Principles of Filtration
Mechanical
Mechanical air filters remove particles from the airstream
because particles come in contact with the surface of fibers
in the filter media and adhere to the fibers. The mechanisms
by which the particles come in contact with the fibers in
the filter media is covered in the air filter mechanisms
section.
There are two broad categories of mechanical air filters
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Fine Fiber Media Air Filters - These filters utilize filter
media with fibers small enough in diameter to allow for the
capture of sub-micron particles at high efficiencies without
the necessity of electrostatic attraction. Fine fiber media
is often made of glass fibers or PTFE.
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Coarse Fiber Media Air Filters - These filters utilize media
with large diameter fibers which normally wouldn't allow for
the capture of sub-micron particles at high efficiencies.
To increase the particle capture efficiency, an electrostatic
charge is placed on the media to provide for electrostatic
attraction to particles. Coarse fiber media is often made
of synthetic fibers.
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Coarse Fiber Media Air Filters - These filters utilize media
with large diameter fibers which normally wouldn't allow for
the capture of sub-micron particles at high efficiencies.
To increase the particle capture efficiency, an electrostatic
charge is placed on the media to provide for electrostatic
attraction to particles. Coarse fiber media is often made
of synthetic fibers.
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Electronic Air Cleaners
These filters require an external power source. The filters
impose a charge on the particles in their first stage, and
often use a set of parallel plates onto which the particles
are collected in their second stage. The charged particles
will be attracted to a plate of the opposite charge. On a
regular basis, the plates need to be cleaned in order for
the filter to retain its maximum efficiency.
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