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A cryocooler is a device used to cool the environment and everything inside it to extremely low temperatures, typically used in scientific and engineering applications. Different types of cryocoolers operate on a common process of circulating gas through a closed loop to absorb heat from within the device and transfer it to the outside environment. Cryocoolers are used in many fields, including medical, automotive, aerospace, scientific research, and military operations. Cryogenic hardening of metal components and infrared sensors used in satellite surveillance and missile guidance require cryogenic cooling.
A cryocooler is a device used to cool the environment and everything inside it to extremely low temperatures. Typically used in scientific and engineering applications, it is designed to reach temperatures well below those reached by standard appliances. There is no officially defined temperature requirement for what is considered a cryocooler. A device that can cool down to about -238 degrees Fahrenheit (or about -150 degrees Celsius) or colder, however, is usually referred to as a cryocooler.
While there are different types of cryocoolers, most operate on some variation of a common process. The gas is typically circulated through a closed loop to absorb heat from within the device and transfer it to the outside environment. This gas can be hydrogen, helium, or some other gas or gas mixture. The ability of the device to cool the internal environment largely depends on the thermodynamic properties of the gas circulating in the system.
The cooling cycles in these devices typically begin with the compression of the gas in a compressor. As compressed gas passes through a heat exchanger, it absorbs heat from within the cryocooler, thereby cooling everything inside. As this gas absorbs heat at a constant volume in the heat exchanger, its pressure increases. It expands in volume and its pressure decreases in the later part of the cycle. Finally, it returns to the compressor, which completes a closed cycle through the cycle, and cycles through the cycle again.
A cryocooler may sometimes be incorrectly referred to as a cryostat. There is a small but clear difference, however, between the two. A cryostat is used to maintain cryogenic temperatures already in place, usually passively such as with insulation. On the other hand, a cryocooler actively works to cool the environment to cryogenic temperatures rather than just maintaining the already existing environmental conditions. This difference can be thought of as similar to the difference between a thermos and a refrigerator.
There are many types of cryocoolers available with different benefits and features suitable for a wide variety of applications. Common types of cryocoolers include the Joule–Thomson cooler, Gifford–McMahon cooler, Stirling cooler, pulse tube refrigerator, and adiabatic degaussing refrigerator. While significantly less efficient than many other devices, Joule-Thomson cryocoolers offer advantages in terms of reliability and low levels of electrical and mechanical noise. Gifford-McMahon chillers, on the other hand, generate vibration due to a piston that pushes gas through the system. However, they offer flexibility to the user as they can be used in any orientation.
Typically, special consideration is given to choosing a cryocooler for use in space. In such applications, energy typically has to be used efficiently and repair is extremely expensive or even impossible, as with missions to other planets. Renowned for both reliability and efficiency, Stirling coolers are the first to be used successfully in space. With even greater reliability than Stirling coolers, pulse tube coolers are often chosen for space even though they are typically slightly less efficient. An adiabatic degaussing refrigerator can also be chosen due to its excellent efficiency and ability to operate in zero gravity environments.
There are many fields in which cryocoolers play a vital role. These include medical, automotive and aerospace applications, use in scientific research and military operations, and more. For example, cryogenic hardening of metal components can change their physical properties, increasing strength, hardness and wear resistance. Infrared sensors used in satellite surveillance and missile guidance, as well as atmospheric and other studies, typically require cryogenic cooling.
