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Centrifuge

Centrifuge

Gravity can eventually separate a sediment (material that settles to the bottom of a liquid) from a liquid or separate two liquids which do not mix. The heavier element within a container sinks to the bottom, while the lighter element rises to the surface. This process is very slow if left up to nature alone. It can also be wasteful, as evidenced by the way farmers used to separate cream from milk. They would let whole milk stand for several hours until the lighter cream rose to the top. They then skimmed off the cream with a wooden spoon, but as much as 40 percent of the cream was left in the milk. Later, small strainer dishes were used to extract the cream, yet this too was a slow process.

In 1877 Swedish inventor Carl Gustaf Patrik de Laval introduced a high-speed centrifugal cream separator. Milk was placed in a chamber where it was heated. Once heated, it was sent through tubes to a container that was spun at 4,000 revolutions per minute by a steam engine. The centrifugal (moving away from the center) force separated the lighter cream, causing it to settle in the center of the container. The heavier milk was pushed to the outer part and forced up a discharge pipe. Thus, only the cream was left in the container. Several years later an improved cream separator was introduced with the capability for self-skimming and self-emptying. This type of separator can be used for other purposes and can extract impurities from lubricating oils, beer and wine, and other substances.

Spin Dryers

Other types of centrifuges were created in which spin dryers were used for filtering solids. In these dryers, a perforated (full of holes) drum is spun, driving any separated liquids to the outside where they were collected. Spin dryers can now develop accelerations of up to 2,000 times the force of gravity. They are used in the food, chemical, and mineral industries to separate water from all sorts of solids. Other centrifuges remove blood serum (plasma) from the heavier blood cells.

Scientists needed faster rotations for separating smaller particles. Particles, like DNA (deoxyribonucleic acid), proteins, and viruses are too small to settle out with normal gravity. The banging of water molecules is enough to keep the particles from separating. The key to separating smaller particles was to build an ultracentrifuge. A centrifuge that could spin fast enough to cause these small particles to settle out. In 1923 the Swedish chemist Theodor Svedberg developed a device that could spin fast enough to create gravity over 100,000 times normal. It could take small samples in glass containers, balance them on a cushion of air, and send jets of compressed air that touched the outer surface. By 1936 Svedberg had produced an ultracentrifuge that spun at 120,000 times per minute and created a centrifugal force equal to 525,000 times that of normal gravity. Newer models can accelerate samples to 2,000,000 times the force of gravity.

The ultracentrifuge enabled biologists, biochemists, physicians, and other life scientists to examine viruses, cell nuclei, small parts within cells, and individual protein and nucleic acid molecules. These new tools helped make the genetic engineering field ripe with possibility.

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Centrifuge

Centrifuge

A centrifuge is a device that uses centrifugal force to separate two or more substances of different density or mass from each other. Centrifugal force is the tendency of an object traveling around a central point to fly away from that point in a straight line. A centrifuge is able to separate different substances from each other because materials with heavier masses move faster and farther away from the central point than materials with lighter masses. The first successful centrifuge was invented in 1883 by Swiss engineer Carl de Laval.

A centrifuge consists of a fixed base and center stem to which arms or holders containing hollow tubes are attached. When the device is turned on, the arms spin around the center stem at a high rate of speed. In the process, the heavier material is thrown outward within the tube while the lighter material stays near the center of the device.

Applications of the centrifuge

Large-scale centrifugation has found a great variety of commercial and industrial uses. For example, the separation of cream from whole milk has been accomplished by this process for more than a century. Today, the food, chemical, and mineral industries use centrifuges to separate water from all sorts of solids. Medical laboratories use centrifuges to separate plasma from heavier blood cells.

Modern centrifuges can even separate mixtures of different sized molecules or microscopic particles such as parts of cells. These instruments, called ultracentrifuges, spin so fast that the centrifugal force created can be more than one-half million times greater than the force of gravity.

Centrifuge studies have been very important in the development of manned space flight programs. Human volunteers are placed into very large centrifuges and then spun at high speeds. Inside the centrifuge, humans feel intense gravitational forces (g forces) similar to those that occur during the launch of space vehicles. Such experiments help space scientists understand the limits of acceleration that humans can endure in such situations.

[See also Gravity and gravitation ]

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centrifuge

centrifuge (sĕn´trəfyōōj), 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.

