EXPERIMENTAL AND NUMERICAL STUDY OF CENTRIFUGAL SEPARATION OF PARTICLE-LIQUID SUSPENSION IN A CYLINDRICAL CONTAINER

Abstract

Results of the experimental and numerical studies of the centrifugal separation in a cylindrical container are presented. The numerical calculations are based on the Ungarish' s formulation on solid-liquid two-phase flow in a "finite" cylinder. Apart from examining the influence of various parameters such as ?O , ?, H, ?i, ? and ?O (defined in List of Symbols) on the flow field, the propagation of the kinematic shocks was also studied. The numerical results show that the major parameters ?O , ?, ?, H and ?O have a strong influence on the angular velocity VC, VD, VR through the Ekman layers. The influence of these parameters on the radial velocity and the volume fraction, however, is small. Also, it is found that the inner radius ri doesn't significantly affect the flow field in the container, it however has considerable influences on the kinematic shocks and the separation. As for the experimental study, it is made up of two parts. In the first part, we examine the variations of the settling time with the angular speed ? and the size of particles in a real centrifugal spectrometer. In addition, we studied how the angular speed ? and the density difference c influence the kinematic shocks. The results show that the separation time decreases hyperbolically as the angular speed ? increases. Likewise, it is also found that the separation time decreases with the increase in the size of the particles. In addition, the angular speed ? is found to have a strong influence on the kinematic shock through the effect of the spin-up. However, the density difference ? only has a slight influence on the kinematic shock. In the second part of the experiment, we focus only on the separation of light particles. The underlying motivation is to examine how the aspect ratio of the cylinder H, angular speed ?*, density difference £ affect the separation time of the particles, and the propagation of the kinematic shocks (or interface). The results show the separation time slightly elongates as the aspect ratio increases. But the separation time is strongly influenced by the corresponding dimensionless numbers Ek, Ta and ?. Qualitatively, although the experimental results look similar to the theoretical and numerical solutions, but quantitatively, the asymptotic interfaces of Ungarish always lag behind the experimental interfaces. It is also shown that during the period of the spin-up, the interface moves farther and faster as the aspect ratio H of the container or the angular speed ?* increases. All of these indicate that ? plays a very important role in the spin-up stage of the centrifugal separation. In addition, the interface shows the non-symmetry and unsteadiness when the density difference is large.