C02 tank refill - not cold?

[CDS]

Probably a dumb question with an easy explanation, but Im curious: my regular LHB store where I used to go to get my C02 tank refilled closed down. No others around within easy travel distance, but I did find a place that just refills c02 tanks so I decided to go there. In my experience, after filling, my tank is ice cold and covered in frost (too cold to handle without gloves), which i thought was an unavoidable side-effect of liquid C02 -> gas. This fill the tank wasn't cold in the slightest. In fact I wondered if they even filled it, but i weighed it when i got home and it's full. Just wondering why it wasn't cold.

 

[IslandLizard]

Just wondering why it wasn't cold.

Most places that fill while you wait will purge the cylinder with a small forerun of liquid CO2, then blow that out. That causes the cylinder to get ice cold (and probably frosted over), which allows the cylinder to be filled (more) completely to its rated capacity. They should get filled by weight on a scale.

How much CO2 did you actually get?

 

[doug293cz]

The cold is "generated" (actually heat is absorbed by the evaporating CO2) where the CO2 transitions from liquid to gas. I suspect the supplier is filling from a siphon cylinder, so the CO2 comes out of the tank, and goes thru the plumbing, as a liquid. It then converts to a gas in the cylinder being filled, at least until the pressure in the receiving cylinder is in equilibrium with whatever the temp of the liquid CO2 is. Since no liquid to gas transition takes place in the supply cylinder, it does not get cold.

Brew on

 

[CDS]

Most places that fill while you wait will purge the cylinder with a small forerun of liquid CO2, then blow that out. That causes the cylinder to get ice cold (and probably frosted over), which allows the cylinder to be filled (more) completely to its rated capacity. They should get filled by weight on a scale.

How much CO2 did you actually get?

it's a 5lb tank - I weighed it just before I left and it was at the tare weight of 7.70lbs. Had to use the bathroom scale to weigh it just now as the filled tank is too heavy for the scale I used before i left. The bathroom scale reads 13lbs exactly so it's definitely full.

 

[50calshooter]

Probably a dumb question with an easy explanation, but Im curious: my regular LHB store where I used to go to get my C02 tank refilled closed down. No others around within easy travel distance, but I did find a place that just refills c02 tanks so I decided to go there. In my experience, after filling, my tank is ice cold and covered in frost (too cold to handle without gloves), which i thought was an unavoidable side-effect of liquid C02 -> gas. This fill the tank wasn't cold in the slightest. In fact I wondered if they even filled it, but i weighed it when i got home and it's full. Just wondering why it wasn't cold.

Most places don't fill the tank, they swap it out for a full one.

 

[day_trippr]

fwiw, 16 years ago I could get my cylinders filled on demand by my favorite and closest lhbs. They had humungous siphon tanks from which to draw liquid CO2, but unless one pre-chills the receiving cylinder the first fill is going to gasify bigly and frost the cylinder in fairly short order. That phase transition in turn would limit the max fill volume unless the pressure was relieved - which is where the frost can get thick, as the operator bleeds the receiving cylinder to make room for more liquid. A typical path to a full 5 pounds required multiple bleed cycles, so I had to wrap the cylinder in a towel so it wouldn't stick to my truck's leather seats.

When I picked up a 20 pound siphon tank of my own to refill my collection of 5 pounders I easily decided to not go the aggressive route and just fill the little dudes until the flow stopped and call it done. I end up with around 3.5 pounds instead of 5, and a cold but not frosted cylinder. I'm ok with it, it's not like I have to go far for another "mostly fill"

Cheers!

 

[doug293cz]

fwiw, 16 years ago I could get my cylinders filled on demand by my favorite and closest lhbs. They had humungous siphon tanks from which to draw liquid CO2, but unless one pre-chills the receiving cylinder the first fill is going to gasify bigly and frost the cylinder in fairly short order. That phase transition in turn would limit the max fill volume unless the pressure was relieved - which is where the frost can get thick, as the operator bleeds the receiving cylinder to make room for more liquid. A typical path to a full 5 pounds required multiple bleed cycles, so I had to wrap the cylinder in a towel so it wouldn't stick to my truck's leather seats.

When I picked up a 20 pound siphon tank of my own to refill my collection of 5 pounders I easily decided to not go the aggressive route and just fill the little dudes until the flow stopped and call it done. I end up with around 3.5 pounds instead of 5, and a cold but not frosted cylinder. I'm ok with it, it's not like I have to go far for another "mostly fill"

Cheers!

This doesn't seem to match up well with the physical chemistry. The tank being filled from a siphon tank gets cold, which means the headspace pressure will be lower in the receiving tank than in the supply tank. This should allow CO2 to flow until the desired fill level, as long as the temperature differential is maintained. Things might slow down when the headspace pressure reaches (or even exceeds) the equilibrium pressure at the receiving tank temperature. Then to get more CO2 in the tank, CO2 has to condense from the headspace back to the liquid. This condensation process may be the rate limiting step to get a complete fill, especially if you are in a hurry. The condensation in the receiving tank would also release heat, thus warming up the receiving tank, reducing the pressure differential, and slowing the fill rate.

Things would be a little different if there were gasses other than pure CO2 in the receiving tank headspace. The partial pressures of the contaminant gasses would add to the CO2 partial pressure, and reduce the pressure differential between the supply tank and the receiving tank, thus slowing flow. In this case venting the headspace might be required for a complete fill (depending on the amount of contaminate gasses.)

Brew on

 

[day_trippr]

Have you ever actually watched someone try to fill a CO2 cylinder to its rated capacity?
"Gasification Happens" and it significantly limits the liquid transfer, as I said, unless one wants to bleed off pressure to achieve a greater fill.
I choose not to waste the CO2...

[edit] I should note, if I pre-chill the receiving cylinder in one of my freezers I can transfer an extra ~ half pound of CO2 without doing the bleed thing. It's all about temperature differential...

Cheers!

 

[doug293cz]

Have you ever actually watched someone try to fill a CO2 cylinder to its rated capacity?
"Gasification Happens" and it significantly limits the liquid transfer, as I said, unless one wants to bleed off pressure to achieve a greater fill.
I choose not to waste the CO2...

[edit] I should note, if I pre-chill the receiving cylinder in one of my freezers I can transfer an extra ~ half pound of CO2 without doing the bleed thing. It's all about temperature differential...

Cheers!

Agree, you have to have a pressure differential to move CO2 from one tank to another. You can create that pressure differential with a pump or a temperature difference. The point I was making is that as long as you have a temperature differential you should also have a pressure differential, and CO2 should move from the warmer tank to the cooler tank, but rates might be an issue at some point.

Brew on

 

[hottpeper13]

I never noticed a cold cylinder after filling because mine sit in the freezer overnite before getting filled. It's a balance transfer and most times 1/2 in the green.