Mechanisms in fibrous air filtration: Which mechanisms contribute to particle capture in fibrous filters used for bioprocess air handling and sterilizing ventilation?

Introduction / Context:
Air intake and exhaust filters protect cultures and the environment by removing aerosols and microorganisms. Fibrous filters (e.g., HEPA) capitalize on multiple capture mechanisms that act over different particle size ranges and flow conditions. Recognizing the full suite of mechanisms explains why these filters achieve high overall efficiency.

Given Data / Assumptions:

• Depth-type fibrous media under moderate face velocity.
• Particles spanning the submicron to several microns range.
• Dielectric fibers possibly exhibiting static charge.

Concept / Approach:
Three principal mechanisms are: interception (streamline contact with a fiber when the particle’s centerline comes within a radius), inertial impaction (particles deviate from streamlines due to inertia and impact fibers), and Brownian diffusion (for ultrafine particles). Electrostatic attraction can further enhance capture when fibers or particles are charged.

Step-by-Step Solution:
Associate small particles (< ~0.25–0.3 μm) with diffusion.Associate intermediate sizes with interception as they closely follow streamlines.Associate larger/faster particles with impaction due to inertia.Acknowledge electrostatic forces that raise capture probability across sizes.

Verification / Alternative check:
Filter performance curves vs. particle diameter exhibit a “U-shape,” reflecting different dominant mechanisms; adding electrostatics shifts the curve upward (higher efficiency) across ranges.

Why Other Options Are Wrong:
Each single mechanism alone understates overall filter action; practical performance comes from the combination.

Common Pitfalls:

• Assuming HEPA relies only on sieving; depth loading and multiple mechanisms are central.
• Ignoring humidity and charge dissipation, which can reduce electrostatic benefits.

Final Answer:
All of these