A dewar is a type of cryostat named after Sir James Dewar, the researcher who first developed the concept of a vacuum insulated container with silvered walls to reflect thermal radiation. Dewar was the first to liquefy hydrogen, and he created the device to store his discovery. The thermos bottle …
Category: Defining Cryogenics
Stirling and Gifford-McMahon (GM) cryocoolers are two of the most commonly used cryocoolers in cryogenics. Both devices have a significant industrial base and operate at a wide range of temperatures and capacities. The thermodynamic cycles for both of these cryocoolers are quite similar. The Stirling cycle consists of a compressor, …
A significant commercial application of cryogenics is the liquefaction, transport and storage of natural gas. Liquefied Natural Gas (LNG) is generally 95 percent methane with a few percent ethane and much lower concentrations of propane and butane. LNG liquefies at 111.6 K. Unlike many applications of cryogenics, the motivation for …
Stability refers to the ability of a device employing superconductors to remain in its superconducting state after part of the superconductor transitions back to its normal conducting state due to a disturbance. While the concept can apply to many superconducting devices—transmission lines, generators, motors, etc.—it is most commonly considered in …
Cable-in-Conduit Conductors (CICC) are a common form of superconducting cable used in large-scale applications. There are several varieties of CICCs, but they all consist of many small, stabilized superconducting wires contained within a conduit through which a coolant (typically supercritical He II) flows. Figure 1 shows the cross section of …
A bayonet coupling is a demountable joint that allows for quick and easy connection and disconnection of cryogenic components, including transfer lines, cryostats, liquefiers and refrigerators. Bayonets provide a number of advantages, chief among them the ability to connect and disconnect the bayonets while components they connect are still at …
Space cryogenics is, somewhat obviously, the application of cryogenics to space exploration and science. The use of cryogenics in space optimizes the launching of vehicles, provides power and life support to spacecraft and is critical for many scientific observations.Space cryogenics has a number of challenges and has driven both pure …
The science of thermodynamics plays a major role in cryogenics. It underlies the various refrigeration cycles, from Carnot to Brayton (Cold Facts Vol. 32 No. 2) and Joule-Thomson, is a fundamental part of the definition of terms such as coefficient of performance (Cold Facts Vol. 31 No. 1) and even …
Cryogenic treatment is the process of cooling materials to cryogenic temperatures temporarily to improve their material properties at room temperature. This is distinct from cooling materials down to cryogenic temperatures to take advantage of phenomena such as superconductivity that only occur at cryogenic temperatures. Cryogenic treatment, sometimes also referred to …
Two-phase flows are those flows in which there is a mixture of two physical states (solid, liquid or vapor). In cryogenic applications, such flows are almost always a mixture of a cryogenic liquid along with its corresponding vapor. A mixture of liquid helium and helium vapor would be a typical …
A supercritical fluid is defined as a substance whose temperature and pressure exceed those of its critical point. Every pure substance has a critical point that is defined in thermodynamic space by a critical temperature and a corresponding critical pressure. For example, the critical point for helium has a critical …
The Brayton cycle is one of the many thermodynamic cycles used to generate cooling at cryogenic temperatures. Strictly speaking, when referring to cooling we should call this the reverse Brayton cycle as the original Brayton cycle describes the process of power generation or propulsion via a gas turbine. In many …
Most cryogenic refrigeration systems, both large scale systems and cryocoolers, use helium as a working fluid. There are a number of advantages to helium, not the least of which is that helium remains a fluid down to the lowest achievable temperatures. In order to freeze helium, pressures of over 20 …
Helium II (He II), the second liquid phase of the 4He isotope described in this column in Cold Facts Spring 2010 (http://2csa.us/he2), can be modeled as consisting of two interpenetrating fluids. One, the superfluid component, has zero viscosity and entropy and the other, the normal fluid component, has nonzero viscosity …
A vital technology in the refrigerators and liquefiers described in Cold Facts Volume 31 Number 3 is that of turboexpanders. These devices are rotating machines in which the process fluid (e.g., helium) does work against the turboexpander while moving from high pressure to a lower pressure and thus is cooled. …
Two of the most common terms used in cryogenics are “refrigerator” and “liquefier.” These terms describe similar and, as will be seen, in some cases identical components. A refrigerator provides cooling (that is, absorbs heat) at cryogenic temperatures. Refrigerators typically put a working fluid (such as helium) through one of …
Air separation is one of the largest, as well as earliest, industrial applications of cryogenics. In this process, cryogenic temperatures are used to separate air into its constituent gases: nitrogen (78.08%), oxygen (20.95%), argon (0.93%) and carbon dioxide (0.3%). Trace gases such as krypton, neon, xenon and helium total far …
The coefficient of performance (COP) is used to describe the effectiveness of refrigerators, including those operating at cryogenic temperatures. The COP is defined as the amount of heat removed at the cryogenic operating temperature of the refrigerator divided by the amount of work that must be applied to remove the …
Regenerators or regenerative heat exchangers are a key component of cryocoolers such as pulse tube cryocoolers (Cold Facts, August 2014). Regenerator performance greatly affects the coefficient of performance of cryocoolers. Improvements in regenerator design and, in particular, regenerator materials have been an important factor in the improvement of the performance …
The development of pulse tube cryocoolers has been a significant topic of research and development over the past 20 or so years. Pulse tube cryocoolers have a number of advantages over other types of cryocoolers and are now available commercially. In order to understand pulse tube cryocoolers, it’s best to …
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