Rotation coefficients spheroid

The machine SorTech has developed uses a rotating conical bowl with a cone angle, surface roughness and rotational speed calculated to best suit the particular classification requirement. The machine concept is based on the observation that for particles sliding over a surface of roughness comparable to the particle size, the apparent friction coefficient depends on the particle size. The complete machine is fully enclosed, has a small footprint and a very modest power requirement, and depending on size can process powder at the rate of kilograms to tons per hour. To date, classification has been obtained with several different metal spheroidal particles, coal powder, crushed limestone, fly ash, calcium carbonate and other powders. 

Pa is the relaxation time of the axis of revolution, pb, the relaxation time of the rotation of any direction normal to the first. The frictional coefficients for an ellipsoid of revolution have been calculated by Edwardes (1893). Gans (1928) and Perrin (1934) have used these frictional coefficients to calculate pa/po and pt/po, the ratios of the principal relaxation times to the relaxation time of a sphere of equal volume. Perrin characterizes the ellipsoid by the ratio of the axes (b/a), this ratio being smaller than 1 for prolate and greater than 1 for oblate spheroids. 

C. Hu and R. Zwanzig,/. Chem. Phys., 60, 4354 (1974). Rotational Friction Coefficients for Spheroids with the Slipping Boundary Condition. 

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