Tutorial Questions on Sedimentation
October 2018
1. Calculate the terminal velocities and drag coefficients for particles of diameter 0.01, 0.02 and
0.5 cm diameter, respectively, falling in water if the particles have a density of 1.2 g/cm3.
2. If two particles of diameter 0.05 and 0.02 cm, respectively, and density 1.2 g/cm3 falling at
their terminal velocities in water are initially separated by a vertical distance of 10 cm, how
long will it be before the particles collide?
3. An aqueous suspension of particles 0.2 mm diameter is introduced into a horizontal-flow
settling tank, 5m deep and l0 m long. Calculate the linear velocity at which 95% of the
suspended particles will be removed, assuming that the depth of the sludge layer at the outlet
is 0.2m. You may assume that the flow is uniform, that the effluent is removed throughout the
full depth of the tank above the sludge layer and that no flocculation occurs.
How wide must the tank be to deal with a daily flow of 10,0003 ?