Theory of Centrifugation

Figure 1 Tubular bowl (X represents the initial position). Centrifugal field is high enough that separating capacity of bowl is considered the same when rotating vertically or horizontally. Same sigma formula applies to tubular bowl, decanter and imperforate basket.

G-level

The fundamental characteristic of all centrifuges is that they contain a rotor that spins. A centrifugal field is used to augment separation. The magnitude of the enhancement is sometimes incorrectly described as the G-force. The relative centrifugal force (RCF) or G-level is not a force; it is a ratio, that of acceleration of the centrifugal field to that of acceleration owing to the Earth's gravity. It has dimensionally no units:

This ratio may reach 60 000 on small laboratory units and 20 000 on small industrial scale units. This ratio tends to decrease as the size of the rotor increases. The ratio is normally large enough that a rotor rotating horizontally is considered to have the same separating capacity that it would have if it rotated

Figure 2 Disc centrifuge (X represents the initial position).

Figure 3 Decanter.

vertically, i.e. the influence of the Earth's gravitational field is negligible while the rotor is spinning.

Performance

Since centrifuges typically remove solids from one or more liquid streams, some measure of how well this is being performed is usually desirable. The recovery, sometimes (especially in the case of filtering centrifuges) referred to as yield, is defined as:

Collected insoluble solids Feed insoluble solids

Cake insolubles (%) x Cake rate Feed insolubles (%) x Feed rate

x 100

The liquids balance:

By substitution:

fF = cC + e(F — C) = cC + eF — eC F(f — e) = C(c — e) C/F = (f-e)/(c-e)

those on applications such as classification when recovery levels are kept low.

Centrifuges may have the effect of altering the particle-size distribution. Two different types of centrifuges, even if operating at the same overall recovery level, may split a slurry into components having significantly different particle-size distributions.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment