Weight of Compressed Air

[AGD]

Our friend Ed Head did try helium. Didn't hardly shoot the ball but make big boom! Not enough gram moles to get the ball going and it leaked out of all the orings (really small molecules). Great discussion here guys.

AGD

[Thordic]

Here are numbers to chew on for Compressed Air when compared to pure Nitrogen.

29 Grams equals 1.02294 Ounces (Molar weight of air)
28 Grams equals 0.987671 Ounces (Molar weight of nitrogen)

When I did the original calculations, I rounded 29 grams off to 1 ounce. It made things a lot easier, and due to the small amount I rounded off, didn't have a significant impact on the numbers.

Its under a 5% difference (3.44780730052593504995405400122 if you wanna get real picky :) ) between compressed air and nitrogen.

So in a 68/3K tank, you are looking at around .3oz lighter with pure nitrogen. You won't even shave off a full ounce in a 114/4.5K tank.

[CHK6]

Your not getting strong, it's getting hotter.

Thordic,

Thanks for turning us in the right direction when calculating weight of compressed gasses. However the gears in my brain is always turning (that doesn't mean the gears always catch thou), so I was wondering if there is a difference in weight of compressible gases due to temperature? Here are my findings.... it also a validation of everything you said earlier.

Ideal gas equation: PV=nRT
P = pressure (atm)
V = volume (liters)
n = number of molecules in the container (mol)
R = universal gas constant (l-atm/mol-K) [0.082057]
T = temperature (K)

Lets plug and play.....

For a 80 degeee day (in Farhienhiet (sp?)), with a 47 ci tank, at a pressure of 3000 PSIG, and using compressed air.

T = 80 F = 299.816666 K
V = 47 ci = 0.770189 l
P = 3000 PSIG = 204.137883 atm

n = (204.137883 * 0.770189) / (0.082057 * 299.816666)
n = 6.390715 (mol)

n * Mw = 6.390725 * 28.96 (molecular weight of air) = 185.08 grams. Convert the grams to troy ounces and we get 5.95 ounces.

Now in Texas most summer mornings start out at 80 degrees, but by 11:00 it's usually 100. Using the same formula, but instead of 80 I use 100 degrees and we get 5.73 ounces.

So after a couple of games in the heat and your arm is getting tired, don't worry mother nature tries to help you out....just a tad of 3% difference for 20+ degrees. I think I lose more than that percentage in sweat alone. ( C :"

Helium would be an awesome break through for paintball.

[Thordic]

If you look up, I already went into the effect of temperature on the weight.

As for helium, as Tom just said, it isn't dense enough to propel the paintball.

I believe the best gas for paintball in theory is Argon, but its just too expensive to be practical.

[AGD]

Argon does have the best molecular weight numbers and doesn't go liquid. We were discussing this in the early 90's and again my buddy Ed Head shot several tanks of argon to try it out. Unfortunately didn't write down the numbers but he reported that it didn't seem to make that much of a difference. Someone should try it again for grins.

AGD

[clockworkmiller]

Does anybody know the cost to fill a 88cuft 3kpsi scuba tank with argon as opposed to compressed air? Unless the numbers are very similar, then Argon would need extrodinarily better in order for it to be feasible. Also, what would the NPPL or NCPA or other paintball associations say about using argon in tournaments.

[Dubstar112]

Tom I could try Argon... Im good friends with my local welding shop and I bet I could get one fill for a little bit of dough .. But would it be safe? especially for the Flatline regulator?)(i have a 68/3k)

Either way, Im not sure because I dont think they have the proper regulated fill station.. but I could try.)

[Doc Nickel]

Argon fills will be considerably more expensive than Nitrogen.

I can't recall specific costs off the top of my head at the moment, but I do know that refilling a helium or argon cylinder for the TIG is quite a bit more than refilling my nitrogen tank for paintball fills. Keep in mind those are Alaska prices, though. Your mileage may vary.

In any case, for the purposes of the discussion, the additional cost of Argon probably far outweighs the miniscule performace benefit of the gas.

Hey Tom: Next time you have a chance, see if there's any difference in regulator recharge rate between HPA, Nitrogen, Argon or Helium. And I mean on some of the aftermarket regs you've been trying, not just the RT and 'Mag valves.

That's something I'd like to see.

Doc.

[bjjb99]

Re: argon fills

Doc Nickel wrote:
>
>Argon fills will be considerably more expensive than Nitrogen.
>

Absolutely. Considering that the air we breathe is 78% nitrogen and only 0.9% argon, it's easy to see why nitrogen costs less... it's just plain easier to extract a given volume of pure nitrogen from the air than it is to get the same volume of pure argon.

Of course, a fill of compressed air should be less expensive than either nitrogen or argon, since no extraction equipment is required at all.

BJJB

[AGD]

Argon here in the big city is more expensive but not rediculous. I think its about 20-30 bucks for a tank. This would be important for tourney players looking to maximize the air capacity while minimizing the weight and going with a smaller tank. Someone should really try it just so we know.

Doc, it's good to see you hanging around again. I am deeep in the throws of paint breakage testing and haven't done any more with the regs. When I get back to it I'll try the different gasses, could be interesting.

AGD

[Redkey]

how are you measuring paint breakage?

Are you measuring hard numbers or is it a guesstimation type of test?

Are you doing your tests at impact velocities or are you just performing a crush test and measuring max load? Are you generating load - displacement curves for the tests?

Are the tests being performed at various temperatures or are you just doing them at room temp?

What about preconditioning the paintballs to determine the affects of humidity? If so, are you measuring the weight gain due to absorbed water? What about the paintball dimensions?

Are you keeping track of the paintball orientation?

Shell thickness?

My concerns would be with the batch to batch variability. Do balls produced one week have similar characteristics to balls produced weeks or months later? If the company cannot hold tight tolerances you'll never know what you'll get.

thanks
Jack

[etnie002]

Hey thordic great work. One quesiton for you though. I'm doing a project dealing with the differences between CO2 and compressed air and thought this thread would defintely help. However what do you mean by

Air has an average molecular weight of 29 (28 for N2*.8 + 32 for O2 * .2)

. Wouldn't the molecular weight for N2O2 be 60 considering ((14.0 x 2) + (16.0 x 2)=60), meaning the avg. weight would be 60g. I was wondering where the .8 and .2 came from because it really confused me.

[etnie002]

Ahh sorry I think I just figured out what I did wrong. By N2 and O2 i thought u meant the formula for compressed air is N202 (i didn't bother to look it up) but as i re-read your post i realized you were merely displaying nitrogen and oxygen as diatomic (which totally slipped out of my mind for some reason). So by the .8 and .2 im guessing u meant that compressed air is 80% nitrogen and 20% oxygen, meaning its formula is N4O. But then i sitll dont see why its only 29g considering N40 would weigh 72g. SO im sitll kinda' lost.

[bjjb99]

You're basically doing a weighted average of the molecular weights of the two primary gases in the atmosphere.

Compute the molecular weight for nitrogen gas (N2). It's right around 28. Do the same for oxygen gas (O2). It's right around 32.

Air is about 80 percent nitrogen and 20 percent oxygen by volume.

Take 80 percent of nitrogen's molecular weight (0.8 * 28 = 22.4). This is the weight contribution that nitrogen will provide to air's molecular weight.

Take 20 percent of oxygen's molecular weight (0.2 * 32 = 6.4). This is the oxygen's weight contribution to air.

Add the two results together to get the molecular weight of air (28.8).

BJJB

[etnie002]

yeah i had my chemistry teacher explain this to me she was like "oh yeah i forgot to teach you this part". So i understand now, thanks.