Flow field in a stirred vessel is usually divided into chaotic and regular mixing regions. It is an alternative way to improve mixing performance and lower the energy consumption by enlarging chaotic mixing region. Reasonable design of impeller is helpful to form appropriate flow condition and to improve the fluid mixing efficiency. Rigid-flexible combination can be designed by flexible body and rigid body with multiple-body motion behavior

intensifying the chaotic mixing. In this study

with the software Matlab

the largest Lyapunov exponent and multi-scale entropy in the tap water mixing system are investigated with double mechanical impellers. The difference between rigid and rigid-flexible impellers is analyzed in mixing performance. Results show that the rigid-flexible impeller enhances fluid movement and the fluid goes into chaotic mixing. At 210 r·min-1

the fluid is chaotic mixing

and the largest Lyapunov exponent is 0.041 for rigid impeller

while it is 0.048 for rigid-flexible impeller. The rigid-flexible impeller could transfer energy effectively and make the energy distribute uniformly. At agitation speed 150 r·min-1

the multi-scale entropy rate of rigid-flexible impeller is similar to that of rigid one at 210 r·min-1. Compared with rigid impeller system

the mixing time is shortened by about 26% with rigid-flexible impeller system. The rigid-flexible impeller could enhance the fluid chaotic mixing and save energy by changing the flow field structure and energy dissipation.