Question

What is the settling velocity of the particle in the wastewater if its diameter is 2 * 10^-3cm. Given G=2.65, viscosity v=8 * 10^-3cm^2/Sec?

(a) 0.01cm/Sec

(b) 0.13cm/Sec

(c) 0.24cm/Sec

(d) 0.36cm/Sec

I got this question during an interview for a job.

The doubt is from Types of Settling Tanks in chapter Sedimentation and Chemical Clarification of Environmental Engineering

Answer 1

Right option is (b) 0.13cm/Sec

The explanation is: Settling velocity of the particle in wastewater is given by vs=g (G-1) d^2/18v

Specific gravity G=1, g=981cm^2/Sec, viscosity v=8 * 10^-3cm^2/Sec

vs = 981 * (2.65-1) * 0.002 * 0.002/(18 * 0.008) = 0.13cm/Sec.