cryogenic tanks, dewars

What Is Cryogenics?

Cryogenics is the scientific study of materials and their behaviors at extremely low temperatures. The word is derived from Greek words meaning cold (cryo) and producing (genic). Cryogenics is often encountered within physics, materials science, or medicine contexts; typically, scientists who specialize in it are known as cryogenicists, while materials undergoing cryogenic processes may be known as cryogens or cryogens; temperatures reported using any scale can be said; Kelvin or Rankine scales are often preferred due to being absolute scales with positive numbers representing favorable temperatures (Kelvin or Rankine scales are most popular).

Exactly how cold a substance has to be to be considered “cryogenic” is a matter of some debate by the scientific community. The U.S. National Institute of Standards and Technology (NIST) considers cryogenics to include temperatures below −180 °C (93.15 K; −292.00 °F), which is a temperature above which common refrigerants (e.g., hydrogen sulfide, freon) are gases and below which “permanent gases” (e.g., air, nitrogen, oxygen, neon, hydrogen, helium) are liquids. There is also a field of study called “high-temperature cryogenics,” which involves temperatures above the boiling point of liquid nitrogen at ordinary pressure (−195.79 °C (77.36 K; −320.42 °F), up to −50 °C (223.15 K; −58.00 °F).

What is a cryogenic tank?

Cryogenic tanks are the containers that are used to store cryogenic liquids such as liquid nitrogen, helium, argon, oxygen, hydrogen, helium, etc. Cryogenic liquids are typically liquefied gases at -150 °C or lower. Cryogenic tanks also store gases like liquefied natural gas and nitrous oxide at higher temperatures.
These tanks need to be thermally insulated to maintain the low temperatures. This is achieved through the use of a vacuum jacket. It’s essential that this component be designed and manufactured to a high specification, following established international design codes.
Cryogenic tanks can be of several different kinds. Static or fixed tanks are used in a fixed location, such as a cryogenic processing facility. Static tanks also include small mobile tanks called microbulk tanks that are mounted on wheels for use in labs and workshops.
Also known as pressure vessels, these small cryogenic tanks can also be called Dewar flasks. Dewar flasks are also available with an open neck that is not pressurized for situations where direct access to cryogenic liquids is needed. A cryogenic storage dewar (or simply dewar) is a specialized type of vacuum flask used for storing cryogens (such as liquid nitrogen or liquid helium), whose boiling points are much lower than room temperature.

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