AGGLOMERATION: The recombining of finely dispersed particles into larger particles, usually caused by a rearrangement of surface forces resulting from a change of environment. It is the opposite of dispersion.

BAFFLE: A stationary device usually installed at or near tank walls to prevent liquid swirl and promote vertical flow in the vessel.

CRITICAL SPEED: The rotational speed of a shaft equal to the frequency of the natural harmonic vibration of the shaft.

DILATANT FLUID: A material in which the viscosity increases with increasing shear rate.

EMULSION: A colloidal dispersion of two or more liquids that are immiscible with each other.

FLASH MIXER: An agitator used to mix a small amount of additive into a continuous stream where the residence time is extremely short (usually less than one minute). It most often refers to addition of chemicals, which cause or aid flocculation in water or waste treatment operations.

GEAR RATING: The horsepower capability of a drive unit meeting life and strength standards established by the American Gear Manufacturers Association (

HELIX: A type of impeller consisting of one or more narrow ribbons that spiral around the shaft, affixed to arms mounted on the shaft, and having a diameter near that of the vessel. It is used for high-viscosity liquids or solids.

NEWTONIAN FLUID: A fluid whose rate of flow is proportional to the stress applied to it. The viscosity is therefore constant and independent of shear rate.

PADDLE: A two-bladed impeller whose diameter is usually greater than 60 percent of the tank diameter.

RADIAL FLOW: The movement of a fluid generally from the center of the tank to the wall.

SCRAPERS: Flexible or hinged members attached to the outer periphery of an anchor impeller to scrape the vessel wall, preventing buildup and improving heat transfer.

THIXOTROPIC: A material whose viscosity drops gradually even at a constant shear rate, as opposed to materials whose viscosity changes instantaneously with changing shear rate.

UMBRELLA SEAL: A liquid trap around a shaft to prevent vapor leakage from the vessel. Used in very low-pressure systems.

VISCOSITY FACTOR: The correction factor applied to standard impeller power draw to account for the difference caused by high liquid viscosity.

The terms and definitions for this issue’s Word Search come from a glossary of terms compiled by Cleveland Eastern Mixers (, a manufacturer of industrial mixers and agitators for batch sizes from five gallons to 500,000 gallons.