 Helium Dilution Refrigerator A dilution refrigerator is a cryogenic device first proposed by Heinz London. Its refrigeration process uses a mixture of two isotopes of helium: helium-3 and helium-4. When cooled below 700 millikelvin, the mixture undergoes spontaneous phase separation to form a 3He-rich phase and a 3He-poor phase. Image File history File links Metadata Size of this preview: 595 × 599 pixelsFull resolution (953 × 960 pixel, file size: 723 KB, MIME type: image/jpeg) Digital photograph of helium dilution refrigerator take by Mark Somoza File historyClick on a date/time to view the file as it appeared at that...
Image File history File links Metadata Size of this preview: 595 × 599 pixelsFull resolution (953 × 960 pixel, file size: 723 KB, MIME type: image/jpeg) Digital photograph of helium dilution refrigerator take by Mark Somoza File historyClick on a date/time to view the file as it appeared at that...
Cryogenics is a branch of physics (or engineering) that studies the production of very low temperatures (below –150 °C, –238 °F or 123 K) and the behavior of materials at those temperatures. ...
Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ...
General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ...
Helium-3 is a non-radioactive and light isotope of helium. ...
Helium-4 is a non-radioactive and light isotope of helium. ...
Circumstances where water naturally occurs in liquid form are shown in light grey. ...
The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ...
In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ...
As with evaporative cooling, energy is required to transport helium-3 atoms from the 3He-rich phase into the 3He-poor phase. If the atoms can be made to continuously cross this boundary, they effectively cool the mixture. Because the 3He-poor phase cannot have less than 6% helium-3 at equilibrium, even at absolute zero, dilution refrigeration can be effective at very low temperatures. The volume in which this takes place is known as the mixing chamber. Evaporative cooling is a system in which latent heat of evaporation is used to carry heat away from an object to cool it. ...
The simplest application is a "single-shot" dilution refrigerator. In single-shot mode, a large initial reservoir of helium-3 is gradually moved across the boundary into the 3He-poor phase. Once the helium-3 is all in the 3He-poor phase, the refrigerator cannot continue to operate.
More commonly, dilution refrigerators run in a continuous cycle. The 3He / 4He mixture is liquified in a condenser, which is connected through an impedance to the 3He-rich area of the mixing chamber. Atoms of helium-3 migrate across into the 3He-poor phase, providing cooling power, and then into a still where the liquid helium-3 evaporates. Outside the refrigerator, this gas is pumped up to a higher pressure and usually purified, and finally returns to the condenser to start the cycle again. Look up condenser in Wiktionary, the free dictionary. ...
The term still is a contraction of the verb to distill. A still is an apparatus used to distill miscible or immiscible (eg. ...
Continuous-cycle dilution refrigerators are commonly used for low-temperature physics experiments. Temperatures below 2 millikelvin can be achieved with the best systems.
See also Adiabatic demagnetization that can be used over the temperature range 4 kelvin down to microkelvin and the related room temperature application of Magnetic refrigeration. Adiabatic demagnetization is a technique for attaining temperatures well below 1 kelvin. ...
Circumstances where water naturally occurs in liquid form are shown in light grey. ...
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. ...
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