look like?

I know I know - I should get a life - apparently I have too much time on my hands.

 

[Atom]

http://www.scubaboard.com/forums/co...s/311954-trans-filling-true-tank-volumes.html

Al13 Catalina = 13ft, 3000PSI => 0.43ft per 100PSI = TF1
Al80 Catalina = 80ft, 3000PSI => 2.6ft per 100PSI = TF2

SP1 = 0
SP2 = 3200 PSI

x*TF1 = y*TF2
SP1 + x = SP2 - y

x = (TF2 * (SP2-SP1) / TF1) / (1 + TF2/TF1)

x is the pressure rise in the lowest tank

so

x = ((2.6 * 3200) / 0.42) / (1 + 2.6/0.43)
x = 2811 PSI

And to verify...

2811 PSI * 0.43 ft/100 PSI = 12ft
2811 PSI * 2.6 ft/100 PSI = 73ft

which matches the 85ft of gas you had at 3200PSI in the AL80

 

[Superlyte27]

That's bad math as an AL80 has 77cu' at 3000psi.

 

[john844]

assuming the 80 has a 3200 max psi and the 13 has the same.

3200*80/93 = 2752.688psi in each tank (splitting 80 cu between 93 total)
80 will have 68.8172 cu ft
13 will have 11.1828 cu ft

I will let someone else pick this apart, since it was my first attempt at calculating something like this.

 

[Atom]

That's bad math as an AL80 has 77cu' at 3000psi.

Doh!!!! forgot to read the little remark....

SCUBA Cylinders

"All capacities are exact except the industry standard S80 and C80 which have an actual capacity of 77.4 cu ft"

The maths are good, the spec was wrong ; )

So...

AL80, 77.4ft, 3000PSI => 2.58ft / 100PSI = TF2
x = 2742 PSI

11.8 ft in the pony
70.7 ft in the AL77.4

 

[oldflounder]

So the pony will have 11.8 ft and the 80 will have 70.7. And the pressure between the 2 tanks does not equalize out at 3200/2 = 1600!
Thank you for the links to previous threads. They help a lot to understand.

 

[Atom]

So the pony will have 11.8 ft and the 80 will have 70.7. And the pressure between the 2 tanks does not equalize out at 3200/2 = 1600!

Pressure is related to volume and temperature like this....

pV = nRT

Let's ignore any temperature issues and assume the right part of the equation pertains only to the number of moles (n).

n will remain contant, so...

p * V = p1 * V1

if you want p1 to be half of what it was....

p1 = p/2
p * V = p/2 * V1
V1 = p* V / (p/2) = 2 * V

you'd need twice the volume... which you're not providing with an AL13... an AL13 has a volume of 1.9L and a AL80 has a volume of 11.1L...

In fact... you can answer the 1st question pretty easily this way...

3200 * 11.1 = p * (11.1+1.9)
p = 3200 *11.1 / (11.1+1.9)
p = 2732 PSI

(it's not an exact match due to rounding errors)

 

[Superlyte27]

You guys have no idea how happy I am that I passed that class, and never have to return to it.

 

[joystershell]

You guys have no idea how happy I am that I passed that class, and never have to return to it.

And I think that I passed out in that class...........

 

[Atom]

You guys have no idea how happy I am that I passed that class, and never have to return to it.

Talking about high school chemistry? I had it easy, our teacher was a raging pyromaniac, easy to get the students attention when you keeping setting things on fire during demonstrations.