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centrifuge

 
Dictionary: cen·tri·fuge   (sĕn'trə-fyūj') pronunciation
 
n.
  1. An apparatus consisting essentially of a compartment spun about a central axis to separate contained materials of different specific gravities, or to separate colloidal particles suspended in a liquid.
  2. An apparatus in which humans or animals are enclosed and which is revolved to simulate the effects of acceleration in a spacecraft.
tr.v., -fuged, -fug·ing, -fug·es.

To rotate (something) in a centrifuge or to separate, dehydrate, or test by means of this apparatus.

[French, centrifugal, from New Latin centrifugus. See centrifugal.]

centrifugation cen·trif'u·ga'tion (sĕn-trĭf'yə-gā'shən, -trĭf'ə-) n.
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A device in which solid or liquid particles of different densities are separated by rotating them in a tube in a horizontal circle. The denser particles tend to move along the length of the tube to a greater radius of rotation, displacing the lighter particles to the other end.



 
Food and Nutrition: centrifuge
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A machine that exerts a force many thousand times that of gravity, by spinning. Commonly used to clarify liquids by settling the heavier solids in a few minutes, a process that might take several days under gravity. Liquids of different density can also be separated by centrifugation, e.g. cream from milk.

 

Machine that applies a sustained centrifugal force. Effectively, the centrifuge substitutes a similar, stronger force for that of gravity. Every centrifuge contains a spinning vessel; there are many configurations, depending on use. A revolving object exerts a force away from the centre of rotation (see Newton's laws of motion), called the centrifugal force; it is usually stated as so many "times gravity" or so many "G," and may range from a few G for the basket in a home washing machine or an industrial separator to hundreds of thousands of G for centrifuges to separate isotopes of uranium or to purify vaccines.

For more information on centrifuge, visit Britannica.com.

 
Columbia Encyclopedia: centrifuge
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centrifuge (sĕn'trəfyūj) , device using centrifugal force to separate two or more substances of different density, e.g., two liquids or a liquid and a solid. The centrifuge consists of a fixed base or frame and a rotating part in which the mixture is placed and then spun at high speed. One type is used for the separation of the solid and the liquid parts of blood. Test tubes containing blood specimens are set in the rotating part in holders so arranged that when the rotary motion begins the test tubes swing into a slanted or a horizontal position with the open ends toward the axis of rotation; the heavier, solid part of the blood is thrown outward into the bottom of the tube and the lighter liquid part comes to the top. Another common type of centrifuge called the cream separator is used to separate cream from whole milk. Uranium-235, which is found in nature mixed with uranium-238, must be separated to be used to produce nuclear energy. The separation can be done by a centrifuging process in which the uranium, contained in gas molecules, is rotated at high speed in a chamber so that the more massive molecules containing uranium-238 concentrate near the outer edge of the chamber and the lighter molecules containing uranium-235 concentrate near the axis. Several stages of centrifuging are needed to effect the required degree of separation. The first successful centrifuge was built in 1883 by Carl G. P. de Laval, a Swedish engineer, whose design was used chiefly for cream separators. The ultracentrifuge, devised in the 1920s by the Swedish chemist Theodor Svedberg, found wide application in scientific research. Using an optical system with it to observe sedimentation rates, Svedberg determined accurately the molecular weights of substances including proteins and viruses. Centrifuges are also used for such diverse purposes as simulating gravitational fields in space and for drying laundry.


 
Wine Lover's Companion: centrifuge; centrifuging
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[SIHN-truh-fyooj] A high-speed, rotating apparatus that separates substances of varying densities through centrifugal force. Centrifuging is used in winemaking to remove yeast cells from a wine before it completes the fermentation process. It's also used instead of other processes (such as filtering) to remove particles from wine.

 
Veterinary Dictionary: centrifuge
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1. to rotate, in a suitable container, at extremely high speed, to cause the deposition of solids in solution.
2. a laboratory device for subjecting substances in solution to relative centrifugal force up to 25,000 times gravity. See also cytocentrifuge.

 
Wikipedia: Centrifuge
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A laboratory tabletop centrifuge

A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to evenly distribute substances (usually present in a solution for small scale applications) of greater and lesser density. There are many different kinds of centrifuges, including those for very specialized purposes. It can be used for viable counts, when shaking the culture e.g. yeast, out of suspension.

