Cryogenics

Cryogenics is a field of physics that primarily deals with how different materials are affected when cooled to very low temperatures and what their reactions to these low temperatures are. In a certain sense, cryogenics can also be understood as a technical device that helps maintain low temperatures.

The use of cryogenics is very broad, so it is no surprise that it can be found in several fields. For example, in the field of superconductivity research, very low temperatures are required, which are achieved using liquefied gases such as helium or nitrogen. For instance, the Large Hadron Collider at CERN uses liquid helium for cooling. Moreover, liquid helium also finds application in astronautics, apart from being used as a technical gas to maintain pressure in rocket stage tanks, it is also used for cooling.

Probes and satellites exposed to direct sunlight are equipped with a helium cooling system. This system not only serves as protection from the sun but is also used for cooling instruments that record the infrared spectrum. Another example is the Herschel Space Observatory. Another space application is cryogenic propellants. These include liquid hydrogen and oxygen. This combination is used by the Space Shuttle or the Delta IV rocket. In engineering, cryogenic heat treatment is used to modify the structure of steel. This process improves the structure of martensite and results in the breakdown of residual austenite.

There are several methods used to achieve very low temperatures. For example, in cooling instruments or deep freezing, liquefied gases such as helium and nitrogen are used. Further, for the liquefaction of gases, multi-stage compression and cooling are used. An example can be the Siemens cycle. In this cycle, Gay-Lussac's law is utilized, according to which compressing a gas increases its thermodynamic temperature. The resulting heat is removed by a heat exchanger. When the pressure is reduced, the temperature also drops. Modern techniques include magnetic cooling based on the magnetocaloric effect.