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centrifuge

cen·tri·fuge / ˈsentrəˌfyoōj/ • n. a machine with a rapidly rotating container that applies centrifugal force to its contents, typically to separate fluids of different densities (e.g., cream from milk) or liquids from solids. • v. [tr.] (usu. be centrifuged) subject to the action of a centrifuge. ∎  separate by centrifuge: the black liquid is centrifuged into oil and water. DERIVATIVES: cen·trif·u·ga·tion / ˌsentrəˌfyoŏˈgāshən; senˌtrif(y)ə-/ n.

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centrifuge

centrifuge Rotating device used for separating substances. In laboratories, centrifuges separate particles from suspensions, and red blood cells from plasma. In the food industry, centrifuges separate cream from milk and sugar from syrup. In each case, the denser substance is forced to the outside of a rotating container. A spin dryer uses the same principle to remove water from clothes.

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centrifuge

centrifuge An apparatus used for the separation of substances by the application of centrifugal force: this is generated by high-speed rotation of a vessel containing tubes filled with a fluid in which the substances are suspended but not dissolved. Separation occurs because different substances have different rates of sedimentation according to their molecular size and shape.

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centrifuge

centrifuge An apparatus that is used for the separation of substances by the application of centrifugal force: this is generated by high-speed rotation of a vessel containing a fluid in which the substances are suspended but not dissolved. Separation occurs because different substances have different rates of sedimentation according to their molecular size and shape.

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centrifuge

centrifuge 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.

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centrifuge

centrifuge 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.

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centrifuge

centrifuge (sen-tri-fewj) n. a device for separating components of different densities in a liquid, using centrifugal force. The liquid is placed in special containers that are spun at high speed around a central axis.

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centrifuge

centrifugehuge, kludge, luge, scrooge, smoodge, stooge •refuge • centrifuge • subterfuge

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Centrifuge

Centrifuge

Types of centrifuges

Rotating centrifuges

Centrifuge studies in the space sciences

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A centrifuge is a device for separating two or more substances by using centrifugal forcethe tendency of an object traveling around a central point to continue in a linear motion away from that central point.

Centrifugation can be used to separate substances because materials with different masses experience different centrifugal forces when traveling at the same velocity and distance from a common center. For example, if two balls of different mass are attached to strings and swung around a common point at the same velocity, the ball with the greater mass will experience a greater centrifugal force. If the two strings are cut simultaneously, the heavier ball will fly farther from the common center than the lighter one.

Centrifuges increase the effects of Earths gravitational pull. For example, if a spoonful of clay is mixed vigorously with a cup of water and then allowed to sit for a period of time, the clay will eventually settle out because it experiences a greater gravitational pull than does the water. If the same mixture is centrifuged, however, the separation will take place much more quickly.

Types of centrifuges

Centrifuges can be subdivided into two major categories, stationary and rotating. Both types work by setting a collection of particles of different mass into motion around a common center. The faster these particles move, the greater the difference with

which they tend to escape from their common center, and the more easily they will be separated from each other.

In a stationary centrifuge, a fluid (a gas or liquid) consisting of two or more components is sprayed into a cylindrical or conical chamber at a high rate of speed. As the fluid travels around the inside of the chamber, it separates into its components, with the heavier substance(s) traveling to the outside of the container, and the lighter substance(s) remaining closer to the center of the cylinder.

Stationary centrifuges are used to separate uranium isotopes. Naturally occurring uranium consists of a mixture of uranium-235, which will undergo fission, and uranium-238, which will not. A uranium sample is first converted into the gaseous compound uranium hexafluoride and then injected into a stationary centrifuge. As the rapidly moving stream of uranium hexafluoride travels around inside the centrifuge, it begins to separate. The heavier uranium uranium-235-hexafluoride concentrates along the outer wall of the centrifuge, while the lighter uranium-238-hexafluoride is left toward the center of the stream. The heavier isotope can then be drawn out of the centrifuge, leaving behind a sample of uranium hexafluoride slightly richer in the desired uranium-235 isotope. This sample can then be recentrifuged and made still richer in the lighter isotope.

Rotating centrifuges

Rotating centrifuges are familiar to most beginning chemistry students. The fluid to be separated is introduced into a container, which is then set into rapid rotational motion. It is commonly used as a substitute for filtration in the separation of a solid precipitate from the liquid in which it is suspended.

