for the joule thompson coefficent, when do you get heating and when do you get cooling?
You get heating when you use real gases that have an inversion temperature that are above normal ambient temperatures. Those gases are Helium, Hydrogen and Neon. These gases, if compressed and cooled back to ambient temperatures will not cool when throttled thru a J-T valve, but will heat up instead, so these gases cannot be liquefied by throttling and running thru counter current heat exchangers at ambient temperatures. The inversion temperature of helium is around -68C so this gas cannot cool until other refrigeration means bring this gas down to at least -68C before it can be throttled thru a J-T valve and the gases would then cool with throttling instead of heating up. All the other real gases, mainly atmospheric gases (nitrogen, argon, oxygen, CO2, etc) and petroleum gases have an inversion temperature above ambient so they all will cool when compressed and throttled thru a J-T valve. This is how they cryogenically liquidfy normal gases and hydrocarbons with a combination of a JT (Joule-Thompson) valve and adiabatic expansion (letting the compressed gasses do work to magnify the cooling effect greatly) Look at some T-P diagrams for the various gases to see the inversion temperatures. LPG, oxygen and nitrogen all have inversion temperatures well above ambient, so they will all cool when they are compressed and throttled thru J-T valve
