Seepage effects on settling velocity

Abstract

Settling is the process by which particulates settle to the bottom of a liquid and form bed sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force. Settling is an important operation in many applications such as mining, wastewater treatment, biological science and particle mechanics. The terminal or settling velocity of a rigid particle is also an important parameter in many solid liquid separation processes. This experimental project investigates the possible effect of upward seepage on the terminal or settling velocity of sediment particles as well as its influence on the different zones of sediment particle motion. The analysis involves both experimental and analytical approaches. The experiments are conducted in a vertical water column that is 0.4m long, 0.4m wide and 1.12m deep. Uniform plastic spherical particles of varying diameters (0.630cm, 0.790cm, 0.950cm and 1.285cm) and densities under different seepage inflow rates (0 m3/s, 1X10-4 m3/s, 2X10-4 m3/s and 5X10-4 m3/s) are used.

The drag coefficient is the most important property in the mechanics of particle motion and fluid dynamics because most particles in real life are employed either to overcome or to utilize the drag caused by the fluid. The results provided clear evidence that upward seepage has modified the drag coefficient as well as implication of profound effect on the settling velocity of particle. The variation of zones of acceleration, settling and deceleration of the particle under upward seepage influence remains insignificant.