Page 258 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

230 Applied Process Design for Chemical and Petrochemical Plants

Figure 4-4. Comparison chart showing ranges of
performance of several collection/control devices
in air streams. By permission, Vandegrift, et. a/.
Chemical Engineering, Deskbook Issue, June 18, 0.01 0.1
1973, p. 109. Particle diameter, microns

(b) Spherical particles between 100 and 1500 microns (d) Spherical particles between 0.1 and 3 microns:
diameter [ 131 : Stokes-Cunningham Law [ 121 :

(46)
0.153g,0~71D,'"4 (p, - p)'.'
Ut =
p 0.29 p 0.43 (4-7)
he 1.64 +
C = 18.5 N,C0.6 , (See Figure 4- 1) = (48)

This represents a correction on Stokes Law and is sig-
(C) For spherical Particles between and loo microns nificant for 3 micron and smaller particles in gases and
and Reynolds numbers O.Oool and 2.O5 0.01 micron and smaller particles in liquids. Table 48
Stokes Law: gives values of K.
When two free settling particles of different dimen-
CNR, = 24 sions, D',1 and D'p2 and different densities, ppl and pp2,
fall through a fluid of density, pf, they will attain equal
velocities when:
Fd = ~TWD~/~L

and:
(4-9)

(4-5) where n = 1 in eddy-resistance zone (more turbulent) and n =
0.5 in streamline fall.

Alternate Terminal Velocity Calculation
For particles smaller than 0.11.1 the random Brownian
motion is greater than the motion due to gravitational set- In contrast to individual particles settling in a very
tling. Therefore the above relations based on Stokes Law dilute solution/fluid, is the case of sedimentation where
will not hold. particles must settle in more concentrated environment,