HPA and Co2 mix- someone around here somewhere has done this...

[FRANK]

beats me lol. { I understand } but I could put the co2 tank on the scale, before and after filling.
but I'm not doing this any more for now till we find it's 100% safe.


Yes the double tube for the Disco looks like a good investement in the long run, but with the modding of the stock it's going to have to wait.

[SeanMP]

The one thing that confuses me with Voltar's data is why did the pressure drop from 2000 psi to 110 bar (1595 psi) when it stabilized at 19*C?.... More tests need to be done to insure safety, IMO.... After all, an 11*C change of temperature raised the pressure from 1595 psi to 2175 psi.... If we were talking about a properly filled CO2 tank the corresponding pressures would have been ~800 psi and ~1150 psi.... Food for thought....

Bob

What I'm seeing here straight off is an anomaly with the tank gauge. It's sticking. The tank gauge should have read 138 bar right off the bat and climbed to 150. That's pretty close to predictable. I'll assume that the gauge at the bottle is more accurate than the small one at the cylinder. (Hatsan's gauges are also notoriously unreliable if the info online is to be believed)

Also neither of those gas are capable of that amount of rise over 20degF even at 100% fill.

Also we can't be sure the entire mixture was supercritical until it hit 304Kelvin

[rsterne]

The gauge could be sticking.... but what about Walter's statement that the gun had liquid CO2 in it after the 2000 psi top up with air.... He only had 50% CO2 by volume, and the CP I calculated for 55% was 2*C at 982 psi.... so at 50% would be even lower, certainly lower than 19*C.... While CO2 won't rise that much over 20*F at 100% fill, it certainly will at 130%, in fact it would go off scale on the chart.... I still think the CO2 is liquid once you add the air, and stays that way until the pressure drops to the boiling point at the ambient temperature.... but I've been wrong before and I will be again....

For sure there needs to be more testing....

Bob

[SeanMP]

I agree there was liquid sloshing around.

What I was trying to suggest is there is no way to guarantee that there was 100% mix until all the co2 was in a superfluid state. As you remember from gr 11 physics the phase change happens progressively. So there could have been both a superfluid mixture and pure liquid co2 existing at the same time. I know the data of 30deg C was probably a ballpark but I think it would take a true 31.5degC to ensure that everything was superfluid and mixed all at the same time.

The fact that Walter could hear liquid sloshing alone says that it wasn't superfluid

[rsterne]

not sure why you keep going back to the 31.5*C.... That was for a tank filled with CO2 to 100% by weight which was 87% by volume.... The other figures I did in the same post, for 55% by volume showed a CP of only 2*C and 982 psi.... At 50%, it would be even lower.... I'm thinking that if my math was right, according to the equations, Walter's recent test should have been all superfliud.... However, it wasn't as he could hear the liquid....

Colour me confused....

Bob

[SeanMP]

I believe you need to hit the supercritical point of both gases before a full mix will occur. Up until that point the mix is only partial. After the mix has occurred you can then use the new combined CP. I keep going back to 31.5 because that's the point at which all the co2 will be supercritical.

[rsterne]

ahhhhh.... got it....

What then happens if you cool the mixture?.... Does it stay mixed, or does the CO2 start to condense out?.... I'm thinking that in theory it should remain a mix of two supercritical fluids with a CP determined by the mole fractions?.... If so, and the mixture is kept above the "combined" CP, no liquids form?....

Now let's see.... Take one part liquid CO2 and one part HPA.... mix and heat to 32*C and stir until blended.... Rebottle and sell as "Airgun Supergas".... *LOL*....

Bob

[SeanMP]

Uh oh...I feel a patent coming on

Yes if you cool it it stays as a mix retaining the new CP

Until someone else comes along and decides it would be better as two separate gases. Then they would have to supercool it by rapid expansion in a gas distillation process.

[SeanMP]

The trouble with gas physics is everyone wont play the same game at the same time.

For example water at 0 degrees. It can exist as a solid, liquid and a gas all at the same time.

So who knows whats in Walter's tube?....The safe bet would be a bit of everything

[rsterne]

However, if Walter warmed his gun to 32*C and kept it there until it stabilzed, then it should have no liquid in it.... and additionally, it should not have any condense all the way down to refridgerator temperatures (~3*C).... Over that temperature range, the pressure shouldn't change more than about 10%.... Correct?....

Bob