I encountered a problem that I thought was discussed previously on phys-l but I can't find it in the archives.
I would like to know the main reason why a propane tank cools when it is used. When I look online, I typically find one of four explanations:
1. Adiabatic cooling -- The gas that remains inside is colder because it does work pushing the rest of the gas out.
2. Evaporative cooling - Removing the gas lowers the pressure and the liquid propane boils as a result, leading to evaporative cooling.
3. Joule-Thomson cooling - The expanding gas must work against the attractive force between the propane molecules.
4. Colder molecules "left behind" - the faster molecules are more likely to leave, and so the slower and cooler molecules remain behind.
My feeling is that #1 is the main reason, as my back-of-the-envelope predictive* cooling is pretty big (i.e., bigger than I think the others produce). However, #1 does not seem to be the most popular reason provided in either my internet search or on the NSTA physics teachers list where this issue has come up.
Since I am not entirely confident in my theoretical predictions, I figured I could compare my results with actual cooling of a propane tank. However, I don't have access to one and I could not find any data online.
Does anyone have actual data that shows the amount of the cooling when a propane tank is used? (or has data that definitively shows which reason is most significant?)