Glossary of Mixing Terms

Glossary Term Term Definition
Absolute Viscosity Absolute Viscosity is usually measured in centipoises (cp). Water at room temperature has a viscosity of one cp.
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.
Agitators  A device consisting of at least a Power Package, a shaft and an Impeller to provide agitation of the contents of a vessel. Agitators commonly mix substances with low viscosities in low-shear applications. Agitators range in size from small agitators used in laboratory applications to large industrial agitators with 10,000-gallon capacities.
Alginate  Salt found in the cell wall of brown algae. Alginates are used in food processing to stabilize certain mixtures (e.g. emulsions), to seal in moisture and to thicken texture, among other things.
American Society of Mechanical Engineers (ASME) (ASME) creates consensus standards for Mechanical Engineering. 
Anchor Impeller An Impeller with vertical blades whose contour closely conforms to the vessel bottom and walls.
Anchor Paddle  An Impeller whose contour closely conforms to the vessel bottom and walls.
Apparent Viscosity The viscosity of a Non-Newtonian Fluid at a specified shear rate. Also, the consistency of a material at some particular velocity.
Apparent Viscosity The flow resistance of a Non-Newtonian Fluid at some arbitrary point on its stress-flow curve and the consistency of a material at some particular velocity.
Axial Flow  The movement of fluid from the top to the bottom of a tank.
Axial Turbine A Turbine with pitched blades, (usually 45°) whose discharge is a mixture of Axial and Radial Flows.
Baffle A stationary device usually installed at, or near tank walls to prevent liquid swirl and promote vertical flow in the vessel.
Batch mixers  Batch Mixers mix one load of material at a time and are refilled with one load after another.
Batch Mixing  Mixing process that involves the weighing and measuring of ingredients, the creation of a mixture from separate ingredients, the removal of the mixture and the cleaning of the mixer and mixing tools before the start of a new batch.
Bearing life Bearing life is most often reported as B-10 life, which is the number of hours of operation under a given set of load conditions during which a bearing has a 10% chance of failure. The B-10 life is about one-fifth the average life.
Bio-Film A layer of trace organic material that can adhere to the interior wall of process line components. 
Blade One of the vanes on any type of impeller, sometimes misused to indicate the whole impeller.
Blenders  Blenders usually mix miscible substances possessing comparable viscosities. Because substance properties remain similar, blending can usually be accomplished with relative ease.
Blending Mixing two or more miscible liquid components into a more uniform mass.
Breaker Bars Baffles positioned adjacent to the path of the Impeller or the Paddle to prevent the entire mass from rotating with the Impeller.
Brine  Mineralized water consisting of sodium chloride, metallic and/or organic contaminants. Brine solutions are utilized in food processing procedures.
Bulk Density  The Density of a granule or powdered solid material including the voids between the particles. It is always les than the true Density.
Centipoise, Centistoke See Viscosity.
Cleanup Impeller See Slinger
Colloid  Fine particles of a substance that remain between the dissolution phase and the suspension phase. Colloids neither dissolve into other substances, remain suspended within the other substances nor settle out of the substances.
Consistency The resistance of a fluid 1 deformation when subjected to shear stress, usually synonymous with Viscosity.
Continuous Mixers  Continuous Mixers are important parts of large production lines that typically have paddle type agitators with a series of mixing stages that progressively move and blend ingredients. Materials are constantly fed in specified proportions into continuous mixers, then are mixed, conveyed to the opposite end and discharged.
Continuous Mixing  Mixing process, involving the automatic creation of a series of mixtures, in which the mixer contains a metering mechanism, such as a pump, and measures, combines and mixes the ingredients. Because smaller amounts are mixed continuously, cleaning of the mixer and mixing tools usually remains fast and easy.
Critical Speed The rotational speed of a shaft equal to the frequency of the natural harmonic vibration of the shaft.
Crystallization Formation of a solid phase from a liquid solution. It is the opposite of dissolving.
Curved Blade Turbine  A Radial Turbine whose blades form arcs.
Density The mass per unit volume of a substance. See Bulk Density and Specific Gravity. measured in g/cm3 (grams per cubic cm).
Dilant Fluid A material in which the (Viscosity increases with increasing shear rate. It is the opposite of Pseudo-plastic.)
Dispersers  Dispersers are single-shaft mixers that break apart or dissolve solid particles into liquid using a high-speed, rotating saw-tooth blade. The blade provides high shear forces that break apart the ingredients of low viscosity products, such as paints.
