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Filtration 101 - A Deeper Cut |
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Most people believe
that all air filters function on a go/no go basis where dirt particles
that are larger than the openings in the filter media are trapped while
particles that are smaller than the openings can pass right through. A
dry paper air filter does function in this manner. That’s why paper
filters are so restrictive to air flow. The openings in this type of
filter have to be very small to filter efficiently. |
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The oiled cotton media
used in the K&N air filter functions in an entirely different manner.
There are scientific principles that determine how an air filter removes
dirt particles from the air stream. The first of these principles is
known as interception, which applies to dirt particles traveling with
the air stream. Air flow will always take the shortest path and as the
air is forced to flow around the filter’s fibers some of the particles
will contact the sides of the fibers and be captured. These particles
are then held in place by the oil or tacking agent in the fiber. |
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Another principle is
known as impaction, which mostly affects larger or heavier dirt
particles. Impaction occurs when the inertia or momentum of the particle
causes it to deviate from the flow path. In other words the heavy
particles do not follow the air stream around the filter’s fibers but
instead they run straight into the fibers and are captured. |
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| The most
important principle for our use is diffusion, which deals with the laws
of physics that govern the motion of very small dirt particles. Small
particles are highly affected by the forces in the air stream. Forces
such as velocity changes, pressure changes, turbulence caused by other
particles and interaction with the air molecules cause these very small
particles to become random and chaotic. As a result, these particles do
not follow the air stream and their erratic motion causes them to
collide with the filter’s fibers. This phenomenon enables an air filter
to capture dirt particles that are much smaller than the openings in the
media. In addition, the way that dirt collects or loads on the K&N
filter is very different. A paper filter exhibits "surface loading"
which means dust collects only on the surface of the media. In contrast,
K&N filters exhibit "depth loading". The multiple layers of cotton
fibers provide many levels of dust retention. This characteristic
allows the K&N filter to hold significantly more dirt per square inch of
media than the average paper filter. Utilizing these scientific
principles, K&N has been able to design an air filter that is very free
flowing while also being highly efficient at removing dirt from the air. |
