centrifuge n : an apparatus that uses centrifugal force to separate particles from a suspension [syn: extractor, separator] v : rotate at very high speed in order to separate the liquids from the solids [syn: centrifugate]

English

Pronunciation

• a UK /ˈsɛntɹɪˌfjʊdʒ/ /"sEntrI%fjUdZ/

Noun

1. A device in which a mixture of denser and lighter materials (normally dispersed in a liquid) is separated by being spun about a central axis at high speed.
2. An apparatus in which humans are spun to simulate acceleration in an aircraft or spacecraft.

Derived terms

• gas centrifuge
• ultracentrifuge

Related terms

• centrifugal force

Translations

Verb

1. To rotate something in a centrifuge in order to separate its constituents

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 separate substances of greater and lesser density. There are many different kinds of centrifuges, including those for very specialised purposes. It can be used for viable counts, when shaking the culture e.g. yeast, out of suspension.

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.

The acceleration can be calculated as the product of the radius and the square of the angular velocity.

History and predecessors

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

Types and uses

There are basically four types of centrifuge:

• Tabletop/clinical/desktop centrifuge or microcentrifuge
• High-speed centrifuge
• Cooling centrifuge
• Ultracentrifuge

Laboratory centrifuge

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 atomic bomb-grade (around 90% enrichment).

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.

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.

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.
• 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.

Calculating relative centrifugal force (RCF)

Relative centrifugal force is the measurement of the force applied to a sample within a centrifuge. This can be calculated from the speed (RPM) and the rotational radius (cm) using the following calculation.

g = RCF = 0.00001118\,r \, N^2 \,

where

g = Relative centrifuge force

r = rotational radius (centimetres, cm)

N = rotating speed (revolutions per minute, r/min)

See also

• Centrifugation
• Gas centrifuge

External links

• RCF Calculator and Nomograph
• Centrifugation Rotor Calculator
• Selection of historical centrifuges in the Virtual Laboratory of the Max Planck Institute for the History of Science

analyzer, breaker, centrifugate, cutter, eddy, gurge, reel, separator, sieve, spin, stripper, surge, swirl, twirl, wheel, whirl, whirligig, whirlpool