Filter medias have openings through which air and fluid passes. If the particles in the flow stream are larger than the pores or openings in the filter medium, they will be removed as a result of direct interception by the holes.
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.