Space Grant Consortium - University of Wisconsin - Green Bay

particles results in reduced centrifugal and inertial forces on the particles, and the particles stay
largely entrained in the air flow as it travels through the cyclone. Most of these smaller particles
escape with the air through the axial vortex finder. The heavier (dp = 10µm) particles experience
larger inertial and centrifugal forces, and travel to the walls of the cyclone where they are eventually
trapped.
Figure 2: Representative particle traces for particles of diameter (a) 0.1 µm, and (b) 10.0 µm. The
larger particles are more efficiently captured in the cyclone, while most of the smaller particles
escape.
Collection efficiencies for each set of particles are calculated according to Eqn. 1. The efficiency
results for both zero and 1-g calculations are displayed in Fig. 3. There is no statistically significant
difference between the collection efficiencies obtained under the different gravitational fields. This
result agrees well with our experimental data which are also displayed in Fig. 3. For particles
with 1.0µm < dp < 5µm, the CFD calculations underestimate the efficiency of particle capture
relative to experimental data. This is due to the inability of the standard k − ɛ model to reproduce
the strong inner vortex present in real cyclones. In a real cyclone, the inner vortex core extends
nearly the entire length of the cyclone and serves to provide particle trajectories that can also span
the length of the cyclone. In contrast, the CFD calculations produce an axially compressed inner
vortex that results in a “short-circuit” of the flow for particles entrained in the inner vortex. The
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