Dispersion A two-phase system in which one phase is broken into discrete particles which are completely surrounded by the second phase. Particles may be solid, liquid or gas. For Mixing purposes, the second phase is generally a liquid. Not to be confused with Solids Wetting. Small particles of a substance evenly distributed throughout another substance. Dispersed particles are small, but remain larger than colloids.
Dissolving A change of phase from solid to liquid by combining with a liquid solvent. (Opposite of Crystallization).
Draft Tube A hollow stationary cylinder mounted concentric with and above or around the Impeller to promote increased vertical fluid flow during agitation.
Drive Unit The mechanism in the Agitator's Power Package which converts motor Torque into shaft Torque.
Drum Mixers  Drum Mixers have adjustable blades in a swing-blade design that maximize liquid movement at all speeds.
Dry Well A sleeve around the output shaft of a gear box to prevent leakage of the gear lubricant down the shaft.
Drywell A weir or hollow quill designed around the output shaft of a drive unit to prevent leakage of the gear lubricant down the shaft.
Dual-Shaft Paddle Mixers  Dual-Shaft Paddle Mixers are fast mixers that use horizontal rotating shafts with fixed arms and attached paddle-shaped feet to impact the solids and throw some of them onto the second shaft, while pushing the rest toward one end of the device. The paddles on the other shaft push the solids toward the opposite end and toward the other shaft and paddle set.
Emulsifiers  Emulsifiers provide high speed rotation and centrifugal force through a perforated screen to achieve emulsification. Emulsifiers are very effective where a high shear is required, as they can provide fast mechanical and hydraulic shear
Emulsion  A suspension in which one substance is suspended within the other. They are unable to be blended or mixed but can be combined, though not dissolved (e.g. oil and vinegar). A colloidal dispersion of two or more liquids which are immiscible with each other. See Dispersion.
Equivalent Impeller Weight The weight, which if placed at the end of a shaft, would have the same effect as one or more Impellers located elsewhere on the shaft.
Equivalent Shaft Weight The effective weight of a shaft if it were concentrated at the lower end of the shaft, used in critical speed calculations.
Extraction A process involving material transfer from one phase to another.
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. A flash mixer is usually used where all of the addition is at a single point, whereas Rapid Mixers are used where addition is made at several points in a channel; however, the terms are somewhat interchangeable.
Flocculation A mixing process whose object is to cause fine particles to collide and/or Agglomerate to larger sizes or to adhere to larger particles so they can more easily be separated from the liquid.
Flooding In gas-liquid mixing, an accumulation of gas which collects with in the impeller, reducing liquid circulation to a small fraction of normal, and thereby reducing mixing effectiveness. It can also occur when air is drawn into the liquid from the surface, either from Vortexing or accompanying solids, which are being wetted.
Ford Cup A common tool for measuring Kinematic Viscosity, used in the paint industry.
Full Vacuum A zero pressure on the absolute pressure scale. Theoretically, no molecules are left in the system; practically, it is the minimum pressure obtained with the vacuum equipment being used and should be defined numerically. It is usually 26-27" of mercury (29.95" = theoretical limit).
Fusion  The melting together of filler metal and base metal, or of base metal only, that results in coalescence. 
Gate Impeller An Anchor type Impeller having additional horizontal and vertical blades. Gate Impeller
Gear Box Rating The horsepower capacity of a gear box meeting life and strength standards established by the American gear Manufacturers Association.
Gear Rating The horsepower capability of a drive unit meeting life and strength standards established by the American Gear Manufacturers Association.
Gear Types SPIRAL BEVEL: A curved-tooth gear form used to connect intersection shafts.
Gear Types HELICAL: An angle-tooth gear used to connect parallel or non-intersecting shafts.
Helix A type of Impeller consisting of one or more narrow ribbons which spiral around the shaft, affixed to arms mounted on 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.  
Heterogeneous  Consisting of different components that may not be distributed evenly throughout a mixture. The components, while mixed together, still remain separate entities.
High Shear Mixers  High Shear mixers utilize counter-current mixing, which places very high parallel forces upon substances. During counter-current mixing, the mixing pan and the mixing tools rapidly revolve in opposite directions, resulting in substance uniformity.
High Speed Dispersion Mills  High Speed Dispersion Mills are continuous mixers that break down particle masses to efficiently provide fine dispersions and stable emulsions.
Hindered Settling Behavior of a Slurry having a high frequency of particle collisions, evidenced by reduced Settling Velocity and Non-Newtonian behavior of the Slurry. Generally, it becomes noticeable at solids concentrations above 40-50% by volume, but may occur at much lower concentrations if the particles are extremely fine or highly irregular in shape. Most Non-Newtonian Slurries are Pseudoplastic but a few are Dilatant.
