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
It basically has to do with whether or not the gas requires energy beyond its pressure release to occupy more volume (gas cools) or whether it sheds its stored energy as pressure to occupy more volume (gas heats up). In the first case, the gas needs an extra push to spread out and draws that energy from its surroundings. In the latter case, it readily spreads and gives off heat as part of its stored potential energy (pressure).
This phenomenon is known as the Joule Thomson Effect. The temperature at which the direction of the energy transfer changes, is called the inversion temperature.
In the case of hydrogen and helium, the inversion temperature is close enough to room temperature to be a factor when designing pressure systems with them.
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