Chaotic mixing behavior of non-Newtonian fluid intensified by multilayer rigid-flexible impeller induced flow field interface instability

The traditional multilayer rigid impeller has large dead zone for the mixing of pseudoplastic non-Newtonian fluid, stable flow field interface and low mixing efficiency. A method for enhancing the chaotic mixing of non-Newtonian fluid by multilayer rigid-flexible impeller induced flow field interface instability was proposed. In the experiment, sodium carboxymethylcellulose was used as the non-Newtonian fluid system. The power characteristics were measured by the torque sensor. The mixing time was determined by the acid-base neutralization and decolorization method. The largest Lyapunov exponents were calculated by using Matlab software programming. The chaotic characteristics and mixing performance in the mixing process are analyzed. The results show that when the combination mode was RF-(PBTD+PBTD+DT), the impeller arrangement mode θ=60°, and the flexible sheet length installation ratio r=0.8, 1.2, the degree of chaos was higher and the mixing performance was better. Multilayer rigid-flexible impeller can generate multiple spiral flows, and realize the flow field interface instability under the disturbance frequency difference of the flexible sheet between the layers, the stirring dead zone was reduced, and the system enters a chaotic state at a lower speed (when the multilayer rigid-flexible impeller system N>88 r/min, LLE>0; when the multilayer rigid impeller system N>125 r/min, LLE>0). At the same speed, the mixing rate and power per unit volume of the multilayer rigid-flexible combined impeller are higher than that of the multilayer rigid impeller, but the mixing energy per unit volume is approximately the same.