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Absolute zero is the lowest limit of the thermodynamic temperature scale; a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value. The fundamental particles of nature have minimum vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as 0 kelvin, which is −273.15 degrees on the Celsius scale, and equals −459.67 degrees on the Fahrenheit scale. The Kelvin and Rankine temperature scales set their zero points at absolute zero by definition.
In physics, cryogenics is the production and behaviour of materials at very low temperatures.
Superfluid helium-4 is the superfluid form of helium-4, an isotope of the element helium. A superfluid is a state of matter in which matter behaves like a fluid with zero viscosity. The substance, which resembles other liquids such as helium I, flows without friction past any surface, which allows it to continue to circulate over obstructions and through pores in containers which hold it, subject only to its own inertia.
Thermodynamic temperature is a quantity defined in thermodynamics as distinct from kinetic theory or statistical mechanics.
The following is a timeline of low-temperature technology and cryogenic technology. It also lists important milestones in thermometry, thermodynamics, statistical physics and calorimetry, that were crucial in development of low temperature systems.
Heike Kamerlingh Onnes was a Dutch physicist. He exploited the Hampson–Linde cycle to investigate how materials behave when cooled to nearly absolute zero and later to liquefy helium for the first time, in 1908, which earned him the Nobel Prize in Physics in 1913. He also discovered superconductivity in 1911.
In thermodynamics, the Joule–Thomson effect describes the temperature change of a real gas or liquid when it is expanding; typically caused by the pressure loss from flow through a valve or porous plug while keeping it insulated so that no heat is exchanged with the environment. This procedure is called a throttling process or Joule–Thomson process. The effect is purely an effect due to deviation from ideality, as any ideal gas has no JT effect.
A cryopump or a "cryogenic pump" is a vacuum pump that traps gases and vapours by condensing them on a cold surface, but are only effective on some gases. The effectiveness depends on the freezing and boiling points of the gas relative to the cryopump's temperature. They are sometimes used to block particular contaminants, for example in front of a diffusion pump to trap backstreaming oil, or in front of a McLeod gauge to keep out water. In this function, they are called a cryotrap, waterpump or cold trap, even though the physical mechanism is the same as for a cryopump.
The lowest natural temperature ever directly recorded at ground level on Earth is −89.2 °C at the then-Soviet Vostok Station in Antarctica on 21 July 1983 by ground measurements.
Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity.
A 3He/4He dilution refrigerator is a cryogenic device that provides continuous cooling to temperatures as low as 2 mK, with no moving parts in the low-temperature region. The cooling power is provided by the heat of mixing of the helium-3 and helium-4 isotopes.
A refrigerator designed to reach cryogenic temperatures is often called a cryocooler. The term is most often used for smaller systems, typically table-top size, with input powers less than about 20 kW. Some can have input powers as low as 2–3 W. Large systems, such as those used for cooling the superconducting magnets in particle accelerators are more often called cryogenic refrigerators. Their input powers can be as high as 1 MW. In most cases cryocoolers use a cryogenic fluid as the working substance and employ moving parts to cycle the fluid around a thermodynamic cycle. The fluid is typically compressed at room temperature, precooled in a heat exchanger, then expanded at some low temperature. The returning low-pressure fluid passes through the heat exchanger to precool the high-pressure fluid before entering the compressor intake. The cycle is then repeated.
A cryostat is a device used to maintain low cryogenic temperatures of samples or devices mounted within the cryostat. Low temperatures may be maintained within a cryostat by using various refrigeration methods, most commonly using cryogenic fluid bath such as liquid helium. Hence it is usually assembled into a vessel, similar in construction to a vacuum flask or Dewar. Cryostats have numerous applications within science, engineering, and medicine.
