Air Pollution MCQ with answer and solution

Concept

Cyclone separator particulate collection efficiency

Formula

d_pc = √(9 × μ × b / (2 × π × N_e × v_i × (ρ_p - ρ)))

Step-by-step solution

1. Cyclone separators collect dust particles using centrifugal force generated by tangential gas flow: F_c = m × v² / r. 2. Centrifugal force increases with particle mass (proportional to particle diameter cubed). 3. Larger particles experience greater outward force, crossing streamlines faster to strike the outer wall and settle. 4. Therefore, cyclone efficiency increases with an increase in particle diameter. Answer: A

Explanation

The collection efficiency of a cyclone separator is directly related to the centrifugal force exerted on incoming particles, which is directly proportional to particle mass and diameter. Larger particles experience greater outward centrifugal acceleration, causing them to move radially to the outer wall and settle into the hopper more effectively than smaller dust particles.

Why the other options are wrong

B) Increasing cyclone body diameter decreases centrifugal acceleration (v²/r), reducing collection efficiency. C) Decreasing gas inlet velocity lowers tangential speed and centrifugal force, reducing efficiency. D) Higher gas temperature increases gas viscosity, raising aerodynamic drag and lowering efficiency.

Shortcut

Cyclone efficiency increases with: larger particle diameter, higher inlet velocity, smaller cyclone radius, and lower gas viscosity.

Common mistake

Thinking larger cyclone body diameters increase efficiency when they actually decrease centrifugal acceleration.