Numerical Simulation On Mixing Performance Of The High Viscosity Stirred Tank With Combined Agitator

The mixing performance of four types of impeller combination, including double helix and Paravisc as main impeller and inducing anchor and reducing helix impellers as the bottom impeller, is studied by means of Computational Fluid Dynamic way in a high viscosity stirred tank (T=0.476 m). The laminar model is used and both steady and transient simulations are established to study the power and mixing time for Newtonian fluid, and the optimal combination of the impeller is also simulated in a scale-up tank.Results show that the power of double helix ribbon, Paravisc and anchor increase with the increase of impeller width, and the power of double helix ribbon is largely influenced by the pitch. The correlations of KP of the mentioned impellers are obtained, providing important support for combined agitator design. The mixing performances of all types of combined agitators conform to a consistent rule, although the absolute mixing time varies with the position of monitoring point of tracer. The mixing time of the combined agitator with anchor as the bottom impeller is generally shorter than that with helix impeller as the bottom impeller. In the tested ten combinations, the Paravisc-Anchor requires the least mixing time, rotations and mixing energy per unit volume to reach a fully mixing; meanwhile, it shows the largest slope of dimensionless shear capacity versus rotational speed curve, showing the Paravisc-Anchor is better than other tested combinations. In the scaling-up of such a tank with the optimal combination from 100 L to 200 L and 500 L, it is found that the power curve remains the same under different scales, and also the scale-up follows the tip velocity principle.