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CO2 Steam mixture heat transfer

CO2 Steam mixture heat transfer

CO2 Steam mixture heat transfer

(OP)
2 questions:

Begin with an autoclave full of air at atmospheric pressure, open a valve to supply CO2 for 10 minutes (I understand mass flow rate increases with temp drop), now start supplying steam to bring up to a certain temperature.
Supply steam pressure-temp is constant, as is CO2 pressure in supply tank.

1) Why would there be a lower pressure for a certain temperature as the CO2 is emptied, followed by a sharp spike upward right after being refilled?
2) Why would I have lower pressure during the summer months at a certain temperature (I would expect lower in the winter based on more CO2 in the tank due to the increased mass flow rate.)  

RE: CO2 Steam mixture heat transfer

shardik,

As CO2 vaporizes, the liquid cools as it gives up the needed heat of vaporization. This heat is only restored by heat transfer from the environment. When a large mass of liquid exists, the temperature change for a given mass vaporized is small. As the liquid mass decreases (bottle empties) the apparent effect is that there is a greater cooling. Since the pressure depends on the liquid temperature, there is actually a decrease in pressure as the bottle empties. This effect is well known by users of  CO2 powered guns (like paintball)- you can feel the bottle cool as you shoot and your muzzle velocity will be lower.

I think this may explain your observations.

best wishes, sshep

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