This presentation contains all information on mixing and different mixing equipment used in food industry. The different equipment includes those for solids, liquids and semi solids. It consist of tumbling mixers, rotational screw mixers, agitators, impellers, paddle mixers, planetary mixers and so much more.

1. MIXING
A N D D I F F E R E N T T Y P E S O F M I X E R S
Submitted by,
Abel Jacob Thomas
MSc 2nd Semester
CFT-k

2. Mixing
○ Mixing or blending is an unit operation in which a uniform mixture is obtained
from two or more components, by dispersing one within the other.
○ Like emulsion, the larger components are sometimes called continuous phase
and the smaller components are called dispersed phase in mixing also.
○ Mixing has no specific preservative effect and is intended solely as a
processing aid or to alter the eating quality of foods.
○ It has wide applications in many food industries where it is used to combine
ingredients to achieve different functional properties or sensory characteristics
for example to obtain sensory characteristics in doughs and control of sugar
crystallization in ice creams etc.
○ In some foods adequate mixing is necessary to ensure that the proportion of
each component complies with the legislative standards.
○ Extruders and some type of size reduction equipments also have a mixing
action.

3. OBJECTIVES OF MIXING
○ To increase homogeneity of a mixture by reducing non uniformity or
gradients in composition, properties or temperature
○ Control rates and heat transfer
○ To achieve dispersion
○ To bring physical or structural changes
○ To promote chemical reactions
 Ideal mix – When one particle lay adjacent to a particle of the other
component (each particle lies as closely as possible in contact with a
particle or the other component)
 Random mix – A mix where probability of selecting a particular type of
particle is the same at all positions of the mix, and is equal to the proportion
of such particles in the total mix.
 Segregation or de-mixing – A mix where particles differ in size, shape or
density. These differences make this particles behave differently when
forced to move and hence tends to separate.

4. THEORY OF SOLIDS MIXING
○ In contrast with liquids and viscous pastes, it is not possible to achieve a
completely uniform mixture of dry powder or particulate solids. The degree of
mixing achieved depends upon ;
 The relative particle size, shape and density of each component
 The moisture content, surface characteristics and flow characteristics of
each component.
 The tendency of materials to aggregate.
 The efficiency of a particular mixture for those components
o The materials that are similar in size, shape and density are able to form a
more uniform mixture than dissimilar materials. During mixing, difference in
these properties cause unmixing of component parts. In some mixtures, it is
achieved by, after a given period and then unmixing begins.
o It is therefore important in such cases to time the mixing operations
accurately.
o The uniformity of final product depends upon equilibrium achieved between
mechanisms of mixing and unmixing, which then is related to type of mixer,
operating conditions and component foods.

5. THEORY OF LIQUIDS MIXING
○ The component velocities induced in low viscosity liquids by a mixer are as
follows ;
 A longitudinal velocity (parallel to the mixer shaft)
 A rotational velocity ( tangential to the mixer shaft)
 A radial velocity which acts in a direction perpendicular to the mixer
shaft.
o To achieve successful mixing, the radial
and longitudinal velocities imparted to the
liquid are maximized by baffles, off center
or angled mixer shafts or angled blades.
o To mix low viscosity liquids adequately,
turbulence must be induced throughout the
bulk of the liquid to entrain slow moving
parts within faster moving parts.

6. ○ A vortex must be avoided because adjoining layers of circulating liquid travel
at a similar speed and mixing does not take place. The liquids simply rotate
around the mixer.
○ In high viscosity liquids, pastes or doughs, a different action is needed. Here
mixing occurs by ;
● Kneading the material against the vessel wall or into other material
● Folding unmixed food into the mixed part
● Shearing to stretch the material.
○ Efficient mixing is achieved by creating and recombining fresh surfaces in the
food as often as possible. However, because the material does not easily flow,
it is necessary either to move the mixer blades throughout the vessel or to
move the food to the mixer blades.
○ Most liquid foods are non - Newtonian, and they are of mainly viscoelastic,
pseudo plastic and dilatant foods
 Visco elastic foods – A certain shearing stress called yield value must be
exerted before flow begins. This system behaves like a solid when small
stresses are applied and only small deformations that are reversible.
Eg ; bread dough

