So like refrigerators and freezers and things like that use the Carnot Cycle. And I understand how that cools things down. But I’ve also heard that with conventional methods the biggest temperature difference you can make is about 100⁰C. So how do we get something like liquid nitrogen at -195⁰C? Are we putting a freezer inside a freezer inside a freezer? Or how do we get stuff that cold?
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Basically yes, usually this is done with multi-level refrigeration. The same basic concept, stacked like Russian nesting dolls with different refrigerants that work over different temperature ranges.
Use your basic household R-22 coolant or whatever to get *cold*, and then a second stage with a cryogenic coolant that works over a much lower temp range will kick in. Then maybe even a third or fourth stage until you get down to liquid helium as a working refrigerant.
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