Cryogenics is the science of materials at temperatures below 120 K (−153 °C)
The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of "cryogenics" and "cryogenic" by accepting a threshold of 120 K (−153 °C) to distinguish these terms from the conventional refrigeration
The technologies by which materials are cooled up to this temperature are collected under the term refrigeration.
Cryogenicists use the Kelvin or Rankine temperature scale, both of which measure from absolute zero, rather than more usual scales such as Celsius which measures from the freezing point of water at sea level or Fahrenheit which measures from the freezing point of a particular brine solution at sea level
Cryogenics deals with thermal conditions in which even the substances that we encounter in our daily lives as gases — such as hydrogen, nitrogen and, of course, the air in our atmosphere — are liquid.
This field typically uses helium and nitrogen as the cryogenic fluid, the thing that cools a substance.
Nitrogen has a boiling point of negative 196 degrees C, and helium, negative 269 degrees C.
So below these temperatures, they are liquid.
Such fluids need to be stored in vacuum flasks or they could leak and damage their surroundings.
Many cryogenic materials have desirable properties.
For example, hydrogen is one of the best rocket fuels but it can only be used as a liquid, so it needs to be cryogenically cooled.
Cryogenic hydrogen and cryogenic oxygen power the third stage of ISRO’s LVM-3 rocket.
In the process of cryogenic hardening, a material — steel in particular — can be made harder and stronger.
This is because as it is cooled to around negative 185 degrees C, more of the steel’s crystal structure acquires the martensite configuration.
Magnetic resonance imaging (MRI) devices used in medical diagnostics use cryogenic fluids to cool their magnets
Magnetic resonance imaging (MRI) devices used in medical diagnostics use cryogenic fluids to cool their magnets
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