Rocco Moretti wrote:
Nikki Casali wrote:

It's 31 degrees centigrade in my dining room where I keep my planted
aquarium. It's rather hot today! So at what temperature will my CO2
canister likely to "unload" its contents? According to the pressure
gauge, it's over 70 bar. I have just read that the critical
temperature is 31.6 degrees or 88.88 degrees F. Should I be worried?


I probably wouldn't worry about it much. CO2 cylinders are used for
fountain soda dispensers, and if we had them exploding whenever the
temperature got above 90F, we'd hear about it more often. (Soda machine
at a fair, outdoors on a summers day ...)

Also when a scientist talks about a "critical temperature" for a
substance, what that means is just that above the 32C temperature the
distinction between a liquid and a gas disappears. (At 70 atm and 25C,
CO2 is in it's liquid form. If you were able to see inside the tank,
you'd have liquid CO2 on the bottom, and gasseous CO2 on top. As you
heat the tank past 31C, the interface between the liquid and the gas
would start to shimmer & get diffuse. At 32C, the interface disappears
entirely. The fluid in the tank at that point is neither a liquid or a
gas, but exhibits properties of both.) It's an interesting property of
gasses/liquids, but it doesn't mean that your tank will explode.

Look at the pressure rating of your tank, and when the gauge reads close
to that, then start to worry.

P.S. Supercritical CO2 is used in a bunch of industrial processes,
including drycleaning and coffee decaffination.

What about this safety valve I keep hearing about that sometimes blows
out in a hot car or room? I'm worried about that one. It sounds like a
jet taking off when it happens, apparently.

Nikki