= Dilution refrigerator
{wiki}
A <dilution refrigerator> removes <heat> at very low <temperatures> by transferring <helium-3> from a concentrated phase into a dilute phase rich in <helium-4>. The <enthalpy> per circulating helium-3 atom is higher in the dilute phase, so crossing the phase boundary absorbs <energy> from the <mixing chamber of a dilution refrigerator>. This is the useful cooling process.
Continuous operation requires a circulation loop. A <dilution refrigerator still> preferentially evaporates helium-3 from the returning mixture; pumps return it through a condensing and precooling path. <Heat exchangers> let the outgoing cold stream cool the incoming stream before it reaches the mixing region.<How Does a Dilution Refrigerator Work? by Bluefors>[Phase Separation of Helium Isotopes and Operation of the Dilution Unit: enthalpy difference, mixing chamber, still and return heat exchangers]{ref} A heater attached to the cold stage can impose a known test load, allowing a measurement of cooling power versus <temperature>. Unwanted <heat conduction> through supports and wiring, and absorbed <thermal radiation>, enter that same load budget. The refrigerator therefore needs both the microscopic mixing mechanism and careful thermal coupling to the experiment.
Back to article page
