I’m a medical student in an interventional radiology rotation. Today I saw a procedure called “cryoablation” in which compressed argon is circulated through a needle that is inserted into a tumor. Argon expands rapidly when reaching the end of the needle and causes a decrease in temperature freezing the tumor from the inside out ( I understand how this works, I think). Then compressed helium is pumped through the same needle, but in this case the expansion of helium causes an INCREASE in temperature. How is this possible? I tried reading about the Joule-Thomson effect, but it is still really confusing to me. Maybe someone can explain it more simply. Thanks in advance!
In: Physics
Ouf, Thermodynamics is complicated no matter how you look at it lol. It has to do with inversion temperature, Hydrogen and Helium have a much lower inversion temperature than other gases. So when they expand at constant enthalpy at room temperature they hit their inversion temperature where the gases experience temperature rise.
The inversion temperature in thermodynamics and cryogenics is the critical temperature below which a non-ideal gas (all gases in reality) that is expanding at constant enthalpy will experience a temperature decrease, and above which will experience a temperature increase.
**Helium and hydrogen are two gases whose Joule–Thomson inversion temperatures at a pressure of one atmosphere are very low (e.g., about 40 K, −233 °C for helium). Thus, helium and hydrogen warm when expanded at constant enthalpy at typical room temperatures**.
https://en.m.wikipedia.org/wiki/Inversion_temperature.
Tl;Dr Eli5: Helium at room temperature is far above that special temperature where it would have cooled down at expansion, thus it heats up at expansion because of the Joule Thompson effect
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