The International Temperature Scale of 1990 (ITS-90) is an equipment calibration standard specified by the International Committee of Weights and Measures (CIPM) for making measurements on the Kelvin and Celsius temperature scales. It is an approximation of thermodynamic temperature that facilitates the comparability and compatibility of temperature measurements internationally. It defines fourteen calibration points ranging from 0.65 K to 1357.77 K and is subdivided into multiple temperature ranges which overlap in some instances. ITS-90 is the most recent of a series of International Temperature Scales adopted by the CIPM since 1927. Adopted at the 1989 General Conference on Weights and Measures, it supersedes the International Practical Temperature Scale of 1968 and the 1976 "Provisional 0.5 K to 30 K Temperature Scale". The CCT has also published several online guidebooks to aid realisations of the ITS-90. The lowest temperature covered by the ITS-90 is 0.65 K. In 2000, the temperature scale was extended further, to 0.9 mK, by the adoption of a supplemental scale, known as the Provisional Low Temperature Scale of 2000 (PLTS-2000).
A 1-K pot is a cryogenic device used to attain temperatures down to approximately 1 kelvin.
Cryochemistry is the study of chemical interactions at temperatures below −150 °C. It is derived from the Greek word cryos, meaning 'cold'. It overlaps with many other sciences, including chemistry, cryobiology, condensed matter physics, and even astrochemistry.
The pulse tube refrigerator (PTR) or pulse tube cryocooler is a developing technology that emerged largely in the early 1980s with a series of other innovations in the broader field of thermoacoustics. In contrast with other cryocoolers, this cryocooler can be made without moving parts in the low temperature part of the device, making the cooler suitable for a wide variety of applications.
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making up a substance.
Scale of temperature is a methodology of calibrating the physical quantity temperature in metrology. Empirical scales measure temperature in relation to convenient and stable parameters or reference points, such as the freezing and boiling point of water. Absolute temperature is based on thermodynamic principles: using the lowest possible temperature as the zero point, and selecting a convenient incremental unit.
Howard Oldford McMahon (1914–1990) was an American electrical engineer who was Science Director, Vice President, Head of the Research and Development Division, and then President of Arthur D. Little, Inc, of Cambridge, Massachusetts, retiring from the Company in 1977. He was born in Alberta, Canada, and became a naturalized citizen of the United States. He made contributions to the field of cryogenics as inventor during the 1940s through the 1960s, and subsequently as an executive and member of the Board of Directors of both ADL and the Helix Technology Corporation, of Waltham, Massachusetts.
References
- Berman, A.; Zemansky, M. W.; and Boorse, H. A.; Normal and Superconducting Heat Capacities of Lanthanum , Physical Review, Vol. 109, No. 1 (January 1958), pp. 70–76. Quote:
- "The 1955 Leiden scale13 was used to convert helium vapor pressures into temperatures [...] (13) H. van Dijk and M. Durieux, in Progress in Low Temperature Physics II, edited by C. J. Gorter (North-Holland Publishing Company, Amsterdam, 1957), p. 461. In the region of calibration the 1955 Leiden scale, TL55, differs from the Clement scale, T55E, by less than 0.004 deg." (emphasis added)
- Grebenkemper, C. J.; and Hagen, John P.; The Dielectric Constant of Liquid Helium , Physical Review, Vol. 80, No. 1 (October 1950), pp. 89–89. Quote:
- "The temperature scale used was the 1937 Leiden scale." (emphasis added)
- Awbery, J. H.; Heat [ permanent dead link ], Rep. Prog. Phys. 1934, No. 1, pp. 161–197 doi : 10.1088/0034-4885/1/1/308. Quote:
- "It should be mentioned that below −183 °C, the Leiden workers do not entirely agree with some of the other cryogenic laboratories, but use a scale of their own, generally known as the Leiden scale." (emphasis added)
- H. van Dijk, M. Durieux.; The Temperature Scale in the Liquid Helium Region, Progress in Low Temperature Physics. - 1957. - Vol. 2. — P. 431–464.
- Hubbard, Joanna; Are icebergs made of salt water or fresh water? Archived at the Wayback Machine (07-16-2011)
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