Hold-Up In gas-liquid mixing, the increase in batch volume over the liquid volume, resulting from the gas which is Dispersed in the liquid.
Homogenizing Mixers  Homogenizing mixers are high-shear mixers that subject mixtures of varying viscosities to intense mechanical and hydraulic forces, reducing mixing time and assuring uniform blend.
Homogenous  Consisting of identical components distributed uniformly throughout the mixture. The components no longer remain separate entities, but have become one entity, as in a solution.
Horizontal Mixers  Horizontal mixers have three or four augers and are used for quick mechanical mixing of particular substances, especially in feed processing.
Impeller  The part of the agitator that imparts force to the material being mixed. Examples of impellers are propellers, turbines, gates, anchors and paddles.
In-line Mixers  In-Line Mixers are being used more and more in large volume operations, as they can handle an extremely large batch with much lower horsepower and with predictable batch turnover. Dynamic in-line mixers utilize a combination of pump pressure and high-speed rotating elements, while static in-line mixers have specially contoured stationary mixing elements located in a tubular housing that serves as part of the pipeline.
Interfacial Area The average total area between phases in a dispersion. As interfacial area is increased, more power is required to create and/or maintain it.
Involute Helicoid Worm Gear Involute Helicoid Worm Gear - A high efficiency type of Worm Gearing equivalent to wrapping helical teeth around a cylinder rather than around the edge of a disc.
Kinematic Viscosity  Kinematic Viscosity is reported in manydifferent forms depending on the measuring instrument. It is convertible into centistokes. Centipoises equals centistokes multiplied by Specific Gravity of the fluid.
Kinetic Energy  The use of motion to create and transmit power.
Krebs Unit (KU) A common method of reporting Consistency of paint and other coatings.
Laboratory Mixers  Laboratory Mixers are an integral part of any laboratory or processing environment, as they can perform a variety of functions, such as mixing, emulsifying, homogenizing, disintegrating and dissolving. Types of lab mixers include compact, dual-shaft, constant-torque and high viscosity.
Laminar Flow Fluid flow characterized by long, smooth flow currents, mainly in the same direction as the bulk of the flow with little interaction between them. See Turbulent Flow.
Lifter Turbine   A Single Inlet Turbine which is open at the bottom of the blades.
Mechanical Seal A device for sealing against pressure where the agitator shaft enters the vessel. It consists of two rings, one of which is stationary and the other rotating with the shaft. The accurately machined faces of these rings are forced together either by springs or by the tank pressure. When used to seal vapor (as on top-entering agitators) the seal must be lubricated by a liquid separate from the tank contents. For higher pressures, Double Mechanical Seals consisting of two opposed seals in a pressure-tight housing are used. A pressurized liquid lubricant and coolant is introduced to or flushed through the cavity between the seals. Many variations in construction and materials are available to meet special requirements.
Micrometer or Micron  A unit of measurement equivalent to one-millionth of a meter.
Mixer See Agitator.
Mixers  Mixers create a uniform mixture from various combined substances.
Mixing The process of putting power into a system, usually for the purpose of producing greater material uniformity.
Mixing Blades  push materials around the mixer.
Mixture  A substance containing two or more substances that may not be distributed evenly throughout and do not bond together chemically. Substances in mixtures, although combined, maintain separateness.  
Motionless Mixers Motionless Mixers are also known as static mixers, inline mixers and pipeline mixers, are continuous mixers that operate inline and have no moving parts. Motionless mixers allow for the blending of two or more fluids and disperse treatment chemicals into fluid streams.
Non-Newtonian A fluid whose rate of flow is non-proportional to the stress applied. The Viscosity is variable and may increase or decrease with shear rate, with time, or with a combination of both. See also Pseudoplastic, Thixotropic, Dilatant.
Non-Newtonian Fluid A fluid whose rate of flow is not proportional to the stress applied. The Viscosity is variable and may increase or decrease with stress, with time, or with a combination of both. See also Pseudoplastic, Thixotropic, Dilatant.
Paddle  A two-bladed impeller whose diameter is somewhat larger than the radius of the tank. It is sually greater than 60% of the tank diameter.
Particle Diameter The size to which the individual bodies of the dispersed phase are reduced in a two-phase Dispersion. Often called drop diameter if the dispersed phase is a liquid or bubble diameter if the dispersed phase is a gas. The smaller the particle size, the larger the Interfacial Area.
