Numerical Study Of Internal Flow Fields Of Stirred Tanks

In this paper, numerical simulation is carried out to study the flow fields in three stirred tanks such as the general pitched blade turbines (PDT), the standard RUSHTON, and a stirred equipment with special usage. The internal flow character and energy distribution rule of the different stirred tanks are anzlyzed. Meanwhile the effects of ultrasonic added for mixing enhancement in the stirred vessel are numerically simulated and validated by PIV measurement.The results show that there is a large-scale vortex in the outer of the blade and a small vortex below the blade. The RUSHTON stirred tank also has two vortices which can make the full vessel in flow recirculation. But there is very little flow exchange between the vortices. The region of the stirred blade has a relative large turbulence and high turbulence dissipation rate. The special usage stirred mixer has trapezoidal shape in the gap between the blades. When the rotor runs, it works just like a pump, the fluid in below is pumped up to the rotation blade and then discharge into the outer space through the gap, forming two vortices in upper and lower of blades, respectively.This paper give a relatively complete descrioption of the flow phenomena for the three types of stirred tanks. Also, a preliminary result for the study processing enhancement by using ultrasound is presented.