7.  Pseuodoplastic foods – Here flow begins immediately after stress is exerted.
They form a zone of thin layer around a small agitator as mixing proceeds
and the bulk of the food doesn’t move. The higher the agitator speed, the
more quickly the zones become apparent.
Eg ; sauces
 Dilatant foods – These foods exhibit shear thickening and hence should be
mixed with great care. If adequate power is not available in the mixer,
increase in viscosity causes damage to drive mechanisms and drafts.
Eg ; Cournflour and chocolate

8. TYPES OF MIXERS
○ The selection of correct type and size of mixer depends on the type and amount
of food being mixed and the speed of operation needed to achieve the required
degree of mixing with minimum energy consumption.
○ There are a very large variety of mixers available, due to the large number of
mixing applications and the empirical nature of mixer design and development.
○ Mixers are classified into types that are suitable for :
1. Dry powders or particulate solids (Solids)
2. Low or medium viscosity liquids (Liquids)
3. High viscosity liquids and pastes (Semi-Solids)
1. Mixers for dry powders and particulate solids – These mixers have two basic
designs, the tumbling action of rotating vessels and the positive movement of
materials in screw types. They are used for blending grains, flours and the
preparation of powdered mixes like cake mixes and dried soups.

9. TUMBLING MIXER
○ In this type of mixer, the movement of whole mixer is responsible for mixing
action of solid.
 CONSTRUCTION
○ Tumbling mixer usually consist of a metallic vessel which rotates on its
horizontal axis at optimum speed by means of motor.
○ The mixing vessel is usually made up of stainless steel and have door where
we can load and unload materials. The door is lined with rubber which
provides a perfect seal after closure.
 The degree of mixing/blending achieved by using tumbling mixer in carrying
out a mixing operation is dependent on :
o The fill-up volume (should not be more than 50-60% of the total blender
volume)
o The residence time.
o The rotation speed (increasing the speed above the optimum speed causes
adhesion of the powder on the walls of the mixer)
o Inclination angle of the mixer.

10. ○ Tumbling mixers are available in variety of shapes and sizes, which include :
 Twin shell or V shaped mixer - The V-blender, consists of two hollow cylindrical
vessels that are joined at an angle of 750 to 900 which is mounted on trunnion
to allow it to tumble. The free fall of the material within the vessel, and the
repetitive converging and diverging motion, coupled with increased frictional
contact between the material and the vessel’s long, straight sides as the mixer
tumbles, split the material and recombines them continuously results in a
homogenized blend. Removal of the blended material from the V-blender is
normally through the apex port which is fitted with a discharge tube. A V-
blender can be modified by providing it with a high-speed intensifier bar also
known as lump breaker running through trunnion into the vessel along with
spray pipes for liquid addition. This modified v-blender is called V-Blender with
intensifier bar.

11.  Double cone mixer - The double cone blender is an efficient and multipurpose
tumbler blender for mixing dry powders and granules homogeneously. It is
made of two conical shaped stainless vessels (available in different capacity
ranging from 5 – 200 kg or even more) that are separated by a cylindrical
section. It is mounted at the center of the container between two trunnions that
allow the blender to turn end over end.
○ Double cone blender has no dead spots mixing and it is easily cleanly after
use. Double cone blender is not a suitable choice of blender for very fine
particles and particles with greater particle size difference due to less shear.

