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Medium Viscosity

Medium viscosity is the measure of the medium’s resistance to flow – its consistency. It is determined by the concentration, shape and size distribution of the solids making up the medium.

Once the ferrosilicon grades have been selected, the most important variable affecting the viscosity is the medium density, determined by the solids concentration. The relationship between the viscosity and solids concentration is non-linear, a shown in the figure to the right.

At low densities, there is little change of viscosity with density (as determined by the solids concentration), but there comes a point at which viscosity rapidly increases with density. In practice it is unwise to operate even close to this point because the medium is then too viscous to use, and small changes in density will result in large changes in viscosity.

Apart from ferrosilicon of a particular grade (size and shape), the solids present in the medium often include fine contaminants from the feed being treated. Because these contaminants will nearly always be of a lower density than the ferrosilicon, a contaminated medium will need to contain a higher amount of solids concentration to achieve the same medium density, and will therefore have a higher medium viscosity than a clean medium.

The viscosity is an important property of the medium, but because it is difficult to measure, its influence on the separation is not always well understood. In general, however, high viscosity media are undesirable because it reduces the velocity of the particles being separated increases, increasing the chance of particle misplacement and thus reducing the efficiency of separation.

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