In this kind of machine, hollow tubes about 2 in (5 cm) long are attached to arms radiating from the center of the machine. When the machine is turned on, the arms are spun around the center at a speed of about 30,000 revolutions per minute (rpm). The gravitational force experienced by materials inside the tubesabout 25,000 times that of gravityseparates materials much more efficiently than a conventional filtration system.

Laboratory centrifuges are invaluable tools in many kinds of scientific research. For example, a widely used method of studying cells is to break apart a tissue sample and centrifuge the resulting fluid. In this way, the discrete components of the cell can be separated and identified.

Applications of the rotating centrifuge

The basic centrifuge design described above can be adapted for use in many different settings. Industrial centrifuges, for example, tend to be quite large, ranging in size from 4 in to 4 ft (10 cm to 1.2 m) in diameter, with rotational velocities from 1,000 to 15,000 rpm. They can be designed to remove separated portions continuously, all at once after the machine has been stopped, or intermittently.

Large-scale centrifugation has found a great variety of commercial and industrial uses. Cream has been separated from milk by this process for well over a hundred years. Centrifuges are also used to remove water from oil and jet fuel, and to purify water by removing solid materials from waste water.

A centrifuge for use with very small particles of similar weight was first developed by the Swedish

KEY TERMS

Centrifugal force The tendency of an object traveling in a circle around a central point to escape from the center in a straight line.

Gravitation The pull of Earths mass on an object.

Revolutions per minute (rpm) The number of times per minute an object travels around a central point.

Rotation The spinning of an object on its axis.

chemist Theodor Svedberg in 1923. The ultracentrifuge uses containers no more than about 0.2 in (0.6 cm) in diameter that rotate at speeds of about 230,000 rpm to separate colloidal particles not much larger than the size of molecules.

Centrifuge studies in the space sciences

Centrifuge studies have been very important in the development of manned space flight. Human volunteers are placed into very large centrifuges and then spun at high velocities, creating the high gravitational velocities that correspond to high gravitational forces (g forces) that occur during the launch of space vehicles. Such experiments help scientists understand the limits of acceleration that humans can endure.

See also Gravity and gravitation.

Resources

BOOKS

Dufour, John W., and W. Ed Nelson. Centrifugal Pump Sourcebook. New York: McGraw-Hill, 1992.

Lobanoff, Val S., and Robert R. Ross. Centrifugal Pumps. 2nd edition. Houston: Gulf Publications, 1992.

OTHER

Gustavus Adolphus University. Cell Biology Laboratory Manual, Appendix F: Centrifugation. <http://homepages.gac.edu/~cellab/appds/appd-f.html> (accessed October 7, 2006).

David E. Newton

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Centrifuge

Centrifuge

A centrifuge is a device for separating two or more substances from each other by using centrifugal force . Centrifugal force is the tendency of an object traveling around a central point to continue in a linear motion and fly away from that central point.

Centrifugation can be used to separate substances from each other becausematerials with different masses experience different centrifugal forces when traveling at the same velocityand at the same distance from the common center. For example, if two balls of different mass are attached to strings and swung around a common point at the same velocity , the ball with the greater mass will experience a greater centrifugal force. If the two strings are cut simultaneously, the heavier ball will tend to fly farther from the common center than will the lighter ball.

Centrifuges can be considered devices for increasing the effects of the earth's gravitational pull. For example, if a spoonful of clay is mixed vigorously with a cup of water and then allowed to sit for a period of time, the clay will eventually settle out because it experiences a greater gravitational pull than does the water. If the same clay-water mixture is centrifuged, however, the separation will take place much more quickly.


Types of centrifuges

Centrifuges can be sub-divided into two major categories, stationary devices and rotating devices. Both types of centrifuge work on a common principle, however. A collection of particles of different mass is set into motion around a common center. The faster these particles move, the greater will be the difference with which they tend to escape from their common center, and the more easily they will be separated from each other.

In a stationary centrifuge, a fluid (a gas or liquid) consisting of two or more components is sprayed into a cylindrical or conical chamber at a high rate of speed. As the fluid travels around the inside of the chamber, it separates into its components, the heavier substance(s) traveling to the outside of the container, and the lighter substance(s) remaining closer to the center of the cylinder.

