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Difference between revisions of "Centrifugation"
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→Solid bowl centrifugation: added picture, changed pictures sizes
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==Feedstock== | ==Feedstock== | ||
[[File:Centrifuga_Hermle_2.jpg|thumb|upright|Laboratory centrifuge]] | [[File:Centrifuga_Hermle_2.jpg|thumb|upright|Laboratory centrifuge]] | ||
[[File:How centrifuge works.png|thumb | [[File:How centrifuge works.png|thumb|Testtube with precipitate (pellet) and supernatant after centrifugation|150x150px]] | ||
=== Origin and composition === | === Origin and composition === | ||
The centrifugation method is used to separate two miscible substances. The most common application is the separation of solids from highly concentrated suspensions, which is used in the treatment of sewage sludges for dewatering where less consistent sediment is produced. In the food industries, special centrifuges can process a continuous stream of particle-laden liquid. | The centrifugation method is used to separate two miscible substances. The most common application is the separation of solids from highly concentrated suspensions, which is used in the treatment of sewage sludges for dewatering where less consistent sediment is produced. In the food industries, special centrifuges can process a continuous stream of particle-laden liquid. | ||
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There is a correlation between the size and density of a particle and the speed at which the particle separates from a heterogeneous mixture, when the only force applied is gravity. The larger the size and the larger the density of the particles, the faster they separate from the mixture. By applying a larger effective gravitational force to the mixture, like a centrifuge does, the separation of the particles is accelerated. This way, in industrial and lab settings, particles that would naturally separate over a long period of time can be separated much faster. | There is a correlation between the size and density of a particle and the speed at which the particle separates from a heterogeneous mixture, when the only force applied is gravity. The larger the size and the larger the density of the particles, the faster they separate from the mixture. By applying a larger effective gravitational force to the mixture, like a centrifuge does, the separation of the particles is accelerated. This way, in industrial and lab settings, particles that would naturally separate over a long period of time can be separated much faster. | ||
The centrifugation speed is specified by the angular velocity, usually expressed as revolutions per minute (rpm), or acceleration expressed as ''g''. The conversion factor between rpm and ''g'' depends on the radius of the centrifuge rotor. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity. [[File:HD.16.088 (12523557255).jpg|alt=Picture showing basket centrifuge for the continuous collection of algae in 1966|thumb|Basket centrifuge for the continuous collection of algae in 1966]]The sedimentation of particles can be explained by Stoke's law. The equation can be used to calculate the velocity of sedimentation based on five parameters: | The centrifugation speed is specified by the angular velocity, usually expressed as revolutions per minute (rpm), or acceleration expressed as ''g''. The conversion factor between rpm and ''g'' depends on the radius of the centrifuge rotor. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity. [[File:HD.16.088 (12523557255).jpg|alt=Picture showing basket centrifuge for the continuous collection of algae in 1966|thumb|Basket centrifuge for the continuous collection of algae in 1966|312x312px]]The sedimentation of particles can be explained by Stoke's law. The equation can be used to calculate the velocity of sedimentation based on five parameters: | ||
[[File:Stokes-equation.jpg|center]] | [[File:Stokes-equation.jpg|center]] | ||
From the Stokes equation, five important behaviours of particles can be explained: | From the Stokes equation, five important behaviours of particles can be explained: | ||
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=== Basket centrifugation === | === Basket centrifugation === | ||
Basket centrifuges are often called centrifugal filters or clarifiers. The basket centrifuge uses centrifugal force to generate a pressure which forces the liquid through the caked solids, the filter cloth, the backing screen, and finally the basket perforations. The filter cloth retains the solid particles inside the rotating basket while the permeating liquid is continuously discharged. | Basket centrifuges are often called centrifugal filters or clarifiers. The basket centrifuge uses centrifugal force to generate a pressure which forces the liquid through the caked solids, the filter cloth, the backing screen, and finally the basket perforations. The filter cloth retains the solid particles inside the rotating basket while the permeating liquid is continuously discharged. | ||
[[File:Solid Bowl Centrifuge 3.png|alt=Solid Bowl Centrifuge – A drawing showing the principle|thumb|Solid Bowl Centrifuge]] | |||
=== Solid bowl centrifugation === | === Solid bowl centrifugation === | ||