mixed gasses question

At the critical temperature of 87.8 degrees carbon dioxide liquifies at 72.9 atmospheres. 72.9 atm is about 1071 PSI. In a cylinder of the gas mix C25 (25% CO2, 75% argon) at 70 degrees and 2000 PSI what state is the CO2 in? Is there liquid at the bottom of the cylinder? I know there is a gas mix leaving the cylinder but I don't know if the CO2 just boils off liquid at the bottom. I don't think it does, I think it remains a gas until the argon becomes a liquid. What's the answer and why? Thanks, Eric

Reply to
etpm
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It's a gas! (Chemistry, that is :-)). The partial pressure of CO2 in 25% CO2 at 2000 psi is 500 psi, well below the critical pressure (and 70F is well below the critical temp, as well). Below the critical temp and pressure pure CO2 will exist in some combination of liquid, solid, and gas forms, depending on the temp and pressure. Above the critical temp and critical pressure there will exist only one, supercritical fluid, phase. Not far above the critical temp the density will be quite high, approaching that of liquid CO2, while the viscosity will be almost gas-like. At temps way over the critical temp it will behave like a gas.

At the critical temperature of 87.8 degrees carbon dioxide liquifies at 72.9 atmospheres. 72.9 atm is about 1071 PSI. In a cylinder of the gas mix C25 (25% CO2, 75% argon) at 70 degrees and 2000 PSI what state is the CO2 in? Is there liquid at the bottom of the cylinder? I know there is a gas mix leaving the cylinder but I don't know if the CO2 just boils off liquid at the bottom. I don't think it does, I think it remains a gas until the argon becomes a liquid. What's the answer and why? Thanks, Eric

Reply to
Carl Ijames

The partial pressure of the CO2 is only 500PSI.

Gases behave like animal populations that ignore other species on their territory:

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Reply to
Jim Wilkins

I suppose the OP was wondering how well the gases are actually mixed when they come out of the tank and out the gun, and how much or if the mix changes with temperatures that might be expected when welding things together???? If so, are you saying that the CO2 and argon gases don't mix well? Sounds contrary.

Pete Stanaitis

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Reply to
Pete S

Thanks Carl and Jim for the responses. I had forgotten about partial pressure and how it works. It of course makes sense of what I was thinking was happening, that the CO2 was gaseous, not liquid. I really appreciate the knowledge this group disseminates. Eric

Reply to
etpm

IF there would be liquid CO2:

There is the liquid CO2 at the bottom of tank. Some argon gas is dissolved to the liquid CO2 (insignificant amount).

At the gas phase there is the argon (at partial pressure of argon) and saturated vapour pressure of CO2 (around 64bar at 25C). Bottle pressure is the sum of these two pressures, at 200bar there would be 64bar CO2 and 136bar argon. The CO2 sat.vapour.pressure remains as long as there is any liquid CO2, argon pressure goes linearly down as it is consumed.

Amount of argon in gas mixture goes down as gas is consumed. At beginning: 64 bar CO2 : 136 bar Ar At end : 64 bar CO2 : 1 bar Ar

But there isn't any liquid CO2 there.. The reason is above, the gas mixture would change.

In the bottle, really, there is at 200bar total pressure, CO2 gas at 50bar (which is below saturated vapour pressure, so no liquid phase), and Argon gas at 150bar. As the pressure goes down, the mixture remains 25% CO2, 75% Ar.

Reply to
Kristian Ukkonen

That was my next move. How did you know? Must be great minds think alike. Eric

Reply to
etpm

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