Power consumption and flow field characteristics of a coaxial mixer with a double inner impeller

A coaxial mixer meeting the actual demand of a system with high and variable viscosity is investigated. It has an outer wall-scraping frame and a double inner impeller consisting of a four-pitched-blade turbine and Rushton turbine. The power consumption and flow field characteristics of the coaxial mixer in laminar and transitional flow are simulated numerically, and then the distribution of velocity field, shear rate and mass flow rate are analyzed. The simulation results indicate that the outer frame has little effect on the power consumption of the double inner impeller whether in laminar or transitional flow, whereas the inner combined impeller has a great effect on the power consumption of the outer frame. Compared with the single rotation mode, the power consumption of the outer frame will decrease in co-rotation mode and increase in counter-rotation mode. The velocity, shear rate and mass flow rate are relatively high near the inner impeller in all operating modes, and only under double-shaft agitation will the mixing performance near the free surface be improved. In addition, these distributions in the co-rotation and counter-rotation modes show little difference, but the co-rotation mode is recommended for the advantage of low power consumption.

The coaxial mixer investigated consists of a low-speed outer wall-scraping frame and high-speed double inner impeller (upper four-pitched-blade turbine and lower Rushton turbine). The numerically simulated flow fields of high viscosity liquid under single rotation of inner impeller, co-rotation and counter-rotation modes are presented. By comparison, double-shaft mixing prevails in rapid mixing comparing to single-shaft mixing, and co-rotation is better than counter-rotation.Figure optionsDownload as PowerPoint slide