Experimental Study And Simulation Of Single Particle Critical Suspension In Stirred Tank

Solid-liquid suspension has a wide application in industry, such as chemical and pharmaceutical engineering, water treatment process, crystallization reaction system, etc. Previous studies of the solid-liquid suspension mechanism in stirred tank, are mainly focused on the macroscopic motion of particle group. And the mechanism of interaction between the particle and the surrounding fluid can't be well explained. In recent years, some researchers begin to study the movement of single particle in order to understand the mechanism of particle suspension. But in their papers, the impeller with simple geometry is used and the movement of particle is in laminar flow.This paper studies the movement of a single sphere, under conditions with different Reynolds number, in a square stirred tank with Rushton turbine (C/T=0.25). By the application of digital Image processing, the trajectories and the velocity of particle can be easily obtained. The details of particle movement and flow field have been described by the simulation based on Lattice-Boltzmann method. The results show:(1) Re-30, the movement of glass spheres under critical condition is similar with the experimental results of disk sauce in literature. For Rushton turbine, the just suspending impeller speed of particle is about 10% lower than disc. The simulation results are in good agreement with the experimental results. Compared with the simulation results of disc, the pressure distribution in stirred tank with Rushton turbine is asymmetry, and the pressure between upper and lower ends of the particle is nearly same during the beginning of suspension. (2) Re?240, the movement of glass spheres under critical condition is similar with Re?30. Glass spheres with three different diameters have almost same just suspended impeller speed (the difference is about 2%), which means the influence of diameter on particle suspension can be ignored. Under the conditions of this Reynolds number, net weight force of particles is the main factor which determines the particle suspension. (3) Re=300?1400, the movement of spheres becomes irregular. It can be described by an average speed for the whole progress of the particle movement on the bottom of tank. PIV method is used to describe the flow field of single phase in stirred tank, which is similar with the simulation results.