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. Rotational motion can occur around more than one axis at once and can involve phenomena such as wobbling and Precession. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density. Sedimentation describes the motion of Molecules in Solutions or particles in suspensions in response to an external force such as gravity The centripetal force is the external force required to make a body follow a curved path 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. Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described

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. Rotational speed (sometimes called speed of revolution) indicates for example how fast a motor is running The acceleration is often quoted in multiples of g, the standard acceleration due to gravity at the Earth's surface. Gravitation is a natural Phenomenon by which objects with Mass attract one another 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. Remote Authentication Dial In User Service ( RADIUS) is a networking protocol that provides centralized access authorization and accounting management for people or computers Do not confuse with Angular frequency The unit for angular velocity is rad/s

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. Benjamin Robins (1707&ndash 29 July 1751) was an English scientist, mathematician, and Engineer. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a 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. Karl Gustaf Patrik de Laval ( May 9 1845 - February 2 1913) was a Swedish engineer and inventor who made important

Types and uses

There are basically four types of centrifuge:

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

Laboratory centrifuge

Main article: Laboratory centrifuge

Simple centrifuges are used in chemistry, biology, and biochemistry for isolating and separating suspensions. The ultracentrifuge is a Centrifuge optimized for spinning a rotor at very high speeds capable of generating acceleration as high as 1000000 g (9800 km/s² A laboratory centrifuge is a piece of Laboratory equipment, driven by a motor which spins liquid samples at high speed 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. The Zippe-type centrifuge is a device designed to collect Uranium-235. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion.

Gas centrifuges are used in uranium enrichment. A gas centrifuge is a separating machine specifically developed to separate Uranium-235 from Uranium-238. Enriched uranium is a kind of Uranium in which the percent composition of Uranium-235 has been increased through the process of Isotope separation. 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. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Uranium-238 (U-238 is the most common isotope of Uranium found in nature Uranium hexafluoride (UF6 referred to as "hex" in the nuclear industry is a compound used in the Uranium enrichment process that produces Uranium-235 is an isotope of uranium that differs from the element's other common isotope Uranium-238, by its ability to cause a rapidly expanding fission It takes many thousands of centrifuges to enrich uranium enough for use in a nuclear reactor (around 3. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled 5% enrichment), and many thousands more to enrich it to atomic bomb-grade (around 90% enrichment).

The 20 G centrifuge at the NASA Ames Research Center

Aeronautics and astronautics

Main article: high-G training

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. NASA Ames Research Center (ARC is a NASA facility located at Moffett Federal Airfield, which covers 43 acres at the borders of the cities of Mountain View High-G training is done by aviators and astronauts who are subject to high levels of acceleration ('G' An astronaut or cosmonaut (космона́вт) is a person trained Gravitation is a natural Phenomenon by which objects with Mass attract one another

The US Air Force at Holloman Air Force Base, NM operates a human centrifuge. Holloman Air Force Base is a United States Air Force base located six miles (10 km) southwest of the Central business district of Alamogordo 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. Aerospace physiology refers to effects on the Human body caused by characteristics of the Aerospace environment 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. Bone decalcification is the removal of Calcium ions from the bone through Histological process thereby making the bone flexible and easy for pathological investigation Muscle atrophy is defined as a decrease in the mass of the muscle it can be a partial or complete wasting away of muscle An example of this can be seen in the film 2001: A Space Odyssey. 2001 A Space Odyssey is a 1968 Science fiction film directed by Stanley Kubrick, written by Kubrick and Arthur C

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. Mission SPACE is a Motion simulator thrill ride at Epcot. It simulates what an Astronaut might experience aboard a spacecraft on a mission to Mars Epcot is a Theme park at the Walt Disney World Resort. The park is dedicated to international Culture and technological Innovation. Walt Disney World Resort is the most visited and largest recreational resort in the world containing four Theme parks two Water parks twenty-three themed hotels A motion simulator or motion platform is a mechanism that encapsulates riders and creates the effect/feelings of being in a moving object Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another
• In soil mechanics, centrifuges utilize centrifugal acceleration to match soil stresses in a scale model to those found in reality. Soil mechanics is a discipline that applies principles of Engineering mechanics, e
• Large industrial centrifuges are commonly used in water and wastewater treatment to dry sludges. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Distinguish from Wastwater (a lake in the Lake District in northwest England SLUDGE (Scripting Language for Unhindered Development of a Gaming Environment is a open source adventure game engine developed by Hungry Software 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. The petroleum industry includes the global processes of exploration, extraction, refining, transporting (often by Oil tankers and pipelines Drilling a very deep hole is a very costly business The hole size is kept very small as the drilled depth increases because it is to cased and cemented after wards
• 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.

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