Extract from
The American Society Of Mechanical Engineers

www.asme.org

PARTICLE SIZE
The characteristic blue color of oil- and tobacco mist comes from refraction of light through mist particles that have the same size as the blue light portion of the spectrum. That is, the particle diameter of the mists are about the same size as the wave length of blue light – from 4270 to 4680 angstrom units (0.427 to 0.468 µ wave length). In fact, the intensity of the refractive blue color is indicative of the particle distribution within that narrow range of the blue spectrum.

To put small particle size of oil mist into a more visual perspective, the range of bacteria size is 0.3 µ to 120 µ. The human eye generally can see shapes no smaller than about 50 µ; the keenest of young eyes can possibly see shapes as small as 40 µ.

Particles smaller than 0.1 µ are seldom considered to be of any practical importance. In fact, the collection and removal efficiency for 0.1 µ diameter particles is greater than for larger, 0.3 to 0.5 µ particles. This apparent contradiction is explained theoretically by the stronger and more active Brownian movement of particles smaller than 0.1 µ plus the deceasing effect of the Cunningham factor correction to Stokes law.

The small size and resultant low mass of oil mist particles severely restricts the collection efficiency of most mist elimination equipment.


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