Flow in the Inlet Region in Tangential Inlet Cyclones

In this paper the flow pattern in a tangential inlet cyclone is studied by laser Doppler anemometry, with emphasis on the inlet region. The particular focus is on axial asymmetry in the flow, which was studied by determining radial profiles of the axial and tangential gas velocity components at four different angular positions. This was done at each of four axial flow stations. The results are shown graphically, discussed, and compared with the literature; in particular, they are compared with two studies: (a) an experimental investigation of the boundary layer flow in cyclones and (b) a study based on three-dimensional computational fluid dynamics (CFD) simulations. The results presented in this paper expose regions where the gas velocity differs considerably from that normally held to exist. Although the results generally agree qualitatively with numerical simulations, they differ considerably quantitatively: they show less axial asymmetry than do the CFD simulations. The results support the notion put forward by some other workers that a recirculatory flow pattern in the axial/radial directions exists in the upper part of the inlet region associated with secondary flows induced by the swirling motion in the boundary layer by the cyclone lid. This feature may have profound influence on the separation efficiency. The likely effects of the flow features on the separation efficiency of the cyclone and its reliability are discussed.