Separation of fine particle dispersions using periodic flows in a spining coiled tube

Abstract

A centrifugal method for fractionating fine (<lo pm) particles by size and /or density is described. Periodic, bidirectional flow through a continuously spinning coiled tube splits fine particle suspensions into two fractions. SCOPEA new method for separating fine (t10 bm) particles in suspension is being developed. It can concentrate or fractionate according to size and/or density. Separation occurs in a spinning helical tube through which periodic, bidirectional fluid displacements are made. The mechanism involves repeated sedimentation and resuspension of particles, resulting in a net movement of all of the particles (concentration), or only a select portion (fractionation). Sedimentation results from the spinning motion, while resuspension is effected by secondary flow, which occurs only during axial flow and is due to the interaction of the helical geometry, steady rotation, and fluid motion. This method is similar in some respects to parame- separates molecules in solution, not particles in suspension, and uses a periodically varying intensive parameter such as temperature to effect separation instead of a steady centrifugal force field. SFFF also uses a steady centrifugal force field, but with a unidirectional rather than a periodic bidirectional flow. This gives a chromatographic-like separation, unlike the new method, which yields two streams of different composition. Concentration experiments have been performed with dilute aqueous dispersions of ground (0.2-3.0 pm) molecular sieve powder. Although continuous operation is feasible, experiments were limited to batch operation. The major objective was to demonstrate that the method can concentrate suspensions. Some data on the effect of process parameters were also obtained. CONCLUSIONS AND SIGNIFICANCEProof-of-principle experiments have demonstrated that this new separation method can concentrate suspensions of fine particles. Aqueous dispersions of molecular sieve powder were split into dilute and concen-

Visualization of Flows in Curved Channels with aModerate or High Rotation Speed

“…Flows in rotating curved channels arise in a variety of practical processes. Examples are flows in centrifuges (Hochrainer 1971 ]), cooling channels of rotating machinery (Ito and Motai [1974], Miyazaki [1971Miyazaki [ , 1973 and Morris [1981]), particle separation devices (Lennartz et al [1987], Papanu et al [1986], Hoover et al [1984, St6ber and Flachsbart [1969] and Kotrappa and Light [1972]) and rotating heat exchangers (Qiu et al [1990]). Studies on the hydrodynamics in the rotating curved channels are, therefore, not only of considerable theoretical interest, but also of practical importance.…”

Separation of fine particles by laminar flow in a tilted slender tube slowly rotating around the longitudinal axis

“…particles, such as with a hydraulic cyclone, spinning coils (Papanu et al, 1986), and coil planet centrifuge (Ito et al, 1966), but they do not give fractions with narrow size distributions.…”

Fractionation of fine particle slurries using periodic flows in a spinning helix

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An unusual method of separating or fractionating fine-particle slurries has been proposed and partially explored by Landin (1980), Papanu (1983Papanu ( , 1986, Menon (1983), Lennartz (1984), and Lennartz et al (1987). A helically coiled tube spinning steadily on its major axis is connected to two agitated reservoir pumps which cycle a slurry bidirectionally through the helix as shown in Figure 1.

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