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October 2020 / 17 the inlet to compress the solids to the outer wall and, thereby, fur- ther promote solids moving to the wall and roping. Other cyclones use a helical (corkscrew-shaped) roof to preset the swirling flow. 5 An unobstructed path For high-loading cyclones, the path of the incoming particles is also a swirls. Too short of an inlet or a biasing of solids in the inlet toward the inside can reduce these swirls in number and stability, which results in lower collection efficiency. Some cyclone designs max- imize this swirling flow. In fluidized beds, an asymmetric horn 3,4 (nonsymmetric expansion at the cyclone inlet) is added to hydrodynamics are not. As gas and particles enter the cyclone through the tangential inlet, the swirling flow produces a cen- trifugal force, which affects the more massive particles more than the much lighter gas. As a result, particles concentrate at the bar- rel wall and fall into the conical region, or cone, as "ropes." Figure 2 shows this roping for a Geldart- classified group A powder in a 17- inch- barrel- diameter cyclone. Inducing swirling flow For high-loading cyclones, such as primary units (first in a series of more than one), only one or two swirls or ropes of particles develop, whereas low-loading units, such as secondary cyclones, can have five to eight swirls, as seen in Figure 2. These swirls are important to the cyclone's collection efficiency. Particles that are clustered together in ropes are less susceptible to wall friction and gas-phase turbulence. Having a good inlet design is essen- tial in the development of these FIGURE 2 Ropes or particle swirls in a 17-inch- diameter cyclone with Geldart- classified group A particles