The collection mechanism of a bag filter includes:
(A) Sedimentation (B) Diffusion (C) Electrostatic Interaction (D) Interception (E) Impaction
Choose the correct answer:

Correct option is C

The correct answer is (c) B, D and E only. The primary mechanisms involved in a bag filter collection process are:
1. Diffusion (B)
2. Interception (D)
3. Impaction (E)
Explanation:
· Bag filters are commonly used for the removal of particulate matter in industrial air filtration. The efficiency of a bag filter relies on different collection mechanisms based on the size and behavior of the particles. The following are the key mechanisms involved:
1. Diffusion (B):
· Small particles (less than 0.1 microns) move randomly due to Brownian motion and collide with the filter fibers, causing them to stick.
2. Interception (D):
· Particles that follow the air streamlines come close enough to the filter fibers to be captured when they make direct contact.
3. Impaction (E):
· Larger particles (greater than 1 micron) deviate from the air streamlines due to inertia and collide directly with the filter fibers.
Other Mechanisms Explained:
1. Sedimentation (A):
· This occurs when particles settle due to gravity. It is not a significant mechanism in bag filters, which rely on airflow.
2. Electrostatic Interaction (C):
· This involves the use of electrical charges to attract and capture particles. While used in electrostatic precipitators, it is not typically a mechanism in conventional bag filters.
Information Booster:
1. Types of Filters:
· Bag Filters: Use mechanical processes (diffusion, interception, and impaction) for filtration.
· Electrostatic Precipitators: Use electrostatic forces to remove particles.
2. Particle Size and Mechanism:
· Diffusion: Effective for small particles (<0.1 µm).
· Interception: Effective for medium-sized particles (~0.1-1 µm).
· Impaction: Effective for large particles (>1 µm).
3. Bag Filter Materials:
· Typically made from woven or felted fabrics (e.g., polyester, fiberglass).
4. Applications:
· Used in cement plants, power plants, steel mills, and chemical industries for air pollution control.
Additional Knowledge:
· (a) Sedimentation:
· More applicable in gravity separators where particles settle by gravitational force.
· (b) Diffusion:
· Works effectively for ultrafine particles due to their random motion.
· (c) Electrostatic Interaction:
· Used in electrostatic precipitators rather than bag filters.
· (d) Interception:
· Captures particles that are too large to follow the airflow path closely.
· (E) Impaction:
· Involves inertial forces causing particles to collide with filter fibers.
Key Points:
1. Bag filters rely on diffusion, interception, and impaction for efficient particle collection.
2. Electrostatic interaction is not applicable for bag filters.
3. Understanding these mechanisms helps in selecting the appropriate filtration method for industrial use.