I’m cooking chili on my coleman camp stove and my propane tank has frost on it it’s so cold. Why?
In: Chemistry
You’re seeing the pressure / temperature equilibrium for propane. Propane is stored as a liquid that has propane gas in the head space above the liquid.
When you cook with propane, you are bleeding off the gas and lowering the pressure above the liquid. The liquid is now above it’s boiling point (because the pressure in the container has dropped). The liquid responds by boiling and creating vapors.
There is an energy need for this phase change – called latent heat. The first place that propane will take energy from is the liquid propane. Removing energy from the liquid to boil vapors causes the liquid to cool. This is known as auto refrigeration and is characteristic of cryogenic liquids stored under pressure.
Propanes boiling point at atmospheric pressure is about -30F. I’m not sure the liquid temp ever gets that low – but a container that is -10F will start cooling air on the outside of the container and condense water vapor out of the air.
When air cools / water is condensed, it provides energy to the propane which will allow it to keep boiling.
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