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

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.

-----
Regards,
Carl Ijames
wrote in message ...

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

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
-------------------------------------------------------------------------------------------------------------------------------

The partial pressure of the CO2 is only 500PSI.

Gases behave like animal populations that ignore other species on their
territory:
http://en.wikipedia.org/wiki/Partial_pressure

jsw

On Sun, 8 Jan 2012 18:32:20 -0500, "Jim Wilkins"
wrote:


wrote in message
.. .
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

The partial pressure of the CO2 is only 500PSI.

Gases behave like animal populations that ignore other species on their
territory:
http://en.wikipedia.org/wiki/Partial_pressure

jsw

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

On 1/9/2012 18:22, Pete S wrote:
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.

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.

On Jan 9, 11:47*am, wrote:
On Sun, 8 Jan 2012 18:32:20 -0500, "Jim Wilkins"









wrote:

wrote in message
.. .
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

The partial pressure of the CO2 is only 500PSI.

Gases behave like animal populations that ignore other species on their
territory:
http://en.wikipedia.org/wiki/Partial_pressure

jsw

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

Saved you from having to build a balancing rig to see if the cylinder
could be made to have either end 'heavy' depending on which way it was
tilted before balancing...


Dave

On Mon, 9 Jan 2012 11:57:57 -0800 (PST), Dave__67
wrote:

On Jan 9, 11:47*am, wrote:
On Sun, 8 Jan 2012 18:32:20 -0500, "Jim Wilkins"









wrote:

wrote in message
.. .
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

The partial pressure of the CO2 is only 500PSI.

Gases behave like animal populations that ignore other species on their
territory:
http://en.wikipedia.org/wiki/Partial_pressure

jsw

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

Saved you from having to build a balancing rig to see if the cylinder
could be made to have either end 'heavy' depending on which way it was
tilted before balancing...


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