12. ○ Cubical mixer - A cubic mixer is a tumbling mixer suitable for gentle blending of
dense powders and granules. As the name implies, it consists of a cube-
shaped stainless container mounted in a titled manner at the center of the
container or hanged from the corner between two trunnions that allows it to
rotate about an axis. Mixing occurs by sliding of powders on its wall. Cubic
blender gives mixing in three dimensions (3D) when hanged from the corner.
○ Despite the fact that corner blender gives mixing in three dimensions, the
presence of different corners makes it difficult to clean after use sliding action
causes abrasion of particles. The above can be said to be the advantages and
disadvantages of using cube-shaped blenders as blending equipment.

13.  Y cone mixer – A Y cone blender can handle large volumes of materials and
comes in various capacities ranging from 45 liters to 3200 liters. Separately
driven internal lump breakers can be provided for breaking of lumps and
aggleromerates. The design consist of two cylindrical cones welded together
and fitted with shaft mounted on bearings. The blender is rotated at slow RPM
because of which the entire mass is tumbled along the angle of the cone
resulting in criss-crossing of the material to produce a uniform mix. Baffles are
provided inside the cone for throughout mixing. It can handle large volumes
and is easily cleanable.

14.  WORKING
o The material to be mixed is loaded into mixing vessel which is rotated at low
speed by electric motor. Due to slow speed of rotation the powder is raised
along the sides of the vessel until the angle of repose is exceeded.
o The powder then tumbles down and mixing of compound occurs.
o If the rotation of vessel is too slow, it will cause sliding and proper mixing will
not occur. If it is rotated too fast, the material will adhere to the walls due to
centrifugal force. So optimum speed of 30-100rpm is required.
o Mixing mostly occurs by convective mechanism
o Shear mixing will occur as a velocity gradient is produced (the top layer
moving with high velocity and velocity decreasing as the distance from the
surface increases)
o When the bed tumbles it dilates, allowing the particles to move downwards
under gravitational force, and so diffusive mixing occurs.
o Addition of baffles or rotating bars will also cause convective mixing.

15.  ADVANTAGES
o Good for free flowing powders/granules
o Mix from 50g (laboratory scale) to over 100kg (large scale)
o Can be used to produce ordered mixes
 DISADVANTAGES
○ Less effective for poorly flowing powders.
○ Segregation is likely to occur if there are significant difference in particle size.

16. HIGH SHEAR MIXER-GRANULATOR
○ It is so called because mixing mainly occurs by shear mixing mechanism and at
the same time granulation is carried out.
 CONSTRUCTION
○ It consist of a vessel having propeller with long blades.
○ The clearance (distance between propeller blades and walls of vessel) is low.
○ There is a closing lid that closes the vessel after material to be mixed is added.
○ For introduction of material/granulating
agent, a funnel is used.
○ For the purpose of granulation, a
chopper is present on side wall.

17.  WORKING
○ The material to be mixed is introduced in the mixer. The centrally mounted
propeller blade at the bottom of the mixer rotates at high speed, throwing
material towards the mixture bowl wall by centrifugal force.
○ The material is then forced upward before dropping back down towards the
centre of the mixer.
○ The particulate movement within the bowl tends to mix the components quickly
owing to high shear forces (arising from the high velocity) and expansion in the
bed volume that allows diffusive mixing.
○ After mixing, the granulating agent (water or alcohol) is then added through the
funnel.
○ It will produce wet mass that will go to the side wall of mixer because of
propeller.
○ On sides, chopper with vertical, short and sharp blades, are present that is
rotating at higher speeds than that of the propeller and will break the wet mass
to produce granules.

18.  ADVANTAGES
○ Can be used for both wet and dry mixing
○ This helps in granulation also
 DISADVANTAGES
○ Materials being mixed can fracture easily due to high speed movement
○ Cannot be used for blending lubricants

19. AGITATOR MIXER
○ These are the mixers in which the container to hold the material is fixed.
Mixing is done by means of mixing screws, paddles or blades.
○ Some of the important agitator mixers include :
 Ribbon mixer
 Planetary mixer
 Nauta mixer

20. RIBBON MIXER
 CONSTRUCTION
○ It consist of a horizontal cylindrical trough with semicircular bottom which
usually opens at the top. It is fitted with two helical blades which are mounted
on the same shaft through the long axis of the trough.
○ Blades have both left and right hand twists
○ Blades are connected to a fixed speed drive.
○ Loading of the materials is done through top and are emptied through bottom.

