A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to evenly distribute substances (usually present in a solution for small scale applications) of greater and lesser density. There are many different kinds of centrifuges, including those for very specialised purposes. It can be used for viable counts, when shaking the culture e.g. yeast, out of suspension.

Theory

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. The acceleration is often quoted in multiples of g, the standard acceleration due to gravity at the Earth's surface. This distinction is important because two rotors with different diameters running at the same rotational speed will subject samples to different accelerations.

The acceleration can be calculated as the product of the radius and the square of the angular velocity.

History and predecessors

Types

There are at least five types of centrifuge:

• Tabletop/clinical/desktop centrifuge or microcentrifuge
• High-speed centrifuge
• Cooling centrifuge
• Ultracentrifuge
• Geotechnical centrifuge

Industrial centrifuges may otherwise be classified according to the type of separation of the high density fraction from the low density one :

• Screen centrifuges, where the centrifugal acceleration allows the liquid to pass through a screen of some sort, through which the solids cannot go (due to granulometry larger than the screen gap or due to agglomeration). Common types are :
• Pusher centrifuges
• Peeler centrifuges
• Decanter centrifuges, in which there is no physical separation between the solid and liquid phase, rather an accelerated settling due to centrifugal acceleration. Common types are :
• Solid bowl centrifuges
• Conical plate centrifuges

Isolating suspensions

main: Laboratory centrifuge Simple centrifuges are used in chemistry, biology, and biochemistry for isolating and separating suspensions. They vary widely in speed and capacity. They usually comprise a rotor containing two, four, six, or many more numbered wells within which the samples containing centrifuge tips may be placed.

Isotope separation

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.