Mixing technology has a wide range of applications in chemical production

pharmaceutical and environmental protection. The mixing efficiency and flow field distribution are important indicators for measuring the quality of the mixing. However

in the laminar agitated flow field

the periodic disturbance of the agitating paddle creates an annular dynamic flow field resulting in the existence of a mixed isolation zone in the agitation tank. The existence of the isolation zone is the main obstacle to achieving efficient mixing. In this study

a planar laser induced fluorescence (PLIF) technology was employed to visualize the dynamic structure of mixing flow field. The post-image processing has been done with MATLAB and the custom-made functions was designed to evaluate the mixing efficiency. The effects of Reynolds number and the geometrical parameter of the stirred tank on the flow features were studied. The results show that the non-mixing zone always appears regardless of the mixing time

and it will not be broken down as the increase of Re in laminar mixing region. Different baffles are designed to destroy the symmetry of the flow field and thus substantial is increased the mixing efficiency. The results show that non-mixed regions of annular flow field can be almost completely removed if the baffle (ring baffles and cuboid baffles) structures are embedded in the specific position

and the mixing efficiency increased from 65% to 97% in 200 s.