The migration velocity in an Electrostatic Precipitator refers to the velocity at which
- Athe gas moves through the chamber.
- Bcharged particles move toward the collection electrodes.Correct
- Cthe dust falls into the hopper during rapping.
- Dthe ions move from the discharge wire to the gas.
Solution
Concept
Migration velocity in electrostatic precipitator
Formula
η = 1 - exp(-w × A / Q)
Step-by-step solution
1. In an Electrostatic Precipitator (ESP), flue gas passes through high-voltage discharge wires and grounded collection plates. 2. Particles become negatively charged by corona discharge ions. 3. The electric field exerts a Coulomb force driving the charged particles toward the collection electrodes. 4. Migration velocity represents this transverse drift speed of charged particles toward the plates. Answer: B
Explanation
In an electrostatic precipitator, migration velocity represents the steady drift speed at which negatively charged particulate matter moves perpendicularly across the gas stream toward the grounded collection plates under electrical field forces. Higher migration velocity enables greater particle capture efficiency across a given treatment area as described by the Deutsch-Anderson relation.
Why the other options are wrong
A) Bulk gas velocity describes convective flow along the flue duct, not particle drift. C) Gravitational falling speed during mechanical rapping is settling speed, not migration velocity. D) Ion drift speed across the corona sheath is ionic mobility, which is several orders of magnitude higher than particle drift.
Shortcut
ESP migration velocity = particle drift speed towards collecting plates under electric field.
Common mistake
Confusing migration velocity with the bulk longitudinal gas flow velocity through the chamber.
Correct answer: B) charged particles move toward the collection electrodes.