Paste Mixer A mixer with a modified Anchor Impeller, having several vertical bars or fingers which intermesh with stationary Baffles extending down from the tank top. Used to make low to medium Viscosity pastes such as caulking compound.
Pharmaceutical Mixers  Pharmaceutical Mixers are used in processing a variety of liquids, powders and crystalline solids in the pharmaceutical processing industry. Common applications that utilize pharmaceutical mixers include the mixing of medicine, such as cough syrups and the creation of tablet coatings for pills.
Pitch For a turbine, the angle the blades make with a horizontal plane.
Poise The absolute unit of Viscosity in the C.G.S. system. One Poise equals one dyne-second per square centimeter, equals one hundred Centipoises.
Power Number A dimensionless ratio used in calculating Impeller power loadings. Impellers of similar design but different sizes will have equal power numbers under dynamically equal conditions.
Power Package The portion of an Agitator, normally above the vessel, to which the Agitator shaft is coupled. It converts power into the mechanical energy for mixing.
Production Mills  Production mills are efficient, high-speed dispersion mills that can quickly disperse, emulsify, suspend, cook, aerate and deaerate masses of particles. Material can be put in the production mill through radial slots where they are hurled off the slot tips against the stator slots, which produces efficient wetting-out of the solid phase and the quick achievement of stable suspensions, dispersions and emulsions.
Progressive Polishing A mechanical grinding procedure where a coarse grit material is used first and the successive operations use finer and finer grit until the desired surface roughness is achieved. 
Propeller A three or four bladed Axial Flow Impeller, having helically shaped blades.
Proportional Mixers  Proportional Mixers properly mix concentrations of water to produce working and make-up solutions for applications that include coolants, cleaners, strippers, degreasers, fertilizers and fungicides. Venturi proportional mixers use water passing over an orifice to create suction to draw the concentrate from the container and mix it with water, while water-driven mixers use water to drive a piston, which then pumps concentrate into a mixing chamber where the concentrate is mixed with water.
Proximity Factor A correction factor used in Impeller power calculations to account for geometric variations, such as Impeller-to-tank bottom distance, Impeller-to-liquid surface distance, multiple Impeller spacing, etc.
Pseudoplastic Liquid A liquid or slurry in which the apparent Viscosity decreases with increasing shear rate.
Pumping Rate The volumetric discharge rate of an Impeller operating at a given speed, measured at the Impeller. 
Radial Flow The movement of a fluid generally from the center of the tank to the wall.
Radial Turbine A turbine whose blades are vertical and whose discharge creates Radial Flow.
Rapid Mixer See Flash Mixer.
Residence Time The average time a process component remains in the mixing environment in a continuous process.
Reynolds Number A dimensionless number used to characterize fluid flow data. The ratio of inertial to viscous forces.
Ribbon Mixers  Ribbon Mixers create an extremely diverse velocity field by using a counter-transport mechanism consisting of an outside right-hand ribbon and an inside left-hand ribbon, both connected to the same horizontal shaft. Ribbon mixers provide fast blending and mixing in the vertical plane, as they can transport an entire mass of solids a short distance in both directions of the axis of the shaft while lifting a portion of the solids a short distance in each direction; however, they are slow when mixing end to end.
Rotary Drum Mixers  Rotary Drum Mixers contain blades that spin around the axis of the drum, mixing the substances, such as concrete. Drum mixer axes may be either horizontal or inclined.
Rotor Stator Technology  Rotor Stator Technology includes high-speed mixers that utilize a rotor and stationary stator to produce high rotor tip speeds. The differential speed between the rotor and the stator in these mixers imparts extremely high shear and turbulent energy in the gap between the rotor and stator.
Saybolt Seconds Universal (SSU) A method of reporting Kinematic Viscosity, most common in the petroleum industry; 100 centistoke: equals 462 SSU.
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.
Service Factor A numerical rating system c gear trains based on operating time, type of drive and duty required. See Gear Rating.
Settling Velocity The velocity attained b a particle freely falling in a fluid due to gravity. See Terminal Settling Velocity and Hindered Settling.
Shear As applied to liquid mixing, it is that portion of the applied power, which appears as turbulence, velocity head, recycling, drag on the blades, etc. It is the action, which produces intimate mixing on a microscopic and molecular scale.
Single Inlet Turbine   A Radial Turbine with one face shrouded for the purpose of controlling the direction of fluid flow. See Lifter Turbine.
Size Reduction  The breakdown of immiscible particles in a mixture that cannot be dissolved.
Slinger  A device attached to a shaft above the liquid level to prevent the liquid from climbing or splashing up on the shaft. Also a small Impeller placed as low as possible in a tank to agitator the "heel" when the tank is nearly empty. Sometimes called a Cleanup Impeller or heel agitator.
