Cryogenics

Cryogenics (from the words Greek. Κρύος “cold, frost” + γένος “genus, origin”) is a section of low temperature physics that studies the patterns of change in the properties of various substances under conditions of extremely low (“cryogenic”) temperatures. In addition, this term refers to technology and hardware-methodical means of work in low temperature conditions. Also defined as a field of science, covering research, development and use of cryogenic technology.

In 1971, the International Institute of Cold adopted a recommendation according to which temperatures below 120 Kelvin ( natural gas condensation temperature) to 0.7 K (liquid helium production temperature under vacuum ) should be called cryogenic temperatures. All temperatures below 0.3 K are an area of ultra low temperatures for which special cooling methods are used.

Content

Methods for producing low temperatures

Refrigeration cycles

Carnot Reverse Cycle

Throttle Cycle

The cycle is built on isenthalpic cooling as it passes through the choke.

Sources of cold in the cycle

Throttling

Throttling is a decrease in pressure due to pushing a substance through a narrow flow area. It is not a source of cold, but only implements the process of reducing the temperature. The source of cold is such a device in which the enthalpy changes. Throttling is an isenthalpic process.

Expanding

Expansion - an adiabatic expansion of a substance flow with the receipt of external work (derived from Fr.). Expanders differ: piston, turbo, rotor and other types. The expander is one of the main sources of "cold" (along with the compressor in the cryogenic cycle). The adiabatic efficiency of piston expanders can reach 90% or more, for turboexpanders at high temperatures, this parameter does not exceed 70% (as the working temperature range decreases, the efficiency decreases).

Adiabatic demagnetization

Adiabatic demagnetization - a method for obtaining temperatures below 0.7 K. The method is based on the effect of heat release from paramagnetic salts during their magnetization and subsequent absorption of heat during their demagnetization.

There is also nuclear adiabatic demagnetization. Currently, this method has reached the lowest temperature.

Recommended literature

Vygodin V. Cold Industry in the XXI Century (Rus) // Empire of Cold: Journal. - M. , 2004. - № 11 . Archived March 4, 2016.
Zaitsev A.V. Cryogenics at the beginning of the XXI century (rus) // Journal NRU ITMO.- SPb., 2014. - №1
Mendelssohn K. Low temperature physics. - M .: IL, 1963. - 277 p.
Brodyansky V.M. From solid water to liquid helium (history of cold)