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100 José Renato Coury et al.

Fig. 3. Cyclone dimensions.

velocity of the gas (v ) increases with the decrease of the radial position to a maximum
t
value (v ), and in the internal vortex the tangential velocity decreases toward the
tmax
center (6,11).
Several theories were proposed in the past 50 yr to predict the performance of
cyclones in terms of collection efficiency and pressure drop associated with the oper-
ation. These parameters are related to the cyclone dimensions, to the physical properties
of the solid and of the gas, and to operational conditions such as gas velocity in the
entrance, temperature, and pressure. The adopted concepts are based on distinct
approaches such as the following: the trajectory of the particle derived from the bal-
ance of forces acting on it, as in the models of Barth (12) and Iozia and Leith (10,13);
the residence time of the particles inside the device, as in Lapple (14), Leith and Licht
(9), and Dietz (8); or the derivation of dimensionless numbers that correlate the col-
lection efficiency with the operational conditions, as the one of Buttner (15) and
Moore and McFarland (16).
Next, the calculation procedure for designing a cyclone based on the models of Barth
(12), Leith and Licht (9), and Iozia and Leith (13) will be presented, followed by an
example of application and by the comparison of the results with the experimental data
obtained by Dirgo and Leith (17). The models were chosen based on their objectivity
and also with the intention of giving a chronological overview of the subject.