Centrifugal filters
Centrifugal force is used to provide the driving force in some filters. These machines
are really centrifuges fitted with a perforated bowl that may also have filter cloth on it.
Liquid is fed into the interior of the bowl and under the centrifugal forces, it passes out
through the filter material. This is illustrated in Fig. 10.8(c).
Air filters
Filters are used quite extensively to remove suspended dust or particles from air
streams. The air or gas moves through a fabric and the dust is left behind. These
filters are particularly useful for the removal of fine particles. One type of bag filter
consists of a number of vertical cylindrical cloth bags 15-30 cm in diameter, the air
passing through the bags in parallel. Air bearing the dust enters the bags, usually at
the bottom and the air passes out through the cloth. A familiar example of a bag filter
for dust is to be found in the domestic vacuum cleaner. Some designs of bag filters
provide for the mechanical removal of the accumulated dust. For removal of particles
less than 5 m diameter in modern air sterilization units, paper filters and packed
tubular filters are used. These cover the range of sizes of bacterial cells and spores