Particulate Emission Control - Mathematics and Statistics for the Environment - page 504

Inner
vortex

Zone of inlet
interference

Outer
vortex

Top view

Gas outlet
Body
Inner
cylinder
(tubular
guard)

Gas inlet

Side view

Outer
vortex

Core

Inner
vortex

Dust outlet

FIGURE 17.5 Convection reverse-flow cyclone. (From USEPA, Control of Gaseous and Particulate
Emissions: Self-Instructional Problem Workbook , EPA 450/2-84-007, U.S. Environmental Protection Agency
Air Pollution Training Institute, Research Triangle Park, NC, 1984.)

17.4.2.1 Factors Affecting Cyclone Performance
The factors that affect cyclone performance include centrifugal force, cut diameter, pressure drop,
collection efficiency, and a variety of performance characteristics. Of these parameters, it is the cut
diameter that is the most convenient way of defining efficiency for a control device because it gives
an idea of the effectiveness for a particle size range. The cut diameter is defined as the size (diam-
eter) of particles collected with 50% efficiency. Note that the cut diameter, [ d p ] cut , is a characteristic
of the control device and should not be confused with the geometric mean particle diameter of the
size distribution. A frequently used expression for cut diameter, where collection efficiency is a
function of the ratio of particle diameter to cut diameter, is known as the Lapple cut diameter equa-
tion (method) and is given below (Copper and Alley, 1986):

9 µ B

d = (17.19)

( )

p

cut

2 π nv pp −

ti p g

where
[ d p ] cut = Cut diameter (ft, µm).
µ = Viscosity (lb/s-ft, Pa-s, kg/s-m).
B = Inlet width (ft, m).
n t = Effective number of turns (5 to 10 for common cyclones).
v i = Inlet gas velocity (ft/s, m/s).
p p = Particle density (lb/ft 3 , kg/m 3 ).
p g = Gas density (lb/ft 3 , kg/m 3 ).