Analysis of flow pattern characteristics and strengthening mechanism of co-rotating and counter-rotating mixing with double impellers on different string shafts

Based on two cases of the double impellers on different shafts in the co-rotating and counter-rotating, the distribution of the velocity, streamline, turbulent kinetic energy, and turbulent energy dissipation rate are obtained through three-dimensional unsteady numerical simulation. Very good agreements between experimental and numerical results have been obtained. The hydrometallurgy purification experimental platform was built with the size of one third of the simulated. The results show that the mechanical string mixing system with double impellers on different shafts can form a more obvious convection effect in the central area of the double impellers, which can effectively break the mixing isolation region and improve the mixing effect. In the co-rotating case, the two impellers can generate strong convection in the central area and form an interactive vortex and a high-speed flow channel between the two impellers. while the convection formed by counter-rotating case is weaker and the vortex structures are independent of each other. The counter-rotating system performs better in the macro momentum transfer and the co-rotating system performs better in the micro-mixing level. In the experiments of hydrometallurgy purification, 7.93% more energy is used in the co-rotating system than that of the counter-rotating system. The average energy consumed by co-rotating in the process of purifying every one percent of Cd2+ ions are 8.65% lower than that of counter-rotating. The co-rotating system can improve microscopic mass transfer effect and finally save energy and time compared to the counter-rotating system.