Fluid macro-instability reflects fluid axial energy and mass transfer behavior. To reveal the unsteady flow rule in a mixer-settler with rigid-flexible impeller

oil and water were used as working fluid

and the wavelet analysis and Matlab numerical calculation were adopted to analyze the power spectrum of pressure fluctuation signal in the mixing tank. The influences of rigid-flexible impeller on the frequency of macro-instability were studied

and CFD simulation was adopted to explore the flow field structure in the mixer-settler. Experiments showed that

while the agitation speed (N) of rigid-flexible impeller was lower than 250 r·min-1

the relationship between macro-instability frequency (fMI) and N was linear. When N was higher than 250 r·min-1

much air was sucked into the liquid and fMI disappeared

so the flow field became multi scale structure and resulted in serious emulsification

which was unfavorable for the operation of clarification. Compared with rigid impeller

the rigid-flexible one can enhance the macro-instability and improve the efficiency of fluid mixing and energy transfer. Computational simulation shows that

the rigid-flexible impeller could obviously increase the blade suction ability and axial movement of fluid

realizing efficient mixing and avoiding excessive stirring of the fluid

which is helpful to mixing and clarification.