Page 188 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

6.3 Electrostatic Precipitation 163

Fig. 6.5 Comparison of field 10000
and diffusive charging of
particles 1000
Number of ions charged 10 1 Diffusive Field
100

charging

0.1
0.01 charging
0.001 0.01 0.1 1 10 100
Particle diameter, micrometer

produced by corona discharge, and they are considered as secondary air pollutants.
More information about nanoparticle generation in corona charger can be found in
Chap. 14.

6.4 Cyclone

A cyclone separates particles from the air by “centrifugal force”. As depicted in
Fig. 6.6, particles and air enter the device from the side. When the air changes
direction following the curvature of the device, particles tend to remain the same
flow direction due to inertia. As a result, the particles move along radial direction
with respect to the air. This is commonly referred to as centrifugal force, which is
actually conceptually incorrect.
Figure 6.6 shows the top view of a cyclone body, the height and width of the
rectangular inlet are H and W, respectively, and radii of the outer and inner tubes are

Fig. 6.6 Particle motion in
rotating fluids