A centrifuge is a device that uses centrifugal force to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby separating fluids of different densities (e.g. cream from milk) or liquids from solids. It works by causing denser substances and particles to move outward in the radial direction. At the same time, less dense objects are displaced and move to the center. In a laboratory centrifuge that uses sample tubes, the radial acceleration causes denser particles to settle to the bottom of the tube, while low-density substances rise to the top. A centrifuge can be a very effective filter that separates contaminants from the main body of fluid.
Industrial-scale centrifuges are commonly used in manufacturing and waste processing to sediment suspended solids or to separate immiscible liquids. An example is the cream separator found in dairies. Very high-speed centrifuges and ultracentrifuges able to provide very high accelerations can separate fine particles down to the nano-scale, and molecules of different masses. Large centrifuges are used to simulate high gravity or acceleration environments (for example, high-G training for test pilots). Medium-sized centrifuges are used in washing machines and at some swimming pools to draw water out of fabrics. Gas centrifuges are used for isotope separation, such as to enrich nuclear fuel for fissile isotopes.
English military engineer Benjamin Robins (1707–1751) invented a whirling arm apparatus to determine drag. In 1864, Antonin Prandtl proposed the idea of a dairy centrifuge to separate cream from milk. The idea was subsequently put into practice by his brother, Alexander Prandtl, who made improvements to his brother's design, and exhibited a working butterfat extraction machine in 1875.
A centrifuge machine can be described as a machine with a rapidly rotating container that applies centrifugal force to its contents. There are multiple types of centrifuge, which can be classified by intended use or by rotor design:
Types by rotor design:
Types by intended use:
Industrial centrifuges may otherwise be classified according to the type of separation of the high density fraction from the low density one.
Generally, there are two types of centrifuges: the filtration and sedimentation centrifuges. For the filtration or the so-called screen centrifuge the drum is perforated and is inserted with a filter, for example a filter cloth, wire mesh or lot screen. The suspension flows through the filter and the drum with the perforated wall from the inside to the outside. In this way the solid material is restrained and can be removed. The kind of removing depends on the type of centrifuge, for example manually or periodically. Common types are:
In the centrifuges the drum is a solid wall (not perforated). This type of centrifuge is used for the purification of a suspension. For the acceleration of the natural deposition process of suspension the centrifuges use centrifugal force. With so-called overflow centrifuges the suspension is drained off and the liquid is added constantly. Common types are:
Though most modern centrifuges are electrically powered, a hand-powered variant inspired by the whirligig has been developed for medical applications in developing countries.
Many designs have been shared for free and open-source centrifuges that can be digitally manufactured. The open-source hardware designs for hand-powered centrifuge for larger volumes of fluids with a radial velocity of over 1750 rpm and over 50 N of relative centrifugal force can be completely 3-D printed for about $25.Other open hardware designs use custom 3-D printed fixtures with inexpensive electric motors to make low-cost centrifuges (e.g. the Dremelfuge that uses a Dremel power tool) or CNC cut out OpenFuge.
A wide variety of laboratory-scale centrifuges are used in chemistry, biology, biochemistry and clinical medicine for isolating and separating suspensions and immiscible liquids. They vary widely in speed, capacity, temperature control, and other characteristics. Laboratory centrifuges often can accept a range of different fixed-angle and swinging bucket rotors able to carry different numbers of centrifuge tubes and rated for specific maximum speeds. Controls vary from simple electrical timers to programmable models able to control acceleration and deceleration rates, running speeds, and temperature regimes. Ultracentrifuges spin the rotors under vacuum, eliminating air resistance and enabling exact temperature control. Zonal rotors and continuous flow systems are capable of handing bulk and larger sample volumes, respectively, in a laboratory-scale instrument.Another application in laboratories is blood separation. Blood separates into cells and proteins (RBC, WBC, platelets, etc.) and serum. DNA preparation is another common application for pharmacogenetics and clinical diagnosis. DNA samples are purified and the DNA is prepped for separation by adding buffers and then centrifuging it for a certain amount of time. The blood waste is then removed and another buffer is added and spun inside the centrifuge again. Once the blood waste is removed and another buffer is added the pellet can be suspended and cooled. Proteins can then be removed and the entire thing can be centrifuged again and the DNA can be isolated completely. Specialized cytocentrifuges are used in medical and biological laboratories to concentrate cells for microscopic examination.
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.
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 first centrifuges used for human research were used by Erasmus Darwin, the grandfather of Charles Darwin. The first largescale human centrifuge designed for Aeronautical training was created in Germany in 1933.
