Centrifuge 1

Centrifuge

A laboratory tabletop centrifuge.

A centrifuge is a piece of equipment, generally driven by an electric motor(some older models were spun by hand), that puts an object in rotation arounda fixed axis, applying a force perpendicular to the axis. The centrifuge worksusing the sedimentation principle, where the centripetal acceleration causesmore dense substances to separate out along the radial direction (the bottomof the tube). By the same token, lighter objects will tend to move to the top(of the tube; in the rotating picture, move to the centre).

In the picture shown, the rotating unit, called the rotor, has fixed holes drilledat an angle (to the vertical). Test tubes are placed in these slots and the rotoris spun. As the centrifugal force is in the horizontal plane and the tubes arefixed at an angle, the particles have to travel only a little distance before theyhit the wall and drop down to the bottom. These angle rotors are very popularin the lab for routine use.

TheoryProtocols for centrifugation typically specify the amount of acceleration to be applied to the sample, rather thanspecifying a rotational speed such as revolutions per minute. The acceleration is often quoted in multiples of g, thestandard acceleration due to gravity at the Earth's surface. This distinction is important because two rotors withdifferent 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 theangular velocity. Traditionally named "relative centrifugal force" (RCF), it is the measurement of the accelerationapplied to a sample within a centrifuge and it is measured in units of gravity (times gravity or × "g"). It is given by

whereis earth's gravitational acceleration,is the rotational radius,is the rotational 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 incentimetres (cm) the above relationship becomes

whereis the rotational radius measured in centimetres (cm),

is rotational speed measured in revolutions per minute (RPM).

Centrifuge 2

History and predecessors

A 19th-century hand cranked laboratory centrifuge.

English military engineer Benjamin Robins (1707–1751) inventeda whirling arm apparatus to determine drag. In 1864, AntoninPrandtl invented the first dairy centrifuge in order to separatecream from milk. In 1879, Gustaf de Laval demonstrated the firstcontinuous centrifugal separator, making its commercialapplication feasible.

Types

There are at least five types of centrifuge:• preparative centrifuge• analytical centrifuge• angle fixed centrifuge• swing head centrifuge• haematocrit centrifugeIndustrial centrifuges may otherwise be classified according to thetype of separation of the high density fraction from the low densityone :• 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 anaccelerated settling due to centrifugal acceleration. Common types are :• Solid bowl centrifuges• Conical plate centrifuges

Uses

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

Isotope separationOther centrifuges, the first being the Zippe-type centrifuge, separate isotopes, and these kinds of centrifuges are inuse in nuclear power and nuclear weapon programs.Gas centrifuges are used in uranium enrichment. The heavier isotope of uranium (uranium-238) in the uraniumhexafluoride gas tend to concentrate at the walls of the centrifuge as it spins, while the desired uranium-235 isotopeis extracted and concentrated with a scoop selectively placed inside the centrifuge. It takes many thousands ofcentrifuges to enrich uranium enough for use in a nuclear reactor (around 3.5% enrichment), and many thousandsmore to enrich it to weapons-grade (around 90% enrichment) for use in nuclear weapons.

Centrifuge 3

The 20 G centrifuge at the NASA Ames ResearchCenter

Aeronautics and astronautics

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

The US Air Force at Holloman Air Force Base, NM operates ahuman centrifuge. The centrifuge at Holloman AFB is operated bythe aerospace physiology department for the purpose of trainingand evaluating prospective fighter pilots for high-g flight in Air Force fighter aircraft.

The use of large centrifuges to simulate a feeling of gravity has been proposed for future long-duration spacemissions. Exposure to this simulated gravity would prevent or reduce the bone decalcification and muscle atrophythat affect individuals exposed to long periods of freefall. An example of this can be seen in the film 2001: A SpaceOdyssey.

Earthquake and blast simulationThe geotechnical centrifuge is used for simulating blasts and earthquake phenomena.[1] For a discussion of theirdesign, see Geotechnical Centrifuges by Philip Turner [2].

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 iscalled 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• Centrifuges are used to separate cream (remove fat) from milk.

