For those that use CO2 - are there any issues with dry ice forming? Better yet, is it possible to form dry ice inside the tire??

The wierd things you think about in the bathroom.....

 

Um...you're the chemist, aren't you supposed to know about these things?

 

I have had mine get frosty. But never Ice-up in such a way as to slow it down.

 

That's the part that's killing me.... At first thought you'd think it would be easy to form solid CO2, but I'm not sure what pressure its at when it comes out of the tank.

 

I think you do form it. You just do so in paper thin slivers that do not stick around like a block of dry ice. They do not "make" commercial dry ice at room temp. The conditions are not good for preserving it once it is made.

 

Make dry ice?

I have never had any problems with it because it flows as a gas and would need tremendous pressure to form a solid.

My regulator did not freeze in Arizona at 115 degrees, but did freeze to the point of slowing flow in Colorado at 9k feet and 75 or so degrees.

 

So its in gaseous form in the tank? I was thinking it was liquid.

 

I do believe it's liquid in the tank when it's still Tom, as you can hear it slosh around if you shake it.

There should be info on www.powertank.com about this.
If not, shoot owner Steve Sasaki an email, and he's very good about getting back to people the same day.

When you release the C02, the liquid turns to a gasious state, just like air is a gas.

I just filled mine up at work today with my Power Tank, as they were down to around 29 from the cold weather we have had, and it's been a good 1.5 months since I last checked them.
I like to run around 34 to 35 for the street.

And yes, the brass hose end that fits to the gauges was a little icy afterwards.
That's normal.

 

Liquid in the tank, gas in the hose.

I mean that I doubt there is sufficient pressure to make dry ice in the hose from gas to solid.

 

From the Power Tank page:

"We now have two distinct CO2 systems in multiple variations to fit any need. They both utilize our own SuperFlow™ regulators designed specifically to provide super high flow rates of CO2 vapor without "freeze clogging,” the number one problem with high pressure regulators not designed to regulate CO2 at a constant high flow rate."

I e-mailed them to see if they could elaborate more on how their SuperFlow regulator works.

 

The last time I was in a chemistry class was several decades ago, so hopefully my memory is good enough to allow me to post a correct answer to this question. The CO2 in the tank is in both a liquid and gas form - as the liquid enters the tank it starts turning into gas, so say on a 10# tank you will have 10#'s of liquid CO2 pumped into the tank and if the tank is standing upright, as opposed to laying on it's side, there will be a large layer of space between the liquid and the top of the tank and this will be CO2 in a gas state under 750#s of pressure at 70'F at sea level. As you bleed off the gas (this is why a regulator is important) the CO2 liquid will continue to turn into gas maintaining a constant pressure within the tank until all the liquid has turned into gas and that's the beauty of CO2 - you will have approximately 750#s of pressure at all times in your tank until that puppy is totally empty. If you could force 15#s of CO2 in a 10# tank you could/might see liquid CO2 in your hose as some liquid can be forced through your regulator and once in your hose it will turn into dry ice when you disconnect the hose from the regulator.

 

So if you turn it upside down can you spray people with liquid CO2?

 

Now that wouldn't be very nice...

 

The freeze clogging they're talking about is likely frozen water in the line/air chuck. As mentioned below, its liquid CO2 in the tank, boils off to form gas as you use it to fill your tires. The tank gets quite cold to the touch, I often get rocks, etc. frozen to the bottom of my tank by the time I'm done- water condenses on the outside of the tank then freezes.

My guess is that turning the tank upside down and opening a valve would be very dangerous (I realize you were just joking BTW)- liquid CO2 would pour into the regulator, then because of the decrease in pressure, would quickly boil and expand, likely fragging your regulator and hose...

 

OK part of the whole thing behind my questions is this - when I was in college, I used to make dry ice for some experiments. We had a huge cylinder of CO2, and we'd run a line from the tank to this little box, and presto - in a few secs we'd have a small brick of dry ice. I don't remember what exactly was special about that box, but I'm hoping someone else might know. Dr. David??

 

Joking? (j/k)

But then again, I would think that somebody in the world was filling up his tires when the tank fell over. If there was a catastrophic failure, hiliarity (or death) would insue and powertank would at least put a warning label somewhere. We need to find a phase transition chart. I'll look into it.

BTW, we didn't really need to know what you were doing when thought of this, Tom.

 

Was Schroedinger's cat in that box?

Its likely a matter of the ideal gas law (PV=NRT)? Equal pressure between the tank and the small box, N and R stay constant, so temperature must decrease to keep two sides of the equation equal, temperature decreases enough to form solid CO2 in small box?

 

Ok, I think I've got it (maybe).

From Tom's account of how they made dry ice: In order for the CO2 in a gas state to become solid at 1 atm, the temperature must be below -78.5C.


The gas coming out of the dewar (tank) is already at or below this temperature because of the ideal gas law. The box simply kept the temperature low for a long enough time for the gas to transition to solid. The reason the box is needed is because if you just let the gas spray out of the hose into air, the air would immediately warm up the CO2 gas above -78.5C and no solid would form.

So, perhaps if somebody were to release their CO2 from a powertank into a enclosed container dry ice would form.

Have you guys ever noticed that water ice will form on the ground when you release the air from an air compressor? This is probably the same phenomenon.

Here's my sources:
http://www.science.uwaterloo.ca/~cch...phasesdgm.html
http://www.chem.leeds.ac.uk/People/CMR/whatarescf.html

The last one explains what joe was talking about with partial pressures. There's also some cool pictures of CO2 at the critical point, that is, the point where liquid and gas co-exist.

 

So, the freeze clogging mentioned above by Powertank is a result of the same effect Tom is talking about. Too much flow of CO2 out of the regulator into a confined space (in this case, the polyurethane tubing connected to the tank) can result in the formation of solid CO2 in the line- "freeze clogging." There must be a fine balance between trying to get maximum flow to air up tires quickly, versus too high a flow that formation of solid CO2 in line becomes a problem. It appears that Powertank has worked on this problem and come up with a better regulator?

 

That very well could be, especially since the pressure in the hose is higher than 1 atm, thus increasing the temperature at which a solid will form.

This begs the question if one were to fill up tires with CO2 and the vehicle traveled to the south pole, would the tires deflate because the CO2 turns into dry ice?

Note: coldest recorded temp is "at the Soviet station of Vostok, 600 miles north of the (south) pole at the top of the 12,000-foot-high ice dome, where a record low of -127°F (-88C) was recorded."