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.