Further readingNaesgaard et al., Modeling flow liquefaction, its mitigation, and comparison with centrifuge tests [3]

See also• Lamm equation• Sedimentation• Centrifugal force• Centrifugation• Gas centrifuge• Sedimentation coefficient• Clearing factor• Hydroextractor

Centrifuge 4

External links• RCF Calculator and Nomograph [4]

• RPI centrifuge video [5]

• Centrifugation Rotor Calculator [6]

• Selection of historical centrifuges [7] in the Virtual Laboratory of the Max Planck Institute for the History ofScience

References[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 (http:/ / books. google. com/ books?id=mzQlFBqJC1wC& pg=RA1-PA186& dq=centrifuge+ earthquake&lr=& as_brr=0& sig=ACfU3U1SZImDanYOwrq15Jre19qtAqpyJw#PRA1-PA135,M1). Taylor & Francis. p. 135. ISBN 0415415861. .

[2] http:/ / www-g. eng. cam. ac. uk/ 125/ achievements/ centrifuges/ index. htm[3] http:/ / www. civil. ubc. ca/ liquefaction/ Publications/ flow%20liq_Naesgaard%20et%20al%20version31. pdf[4] http:/ / www. djblabcare. co. uk/ djb/ info/ 6/ user_tools[5] http:/ / www. nees. rpi. edu/ nees/ video/[6] http:/ / www. changbioscience. com/ cell/ rcf. html[7] http:/ / vlp. mpiwg-berlin. mpg. de/ technology/ search?-max=10& -title=1& -op_varioid=numerical& varioid=3

Article Sources and Contributors 5

Article Sources and ContributorsCentrifuge  Source: http://en.wikipedia.org/w/index.php?oldid=358631080  Contributors: 16@r, Aeconley, Alansohn, Aranel, Ashan vpss, AstareGod, Bensaccount, Bjwebb, Bobblewik,Bobo192, Brettz9, Brews ohare, Cacycle, Callmejakee, Can't sleep, clown will eat me, CattleGirl, Cilliemalan, Ck.mitra, Clancy630, Commander Keane, Cyberman, DaGizza, Dancave,Dancraggs, Dger, Diezba, Dominic, Donreed, Dwmyers, Dúnadan, Edward, Eeekster, Eequor, ElePANTS, Eloy, Etxrge, Fastfission, For great justice., Foxtrotman, Frank, GDibyendu, GLaDOS,Gene Nygaard, Ginsengbomb, Gnowor, Goplat, Gunter, Gus, Hadal, Halldoro, Hmmm, Hophop121, IceKarma, Ike9898, Iridescent, Itub, J.delanoy, Jaganath, Jeffrey Mall, Jeganicecream,Jennavecia, JohnOwens, Jpgordon, Junglecat, Karl-Henner, Kevin Rector, Kierano, Kkmurray, KnowledgeOfSelf, Kuru, Lchiarav, Lilinyee, Llydawr, Lvzon, M1ss1ontomars2k4, Mani1, Mav,McSly, Menchi, Miaow Miaow, Michael Hardy, Mikko Paananen, Mipadi, Moeron, Mrchafe, Mudgineer, NeilFraser, Nigosh, Nonsequiturmine, Northrupr, Octahedron80, OlEnglish, Onco p53,Ozhiker, Ozmaweezer, Patrick, Peter, PeterBrooks, Pizza1512, Prashanthns, Psychofox, Rifleman 82, Roux, Saperaud, Seanherron, Shashankgajjar, Sir Vicious, Slawojarek, Squids and Chips,Sunshine3491, Superandoman2209, Sylwia Ufnalska, THEN WHO WAS PHONE?, Techman224, Temporaluser, TenOfAllTrades, The Anome, Thingg, Tide rolls, Timwi, Tristanb, UbUb, UserA1, Venturia, WLU, Wavelength, Whosyourjudas, Why Not A Duck, Wiki alf, Yorick, రవిచంద్ర, 203 anonymous edits

Image Sources, Licenses and ContributorsFile:Tabletop centrifuge.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Tabletop_centrifuge.jpg  License: GNU Free Documentation License  Contributors: User:Magnus ManskeFile:19thCentrifuge.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:19thCentrifuge.JPG  License: GNU Free Documentation License  Contributors: User:KieranoFile:20G centrifuge.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:20G_centrifuge.jpg  License: Public Domain  Contributors: NASA Original uploader was Dancraggs aten.wikipedia

LicenseCreative Commons Attribution-Share Alike 3.0 Unportedhttp:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/