Cryogenic equipment is used to generate, sustain or operate at extremely low temperatures. The generally acceptable division between refrigeration and cryogenics is minus 180 degrees Celsius. Typical equipment used in cryogenic applications includes containers, pressure vessels, cold traps, purifiers and piping. In many cases, this equipment holds or assists in the transport of supercooled liquids, such as liquid helium, nitrogen, oxygen and argon. Transfer lines, for example, provide a safe means to transfer liquid cryogens from one location to another without endangering workers or machinery.
Cryogenic equipment produces or is used in the production of very low temperature materials or processes. Cryogenics, the study of very low temperatures, involves temperatures that are colder than those that can be attained with conventional refrigeration equipment. Cryogenic equipment is designed to reach ultra-low temperatures at a slow rate in order to prevent thermal shock to the components being treated. Cryogenic temperatures range from -238 °F (-150° C, 123.2 K°) to absolute zero. At these low temperatures, substances that are naturally gases can be liquefied and some metals lose electrical resistance, as they get colder.
Cryogenic equipment includes cryogenic storage racks and boxes, cryogenic refrigerators, temperature controllers, cryogenics accessories and cryogenic tanks. A cryogenic tank or dewar is used to store cryogenic gases such as liquid oxygen, nitrogen, argon, carbon dioxide, and methane in bulk quantities. Cryogenic refrigerators are used to preserve cryogenic materials. In a cryogenic refrigerator, a refrigerant is circulated in a fluid flow path between the first and second chambers by the movement of a displacer.
Cryocoolers and liquid nitrogen equipment are types of cryogenic equipment used to attain cryogenic temperatures. There are two basic types of cryocoolers: a Stirling cryocooler and a pulse tube cryocooler. Cryogenic equipment which uses liquid nitrogen gas as a coolant is called liquid nitrogen equipment. Because of its high density in its liquid state, liquefied nitrogen gas can be stored easily, safely transported, and used as a coolant. Liquid nitrogen refrigerators provide low daily evaporation losses. Both cryocoolers and liquid nitrogen equipment can be controlled by computers.
Cryogenic equipment is used in many applications. Some examples include