21.  PRINCIPLE
○ Mechanism of mixing is shear. Shear is transferred by moving blades. High
shear rates are effective in breaking lumps and aggregates.
○ Convective mixing also occurs as the powder bed is lifted and allowed to
cascade to the bottom of the container. An equilibrium state of mixing can be
achieved.
 ADVANTAGES
○ High shear can be achieved by using perforated baffles, which bring about a
rubbing and breakdown of aggregates.
 DISADVANTAGES
○ Poor mixing as the movement of particles is only two dimensional
○ Has a fixed speed drive
○ Dead spots are observed even though they are minimum

22. PLANETARY MIXER
○ The name planetary mixer comes from the system used in the equipment that
mixes the dough in the planets rotation direction.
 CONSTRUCTION
○ Consist of a vertical cylinder shell for ingredients placement which cant be
removed. Mixing elements like whisk, hook, flat beater, scrapper or other
systems can be used. It consist of a rod that rotates on its own axis and also
moves forward. As the movement is just like planets, it is called planetary
mixers. The blade is mounted from the top of the bowl. Mixing shaft is driven
by planetary gear and it is normally built with variable speed drive.

23.  PRINCIPLE
○ Mechanism of mixing is shear. Shear is applied between moving blade and
stationary wall.
○ Moving arm moves around its own axis and around the central axis so that it
reaches every spot of the vessel. The plates in the blades are sloped so that
powder makes an upward movement to achieve tumbling action also.
 ADVANTAGES
o Speed of rotation can be varied at will.
o Avoids dead zone and vortex formation.
o Break down agglomerates rapidly.
 DISADVANTAGES
○ Mechanical heat buildup within the powder mix.
○ Requires high power.
○ It has limited size and is useful for batch work only.

24. NAUTA MIXER
○ It is a vertical screw mixer. Originally designed as a powder and semi-solid
mixer but now a days also used as a mixer granulator.
 CONSTRUCTION
○ It consist of conical vessel fitted at the base with a rotating screw, which is
fastened to the end of rotating arm. Accessory equipments include, lump
breaker (attached at the bottom, of the conical chamber), temperature monitor,
infrared moisture analyzer.

25.  WORKING
○ The powder to be mixed and liquid granulating agents are added through the
inlet.
○ The screw is moving in a planetary motion and also lifting the material to be
blended from bottom to the near top, where it cascades back into the mass,
thus imparts 3 dimensional mixing.
○ The mixer then combines
Convective mixing
Shear mixing
Diffusive mixing

26. 2. Mixers for low or medium viscosity liquids – A large number of impellers
are used to mix liquids in unbaffled or baffled vessels. The advantages and
limitation of each vary according to particular application.
 IMPELLER
○ Impellers are mixing devices that provide a definite flow pattern in liquid
during mixing, moving at various speeds. Liquids are mixed usually by
impellers, which produce shear forces for inducing the necessary flow pattern
in the mixing container.
○ Impellers exist in different forms :
 Propeller
 Turbine
 Paddles

27. PROPELLER
 CONSTRUCTION
o Consist of angle blades attached at the end of the shat, rotated by means of
motor.
o Any number of blades may be used but three blades design is most common.
o Propeller is quite small when compared to the size of the vessel. Ratio of
diameter between propeller and container is 1:20, but its rotating speed is
usually 8000rpm which compensate for the size and produce efficient mixing
in case of low viscosity fluids.

