Electrostatic precipitators (ESPs): which change increases the dust collection efficiency, all else equal?

Introduction / Context:
Electrostatic precipitators remove fine particulate by charging particles and driving them to collecting plates. Performance depends on electric field strength, particle charge, migration velocity, gas residence time, and collecting area. Designers tune gas velocity and plate area to achieve a target overall efficiency for a given dust load.

Given Data / Assumptions:

• Comparable dust properties and voltage conditions.
• Single-stage, dry ESP behavior.
• Focus on geometric and flow variables: gas rate and collecting area.

Concept / Approach:
A standard performance expression (e.g., Deutsch–Anderson model) relates efficiency to effective migration velocity (w), collecting area (A), and volumetric flow rate (Q): η = 1 − exp(−w * A / Q). For fixed w, increasing A raises wA/Q and thus increases efficiency, while increasing Q reduces residence time and lowers efficiency.

Step-by-Step Solution:

Verification / Alternative check:
Field experience confirms that adding fields/plates (area) boosts performance, while overloading an ESP with higher gas flow degrades capture due to reduced residence time and higher drift requirements.

Why Other Options Are Wrong:

• (a) Increasing gas flow rate reduces efficiency for a given area and field.
• (c) Both changes together are not beneficial because (a) is detrimental.
• (d) Incorrect because area clearly matters through migration length and time.

Common Pitfalls:
Overlooking the impact of non-ideal factors like re-entrainment, rapper settings, and dust resistivity; while these matter in practice, the core trend with A and Q remains as above.

Final Answer:
Increasing the effective electrode (collecting) area