Contents

Theory

Protocols for centrifugation typically specify the amount of acceleration to be applied to the sample, rather than specifying a rotational speed such as revolutions per minute. The acceleration is often quoted in multiples of g, the standard acceleration due to gravity at the Earth's surface. This distinction is important because two rotors with different diameters running at the same rotational speed will subject samples to different accelerations.

Since the motion is circular the acceleration can be calculated as the product of the radius and the square of the angular velocity. Traditionally named "Relative centrifugal force" (RCF), it is the measurement of the acceleration applied to a sample within a centrifuge and it is measured in units of gravity (times gravity or × "g"). It is given by

 \mathrm{RCF} =  r\, (2\pi N)^2/g \,

where

\textstyle g is earth's gravitational acceleration,
\textstyle r is the rotational radius,
\textstyle N is the rotating speed, measured in revolutions per unit of time.

When the rotational speed is given in revolutions per minute (RPM) and the rotational radius is expressed in centimetres (cm) the above relationship becomes

 \mathrm{RCF} = 1.118\, \times 10^{-5}\, r_\mathrm{cm} \, N_\mathrm{RPM}^2 \,

where

\textstyle r_\mathrm{cm} is the rotational radius measured in centimetres (cm),
\textstyle N_\mathrm{RPM} is rotating speed measured in revolutions per minute (RPM).

History and predecessors

A 19th century hand cranked laboratory centrifuge.

English military engineer Benjamin Robins (1707-1751) invented a whirling arm apparatus to determine drag. In 1864, Antonin Prandtl invented the first dairy centrifuge in order to separate cream from milk. In 1879, Gustaf de Laval demonstrated the first continuous centrifugal separator, making its commercial application feasible.

Types

There are at least five types of centrifuge:

  • preparative centrifuge
  • analytical centrifuge
  • angle fixed centrifuge
  • swing head centrifuge
  • haemacrotic centrifuge

Industrial centrifuges may otherwise be classified according to the type of separation of the high density fraction from the low density one :

  • Screen centrifuges, where the centrifugal acceleration allows the liquid to pass through a screen of some sort, through which the solids cannot go (due to granulometry larger than the screen gap or due to agglomeration). Common types are :
    • Pusher centrifuges
    • Peeler centrifuges
  • Decanter centrifuges, in which there is no physical separation between the solid and liquid phase, rather an accelerated settling due to centrifugal acceleration. Common types are :
    • Solid bowl centrifuges
    • Conical plate centrifuges

Uses

Isolating suspensions

Simple centrifuges are used in chemistry, biology, and biochemistry for isolating and separating suspensions. They vary widely in speed and capacity. They usually comprise a rotor containing two, four, six, or many more numbered wells within which the samples containing centrifuge tips may be placed.

Isotope separation

Other centrifuges, the first being the Zippe-type centrifuge, separate isotopes, and these kinds of centrifuges are in use in nuclear power and nuclear weapon programs.

Gas centrifuges are used in uranium enrichment. The heavier isotope of uranium (uranium-238) in the uranium hexafluoride gas tend to concentrate at the walls of the centrifuge as it spins, while the desired uranium-235 isotope is extracted and concentrated with a scoop selectively placed inside the centrifuge. It takes many thousands of centrifuges to enrich uranium enough for use in a nuclear reactor (around 3.5% enrichment), and many thousands more to enrich it to weapons-grade (around 90% enrichment) for use in nuclear weapons.

The 20 G centrifuge at the NASA Ames Research Center

Aeronautics and astronautics

Human centrifuges are exceptionally large centrifuges that test the reactions and tolerance of pilots and astronauts to acceleration above those experienced in the Earth's gravity.

The US Air Force at Holloman Air Force Base, NM operates a human centrifuge. The centrifuge at Holloman AFB is operated by the aerospace physiology department for the purpose of training and evaluating prospective fighter pilots for high-g flight in Air Force fighter aircraft. It is important to note that the centrifuge at Holloman AFB is unrealistic in that it is far more difficult for a pilot to tolerate the high-g environment in the centrifuge than in a real fighter aircraft. This well-known fact is based on countless accounts from experienced operational fighter pilots.[citation needed]

The use of large centrifuges to simulate a feeling of gravity has been proposed for future long-duration space missions. Exposure to this simulated gravity would prevent or reduce the bone decalcification and muscle atrophy that affect individuals exposed to long periods of freefall. An example of this can be seen in the film 2001: A Space Odyssey, while the James Bond film Moonraker shows an astronaut-training centrifuge in action on earth (albeit sabotaged with murderous intent).