28.  WORKING
○ The material to be mixed is taken in a vessel and the propeller bearing shaft is
inserted. The angle blades of propeller cause circulation of the liquid in both
axial and radial direction ensuring good bulk transport but low shearing force.
○ The propeller may be installed in different ways.
○ To prevent vortex formation the impeller should be in any of the following
patterns or baffles should be used. A push pull propeller which consist of two
or more propeller of opposite angles attached to same shaft can also be used.
o The centrally mounted vertical propeller is not
considered good as it produces vortex. Vortex is a
powerful circular mass of water that can draw objects
into its hollow which may result in air entrapped and
bubbles formation. It is formed due to the centrifugal
force on the rotating liquid.

29. TURBINE MIXER
 CONSTRUCTION
○ A turbine consist of a circular disc impeller to which a number of short vertical
blades are attached. Blades may be straight or curved.
○ The blades are surrounded by perforated inner and outer diffusing rings.
○ The diameter of the turbine rings ranges from 30-50 percent of the diameter of
the vessel.
 WORKING
○ Used in similar manner as that of impeller, however it is rotated at a speed
smaller than impeller (50-200rpm)
○ Flat blade turbines produce radial and tangential flow but as the speed
increases radial flow dominates.

30. ○ Shear produced by the turbines can be further enhanced using a diffuser
ring, which is a stationary perforated ring which surrounds the turbine.
Diffuser ring increase the shear forces and liquid passes through perforations
reducing rotational swirling and vortexing.
 ADVANTAGES
○ Turbines give greater shearing force than propellers. Therefore it is also
suitable for emulsification.
○ Turbines are suitable for liquid of large volume and high viscosity, if the tank
is baffled.

31. PADDLE MIXERS
○ Paddles are agitator consisting of usually flat blades attached to a vertical
shaft and normally operated at low speeds of 100rpm.
○ The blades have a larger surface are in relation to the tank in which they
rotate, so they can be used effectively. Primarily paddle mixers produce
tangential flow and somewhat radial flow but no axial action unless blades are
pitched.
○ Paddles for more viscous fluids have a number of blades which are shaped in
such a way to fit closely to the surface of vessel to avoid dead spots and
deposited solids. At very low speeds it gives mild agitation in un baffled tank
but as for high speeds baffles are necessary to avoid swirling and vortexing.

32. 3. Mixers for high viscosity liquids and plates – More viscous liquids are
,mixed using slow speed vertical shaft impellers such as multiple paddle
agitators or more commonly counter rotating agitators to develop high
shearing forces.
○ The basic design in this group is the anchor and gate agitator. It is often
used with heating mixing vessels, where the anchor is fitted with scraper
blades to prevent food from burning on to the hot surface.
○ Some complex design have arms on the gate which intermesh with
stationary arms on the anchor to increase the shearing action whereas
others have inclined vertical blades to promote radial movement in the food.
○ Other commonly used mixers include planetary mixers, screw conveyor or
nauta mixer and sigma blade mixer.

33. SIGMA-BLADE MIXER
○ It is used for foods with semi-solid or plastic consistency.
○ The intermeshing of sigma blades creates high shear and kneading action
which mixes the components
 CONSTRUCTION AND WORKING
○ It consist of double trough shaped stationary bowl.
○ Two sigma shaped blades have very low clearance and are connected to a
fixed speed drive. Mixer is loaded from the top and unloaded by titlting the
entire bowl.

34. ○ The blades rotate tangentially at different speeds, one about twice than the
other (2:1), which allows movement of powder from sides to centers.
○ The materials also moves top to downwards and gets sheared between
the blades and the wall of the trough resulting cascading action.
○ Perforated blades can be used to break lumps and aggregate which create
high shear forces.
 ADVANTAGES
○ Sigma blade mixer creates a minimum dead space during mixing.
○ It has close tolerance between the blades and the side walls as well as
bottom of the mixer shell.
○ The mixer is well suited to high viscosity materials like toffee, bubble gum
etc.
 DISADVANTAGES
○ Has a fixed speed
○ Can cause entrainment of air and therefore lead to decomposition of
oxidisable materials.