Chaotic Simulation And Experimental Research Of The Flow Field Stirred By Dislocated Blades

Stirred tanks are typical process equipment and are widely used in engineering. When the fluid in stirred tanks is turbulent, the fluid can mix well rapidly. But in the cases that the fluid viscosity is large or the fluid material is sensitive to shear force, the fluid in stirred tanks has to be in laminar. In these cases there are isolated mixing regions (IMRs) which are the worst obstacle to mixing existing in stirred tanks. With the rapid development of chaotic and nonlinear theories, chaotic mixing can be utilized to destroy the IMRs and improve the mixing effect.According to the chaotic mixing theory, aperiodic flow perturbations can be used to destroy the IMRs. So the blades of the 6-blade turbine were upper and lower dislocated respectively to generate the aperiodic flow field. The effect of the dislocated baldes on destroying the IMRs was investigated both experimentally and computationally. The main research contents and results are as followings.Firstly, Multi-reference frame(MRF) method was used for simulating the flow field of the standard 6-blade turbine. The positions of the IMRs were accord with the foreign experimental results. So the simulation method is feasible. Through the reliable FLUENT simulation method the velocity fields of different blades can be obtained. The results show that mixing effect of the dislocated blades are better than the standard blades and the improvements of the field depend on the dislocated scope and Re. The lager the blades dislocated, the better the mixing effect is. On the basis of the steady velocity field within the stirred tanks, the simulation of unsteady flow field were carried out by adding tracer. The results show that there are two IMRs whose tracer concentration are low in the standard 6-blade turbine stirred tank, however there aren't IMRs existing in the dislocated 6-blade stirred tanks. So the dislocated blades can destroy the isolated mixing regions.The acid-base neutralization experiments were used to validate the mixing effect on the basis of the former simulations. The experimental results validate the simulation conclusions. There are two IMRs existing above and below the impeller respectively. The dislocated blades can destroy the IMRs and the mixing effect are better. But whether the dislocated blades can destroy the IMRs completely depend on the impeller speed and the dislocated scope of blade.