A type of agitator used in mixing or blending fluids of low viscosity, usually in a cylindrical chamber, either open or closed. The motion induced by an impeller is a combination of flow and turbulence, the proportion of each depending on the size, speed, and position of the impeller. In common use are the marine propeller, the turbine, and the helical ribbon types. Propeller and turbine impellers are attached to a power-driven rotating shaft that enters the container either vertically (top entering) or at an angle (side entering), they may be centered in a liquid or placed off center, depending on the flow pattern desired. The propeller type has from two to four elliptical blades, whereas the turbine has a number of rectangular blades set vertically or at an angle. A wide range of flow-turbulence patterns can be obtained with either type. Helical ribbon impellers are used for viscous liquids and dry powders. Many variations of impellers are available for liquids up to medium viscosity for a multitude of special mixing techniques.See Agitator; Mixing.
