Inertial and Centrifugal Separation

In the preceding processes, the particles were separated from the fluid by gravitational forces acting on the particles. Sometimes gravity separation may be too slow because of the closeness of the densities of the particles and the fluid, because of small particle size leading to low settling velocity or, in the case of liquid-liquid separations, because of the formation of a stable emulsion. 

Centrifugal separators take the idea of an inertial separator a step further and make use of the principle that an object whirled about an axis at a constant radial distance from the point is acted on by a force. Use of centrifugal forces increases the force acting on the particles. Particles that do not settle readily in gravity settlers often can be separated from fluids by centrifugal force. 

Example 8.3 A dryer vent is to be cleaned using a bank of cyclones. The gas flowrate is 60 m3-s density of solids 2700 kg-m 3 and the concentration of solids is 10 g-m 3. The size distribution of the solids is given in Table 8.2  

Particle size (pm) Percentage by weight less than 

Solution The particles are first divided into size ranges and the collection efficiency for the average size applied with the size range as shown in Table 8.3  

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