One application of the stationary centrifuge is in the separation of the isotopes of uranium isotope from each other. Naturally occurring uranium consists of a mixture of uranium-235, which will undergo fission, and uranium-238, which will not. A sample of uranium is first converted into the gaseous compound uranium hexafluoride and then injected into a stationary centrifuge. As the rapidly moving stream of uranium hexafluoride travels around inside the centrifuge, it begins to separate into two parts. The heavier uranium uranium-235-hexafluoride concentrates along the outer wall of the centrifuge, while the lighter uranium-238-hexafluoride is left toward the center of the stream. The heavier isotope can then be drawn out of the centrifuge, leaving behind a sample of uranium hexafluoride slightly richer in the desired uranium-235 isotope. This sample can then be re-centrifuged and made still richer in the lighter isotope.



Rotating centrifuges

Another type of centrifuge is one in which the fluid to be separated is introduced into a container, and the container is then set into rapid rotational motion. Most beginning chemistry students are familiar with this instrument. It is commonly used as a substitute for filtration in the separation of a solid precipitate from the liquid in which it is suspended.

In this kind of machine, hollow tubes about 2 in (5 cm) in length are attached to arms radiating from the center of the machine. When the machine is turned on, the arms are spun around the center at a speed of about 30,000 revolutions per minute. The gravitational force experienced by materials inside the tubes-about 25,000 times that of gravity-causes the separation of materials much more efficiently than would a conventional filtration system.

Laboratory centrifuges have become invaluable tools in many kinds of scientific research. For example, today a widely used method of studying cells is to break apart a tissue sample and then centrifuge the resulting fluid. In this way, the discrete components of the cell can be separated and identified.


Applications of the rotating centrifuge

The basic centrifuge design described above can be adapted for use in many different settings. Industrial centrifuges, for example, tend to be quite large, ranging in size from 4 in to 4 ft (10 cm to 1.2 m) in diameter, with rotational velocities from 1,000 to 15,000 revolutions per minute. They can be designed so as to remove separated portions continuously, all at once after the machine has been stopped, or intermittently.

Large-scale centrifugation has found a great variety of commercial and industrial uses. For example, the separation of cream from milk has been accomplished by this process for well over a hundred years. Today, centrifuges are used to remove water from oil and from jet fuel and in the removal of solid materials from waste water during the process of water purification.

A centrifuge for use with very small particles of similar weight—the ultracentrifuge—was first developed by the Swedish chemist Theodor Svedberg in about 1923. In the ultracentrifuge , containers no more than about 0.2 in (0.6 cm) in diameter are set into rotation at speeds of about 230,000 revolutions per minute. In this device, colloidal particles, not much larger than the size of molecules, can be separated from each other.


Centrifuge studies in the space sciences

Centrifuge studies have been very important in the development of manned space flight programs. Human volunteers are placed into very large centrifuges and then spun at high velocities. Inside the centrifuge, humans feel high gravitational velocities that correspond to high gravitational forces ("g forces") that occur during the launch of space vehicles. Such experiments help space scientists understand the limits of acceleration that humans can endure in such situations.

See also Gravity and gravitation.


Resources

books

"Centrifugation." McGraw-Hill Encyclopedia of Science &Technology. 6th edition. New York: McGraw-Hill Book Company, 1987, volume 3, pp. 392—398.

Dufour, John W., and W. Ed Nelson. Centrifugal Pump Source-book. New York: McGraw-Hill, 1992.

Lobanoff, Val S., and Robert R. Ross. Centrifugal Pumps. 2nd edition. Houston: Gulf Publications, 1992.

Trefil, James. Encyclopedia of Science and Technology. The Reference Works, Inc., 2001.


David E. Newton

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Centrifugal force

—The tendency of an object traveling in a circle around a central point to escape from the center in a straight line.

Gravitation

—The pull of the earth's mass on an object.

Revolutions per minute

—The number of times per minute an object travels around some central point.

Rotation

—The spinning of an object on its axis.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Centrifuge." The Gale Encyclopedia of Science. . Encyclopedia.com. 24 Sep. 2018 <http://www.encyclopedia.com>.

"Centrifuge." The Gale Encyclopedia of Science. . Encyclopedia.com. (September 24, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/centrifuge-0

"Centrifuge." The Gale Encyclopedia of Science. . Retrieved September 24, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/centrifuge-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

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The Chicago Manual of Style

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American Psychological Association

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Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.