Particle Technology

centrifugal separation

Problems 8.6

Question 1.vi


The diagram below illustrates a homogeneous oil emulsion contained in a circular channel rotating at 1000 rpm. The diameter of the outer circle is 30 cm, and the distance between the walls, i.e. the channel width is 2.5 cm. If the oil is less dense than the surrounding water an oil droplet will travel inwards on the application of a centrifugal field force, just as oil floats in a gravitational field.


           centrifuge ring                     centrifuge ring

The oil and water densities are 800 and 1000 kg m3, respectively and the viscosity of water is 0.001 Pa s.


The time taken (neglecting acceleration) before a sample of emulsion withdrawn at the inner radius contains no particles bigger than 10 microns in diameter is (s):

  a) 15
b) 2290
c) -15
c) 150
Note, rearrange the differential equation for particle motion and be very careful with your limits: t=0 r=?; to t=t at r=12.5 cm

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