Environmental Engineering FOURTH EDITION

392 ENVIRONMENTAL ENGINEERING

Table 20-1. Values of K for Calculating

Cyclone Pressure Drop

Cyclone diameter (in.) K

29

16

8

4

10-~

10-~

10-2

0.1

P = absolute pressure (in atm),

p = gas density (in kg/m3),

T = temperature (in K), and

K = proportionality factor, a function of cyclone diameter.

Approximate values of K are given in Table 20- 1. Typical pressure drops in cyclones
are between 1 and 8 in. of water.
The collection efficiency of a cyclone can be estimated by using the concept of a
cut diameter, the particle diameter at which 50% of the particles are removed from the
gas stream by the cyclone. The cut diameter is

where

(20.10)

,!L = gas v,,cosity (in kg/m-h),

b = cyclone inlet width (in m),

N = effective number of outer turns in cyclone (usually about four),

vi = inlet gas velocity (in ds),

ps = particle density (in kg/m3), and

p = gas density (in kg/m3), usually negligible compared to ps.

Figure 20-6 shows how the cut diameter can be used to establish the collection

efficiency for particles of any diameter d. The number of turns N can also be

approximated as

It

N = -(2L2 - Ll), (20.11)

H

where

H = height of the inlet (in m),

L1 = length of cylinder (in m), and

L2 = length of cone (in m).