shows the fluid velocity vectors around the apex cone of the
cone angle from 40 to 80°. For the apex cone angle of 40°, the upward
velocity components are detected on the inclined surface of the apex
cone. But for the apex cone angle of 70°, the critical line between
upward flow and downward flow shown in the dotted line is detected
and the downward flow velocity components are very small
compared to the upward flow. The separation line between upward
and downward flow is clearly found for the apex cone angle of 70°.
The red circles in Fig. 7 show the upward flow region. For the 70° case,
the upward flow region is observed in the upper half area, but the
region is slightly increased for the 80° case. Then it is considered that
particles collected on the upper conical section might be easily moved
to the central upward flow. In order to find out the critical line of the
upward and downward flow on the inclined surface of the apex cone,
visualization experiments were carried out by use of soap foam.
Before running the experiments, all surfaces of the apex cone were
coated with white soap foam. Then inlet flow was introduced to the
cyclone during 10 min, and the observation of the surface of the apex
cone was carried out