Abstract

The hydrocyclone is a very useful tool which utilizes high centrifugal forces to separate solids from liquids. Its success is primarily due to the simplicity of construction and operation, versatility in application, and relative insensitivity to changes in design. In the present study, the Laser Doppler Anemometry (LDA) has been deployed to measure the mean velocities in the 6" hydrocyclone. Traditionally, a flat surface box or jacket is used to encase the hydrocyclone in an auxiliary box to minimize the refraction effects of laser beams which is caused by the curved solid wall of the hydrocyclone and the refractive index of the test medium. A new procedure is developed to reorient the laser beams that permit one to measure two velocity components at a single point. In this new procedure, the probe is tilted by 45° (called the transform position) to force the four laser beams of the LDA to intersect at the same point. Therefore, the tangential and axial velocities yet fully characterized and measured. The measured axial velocity profiles in the transform position were all corrected for index of refraction effects. This gives approximately the same results for this velocity in the traditional optical probe position (called the regular position). The conclusion developed from these experiments enables one to use the LDA directly in the hydrocyclone wall without recourse to auxiliary attachments such as an enclosing box. Further, the new procedure permits the determination of the turbulent intensity as the fluctuations of two velocity components can be measured at the same point. Flow visualization by droplet dye injection shows five different kinds of flow field patterns inside the hydrocyclone. The features of the flow field in the hydrocyclone, as seen in the dye tests, were confirmed by the flow patterns derived from LDA experimental data. The number of turns associated with the flow in the hydrocyclone was also determined. Prediction of flow field characteristic was also achieved by a very short study related to Computational Fluid Dynamic (CFD) modeling. A 3-D turbulence model that uses the Reynolds Stress Model (RSM) was adopted to simulate the flow field patterns. RSM predicted the velocity field in the hydrocyclone very well. The predicted velocities agree well with the experimental results by LDA and flow visualization study.