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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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