MEAN VELOCITY MEASUREMENTS IN A 3'-HYDROCYCLONE USING LASER DOPPLER ANEMOMETRY.

摘要

Within the class of inertial separators, the hydrocyclone is especially noteworthy because of its simplicity of operation and its many diverse applications. Although a good qualitative understanding of solid-liquid separations in hydrocyclones is presently available, the relative importance of the various secondary motions on the separation efficiency of a hydrocyclone has not been quantitatively considered.; In the absence of a particulate phase and an air core, a quantitative study of the axial and tangential components of the mean velocity in a glass 3''-hydrocyclone using laser doppler anemometry has revealed multiple reverse flows in the vortex core. Flow visualization by dye injection shows that these flows are coherent over a significant portion of the hydrocyclone and that little radial mixing occurs between these secondary flows and the outer helical flow, although the Reynolds number based on the entrance diameter and feed flow rate exceeded 10,000. Several different vortex finder designs were studied, including one which satisfies standard optimal scaling rules. It was discovered that a 2:1 contraction in the vortex finder causes four distinct simultaneous countercurrent flows in the conical section of the hydrocyclone. Moreover, for low backpressure operation (< 2 psig), a recirculation zone was detected in the upper part of the hydrocyclone with as many as six reverse flows. For some hydrocyclone designs and operating conditions, a jet-like flow on the axis occurs from the apex region to the vortex finder. This phenomenon partially explains why the design criteria of Rietema are optimal. The measured tangential velocity profiles were independent of axial location, and showed a characteristic "forced" and "free" vortex behavior in the inner and outer regions, respectively. The addition of 100 wppm Separan AP-30 decreased the tangential velocity and reduced the magnitude of the reverse flows in the core region. For the hydrocyclone studied, a split ratio from zero to infinity and a feed rate from 150-500 cm('2)/sec have little effect on the vortex diameter ((TURNEQ) 3 mm) and the conical locus of zero axial velocity in the outer flow domain.