INVESTIGATION OF FLOODING,RE-ENTRAINMENT AND GRADE EFFICIENCY IN AXIAL FLOW CYCLONES

摘要

Slotted wall axial flow cyclones with a conventional center-body swirler are found to exhibit significant flooding at low air velocities.This was observed to be due to significant liquid hold-up on the vanes which eliminated the swirl and led to a pulsating frothing behaviour.At higher velocities,the liquid dispersed and separated through the wall slots.The onset of entrainment of liquid was determined visually.In the low velocity frothing region liquid was entrained directly but coalesced and fell back down the vortex finder.At higher gas velocities entrainment occurred due to several mechanisms.Design changes were introduced to improve performance.The center body was replaced by a new design of vane swirler around the periphery of the tube inlet.This significantly increased the swirl in the tube.Adapting four of the vanes to operate as liquid drainage channels eliminated the flooding phenomenon observed at low gas velocity and enabled the tube slot area to be reduced.This,combined with a larger diameter vortex finder,significantly increased the fraction of flow through the vortex finder,with no extra overall pressure drop.Liquid entrainment in the new design was reduced by positioning liquid slots at the top of the tube and by the use of a skirt.Grade efficiency was determined for the improved cyclone design operating over a range of gas flowrates.The cut size for outflow to the vortex finder was found to vary from about 7 mu m at an air velocity of 4.5 ms~(-1)to about 4.5 mu m at 11 ms~(-1).