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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 rate that the particle separates from a heterogeneous mixture, when the only force applied is that of 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 is ideal in industrial and lab settings because particles that would naturally separate over a long period of time can be separated in much less time. | There is a correlation between the size and density of a particle and the rate that the particle separates from a heterogeneous mixture, when the only force applied is that of 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 is ideal in industrial and lab settings because particles that would naturally separate over a long period of time can be separated in much less time. | ||
The rate of centrifugation 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. | The rate of centrifugation 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. | ||
This sedimentation of particles can be explained by Stoke's law. The equation calculates the velocity of sedimentation utilizing five parameters. | |||
[[File:Stokes-equation.jpg|center]] | |||
From the Stokes equation five important behaviours of particles can be explained: | |||
# The rate of particle sedimentation is proportional to the particle size | |||
# The sedimentation rate is proportional to the difference in density between the particle and the medium. | |||
# The sedimentation rate is zero when the particle density is the same as the medium density. | |||
# The sedimentation rate decreases as the medium viscosity increases. | |||
# The sedimentation rate increases as the gravitational force increases. | |||
==Products== | ==Products== | ||