Rating a Liquid Membrane in Gas

Gas filtration using membranes, particularly hydrophobic PTFE membranes, operate under different mechanisms compared to liquid filtration. While a 0.2µm membrane is effective for bacteria retention in liquids, gas filtration often requires tighter ratings of 0.02µm or 0.01µm.  The efficiency of gas filtration is enhanced by the lower viscosity of air, which allows particles to deviate from the main flow and interact more with the filter media.  Key mechanisms in gas filtration include diffusion, where small particles exhibit random motion, and interception, where medium-sized particles follow gas streamlines. Additionally, impaction captures larger particles that collide with the membrane due to their inertia. This results in the Most Penetrating Particle Size (MPPS) being significantly smaller than the nominal pore size, explaining the higher efficiency of 0.2µmmembranes in gas applications.

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