Earthquake and blast simulation

The geotechnical centrifuge is used for simulating blasts and earthquake phenomena.[1] For a discussion of their design, see Geotechnical Centrifuges by Philip Turner.

Commercial applications

  • Standalone centrifuges for drying (hand-washed) clothes - usually with a water outlet.
  • Centrifuges are used in the attraction Mission: SPACE, located at Epcot in Walt Disney World, which propels riders using a combination of a centrifuge and a motion simulator to simulate the feeling of going into space.
  • In soil mechanics, centrifuges utilize centrifugal acceleration to match soil stresses in a scale model to those found in reality.
  • Large industrial centrifuges are commonly used in water and wastewater treatment to dry sludges. The resulting dry product is often termed cake, and the water leaving a centrifuge after most of the solids have been removed is called centrate.
  • Large industrial centrifuges are also used in the oil industry to remove solids from the drilling fluid.
  • Disc-stack centrifuges used by some companies in Oil Sands industry to separate small amounts of water and solids from bitumen before it's sent to Upgrading.

References and notes

  1. ^ C. W. W. Ng, Y. H. Wang, L. M. Zhang (2006). Physical Modelling in Geotechnics: proceedings of the Sixth International Conference on Physical Modelling in Geotechnics. Taylor & Francis. p. 135. ISBN 0415415861. http://books.google.com/books?id=mzQlFBqJC1wC&pg=RA1-PA186&dq=centrifuge+earthquake&lr=&as_brr=0&sig=ACfU3U1SZImDanYOwrq15Jre19qtAqpyJw#PRA1-PA135,M1. 

Further reading

Naesgaard et al., Modeling flow liquefaction, its mitigation, and comparison with centrifuge tests

See also

External links

Look up centrifuge in Wiktionary, the free dictionary.

 
Translations: Centrifuge
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Dansk (Danish)
n. - centrifuge
v. tr. - centrifugere

Nederlands (Dutch)
centrifugeren, centrifuge

Français (French)
n. - centrifugeuse
v. tr. - centrifuger

Deutsch (German)
n. - Zentrifuge
v. - zentrifugieren, schleudern

Ελληνική (Greek)
n. - (μηχαν.) φυγοκεντρωτής
v. - διαχωρίζω με φυγοκέντριση

Italiano (Italian)
centrifugare

Português (Portuguese)
n. - centrífuga (f)
v. - centrifugar

Русский (Russian)
вращать в центрифуге

Español (Spanish)
n. - centrífuga
v. tr. - centrifugar

Svenska (Swedish)
n. - centrifug
v. - centrifugera

中文(简体)(Chinese (Simplified))
离心分离机, 使受离心作用, 使在离心机内旋转, 用离心机分离

中文(繁體)(Chinese (Traditional))
n. - 離心分離機
v. tr. - 使受離心作用, 使在離心機內旋轉, 用離心機分離

한국어 (Korean)
n. - 원심분리기
v. tr. - 원심 분리하다

日本語 (Japanese)
n. - 遠心機, 遠心分離機
v. - 遠心力を作用させる, 遠心分離機にかける

العربيه (Arabic)
‏(الاسم) جهاز طرد مركزي (فعل) طرد بعيدا عن المركز‏

עברית (Hebrew)
n. - ‮מפרדה, צנטריפוגה‬
v. tr. - ‮הפריד באמצעות מפרדה, הפעיל את המפרדה על‬


 
 

 

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Chemistry Dictionary. A Dictionary of Chemistry. Sixth Edition. Copyright © Market House Books Ltd, 2008. All rights reserved.  Read more
Food and Nutrition. A Dictionary of Food and Nutrition. Copyright © 1995, 2003, 2005 by A. E. Bender and D. A. Bender. All rights reserved.  Read more
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Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/  Read more
Wine Lover's Companion. Wine Lover's Companion. Copyright © 2003 by Barron's Educational Series, Inc. All rights reserved.  Read more
Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Centrifuge" Read more
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