Mixing Time in Rheologically Evolving Model Fluids by Hybrid Dual Mixing Systems

Abstract

Mixing time experiments were performed using a hybrid dual mixing system, which included a helical ribbon impeller (HR) and either a Smith (ST) or Rushton turbine (RT). Xanthan gum solutions were used as rheologically evolving fluids to evaluate changes in mixing time under non-aerated and aerated conditions. The helical ribbon agitator and turbine of the hybrid dual mixing system was kept at a constant rotational speed ratio, N T /N HR =10. Experiments showed that performance of the hybrid mixing system was superior to that of the individual impellers. Flow properties and gassing conditions played an important role in mixing time. While mixing time was practically identical under non-gassed conditions for both the ST-HR and RT-HR mixing systems in low-viscosity fluids, differences up to 1000% were observed in high shear-thinning fluids. In these fluids, the RT-HR combination exhibited better performance than the ST-HR. In high-viscosity fluids, gassing enhanced mixing time particularly when the ST-HR hybrid system was used. Both mixing systems showed similar mixing times under the highest gassed condition evaluated in this work.