Mechanical Operations
Work index is defined as the

Energy needed to crush one ton of feed to 100 microns
Gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the product passes through a 100 micron screen
Energy (kWh/ton of feed) needed to crush small feed to such a size that 80% of the product passes a 200 mesh screen
Energy needed to crush one tonne of feed to 200 microns

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Mechanical Operations
A centrifugal filtration unit operating at a rotational speed of w has inner surface of the liquid (density ρL) located at a radial distance R from the axis of rotation. The thickness of the liquid film is δ and no cake is formed. The initial pressure drop during filtration is

½w² . R² . ρL
½w² . R . ρL(R + 2δ)
½w² . δ² . ρL
½w² . δρL (2R + δ)

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