Fig. 10 shows the relation between 50% cut size and apex cone
angle. It is found that 50% cut size indicated the minimum value for
the apex cone angle of 70°. The calculated results indicated by the
dotted line also shows the minimum 50% cut size for the cone angle of
60–65°. These results of high collection efficiency for cone angle of 70°
agree with the photographs shown in Fig. 9.
The particle trajectories calculated by CFD simulation are shown in
Fig. 11. The initial starting positions of particles are set to the same
points and three types of the apex cones are used in each case. For the
cone angle of 70°, the 1.3 μm diameter particles are collected on the
lower part of the apex cone. The particle collection place shown in
Fig. 11-b corresponds to the down-flow region of the apex cone surface
shown in Fig. 7-d. On the other hand, all particles are not collected for
the apex cone angles of 40 and 80°. Due to the strong upward flow near
these apex cone surface, the probability of particle collection will be
decreased. For the apex cone angle of 40°, the particles entering into the
lower part of the dust boxmove out of the dust box. The purpose of the
apex cone set in the dust box is to decrease the fluid flow component,
but the simulation results show that the apex cone angle of 40° is
ineffective.