Centrifugal principle of centrifuge - Huaqiang Electronic Network

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Centrifuge

Centrifugal principle:

When a suspension containing fine particles is left undisturbed, the suspended particles gradually settle due to the gravitational field. Heavier particles sink faster, while lighter ones may float. The rate at which particles settle depends on their 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 diameter, can be seen under normal gravity.

Additionally, when particles settle in a medium, they also undergo diffusion. Diffusion is a natural and inevitable process. It is inversely proportional to the mass of the particle—smaller particles experience more diffusion. Settling is relative and requires external forces to occur. The settling speed is proportional to the weight of the object; 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 sedimentation by gravity alone. The smaller the particles, the slower they settle and the more pronounced the diffusion effect. Therefore, a centrifuge is used to generate strong centrifugal force, enabling these particles to overcome diffusion and settle effectively.

Centrifugation involves using the powerful centrifugal force generated by a high-speed rotating rotor to accelerate the sedimentation of particles in a liquid, allowing for the separation of materials based on their sedimentation coefficients and buoyant density.

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

Where G represents the centrifugal force, typically expressed as a multiple of g (standard gravity). The term 10^(-5) refers to 10 raised to the power of -5, (RPM)^2 is the square of the rotational speed, and R is the radius of rotation in centimeters.

For example, with a radius of 10 cm and a rotational speed of 8000 RPM, the centrifugal force would be:

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

This means the centrifugal force is 7104 times that of Earth's gravity (7104g).

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

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