Centrifugal Sedimentation Theory

Continuou.s Centrifugal Sedimentation Theory The Stokes settling velocity of a spherical particle under centrifugal field is given... 

This essentially practical text nevertheless covers the underlying theory of centrifugal sedimentation separations in some detail, which further extends its usefulness to the research or design engineer looking for new ideas. 

The design, construction and application of thickeners, centrifuges and filters is a specialised subject, and firms who have expertise in these fields should be consulted when selecting and specifying equipment for new applications. Several specialist texts on the subject are available Svarovsky (2001), Ward (2000) and Wakeman and Tarleton (1998). The theory of sedimentation processes is covered in Volume 2, Chapter 5 and filtration in Chapter 7. 

This approach to describing centrifuge performance has become known as the sigma theory . It provides a means for comparing the performance of sedimentation centrifuges and for scaling up from laboratory and pilot scale tests see Ambler (1952) and Trowbridge (1962). 

Theory. The velocity (v) of particle sedimentation during centrifugation depends on the angular velocity co of the rotor, its effective radius (teff, the distance from the axis of rotation), and the particle s sedimentation properties. These properties are expressed as the sedimentation coef cient S (1 Svedberg, = 10 s). The sedimentation coef cient depends on the mass M of the particle, its shape (expressed as the coef cient of friction, f), and its density (expressed as the reciprocal density v, partial specific volume ). 

Extensive application of the theory has been made in treating pressure effects on velocity centrifugation. If w denotes angular speed, sp the sedimentation coefficient at pressure p, ra the radius of the meniscus, x = (r/ra)2, the usual representation of pressure effects leads to the relation (10),... 

We note that FFF and disc centrifugation both achieve high resolution rankings in Table II. This comparable resolution has been predicted theoretically any field (such as a sedimentation field) applied directly to a sample will lead to approximately the same resolution as found in an FFF system using the same field, providing the displacement distances are comparable (10). While in theory, resolution in FFF can be amplified by the arbitrary length of the separation path (channel length), in practice the two approaches have comparable levels of resolution. 

The equations to quantify this effect were developed by Mason and Weaver in 1924 [2]. For monosize distributions Brownian motion leads to broadened measured distributions [3] but the effect is reduced as the width of the distribution increases [4,5]. Chung and Hogg [6] carried out theoretical and experimental studies of clay particles using centrifugal and gravitational sedimentation. Agreement between theory and practice was not too good. 

Particle size, shape, inter-particle forces, zeta potential, liquid surfactant phenomena, and liquid viscosity are important characteristics of a solid-liquid suspending system. Mechanism of flow through porous medium is fundamental to theories of sedimentation, filtration, centrifugation, and expression operations. Most solid-liquid materials are compacti-ble. Unique and strange behavior of pressure filtration of compactible materials has been identified. More attention should be paid for separation of those materials. 

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