7.10 Liquefaction of Helium
The critical temperature of helium is 5 K. Hence, it must be precooled below 15 K in order that it may be cooled by throttle expansion below its critical temperature. The optimum input pressure for helium is 30 atmospheres for an input temperature of 15 K and expansion to 1 atmosphere.
In the Kapitza helium liquefier at the Mond laboratory, Cambridge, helium is first led through a reducing valve and then through charcoal immersed in liquid air to remove impurities. It then passes through a bath of liquid hydrogen. The gas then passes through the inner tube of the interchanger and expands to 1 atmosphere at the throttle valve. The vapour of the gas then escapes out of the liquefier through the outer tube of the interchanger. ...
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