Glossary of Mixing Terms

AgglomerationThe recombining of small, dispersed particles into larger particles.
This is usually caused by the rearrangement of surface forces that result from change of environment.
This is the opposite of dispersion.
AgitationA device consisting of a Drive, a Shaft and an Impeller to provide agitation of the contents of a vessel.
Also known as a Mixer.
Anchor PaddleAn Impeller with a large diameter and a shape resembling an anchor.
The contour closely conforms to the vessel bottom and walls.
See Impeller Types.
Apparent ViscosityThe flow resistance of a Non-Newtonian fluid at an arbitrary point on its stress-flow curve.
Axial FlowThe movement of a fluid in a tank which generally moves from the top to the bottom of a vessel.
Axial ImpellerAn Impeller with pitched blades at 45° that produces fluid flow in an Axial direction.
See Impeller Types.
BaffleA stationary device installed on or near a tank wall to prevent any liquid swirl and to create vertical flow.
See Baffles.
BladeOne of the vanes on an Impeller, not to be mistaken for the whole Impeller.
Blend TimeThe amount of time needed to blend the vessels contents.
This time is dependent on the materials viscosity.
BlendingMixing two of more miscible liquids into a uniform mass.
Breaker BarsMore commonly referred to as beaver tails – or beaver tail baffles.
Beaver tails are wide baffles that are used when the tank they are in can have no modifications made to it (such as welding baffles to the walls). As such, typically two beaver tails are hung from the bridge and into the tank.
Bulk DensityThe density of a granule including the voids between the particles.
It is always less than the true density.
Centipoise/CentistokeStandard units of Viscosity.
See Viscosity.
ConsistencyThe resistance of a fluid when subjected to a shear stress.
Critical SpeedThe rotational speed equal to the natural frequency of the shaft and impeller.
This can also be affected by the mounting structure.
Crystallisation Formation of a solid from a liquid solution. It is the opposite of dissolving.
DensityThe mass per unit volume of a substance.
See Specific Gravity.
Dilatant FluidA fluid in which the viscosity increases as the shear rate increases.
This is the opposite of a Pseudo-plastic.
DispersionA system of two-phases where one phase is broken down into discrete particles which are surrounded by the second phase.
In mixing, the second phase is generally liquid.
Draft TubeA hollow stationary tube mounted concentric to and above the impeller.
This promotes increased vertical flow during mixing.
DriveThe part of the agitator responsible for converting the power inputted to mechanical energy for mixing.
The drive could be electric or pneumatic, direct drive or gear drive.
DrywellIf the drive lubricant should leak past the oil seals, it is collected in the Drywell.
This collection space includes an oil sensor that is triggered by an oil leak.
EmulsionA colloidal dispersion of at least two liquids that are immiscible with each other.
Flash MixerA mixer used to mix only small amounts of additive into a continuous stream with an extremely short residence time.
It generally refers to the addition of chemicals which aid Flocculation in water and waste water treatment.
FlocculationA process of mixing that causes fine particles to collide and agglomerate to larger sizes.
The process also includes the use of fine particles to adhere to larger particles, so they can be separated from the liquid more easily.
Gate ImpellerAn Anchor impeller with additional horizontal and vertical blades.
See Impeller Types.
Helical GearsA gear with angled teeth that is used to connect either parallel or non-intersecting shafts.
HomogenizeTo homogenize, or homogenous mixing, is the process of mixing components to make them uniform throughout the whole mixture.
The result is the composition of the mixture is the same throughout.
IBCIntermediate bulk container, Tote tank or Pallet tank.
This is a reusable industrial container that can be used for transportation and general storage of chemicals and solvents.
IBC MixerIndustrial fluid mixer designed for use on Intermediate Bulk Containers (IBC’s)
ImpellerThe part of the agitator that produces the force to the materials being mixed.
See Impeller Types for information on the various types of Impellers.
Krebs Unit (KU)A popular method of reporting the consistency of paint and other coatings.
Laminar FlowA fluid flow determined by multiple long, smooth and layered flow currents flowing in the same direction as the bulk of the flow and with little interaction between them. See Turbulent flow and Viscosity.
LiquidA liquid is a substance which is not solid but which flows and can be poured, for example: water.
Liquid solutionA liquid solution is a liquid in which a substance has been completely dissolved.
The substance can either be a solid, gas or another liquid.
Mechanical SealA device for pressure sealing at the point where the lower shaft enters the tank. The seal consists of a stationary ring and a rotary ring that rotates with the shaft. These two rings are forced together by either the tank or by springs. For much higher pressures, a double mechanical seal can be used which consists of two seals in a pressure-tight housing.
MixerMachinery to provide agitation.
See Agitator.
MixingMixing is the process of increasing the homogeneity of a product, usually by imparting mechanical energy into the product.
Newtonian FluidA fluid in which its state of flow is proportional to the stress applied.
Therefore, the fluids viscosity is constant and independent of shear rate.
See Viscosity.
Non-Newtonian FluidA fluid in which its state of flow is non-proportional to the stress applied. Therefore, the fluids viscosity is variable and may vary with shear rate, time or with a combination of the two. See Dilatant, Pseudo-Plastic, Thixotropic and Viscosity.
PaddleAn impeller with two blades. The diameter of a paddle is usually greater than 60% of the tank diameter.
Particle DiameterThe average diameter of the particles in a solid suspension application.
Typically measured in microns (µm)
PitchOn an Impeller, the pitch is the angle of the blades from the horizontal plane.
See Impeller Types.
PoiseThe absolute unit of viscosity. One Poise equals one hundred Centipoise.
See Viscosity.docx
Power NumberA dimensionless ratio that is used to calculate Impeller power loadings.
PropellerA three or four, helically bladed Impeller that produces axial flow.
See Impeller Types.
Proximity FactorThis is a correction factor that is used in Impeller power calculation.
It allows for geometric variations like: Impeller-to-tank bottom distance and Impeller-to-liquid surface distance.
Pseudo-Plastic LiquidA liquid or slurry where the viscosity decreases with an increase in shear rate.
Pumping RateThe volumetric discharge rate, measured at the impeller, when operating at any given speed.
Radial FlowThe movement of fluid in a tank – generally from the tank centre out to the wall.
Radial flow is required in heat transfer applications.
Radial ImpellerAn Impeller or turbine whose blades are vertically mounted to discharge fluid in a radial direction.
See Impeller Types.
Rapid MixerSee Flash Mixer
Residence TimeThe time on average that a process component will remain in a mixing environment in a continuous process.
Reynold NumberA dimensionless number that is used to characterize fluid flow. It is the ratio of inertial forces to viscous forces.
ScrapersHinged or flexible members that are attached to the outer edge of an Anchor impeller.
They are used to scrape the vessel walls to prevent any concentrated build-up.
Service FactorA numerical rating system for gear systems that is based on the gear operating time, type of gear/drive and the duty required.
Settling VelocityThe velocity of a particle that is freely falling due to gravity whilst in a fluid.
ShearWhen applied to liquid mixing, shear is the action which produces mixing of a molecular and microscopic scale.
Shear can be desired in liquid mixing but can also be an unwanted property.
SlingerA sealing device that is attached to a shaft above the liquid level to prevent the liquid from splashing of climbing up the shaft.
SlurryA mixture of liquids and insoluble solids.
See Solid Suspension.
Solid SuspensionA mixture of a liquid with insoluble solids, typically a slurry.
There are three degrees of solid suspension for liquid mixing:

1. Uniform – Where the heaviest particles rise to the surface frequently and particle distribution if uniform.
2. Off Bottom – Where the particles of solids are lifted from the bottom but not to the top.
3. On Bottom – Where the solid particles are maintained in motion, but some particles may remain on the tank floor.
Solids WettingDispersing solid particles so that each particle is coated in a liquid film.
Specific GravityA measure of density for any material against the density of water at standard conditions.
See Specific Gravity.
Spiral Bevel GearsA form of gear with a curved tooth that is used to connect intersecting shafts.
Spiral ImpellerAn impeller type consisting of narrow ribbons that spiral around a central shaft.
These ribbons are connected to the shaft by several arms.
It is common for the spiral to have a diameter near to that of the vessel.
Stabilizing FinsExtra blades attached to an impeller which direct the fluid pattern created by rotation to resist shaft deflection.
This allows agitators to have longer shafts without a steady bearing.
Steady BearingA radial shaft support bearing mounted at the bottom of the vessel used to reduce deflection in longer shafts.
Stuffing BoxA device for sealing against pressure at the point where the mixer shaft enters the vessel.
A stuffing box is made up of a stationary tube around the shaft with multiple rings of close fitting braided packing in the space between the tube and shaft. Often included are means of lubricating the packing.
SwirlThe rotation of a liquid around the mixer shaft where little motion within the liquid itself is obtained.
ThixotropicA material whose viscosity will drop gradually at a constant shear rate.
Opposed to any materials whose viscosity changes immediately with a change in shear rate.
TurbineA relatively short armed, multi-bladed impeller.
The diameter of the impeller to tank ratio tends to vary between 0.2 to 0.5 for turbines.
See Impeller Types.
Turbulent FlowWhen the fluid or gas undergoes irregular fluctuations - contrast to laminar flow.
In turbulent flow, the speed of the fluid constantly experiences changes in magnitude and direction. See Viscosity.
ViscosityA measure of the resistance of a fluid to flow when a force is applied to it.

- ABSOLUTE VISCOSITY is measured in Centipoise (cp.). At room temperature, water has a viscosity of 1cp.

- KINEMATIC VISCOSITY is measured in many different forms depending on the measuring instrument.
As this is convertible into centistokes, centipoise equals centistokes multiplied by the specific gravity of a fluid. See Viscosity.
Viscosity CupA common tool for measuring Kinematic Viscosity. Types of viscosity cup include: DIN, ISO, Shell etc.
See Viscosity Cups for more information.
Viscosity FactorThe correction factor applied to a standard impeller draw value to account for the difference caused by any high viscosity liquid.
VortexWhen an agitator swirls the liquid, a depression occurs in the liquid surface like a whirlpool, this is referred to as a vortex.
WettingA term used for describing dispersing solid particles so that each particle is coated in a liquid film or dissolved in a solution.
Worm GearsGears used to achieve a larger speed reduction between non-intersection shafts where the axes are at a 90° angle to each other.

Jack Hodgkinson BEng(Hons)

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