Particulate control: Which device is the least efficient for capturing submicron (< 1 μm) particles in industrial dust collection?

Introduction / Context:
Industrial processes generate a wide particle-size spectrum. Submicron particles are particularly challenging to capture due to their low inertia and high diffusivity. Choosing an appropriate control device depends on the collection mechanism (inertial impaction, interception, diffusion, electrostatic attraction, and filtration).

Given Data / Assumptions:

• Target: submicron particles (< 1 μm).
• Devices compared: cyclone, gravity chamber (dust catcher), bag filter, wet scrubber.
• Goal: identify the least efficient among the listed for this size range.

Concept / Approach:
Gravity settling chambers remove large, high-inertia particles primarily via gravitational settling. Their cut size is typically hundreds of microns, making them ineffective for fine aerosols. Cyclones improve on gravity by using centrifugal forces, but still struggle below ~3–5 μm unless specially designed. Bag filters and high-energy scrubbers offer significantly better fine-particle capture.

Step-by-Step Solution:
1) Gravity dust catcher: Minimal residence time and low driving force → very poor for submicron particles.2) Cyclone: Better than gravity for 5–10 μm and above, still weak for submicron.3) Bag filter: Surface/depth filtration captures submicron by diffusion and interception; high efficiency.4) Wet scrubber: High-energy types (venturi) can collect submicron via impaction on droplets.5) Therefore, the least efficient is the gravity dust catcher.

Verification / Alternative check:
Device performance curves show precipitous drop in efficiency below a few microns for gravity and standard cyclones, while fabric filters and venturi scrubbers maintain high capture rates.

Why Other Options Are Wrong:
Cyclone separator: Inefficient for submicron but still superior to a gravity chamber.Bag filter: Designed to capture fine particles with very high efficiency.Wet scrubber: High-energy designs achieve notable submicron removal.

Common Pitfalls:
Assuming all dust devices perform similarly regardless of particle size.Overlooking filtration and diffusion mechanisms crucial at small sizes.

Final Answer:
Dust catcher (gravity settling chamber)