Abstract: There is no problem for mixing inside the stirred tank when the flow is in turbulent state. However, how to improve the mixing efficiency becomes a practical problem while the flow inside stirred tank is in laminar condition. For the purpose of enhancing the mixing efficiency inside laminar stirred tank, chaotic mixing is applied with the impeller rotating in periodic form. The particle image velocimetry technique is used to measure the laminar flow field inside the stirred tank, the particle images acquired are post-processed by special image processing software, radial velocity distributions at six different angles are displayed in the form of flood contours. The results velocity curves of mixing with variable rotation speed are compared with that of mixing with constant rotation speed. The experimental study shows that the area disturbed by radial velocity with variable rotating speed is larger than that with constant rotating speed, and proves that the mixing effect and the mixing efficiency are better with the axis rotating with variable speed. The research work is significant for analyzing the mechanism of chaotic mixing and for designing of large scale stirred tank.

Key words: Chaotic mixing Particle image velocimetry, Flow field, Stirred tank, Variable speed