Gravity settling chambers (dust catchers): in which particle-size range do these simple devices perform most effectively and efficiently?

Introduction / Context:
Gravity settling chambers provide low-cost, low-pressure-drop particulate removal by allowing particles to fall out of a gas stream under gravity. Their efficiency depends on particle size, gas residence time, and chamber design.

Given Data / Assumptions:

• Horizontal flow dust catcher with quiescent zone.
• Turbulence kept modest; Stokes/transition settling applies.
• Goal: identify the size range where efficiency is reasonable.

Concept / Approach:
Very fine particles (< ~5 microns) have tiny settling velocities and are poorly captured. Very coarse particles (> ~100 microns) are easy to settle in almost any device. Gravity chambers are typically used for an intermediate size band where they remain economical and simple—commonly around 10–25 microns for industrial gases at moderate velocities.

Step-by-Step Solution:
Compare options with known performance bands.Select the intermediate band where settling velocity allows capture in practical chamber lengths.Hence, 10 to 25 microns is the effective range.

Verification / Alternative check:
Design charts show gravity chambers capturing a meaningful fraction of particles above roughly 10 microns, whereas sub-5 micron control requires cyclones, scrubbers, or ESPs.

Why Other Options Are Wrong:
< 5 microns: too fine for economical gravity capture.< 74 microns: too broad and includes many fines; not specific.> 1000 microns: trivially settle; such oversized particles are rarely the design driver.

Common Pitfalls:
Overestimating efficiency for fines; gravity chambers are often used only as precleaners upstream of higher-efficiency devices.

Final Answer:
10 to 25