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Cyclones 101

Table 1
Dimensions for the Design of Standard Cyclones
Family: Lapple Swift Stairmand Swift Stairmand Swift
Use: General General High High High flow High flow
purpose purpose efficiency efficiency rate a rate a
3
2
Q/D (m /h) 6,860 6,680 5,500 4,940 16,500 12,500
c
a/D 0.5 0.5 0.5 0.44 0.75 0.8
c
b/D 0.25 0.25 0.2 0.21 0.375 0.35
c
H/D 4.0 3.75 4.0 3.9 4.0 3.7
c
h/D 2.0 1.75 1.5 1.4 1.5 1.7
c
D /D 0.5 0.5 0.5 0.4 0.75 0.75
e c
B/D 0.25 0.4 0.375 0.4 0.375 0.4
c
S/D 0.625 0.6 0.5 0.5 0.875 0.85
c
∆H 8.0 7.6 6.4 9.2 7.2 7.0
a Half-scroll entry.
Source: ref. 2.
2.2. Correlations for Cyclone Efficiency
The design of cyclones is usually based on seven geometrical relations of the above-
mentioned dimensions. These dimensions, when expressed as fractions of the body
diameter D , are fixed for a given cyclone “family” that can also be subdivided, according
c
to their use (high efficiency, high flow rate, general purpose). Table 1, taken from Leith
and Jones (2), lists the dimensional relations for the classical Lapple, Stairmand, and
Swift cyclone families and includes a criterion for the adoption of D based on the gas
c
3
volumetric flow rate (in m /h).
2.2.1. The Barth Model
The Barth model (12) predicts the collection efficiency as a function of the relation
between the terminal velocities of a particle of a given diameter and the particle col-
lected with 50% efficiency, which has equal probability of being or not collected
(17,18). For a particle of diameter D , the efficiency is thus given by
i
1
η = [ 1+(ν ν ts ) −32 ] (1)
.
i
m
ts
m
where v and v are the terminal velocities for the particle and for the one with 50%
ts ts
collection, respectively.
m
The ratio v /v can be related to the mean radial velocity of the gas in the central axis
ts ts
of the cyclone, where the maximum tangential velocity, v , occurs. Assuming Stokes
tmax
law and negligible gas density, this ratio can be expressed as
m
v π h ρ v 2 D i 2
ptmax
ts = (2)
v m 9µ Q
ts
m
The height of the cyclone central axis, h , is limited by the gas exit duct diameter,
D , and by the dust exit diameter, B, and can be estimated from Eq. (3) or (4):
e