Slurry A mixture of liquids and insoluble solids; a Solid Suspension.
Solid Suspension The mixture of an insoluble solid material in a liquid. Thee are three degrees of suspension used in mixing: (1) "complete motion" wherein all solid particles are merely maintained in motion; (2) "complete suspension" wherein the solid particles are all lifted from the bottom but not necessarily to the top; and (3) "complete uniformity" where the heavies particles break the surface frequently and particle distribution is uniform through all but the top 3 to 5% of the liquid. See Hindered Settling.
Solids Wetting Dispersing solid particles so that a liquid film coats each particle
Solute  In a solution, the liquid, gaseous or solid substance or substances that dissolve into a liquid or gaseous substance, called a solvent. Solutes usually consist of smaller quantities than the substance into which they are dissolved.
Solution  A homogenous formation created by the dissolution of a substance or substances into another substance.
Solvent The liquid or gaseous substance into which a liquid, gaseous or solid substance, known as a solute, is dissolved.
Sparger A pipe or pipe construction for introducing fluid below the liquid surface in a tank; most often a ring or spider with many small holes, located below the Impeller, through which gas is bubbled.
Specific Gravity The Density of a material compared to the density of water at standard conditions. In the metric system, water has a density of 1 gram/ml, so density and specific gravity are numerically equal.
Stabilizer A device attached to an Impeller which directs the fluid flow pattern generated by rotation so as to resist shaft deflection, thereby allowing the use of longer shafts without Steady Bearings
Static Mixers Static mixers are also referred to as in-line mixers, are motionless mixers that operate continuously. Static mixers remain quite efficient and generally require very little maintenance.
Steady Bearing A radial shaft support bearing mounted in the vessel bottom used to reduce deflection in long shaft installations. Sometimes called a "foot bearing".
Stuffing Box A device for sealing against pressure where the agitator shaft enters the vessel. It consists of a stationary tube around the shaft with several rings of close fitting braided fibrous packing in the annular space between the tube and shaft. Usually included are means to lubricate the packing, a lantern ring to store and distribute lubricant, and a follower or glad to compress the packing further as it wears. Many special variations or features are available.
Superficial Velocity An average velocity value used in computations of fluid flow due to the complexity of velocity distribution in the system. Usually encountered in gas-liquid systems, where it is the volumetric gas flow-rate divided by the cross sectional area of the tank.
Suspension   A heterogeneous mixture in which fine particles of a solid neither dissolve into a liquid or gaseous substance nor settle out, but remain within the substance supported by buoyancy. In suspension, both substances remain separate entities.
Swirl The rotation of a liquid about an agitator shaft where little relative motion within the liquid is obtained.
Thixotropic A material whose Viscosity drops gradually at a constant shear rate, as opposed to materials whose viscosity changes instantaneously with changing shear rate. When shear is removed, Viscosity of Thixotropic materials gradually increases again. These materials may also be Pseudoplastic or Dilatant.
Torque The torsional moment exerted by a body (such as an Impeller) rotating at constant speed.
Turbine A multibladed (usually four or more), relatively short armed Impeller. The impeller diameter to tank diameter ratio usually varies from 0.2 to 0.5 for turbines.
Umbrella Seal A liquid "trap" around a shaft to prevent vapor leakage from the vessel, used only in very low pressure systems.
Vacuum Mixers  Vacuum Mixers have either top- or bottom-mounted mixers and are used to eliminate air pulled into the material during mixing, which increases product quality.
Viscosity The measure of resistance of a fluid to flow when a force is applied to it. See Apparent Viscosity. ABSOLUTE VISCOSITY is usually measured in centipoises (cp.). Water at room temperature has a viscosity of 1 cp. KENEMATJC VISCOSITY is reported in many different forms depending on the measuring instrument. It is convertible into centistokes. Centipoises equals centistokes multiplied by Specific Gravity of the fluid.
Viscosity Factor The correction factor applied to standard Impeller power draw to account for the difference caused by high liquid Viscosity.
Vortex A depression occurring in a liquid surface when an agitator Swirls the liquid; a whirlpool.
Water Horsepower The standard brake HP an Impeller will draw when operated in a water-like liquid (Viscosity = 1 centipoise, Specific Gravity = 1.0) under standard conditions of Baffling and geometric arrangement.
Wetting See Solids Wetting.
Worm Gears A gear form used for obtaining large speed reduction between non-intersecting shafts whose axes are at a 90° angle from each other.