A Numerical Analysis on the Flow Characteristics in a Helical Screw Agitator With a Draught Tube

Mechanical agitators are widely used in several industries which can mix one or more reactants, or mix some of the high viscous fluids. In general, simple impeller type is applied to mix low viscous fluids, while a helical screw agitator (HSA) is applied to the high viscous fluids. The study of flow characteristics inside the agitator is important because the mixing efficiency is greatly affected by the existence of draught tube. The HSA with a draught tube is known more efficient than the others. In this study, three-dimensional model consisting of outer vessel, helical screw and draught tube are considered. The draught tube in the vessel disturbs radial flow, hence it makes intermixing between the screw and tube. Also, the pitch of screw is capable of influencing the flow pattern. Consequently, the shapes of vessel, helical screw and draught tube are the main parameters for improving the performance of HSA. Numerical analyses were carried out with different geometrical configurations. Using a commercial CFD code, Fluent, velocity and pressure distributions inside of the HSA are obtained under steady, laminar flow and no-slip condition. Results are graphically depicted with several parameters.