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Difference between revisions of "Centrifugation"
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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|312x312px]] | 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. | ||
From the Stokes equation, five important behaviours of particles can be explained: | 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: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]]From the Stokes equation, five important behaviours of particles can be explained: | |||
#The rate of particle sedimentation is proportional to the particle size | #The rate of particle sedimentation is proportional to the particle size | ||