Question

When does the particle become suspended in an expanded bed?

(a) When superficial velocity is greater than critical velocity

(b) When superficial velocity is less than critical velocity

(c) When superficial velocity is equal to critical velocity

(d) When superficial velocity is constant

The question was posed to me in an interview.

I want to ask this question from Filtration Hydraulics in chapter Filtration of Environmental Engineering

Answer 1

The correct option is (c) When superficial velocity is equal to critical velocity

To explain: During back washing, the bed remains fixed at low fluid velocity and as the superficial velocity increases, the lighter particles move upward and when this velocity equals the critical velocity, the particle becomes suspended.