Does CO2 cannister temp matter?

[whovous]

Some people put their CO2 cannister inside the kegerator, and some put it outside. Is there any advantage or disadvantage to storing the cannister at the lower temperature? I recognize that there is a space advantage for those who want to squeeze in an extra keg, but that does not matter to me. My current chest-freezer set-up has far more room than I have kegs.

 

[bleme]

Storing it inside the kegerator messes with the pressure gauge, but there is really no difference either way. Mine is inside because I don't want to drill holes.

 

[MoonBrewer]

I think once the canister is full the temp does not matter. When you take an empty tank for refill, a cold canister will accept more C02 so you get more gas for your money. I carry mine in a cooler to the shop.

I leave the tank outside of the fridge (1) more room in the kegerator for kegs and (2) avoid moisture condensation on the valves and gauges. Not sure if that is a problem but why take the chance.

 

[whovous]

Hmm, I never thought about the gauges. Then again, I am working on my own no-gauge solution, so I should be able to stop thinking about them soon. With or without gauges, I will probably leave mine in the chest, just so there will be one less thing to trip over. Thanks for the replies.

I leave the cannister with the shop overnight so they can get it good and cold.

 

[augiedoggy]

Someone once told me the warmer co2 rushing in after a pour or 2 could contribute foaming and it was wise to temp it at serving temp but I dont know how true that is at all.

 

[whovous]

Isn't the CO2 in the tank extremely cold, almost regardless of external temperature?

 

[augiedoggy]

Isn't the CO2 in the tank extremely cold, almost regardless of external temperature?

I think that depends on how fast its flowing but yeah I wondered about that too. the stuff sitting in the lines probably isnt..

I find it odd that kegerators all have the co2 tanks mounted inside if it doesnt matter.. some are a PITA because of it. The gauges should work fine inside.. mine all do.

 

[whovous]

Just did some googling. CO2 in the tank is liquid, and hence extremely cold. Gas boiling off is what creates the pressure. I am sure that is inartfully phrased, but I hope the point comes through.

Temp in the line is probably close to the surrounding temp.

 

[bucketnative]

While the CO2 in the cylinder is indeed liquid, the temperature of the CO2 will be at whatever temperature you hold the cylinder. However, the vapor pressure of the CO2 above the liquid is what will vary with temperature. For a 20°C cylinder with liquid CO2, the vapor pressure will be approximately 831 psi. If you put the same cylinder into a kegerator at 5 °C, the pressure in the cylinder drops to 575 psi.

 

[whovous]

While the CO2 in the cylinder is indeed liquid, the temperature of the CO2 will be at whatever temperature you hold the cylinder. However, the vapor pressure of the CO2 above the liquid is what will vary with temperature. For a 20°C cylinder with liquid CO2, the vapor pressure will be approximately 831 psi. If you put the same cylinder into a kegerator at 5 °C, the pressure in the cylinder drops to 575 psi.

This makes more sense than what I posted above, but...
Why does the tank (or an aerosol spray can, for that matter) get so cold when a large amount of gas is released? It cannot because it is cold in there, or else we would feel the cold on the outside of the cannister, but just what is it about change in state that results in change of temperature?

 

[MoonBrewer]

Expansion of a gas causes the temp to drop. CO2 coming out of the tank at high pressure to low pressure absorbs a lot of heat energy.

PV= nRT
(Pressure * Volume) = n*R*Temperature

If you drop Pressure on the left side of the equation, the Temperature has to drop to keep the equation balanced.

This is how air conditioners work, expanding Freon gets really cold.

 

[bucketnative]

I should have clarified that the situation I gave was for equilibrium. When you are removing gas from the system, it is a dynamic situation. The gas that evolves from the surface of the liquid CO2 requires heat to boil off. That heat comes from the liquid, which in turn takes heat from the walls of the cylinder. Removing heat from the cylinder walls results in the walls losing temperature because they can't pull heat from the surrounding atmoshpere fast enough.

We use a similar system for a different gas in our labs. We have to apply heaters to the small cylinders of liquid off of which we evaporate the gas. When the liquid level in the cylinders gets low, you have a higher surface area to volume ratio, and the evaporating gas can actually draw enough heat from the liquid to freeze the liquid.

You can actually freeze a small dish of water in a vacuum chamber in a similar manner. If you pull the vacuum deep enough, and the surface are to volume ratio is high enough, it will freeze.

If you are removing gas from the system at a very slow rate, you might not notice a temperature change in the liquid. This is true if the heat into the system from the environment through the walls is equal to that required to evolve the gas.

 

[bucketnative]

Expansion of a gas causes the temp to drop. CO2 coming out of the tank at high pressure to low pressure absorbs a lot of heat energy.

This is how air conditioners work, expanding Freon gets really cold.

That explains why your regulator gets cold. But, it doesn't cover the phase transformation that I discussed above. There's a lot going on the system when you remove gas, particularly at a rapid rate.

 

[whovous]

Thanks everyone. I asked a very simple and probably not very important question, but I learned some really interesting stuff.