Any rotating device that induces motion in fluid mixtures over a wide range of viscosities, thus effecting uniform dispersion of their components. An important class of agitators comprises impellers which produce turbulent flow in liquids of low viscosity; their diameter is much less than that of the container. They may be either top-entering (vertical) or side-entering (at an angle of approximately 45°); medium-viscosity liquids are agitated by paddles attached to a central rotating member. Pastes and high-viscosity mixtures in which no turbulent flow is possible require agitators that closely fit the mixing chamber so as to provide the necessary shearing and squeezing action throughout the mass. These are kneading devices utilizing curved or helical rotors or sigma blades, either single or double. Screw-type agitators permit continuous mixing by means of multiple shearing and blending actions. So-called ribbon agitators are effective for dry powders, slurries, etc. A number of ingenious modifications and combinations of these types are widely used in the process industries. Most are available in laboratory sizes.See Impeller; Mixing; Kneading; Screw.
