Deposition from rotating flow

DEPOSITION FROM A ROTATING FLOW CYCLONE SEPARATOR... 

Slides in marine sediments can range from rotational slides to flow slides whose deposits extend over a wide area. Examples of flow slides are shown in Figures 11.3 and 11.4 for slides at Orkdalsfjord, Norway, on May 2,1930, and at the Grand Banks, New Foimdland on November 18,1929. 

The tubular centrifuge, which is shown schematically in Figure 9.3a, incorporates a vertical, hollow cylinder with a diameter on the order of 10 cm, which rotates at between 15000 and 50000 rpm. A suspension is fed from the bottom of the cylinder, whereupon the particles, which are deposited on the inner wall of the cylinder under the influence of centrifugal force, are recovered manually in a batchwise manner. Meanwhile, the liquid flows upwards and is discharged continuously from the top of the tube. 

The governing equation is therefore identical with that for the irrotational flow of an ideal fluid through a circular aperture in a plane wall. The stream lines and equipotential surfaces in this rotationally symmetric flow turn out to be given by oblate spheroidal coordinates. Since, from Eq. (157), the rate of deposition of filter cake depends upon the pressure gradient at the surface, the governing equation and boundary conditions are of precisely the same form as in the quasi-steady-state approximation... 

Fig. 9.50 Schematic view of a three-chamber co-rotating disk devolatilizer. The molten inlet feed is deposited on the disk surface of the first chamber by a spreading block (SB). The film is exposed to vacuum via the vacuum port. The melt is collected at the channel block (CB) and forced to flow over the top of the disk to the feed port of the second chamber. Similarly, the melt is fed into the third chamber from where the devolatilized melt exists.

Gas enters at the center of the electrode along the axis of rotation from the gas panel. It was found that if the gas were allowed to flow in directly and impinge normally to the upper electrode, that excessive deposits built up rapidly at the center of this upper electrode, and poor deposition uniformities were observed. Therefore, a gas injection shield was placed at the center of the lower electrode to provide some radial momentum to the incoming gas flow. This shield is illustrated in Figure 19. 

The theoretical basis of the cylindrical centrifuge is a straightforward application of force balance on particles in the annulus. If the centrifugal force acting on the particle is constant, the length from the entrance where a particle of given size is deposited is proportional to the aerosol flow rate, but inversely proportional to rotation speed and the square of the particle radius. These relationships are borne out by deposition experiments using particles of known radius and density. 

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