There are 4 main principles of how mechanical filters remove particles from the air stream. Particles are captured by coming into contact with the fibers of the filter media in the following ways:
Particles in the air stream have mass and velocity, as the air stream passes through a filter media, the air diverts around the fiber, however because the particles tend to move in a straight line, those particles located at or near the center of the flow line will stick or impact upon the fiber and be removed.
In this process, particles are on a collision course with flow stream molecules. These frequent collisions cause the suspended particles to move in a random fashion around the fluid flow lines, which increases the likelihood of contacting the fiber surface and being removed.
Sieving is a simple technique for separating particles of different sizes. For example when a particle is too large to fit between the media fiber spaces.