Mixing

Fourth stage/2023-2024
• Mixing as a process “in which two or more ingredients in
separate or roughly mixed condition are treated so that each
particle of any one ingredient is as nearly as possible adjacent
to a particle of each of the other ingredients.

• Mixing can be classi ed as positive, negative, or neutral.

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Fluid Mixing
 Fluid Characteristics

• Fluids generally classi es as Newtonian and non Newtonian,

depending on the relationship between their shear rates and the
applied stress.
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 Mixing Mechanism
Mixing mechanisms for uids fall essentially into four categories:

• Bulk transport
• Turbulent mixing
• laminar mixing
• molecular di usion
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 Scale & intensity of segregation
Danckwerts has suggested 2 criteria to describe degree of mixing:

• Scale of segregation
• Intensity of segregation: is a measure of the variation in
composition among the various portions of the mixtures.
 Equipment
A system for liquid mixing commonly consists of two primary components:

• (1) a tank or other container.

• (2) a means of supplying energy to bring rapid mixing.

• Power may be supplied to the uid mass by means of an

impeller, air stream, or liquid jet
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Batch Mixing
Impellers
 Impellers
• These impellers are classi ed as
(a) propellers, (b) turbines and
(c) paddles.

• Diagrammatic representation of
ow patterns induced by
impellers: (A) Radial ow, (B)
Axial ow, (C) Tangential ow
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 a-Propellers

• Propellers of various types and forms are

used, the three-blade design is most
commonly used with uids.
• Propellers are most e cient when they
run at high speeds in liquids of relatively
low viscosity.
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 b-Turbines
• Because they lend themselves
to a simple and rugged design,
these turbines can be operated
satisfactorily in uids 1000 times
more viscous than uids in
which a propeller of comparable
size can be used.
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 c-Paddles
• Paddles are normally operated at
low speeds of 50 rpm or less.
• Their blades have a large surface
area as compared to the tank in
which they are employed, a
feature that permits them to pass
close to the tank walls and
e ectively mix viscous liquids and
semisolids which tend to cling to
these surfaces.
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Air jets
 Air jets

• Air jet devices involve sub-

surface jets of air for e ective
mixing of certain liquids.
• Of necessity and for obvious
reasons, the liquids must be of
low viscosity, non- foaming,
nonreactive with the gas
employed, and reasonably
nonvolatile.
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Fluid jets
 Fluid jets

• They utilize liquids pumped at

high pressure into a tank for
mixing. The power required for
pumping can often be used to
accomplish the mixing operation,
either partially or completely.
 Mixer selection (Equipment selection)
Factors that must be taken into consideration include:

• 1-the physical properties of the materials to be mixed.

• 2-Economic considerations regarding processing.
• 3- Cost of the equipment and its maintenance.
 Sigma-Blade Mixer

• Sigma-blade mixer has counter-

rotating blades.
• The blades rotate tangentially.
 Planetary Mixer

• It imparts planetary mixing action.

• The double rotation of the mixing
element and its o set position
reduces the dead zones and
avoids vortex formation.
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 Mulling Mixers
• These devices are suitable for
mixing previously mixed material
of uniform composition, but
containing aggregates of solid
particles.
 Roller Mills
• Roller mills consist of one or more
rollers and are commonly used. Of
these, the three-roller types are
preferred.
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Mixing of solids
• In the manufacture of tablets or granules normally a number of
additives are added. Therefore, mixing of powder becomes
essential part of the process.
• Mixing is considered as a critical factor, especially in case of
potent drugs and low dose drugs where high amounts of
adjuvants are added.
• Segregation is the central problem associated with the mixing
and handling of the solid particles, such segregation of
particulate solids can occur during mixing as well following the
mixing operation.
• Solid tend to segregate by virtue of di erences in the size,
density, shape, and other properties of the particles of which
they are composed.
• The second requirement for segregation can be met by the
Earth‟s gravitational eld, or by a centrifugal, electrical,
magnetic eld generated in the course of processing
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 Factors A ecting Demixing

• 1)Particle Size and Size Distribution

• 2) Particle shape
• 3) Particle Charge
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 Solid -solid mixing mechanisms

• 1-convective mixing: is an analogous to bulk transport.

• 2-shear mixing
• 3-Di usive mixing
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 Equipments/Batch

• Tumblers/Blenders
• Agitator Mixers
• Ribbon Mixer/Blender
• Continuous Mixers
• Barrel Type Continuous Mixer
• Zig-zag Continuous Blender
 Tumblers/Blenders
• A tumbling mixer consists of a container of the one of several
geometric forms, which is mounted so that it can be rotated about
an axis to cause movement of the material in all planes, which is
necessary for rapid overall mixing.
• The resulting tumbling motion is accentuated by means of ba es,
lifter blades or simply by virtue of the shape of the container.
• Various types of tumblers with di erent geometric shapes such as
twin-shell, double-cone, drum, cube and tetrahedral blenders are
commercially available ,which may be rotated about almost any axis
depending on the manufacturer.
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 Agitator Mixers

• Agitator mixers employ a stationary container to hold the

material and bring about mixing by means of moving screws,
paddles, or blades.
• Since these mixers do not depend entirely on gravity as do the
tumblers, they are useful in mixing solids that have been
wetted, and are therefore in a sticky or plastic state.
• The high shear forces that are set up are e ective in breaking
up lumps or aggregates.

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 Ribbon Mixer/Blender

• It consists of a horizontal cylindrical tank usually opening at the top and

tted with helical blades or ribbons.
• The blades are mounted on the horizontal axle by struts, and are rotated
to circulate the material to be mixed. The helical blades are wound (in
most cases) in the opposite directions to provide for the movement of
material in both directions along the axis of the tank.
• Although little axial mixing in the vicinity of the shaft occurs, mixtures with
high homogeneity can be produced by prolonged mixing even when the
components di er in particle size, shape, or density, or there is some
tendency to aggregate.
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 Continuous Mixers

• A characteristic of solids mixing equipment is that all else being equal,

mixtures produced by large mixers have greater variations in composition
than those produced by small mixers.
• This is an important consideration when relatively small portions of the
mixture are required to fall consistently within a narrow composition
range.
• Continuous mixing processes are somewhat analogous to those
discussed under uid mixing. Metered quantities of the powders or
granules are passed through a device that reduces both the scale and
intensity of segregation, usually by impact or shearing action.
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 Barrel Type Continuous Mixer

• In this mixer, the material is mixed under tumbling motion .

• The presence of ba es further enhances the mixing. When the
material approaches the midpoint of the shell, a set of ba es
causes a part of the material to move backwards. Such a
mechanism provides intense mixing of ingredients.
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 Zig-zag Continuous Blender

• It consists of several “V”-shaped blenders connected in

series ,when the blender is inverted, the material splits into two
portions, one-half of the material moves backwards, while the
other moves forward. In each rotation, a part of the material
moves towards the discharge end.
 Mixer Selection
• Mixer Property: An ideal mixer should produce a complete
blend rapidly with as gentle mixing action as possible to avoid
product damage. It should be dust tight, cleaned and
discharged easily, and require low maintenance and low power
consumption.
• Material Property: Powders that are not free- owing or that
exhibit high forces of cohesion or adhesion between particles
of similar or dissimilar composition are often di cult to mix
owing to agglomeration.

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“Thanks for your attention”