are lifted and moved to various directions in the case without the apex
cone, but themoving particles are not detected in the casewith the apex
cone. This fact indicates that the upward and rotating fluid components
remained in the dust box in the case without the apex cone and the
probability of the outgoing particles from the dust box is increased. In
order to clear the flow difference in the dust box, the flow visualization
using water supplied on the bottom of the transparent dust box was
carried out.