The US Air Force at Brooks City Base, Texas operates a human centrifuge while awaiting completion of the new human centrifuge in construction at Wright-Patterson AFB, Ohio. The centrifuge at Brooks City Base is operated by the United States Air Force School of Aerospace Medicine for the purpose of training and 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 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.
At the European Space Agency (ESA) technology center ESTEC (in Noordwijk, the Netherlands) an 8-meter diameter centrifuge is used to expose samples in both fields of Life Sciences as well as Physical Sciences. This Large Diameter Centrifuge (LDC) kg. Experiments performed in this facility ranged from zebra fish, metal alloys, plasma, cells, liquids, Planaria, Drosophila or plantsbegan operation in 2007. Samples can be exposed to a maximum of 20 times Earth gravity. With its four arms and six freely swing out gondolas it is possible to expose samples with different g-levels at the same time. Gondolas can be fixed at eight different position. Depending on their locations one could e.g. run an experiment at 5 and 10g in the same run. Each gondola can hold an experiment of maximum 80
Industrial centrifugal separator is a coolant filtration system for separating particles from liquid like, grinding machining coolant. It is usually used for non-ferrous particles separation such as, silicon, glass, ceramic, and graphite etc. The filtering process does not require any consumption parts like filter bags, which saves the earth from harm.
Geotechnical centrifuge modeling is used for physical testing of models involving soils. Centrifuge acceleration is applied to scale models to scale the gravitational acceleration and enable prototype scale stresses to be obtained in scale models. Problems such as building and bridge foundations, earth dams, tunnels, and slope stability, including effects such as blast loading and earthquake shaking.
High gravity conditions generated by centrifuge are applied in the chemical industry, casting, and material synthesis.The convection and mass transfer are greatly affected by the gravitational condition. Researchers reported that the high-gravity level can effectively affect the phase composition and morphology of the products.
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. This distinction is important because two rotors with different diameters running at the same rotational speed will subject samples to different accelerations. During circular motion the acceleration is the product of the radius and the square of the angular velocity , and the acceleration relative to "g" is traditionally named "relative centrifugal force" (RCF). The acceleration is measured in multiples of "g" (or × "g"), the standard acceleration due to gravity at the Earth's surface, a dimensionless quantity given by the expression:
This relationship may be written as
To avoid having to perform a mathematical calculation every time, one can find nomograms for converting RCF to rpm for a rotor of a given radius. A ruler or other straight edge lined up with the radius on one scale, and the desired RCF on another scale, will point at the correct rpm on the third scale.Based on automatic rotor recognition, modern centrifuges have a button for automatic conversion from RCF to rpm and vice versa.
|Wikimedia Commons has media related to Centrifuges .|
|Look up centrifuge in Wiktionary, the free dictionary.|
The ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 1 000 000 g. There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge. Both classes of instruments find important uses in molecular biology, biochemistry, and polymer science.
Decantation is a process for the separation of mixtures of immiscible liquids or of a liquid and a solid mixture such as a suspension. The layer closer to the top of the container—the less dense of the two liquids, or the liquid from which the precipitate or sediment has settled out—is poured off, leaving the other component or the more dense liquid of the mixture behind. An incomplete separation is witnessed during the separation of two immiscible liquids. To put it in a simple way decantation is separating an immiscible solution by transferring the top layer of the solution to another container.
Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The more dense components of the mixture migrate away from the axis of the centrifuge, while the less dense components of the mixture migrate towards the axis. Chemists and biologists may increase the effective gravitational force of the test tube so that the precipitate (pellet) will travel quickly and fully to the bottom of the tube. The remaining liquid that lies above the precipitate is called a supernatant or supernate.
Differential centrifugation is a common procedure in biochemistry and cell biology, which is used to separate organelles and other sub-cellular particles based on their sedimentation rate. Although often applied in biological analysis, differential centrifugation is a general technique also suitable for crude purification of non-living suspended particles. In a typical case where differential centrifugation is used to analyze cell-biological phenomena, a tissue sample is first lysed to break the cell membranes and release the organelles and cytosol. The lysate is then subjected to repeated centrifugations, where particles that sediment sufficiently quickly at a given centrifugal force for a given time form a compact "pellet" at the bottom of the centrifugation tube.
Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. When removing particulate matter from liquid, a hydrocyclone is used; while from gas, a gas cyclone is used. Rotational effects and gravity are used to separate mixtures of solids and fluids. The method can also be used to separate fine droplets of liquid from a gaseous stream.
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration, or electromagnetism.
