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Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2023
Superconductors require cooling to cryogenic temperatures (T < 120 K) for all practical applications. Cryogenic fluids (cryogens) are commonly used for cooling superconductors in laboratory environments, but most practical applications require the use of closed-cycle refrigerators, of which smaller units are commonly referred to as cryocoolers. Cryogens may be used along with cryocoolers in some large-scale applications of superconductors to provide for the heat transfer between the superconductor and the cold tip of the cryocooler. Such hybrid systems also provide redundancy for higher reliability. Cryocoolers are required for a wide variety of applications, and the number of applications keeps expanding as improvements to cryocoolers are made. One of the earliest applications, and one that appeared about 60 years ago, was for cooling infrared sensors to about 80 K for night vision capability of the military. By 1998 over 125,000 Stirling cryocoolers for this tactical military application had been produced (Dunmire, 1998). Today the total number probably exceeds 400,000. Refrigeration powers vary from about 0.15 W to 1.75 W at 80 K. Recently, advances in infrared sensors designed for operation at higher temperatures have led to a surge of research and development efforts on miniature 150 K cryocoolers. Such temperatures are too high for current superconductors, but some of the miniature technology can be adapted for lower temperature applications.
Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Highway MC 338 tanks are used for the transportation of cryogenic gases, sometimes referred to as refrigerated liquids (Figure 3.95). These materials are very cold with boiling points of −130 for carbon dioxide to −452 for liquid helium. Common cryogenics include oxygen, nitrogen, helium, argon, and others. Many of the materials carried in 338 tanks are considered inert gases. That is to say, they do not readily react chemically to other materials, are not flammable and are nonpoisonous. They do, however, have significant hazards when released as a liquid or a gas. Liquids are extremely cold and can cause frostbite and solidification of anything it contacts including body parts. They have large expansion ratios, producing huge amounts of vapor from a small spill. In some cases, as little as 1 gallon of a cryogenic liquid can produce over 900 gallons of gas. Although these gases are inert in many cases, they can still displace the oxygen in the air and cause simple asphyxiation.
The Hydrogen Economy
Published in Michael Frank Hordeski, Alternative Fuels—The Future of Hydrogen, 2020
When hydrogen gas is liquefied, it needs to be cooled to −421.6° Fahrenheit, making liquid hydrogen a cryogenic fuel. Cryogenics is the study of low-temperature physics. A beaker of liquid hydrogen at room temperature will boil as if it was on a hot stove. If the beaker of liquid hydrogen is spilled on the floor, it is vaporized and dissipates in a few seconds. If liquid hydrogen is poured on the hand, it would feel cool to the touch as it slides through the fingers. This is due to the thermal barrier that is provided by the skin. But, place a finger in a vessel containing liquid hydrogen and severe injury will occur in seconds because of the extreme cold. This hydrogen fuel on board a vehicle would allow the use of a small, efficient fuel cell Stirling engine cryocooler system to provide air conditioning.
A review on sustainable alternatives for conventional cutting fluid applications for improved machinability
Published in Machining Science and Technology, 2023
D. J. Hiran Gabriel, M. Parthiban, I. Kantharaj, N. Beemkumar
The term cryogenics is associated with the study of the production of fluids at extremely low temperatures and the properties of those materials at that temperature. Gases are liquefied and used as a coolant during metal cutting. Such a cooling technique is referred to as cryogenic cooling. Potential liquid cryogens include nitrogen (N2), carbon dioxide (CO2), and helium (He). This cryogenic liquid, when introduced to the zone of metal cutting, evaporates quickly, creating a gaseous layer between the material to be machined and the cutting face of the tool. The gaseous layer generated as a result of the liquid’s evaporation works as a lubricant. Cryogenic machining is a relatively new technique in the machining process. This approach was used in a variety of machining techniques, such as turning, milling, and drilling. Cryogenic machining is often used on superalloys (such as titanium alloys, Inconel alloys, and tantalum alloys), ferrous metals, viscoelastic polymers, and elastomers. In general, desirable results have been obtained no matter what kind of workpiece materials were used (Dhananchezian and Kumar, 2011).
Deformation behavior at cryogenic temperature in extruded Mg–Al–Zn alloy
Published in Philosophical Magazine Letters, 2022
Hidetoshi Somekawa, Yukiko Ogawa, Yoshinori Ono, Alok Singh
Stress vs. strain curves in tension are shown in Figure 1, and mechanical properties are summarized in Table 1. Tensile behavior is influenced by grain size, regardless of testing temperature. At both temperatures, yield strength as well as ultimate tensile strength increase with grain refinement; however, elongation-to-failure in tension is unlikely to depend on the grain size. The elongation-to-failures at room-temperature are in between 15–20%. The meso-grained alloy exhibits the best ductility among the three alloys at 77 K. Figure 1 also shows that the testing temperature affects the tensile response. The properties of strength and ductility at cryogenic-temperature increase and decrease, respectively, with a lower testing temperature. With the comparison of mechanical properties between 296 K and 77 K, the magnitude of increase in yield strength is around 1.5 times, but the elongation-to-failure in tension shows almost half values, irrespective of grain size. It is interesting to note that the meso-grained alloy appears to show a large strain hardening behavior even at such a low temperature.
A Critical Review on Mechanical Heat Switches for Engineering and Space Applications
Published in Heat Transfer Engineering, 2022
Banka Raghu Ram, Vinit Malik, Bukke Kiran Naik, Kishore Singh Patel
The previously discussed categorization of MHS, GGHS, SCHS, and MRHS is based on their functioning. However, these heat switches can also be subclassified in several other ways. One of the major classifications is based on their operating temperature range. For example, the MHS can operate in both cryogenic temperature and normal/room temperature range. The classifications of MHS based on their operating range can be seen in Figure 1(a). As can be seen, temperature range-based classification starts from absolute zero (0 K) to 123 K for the low/cryogenic temperature range, and normal temperature ranges cover above 123 K [18]. The term cryogenics is derived from the Greek words "kryos" (frost) and "genics" (to produce). The term cryogenics means the production and behavior of the material at ultra-low temperatures. The temperature range-based classification helps identify the appropriate heat switches which can be operated in the chosen temperature range as different material shows their transition from gas to liquid and liquid to solid state at different temperatures.