Four mechanisms are predominant in determining a filter's efficiency versus particle size. These are: interception, inertial impaction, diffusion, and electrostatics. Large particles above 0.4 µm in diameter will be captured due to both the impaction and interception mechanisms. Small particles, below 0.1 µm in diameter, are captured by the diffusion and electrostatics mechanism. Medium particles, generally considered as the most penetrating, in the 0.1 to 0.4 µm diameter range, are captured to lesser extents by all four mechanisms.
The result of the various filtration mechanisms can best be illustrated with a graph of efficiency versus particle size, as illustrated in Figure 4. Note the upside down bell-shaped curve resulting from the additive contributions of filtration via diffusion and interception mechanisms. In general, a filter is generally least effective at removing particles in the 0.1 µm to 0.4 µm particle diameter range.
Click here to view the Overall Efficiency vs Particle Size animation
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