A gas centrifuge is a device that performs isotope separation of gases. A centrifuge relies on the principles of centripetal force accelerating molecules so that particles of different masses are physically separated in a gradient along the radius of a rotating container. A prominent use of gas centrifuges is for the separation of uranium-235 (235U) from uranium-238 (238U). The gas centrifuge was developed to replace the gaseous diffusion method of uranium-235 extraction. High degrees of separation of these isotopes relies on using many individual centrifuges arranged in cascade, that achieve successively higher concentrations. This process yields higher concentrations of uranium-235 while using significantly less energy compared to the gaseous diffusion process.
Analytical ultracentrifugation is an analytical technique which combines an ultracentrifuge with optical monitoring systems.
The sedimentation coefficient(s) of a particle characterizes its sedimentation during centrifugation. It is defined as the ratio of a particle's sedimentation velocity to the applied acceleration causing the sedimentation.
A laboratory centrifuge is a piece of laboratory equipment, driven by a motor, which spins liquid samples at high speed. There are various types of centrifuges, depending on the size and the sample capacity.
Sedimentation potential occurs when dispersed particles move under the influence of either gravity or centrifugation in a medium. This motion disrupts the equilibrium symmetry of the particle's double layer. While the particle moves, the ions in the electric double layer lag behind due to the liquid flow. This causes a slight displacement between the surface charge and the electric charge of the diffuse layer. As a result, the moving particle creates a dipole moment. The sum of all of the dipoles generates an electric field which is called sedimentation potential. It can be measured with an open electrical circuit, which is also called sedimentation current.
A centrifugal extractor—also known as a centrifugal contactor or annular centrifugal contactor—uses the rotation of the rotor inside a centrifuge to mix two immiscible liquids outside the rotor and to separate the liquids in the field of gravity inside the rotor. This way, a centrifugal extractor generates a continuous extraction from one liquid phase into another liquid phase.
Geotechnical centrifuge modeling is a technique for testing physical scale models of geotechnical engineering systems such as natural and man-made slopes and earth retaining structures and building or bridge foundations.
A separation process is a method that converts a mixture or solution of chemical substances into two or more distinct product mixtures. At least one of results of the separation is enriched in one or more of the source mixture's constituents. In some cases, a separation may fully divide the mixture into pure constituents. Separations exploit differences in chemical properties or physical properties between the constituents of a mixture.
A pusher centrifuge is a type of filtration technique that offers continuous operation to de-water and wash materials such as relatively in-compressible feed solids, free-draining crystalline, polymers and fibrous substances. It consists of a constant speed rotor and is fixed to one of several baskets. This assembly is applied with centrifugal force that is generated mechanically for smaller units and hydraulically for larger units to enable separation.
The peeler centrifuge is a device that performs by rotating filtration basket in an axis. A centrifuge follows on the principle of centrifugal force to separate solids from liquids by density difference. High rotation speed provides high centrifugal force that allows the suspended solid in feed to settle on the inner surface of basket. There are three kinds of centrifuge, horizontal, vertical peeler centrifuge and siphon peeler centrifuge. These classes of instrument apply to various areas such as fertilisers, pharmaceutical, plastics and food including artificial sweetener and modified starch.
A centrifuge is a device that employs a high rotational speed to separate components of different densities. This becomes relevant in the majority of industrial jobs where solids, liquids and gases are merged into a single mixture and the separation of these different phases is necessary. A decanter centrifuge separates continuously solid materials from liquids in the slurry, and therefore plays an important role in the wastewater treatment, chemical, oil, and food processing industries. There are several factors that affect the performance of a decanter centrifuge, and some design heuristics are to be followed which are dependent upon given applications.
A solid bowl centrifuge is a type of centrifuge that uses the principle of sedimentation. A centrifuge is used to separate a mixture that consists of two substances with different densities by using the centrifugal force resulting from continuous rotation. It is normally used to separate solid-liquid, liquid-liquid, and solid-solid mixtures. Solid bowl centrifuges are widely used in various industrial applications, such as wastewater treatment, coal manufacturing, and polymer manufacturing. One advantage of solid bowl centrifuges for industrial uses is the simplicity of installation compared to other types of centrifuge. There are three design types of solid bowl centrifuge, which are conical, cylindrical, and conical-cylindrical.
A conical plate centrifuge is a type of centrifuge that has a series of conical discs which provides a parallel configuration of centrifugation spaces.
Centrifugal partition chromatography is a special chromatographic technique where both stationary and mobile phase are liquid, and the stationary phase is immobilized by a strong centrifugal force. Centrifugal partition chromatography consists of a series-connected network of extraction cells, which operates as elemental extractors, and the efficiency is guaranteed by the cascade.