CO2 Steam mixture heat transfer 1

[shardik]

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.)

 

[sshep]

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