How to keep a CO2 cartridge from freezing up 1

[Mech117]

How do I keep a 12g CO2 cartridge (like the ones used in BB guns)from freezing up (forming dry ice) when I puncture it?
I need to be able to expel the gas over a time period of 10 to 20 seconds.
I am sure the experts here will want more information but as this is a subject matter I don't have much experience in I am not sure what information to supply.
Any help is greatly appreciated.

 

[Latexman]

You have to add enough heat to keep the contents a gas.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Mech117]

The design that these cartridges are being used in do not lend themselves to being heated. Meaning the accountants won't pay for heaters. Now with that said this is a fire suppression application so the cartridge will be above room temp, 212F in its worst case but I don't think it will ever see that and it will be more like 150F.
As I understand it, if i assume the worst case then the CO2 will be super critical (all vapor) but when I puncture the cylinder the cooling effect is so strong that the temperature is dropping faster than the pressure is.

 

[Compositepro]

Draw-off the CO2 as a liquid by keeping the cartridge upside down and pass the CO2 though a small passage in a steel or aluminum block that has sufficient heat capacity to vaporize the liquid. Or use an adequate length of small diameter coiled tubing.

 

[Mech117]

Compositepro,
That is an interesting idea I had not considered. I did wonder if orientation would make a difference but hadn't considered that being a good thing.
I am going to go try it now.

Is this throttling the saturated liquid? What does this do other than get more mass out of the cartridge faster?

 

[Compositepro]

When the vaporization takes place outside of the cartridge there is no cooling of the remaining contents of the cartridge, so this maintains the pressure in the cartridge. Actually there will be a small amount of vaporization - that which is required to displace the liquid CO2. Liquid will move out of the cartridge as long as the vapor pressure in the cartridge is higher than the pressure at the other end of the line. You need to get the CO2 fully vaporized before it reaches any expansion valve. Coiling a tube makes sure that liquid stays in contact with the tube wall due to centrifugal force.

 

[EdStainless]

The tube needs to be small diameter, maybe 1/8". Use a few feet of tube coiled up.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Mech117]

Just tried it and it seems to have work liked a champ! Thank you! There was no residual solids left in the cartridge. I was already using capillary tube to help regulate the pressure downstream.

My system doesn't really have an expansion "valve", it just expands into a larger volume container where is it used to push extinguishing agent out.
If the CO2 is still liquid after exiting the capillary tube would it not just convert to a gas due to being at a lower pressure? I am trying not to ask the question because I should probably already know...... but why does the CO2 need to be fully vaporized before reaching any expansion valve?

 

[Mech117]

Capillary tube used was .03" inner diameter

 

[Compositepro]

Well, it does not have to be fully vaporized if you are using it as an extinguishing agent. You will get CO2 snow. It has to be fully vaporized if your expansion valve has to control the down stream pressure. A CO2 fire extinguisher contains a dip tube in the tank so that liquid is drawn from the bottom of the tank, and the liquid is expanded at the valve so that it flashes to cold vapor and solid snow. The vapor and snow have a much lower volume, and therefore lower velocity, than 100% room temperature vapor. This is more effective at cooling and snuffing-out fires. Kind of how water works, as well.

 

[Mech117]

Awesome, thank you all for your help.