Centrifugal principle of centrifuge - Huaqiang Electronic Network

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Centrifuge

Centrifugal Principle:

When a suspension containing fine particles is left undisturbed, the particles gradually settle due to gravity. Heavier particles sink faster, while lighter ones may float. The settling speed depends on particle size, shape, density, as well as the strength of gravity and the viscosity of the liquid. Particles like red blood cells, which are a few micrometers in size, can be seen under normal gravity conditions.

Additionally, when particles settle in a medium, they also exhibit diffusion. Diffusion is an inherent and unavoidable process. It is inversely related to the mass of the material—smaller particles tend to diffuse more. Sedimentation, on the other hand, is conditional and requires external forces to occur. The sedimentation rate is proportional to the weight of the object, so larger particles settle faster. However, for particles smaller than a few micrometers, such as viruses or proteins, they exist in a colloidal or semi-colloidal state in solution, making it impossible to observe their sedimentation through gravity alone. These tiny particles settle very slowly and experience significant diffusion. Therefore, a centrifuge is necessary to generate strong centrifugal force, allowing these particles to overcome diffusion and settle effectively.

Centrifugation involves using a high-speed rotating rotor to create powerful centrifugal force, which accelerates the sedimentation of particles in a liquid. This technique helps separate materials based on their sedimentation coefficients and buoyant density within the sample.

Conversion between Centrifugal Force (g) and Rotational Speed (rpm):

The formula to convert centrifugal force (G) to rotational speed (RPM) is as follows:

G = 1.11 × 10^(-5) × R × (RPM)^2

In this formula, G represents the centrifugal force, usually expressed as a multiple of g (gravitational acceleration). The term 10^(-5) refers to 10 raised to the power of -5, R is the radius in centimeters, and RPM is the rotational speed.

For example, if the centrifugal radius is 10 cm and the rotational speed is 8000 RPM, the centrifugal force would be:

G = 1.11 × 10^(-5) × 10 × (8000)^2 = 7104

This means the centrifugal force is 7104g.

If the desired centrifugal force is 8000g, the required rotational speed would be approximately 8489 rpm or about 8500 rpm.

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