Co2 tank, inside or outside kegerator?

[Twinsbro]

Is there a difference running the Co2 tank inside or outside the kegerator? Will it last longer if its outside rather than the inside where its a lot colder?

[siwelwerd]

Will it last longer if its outside rather than the inside where its a lot colder?

No, CO2 is CO2 is CO2, whether it's hot or cold. Your tank will *read* lower when it's cold (since pressure and temperature are directly proportional), but should last just as long. Outside is preferred by most to maximize beer space inside, although for presentation issues you might choose to put it inside. No major difference either way.

[Twinsbro]

oh ok. someone said on another forum that if you keep it outside it'll last longer. I was a bit confused on why that would be.

[Twinsbro]

maybe someone can break it down for me? Help me get a better understand of this?

[11amas]

I may be off, it has been 12 years or so since physics...

Warm CO2 is less dense in a specific volume than cold CO2 which is why your tank will read lower when warm than cold. Let's say your tank is warm and your keg is cold. As you feed CO2 in, imagine they are "pieces" (molecules), the warm pieces take up more space than the cold ones. So as you feed in warm CO2 it will become more dense in the cold and take more volume to fill. When you put the same temperature CO2 into your keg it won't cool down, won't reduce volume, and (in the end) will take as much gas.
There are no gains here, no way to cheat and get more for your tank.
Here is what you CAN do though. Make sure your tank is cold when you get it filled if you are doing so at a liquor store. They are taking 2 tanks, one large, one small, and making the pressure even. When you take it to a welding gas supply place though, they should be emptying the tank, weighing it, and filling it to weight. Either cold or warm, 30 pounds of CO2 is still 30 pounds--not pounds pressure (PSI) but pounds weight (Lbs).
Does this make sense? Now you can say you are reasonably certain they are full of shit.

[Twinsbro]

Cool thanks!

[dontblake]

OK, I'll give it a try...

First off, I think that whomever said that keeping your CO2 tank outside may have been fooled by the fact that the pressure in the tank would read higher than it would if it were colder. More pressure = more CO2, right?

OK, now let's Palmerize this one and break it down to the ideal gas law: PV = NRT
P= pressure
V= volume
N= Amount of gas
R = Ideal Gas Constant
T = Temperature

and furthermore, assume that CO2 is an ideal gas. Now, if we wanted to compare 2 scenarios, we would rearrange the equation as follows:
(P1 V1) / N1 R T1 = (P2 V2) / N2 R T2

Since R is constant, we can drop it from our figuring. Likewise, since the volume is constant (the size of the tank isn't changing), we can drop that one too to get:

(P1 ) / N1 T1 = ( P2 ) / N2 T2

OK, so if we just move the tank into the fridge and don't use any CO2, N doesn't change, so you have
P1 / T1 = P2 / T2
Or
P2 = P1 * T2 / T1
As Silwewerd mentioned, the pressure and temperature are directly proportional - if you lower your temperature, your pressure will drop proportionally. If you wanted to plug in numbers to get absolutes, you will need to convert the temperature to Kelvins and the pressure to Pa.

Let's take a look at how this equations changes if we want to look at how much CO2 we use in a situation (such as carbonating or pushing beer). Let's assume that we keep the location of the tank constant (inside or outside of the fridge - so that T doesn't change)
We can re-arrange the equation as follows
P1 / N1 = P2 / N2
Or
P2 = P1 * N2 / N1

Basically what this says is that your pressure will change proportionately to how much gas you use, which should make sense. Did you notice that there is no temperature in the figuring?
So, provided that the temperature doesn't change, you can keep your CO2 tank wherever you want and use pretty much the same amount of CO2.

One thing to consider, however, is that the diffusion of CO2 into your beer is greater when the temperature is lower, so you can get carbonated beer quicker if your CO2 and more importantly, your beer, is cold.

Hope this helps.

[11amas]

...yeah, that is what I meant to say, LOL, great explanation.