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 all comes down to a phenomenon called the Joule-Thomson effect.
Heat is one of the ways that energy is stored, and when pressure drops this energy is dispersed over a larger area and temperature drops.
However, the drop in pressure also means that atom knock into each other more seldomly and as this potential energy drops (the work that could be done by letting the gas decompress), heat increases (since energy has to be preserved).
If the first effect is dominant, then temperature drops. If the second is more dominant temperature increases. The temperature at which these forces are equivalent is the inversion temperature.
At room temperature Helium, Hydrogen and Neon heat up when expanded. All other gasses cool down.
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