Abstract: A novel combined inner-outer agitator, which is applicable to working medium with different viscosities from lower to higher, is proposed. The computational fluid dynamics and particle image velocimetry technique are adopted to investigate the flow field stirred by this novel combined agitator. Under the conditions of different working medium or rotating speed ratios between the inner agitator and outer, the mean velocity, rates of the velocity change and shear rate in stirred vessel with this novel agitator are analyzed. Results show that the flow produced by the novel combined inner-outer agitator is dominated by all the three velocity components, and the distributions of radial and axial velocities changes closely depending on the rotating speed ratio. Using the novel combined agitator, the flow fields near the vessel wall can be improved. The improvement level increases with the decreasing rotating speed ratio, and it is better for the pseudoplastic fluid than the Newtonian fluid. The novel combined inner-outer agitator enhances the shear strength in the stirred vessel, especially in the regions near the vessel wall, and the amplification increases with the decreasing rotating speed ratio.

Key words: Flow fields, Novel combined inner-outer agitator, Numerical simulation, Particle image velocimetry