The recombining of finely dispersed particles
into larger particles, usually caused by a rearrangement
of surface forces resulting form a change of environment.
(Opposite of Dispersion).
A device consisting of at least a Power
Package, a shaft and an Impeller to provide agitation of
the contents of a vessel.
An Impeller with vertical blades whose
contour closely conforms to the vessel bottom and walls.
The viscosity of a Non-Newtonian Fluid
at a specified shear rate. Also, the consistency of a material
at some particular velocity.
the circulation of a fluid from top to
the bottom of the tank.
A Turbine with pitched blades, (usually
45°) whose discharge is a mixture of Axial and Radial Flows.
A stationary device usually installed
at or near tank walls to prevent liquid Swirl and promote
axial flow in the vessel.
Bearing life is most often reported as
L-10 life, which is the number of hours of operation under
a given set of load conditions during which a bearing has
a 10% change of failure. The L-10 life is about one-fifth
of the average life.
One of the vanes on any type of Impeller,
sometimes misused to indicate the whole impeller.
Mixing two or more miscible liquid components
into a more uniform mass.
Baffles positioned adjacent to the path
of the Impeller or the Paddle to prevent the entire mass
from rotating with the Impeller.
The Density of a granular or powdered
solid material including the voids between the particles.
It is always less than the true Density.
See Slinger, def. 2.
a. The resistance of a fluid to deformation
when subjected to shear stress; usually synonymous with
- b. The solids concentration in paper
The rotational speed of a shaft equal
to the frequency of the natural harmonic vibration of the
Formation of a solid phase from a liquid
solution. (Opposite of Dissolving).
The mass per unit volume of a substance.
See Bulk Density and Specific Gravity.
A material whose Viscosity increases with
increasing shear rate. (Opposite of Pseudoplastic).
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.
A change of phase from solid to liquid
by combining with a liquid solvent. (Opposite of Crystallization).
A hollow stationary cylinder mounted concentric
with and above or around the Impeller to promote increased
vertical fluid flow during agitation.
A sleeve around the output shaft of a
gear box to prevent leakage of the gear lubricant down the
The mechanism in the Agitator's Power
Package which converts motor Torque into shaft Torque.
A colloidal dispersion of two or more
liquids which are immiscible with each other. See Dispersion.
A process involving material transfer
from one phase to another.
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.
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.
In gas-liquid mixing, an excessive accumulation
of gas around 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.
A common tool for measuring Kinematic
Viscosity, used in the paint industry.
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 inches = theoretical
An Anchor type Impeller having additional
horizontal and vertical blades.
Gear Box Rating
The horsepower capacity of a gear box
meeting life and strength standards established by the American
gear Manufacturers Association.
Gear - A curved-tooth gear form used to connect intersecting
Helical Gears - An angle-tooth
gear used to connect parallel or non-intersecting shafts.
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.
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.
A type of Impeller consisting of one or
more narrow ribbons which 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
The behavior of a Slurry having a high
frequency of particle collisions, evidenced by reduced Settling
Velocity. 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 gas-liquid mixing, the increase in
batch volume over the liquid volume, resulting from the
gas which is Dispersed in the liquid.
The portion of the agitator imparting
force to the material being mixed. Propellers, Turbines,
Gates, Anchors and Paddles are all types of Impellers.
The average total area between phases
in a dispersion. As interfacial area is increased, more
power is required to create and/or maintain it.
A common method of reporting Consistency
of paint and other coatings.
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
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
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.
The process of putting power into a system,
usually for the purpose of producing greater material uniformity.
A fluid whose rate of flow is proportional
to the stress applied to it. The Viscosity is therefore
constant and independent of shear rate.
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.
A two-bladed Impeller whose diameter is
usually greater than 60% of the tank 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.
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
For a Turbine, the angle the blades make
with a horizontal plane.
The absolute unit of Viscosity in the
C.G.S. system. One Poise equals one dyne-second per square
centimeter, equals one hundred Centipoises.
A dimensionless ratio used in calculating
Impeller power loadings. Impellers of similar design but
different sizes will have equal power numbers under dynamically
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.
A three or four bladed Axial Flow Impeller,
having helically shaped blades.
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.
A liquid or slurry in which the apparent
Viscosity decreases with increasing shear rate.
The volumetric discharge rate of an Impeller
operating at a given speed, measured at the Impeller.
The movement of a fluid generally from
the center of the tank to the wall.
A turbine whose blades are vertical and
whose discharge creates Radial Flow.
See Flash Mixer.
The average time a process component remains
in the mixing environment in a continuous process.
A dimensionless number used to characterize
fluid flow data. The ratio of inertial to viscous forces.
A method of reporting Kinematic Viscosity,
most common in the petroleum industry; 100 centistokes equals
Flexible or hinged members attached to
the outer periphery of an Anchor Impeller to scrape the
vessel wall, preventing buildup and improving heat transfer
A numerical rating system of gear trains
based on operating time, type of drive, and duty required.
See Gear Box Rating.
The velocity attained by a particle freely
falling in a fluid due to gravity. See Hindered Settling.
As applied to liquid mixing, it is that
portion of the applied power which appears as turbulence,
recycling drag on the blades, etc. It is the action which
produces intimate mixing on a microscopic and molecular
(1) A device attached
to a shaft above the liquid level to prevent the liquid
from climbing or splashing up on the shaft.
(2) 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.
A mixture of liquids and insoluble solids;
a 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.
Dispersing solid particles so that a liquid
film coats each particle.
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.
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.
A device attached to an Impeller which
directs the fluid flow pattern generated by rotation so
as to resist shaft deflection. Useful when the mixer is
mounted with the shaft at an angle off vertical
A radial shaft support bearing mounted
in the vessel bottom used to reduce deflection in long shaft
installations. Sometimes called a "foot bearing".
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
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.
The rotation of a liquid about an agitator
shaft where little relative motion within the liquid is
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
The torsional moment exerted by a body
(such as an Impeller) rotating at constant speed.
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.
Curved Blade Turbine
- A Radial Turbine whose blades form arcs.
Turbine - A Radial Turbine with one face shrouded
for the purpose of controlling the direction of fluid flow.
See Lifter Turbine.
Lifter Turbine - A Single
Inlet Turbine which is open at the bottom of the blades.
A liquid "trap" around a shaft to prevent
vapor leakage from the vessel, used only in very low pressure
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 one cp.
is reported in manydifferent forms depending on the measuring
instrument. It is convertible into centistokes. Centipoises
equals centistokes multiplied by Specific Gravity of the
The correction factor applied to standard
Impeller power draw to account for the difference caused
by high liquid Viscosity.
A depression occurring in a liquid surface
when an agitator Swirls the liquid; a whirlpool.
The standard brake horsepower an Impeller
will draw when operated in a waterlike liquid (Viscosity
= 1 centipose, Specific gravity = 1.0) under standard conditions
of Baffling and geometrical arrangement.
See Solids Wetting.