The document discusses various factors that affect the mixing of particles, including particle size, shape, charge, density, viscosity, surface tension, moisture content, temperature, flow characteristics, liquid quality, speed of the impeller, mixer volume, type of agitator, type of mixer, and mixing time. It also describes different types of mixers used for solid-liquid and solid-solid mixing, including tumbler mixers, vertical screw mixers, and fluidized bed mixers.

1. Submitted To:
Prof. Shiv Kumar Katiyar
Head of the Department
Submitted By:
Ritik Kumar
M.Sc. 1stSemester
Roll no. 221155081018

2. Mixing operation:
Mixing is basically a process in which components are treated in such
manner so that particles of each component are available to the adjacent
particles of the other component that are required to be mixed.
Factors affecting mixing:
1. Particle size:
Smaller particle results in homogeneous mixture than the larger one.
2. Particle shape:
Particle should be spherical for uniform mixing. If there is irregular
shape of the particle then they become interconnected in such a way so
that their separation is relatively difficult after mixing than if the particle
shape is regular.
3. Particle charge:
If the particle has some electrostatic charge that cause attraction
forces between particles, then there are more chances of segregation or
separation.

3. 4. Nature if the particle:
Particle hardness, elasticity, porosity, texture, angularity and particle
vibrations are also the factors that affect mixing phenomena greatly.
5. Relative Density:
If the components are of different density, the denser material will sink
through the lighter one, the effect of which will depend on the relative
positions of the material in the mixer.
a. If the denser particles form the lower layer in a mixture at the start
of a mixing operation, the degree of mixing will increase gradually until
equilibrium is attained , not necessarily complete mixing.
b. If the denser component is above, the degree of mixing increases to
a maximum , then dropping to equilibrium as the denser component falls
through the lighter one , so that segregation has started.

4. 6. Viscosity:
Mixing is also affected by viscosity. More viscous particles causes
improper mixing as their higher viscosity affects their speed (slow) to flow
that is produced by forces to get mixing . so basically increasing viscosity
reduces mixing extent.
7. Surface tension of liquids:
Surface tension of liquid is also an important factor that effects mixing.
High surface tension reduces extend of mixing. In fact cohesiveness is the
tendency of material to adhere to itself causes difficulty in mixing as
agglomerates are formed.
8. Moisture:
Moisture present in particles heap also affects mixing phenomena. For
example mixing of dry clay is more rapid and efficient than wet mixing of
clay. In fact proper mixing requires specific moisture content in bulk.

5. 9. Temperature:
Temperature also affects mixing as viscosity is changing with temperature
changing.
10. Flow characteristics:
Flow properties are directly related to particle size . as due to
increase/decrease in particle size gravitational forces according to size
increases/decreases.
11. Liquid quality:
In solid-liquid mixing liquid (water) quality is also an important factor .
Liquid quality includes pH value, salt level, organic matter; foreign matter etc.
affects greatly the efficiency of mixing.
12. Speed/rpm of impeller:
Speed of impeller affects the homogeneity of the mixture. As with less rpm
mixture is more homogenous than with greater rpm.

6. 13. Mixer volume:
Mixer volume also affects mixing phenomena. Mixer volume should be
such that over filling should not be done as it decreases efficiency of mixing
and mostly material can’t be mixed thoroughly.
14. Type of agitator:
The shape, size, location and type of agitator present also affects the
extent of mixing achieved and the time required for mixing of specific
components . As the type of agitator required for mixing depends upon
the nature of substances that need to be mixed. However, generally speaking,
a. Impeller type mixers are used for solid-liquid mixing.
b. Paddle type mixers are used for solid-solid mixing operations.
c. The blades are further modified for kneading and dispersing purpose
cohesive solids are needed to be mixed.

7. 15. Type of mixer:
Type of mixer greatly effects on mixing phenomena . as in mixing there is
specific flow patterns due to which mixing taking place. Suitable flow pattern
for mixing can be obtained as a result of balanced components in mixer .
a. If the impeller shaft is vertical, excessive radial movement, especially if
solids are present , will take materials to the vessel periphery, where
they drop to the bottom and may revolve as a mass below the impeller.
b. If the tangential component is leading, a vortex is created and may
deepen until it extents the impeller, when aeration occurs.
c. If the longitudinal component is inadequate, liquids and solids may
present in films without mixing.

8. 16. Mixing time:
Mixing time is also very important for proper mixing. There is always an
optimum mixing time for specific conditions in which mixing is taken place.
As degree of mixing reaches to its limiting equilibrium value asymptotically.
17. Mechanism of mixing:
The mixer must apply suitable shear forces to bring about local mixing
and a convective movement to ensure that the bulk of the material passes
through this area . so this mechanism also affects the mixing process.

9. 1. Three-bladed marine propeller:
Many varieties are existing:
a. with cut out or perforated blades for grinding and breaking up lumps.
b. with saw tooth edges for cutting and scratching action,
c. And with other than three blades . The stabilizing ring sometimes is in
included.
to minimize shaft flutter and vibration particularly at low liquid level.
Where?
They are used at relatively high speeds (up to 1800rpm)
with low viscosity fluids, up to about 4000cP

10. 2. Flat vertical blades turbine:
The simple geometry of this design has stimulated extensivetesting so
that expectation of their action is on a more rationalbasis than that of
any other kind of impeller.
Where?
It is suitable for the vast majority of mixing duties up to 100,000CP
or so at high pumping capacity.

11. 3. Horizontal plate blades turbine:
Where?
The horizontal plate to which the impeller blades
of this turbineare attached has a stabilizing effect.
4. Shrouded turbines:
It is consisting of a rotor and a stator.
Where?
Ensures a high degree of radial flow and shearing action, and arewell
adapted to emulsification and dispersion

12. 5. Cage beaters:
Mostly they are mounted on the same shaft
along with a standard propeller. More violent
action may be achieved with spined blades .
Where?
It imparts a cutting and beating action.
6. Anchor paddles:
Anchor paddles fit the contour of the container.
Where?
It prevents sticking of pasty materials, and promotes good heattransfer
with the wall.

13. Types of mixtures for dry and paste materials
1. Tumbler Mixers:
Free-flowing non-segregating powders may be readily
mixed in batch by use of tumbler mixers. Tumbler mixers operate by
tumbling the mass of solids inside a revolving vessel. Blenders are available
in various geometries, affecting material movement, mixing efficiency and
ease of cleaning between batches. These vessels take various forms, such as
those illustrated , and may be fitted with baffles or stays to improve their
performance. A tumbling batch blender can be of four types, which are
described as follows:
a. Horizontal cylinder :
This cylindrical mixer has a tubular vessel mounted on trunnions. Internal
baffles or lifter bars are mounted along the inner walls of the vessel. The inlet
is typically located at the top center of the vessel and the outlet at the bottom
center. The blender tumbles and the internal baffles gently lift and aerate the
material preventing it from sliding along the blender bottom; they also de-
lump the material. See figure a

14. b. Double cone blender :
The double cone blender consists of two cone-shaped sections, typically with
45o slopes. The cone sections are welded at their ends to a center band. The
blender is mounted between two trunnions that permit the unit to tumble
end over end. An opening in one of the ends of the cones serves as inlet and
outlet, or the inlet can be in one cone end with the outlet in the other.
Cleaning access is through the outlet. The blender tumbles, and the material
in the vessel spreads out. The transition area at the band between the cones
prevents the material from sliding along the inner wall and instead causes
the material to fold over itself. This provides gentle mixing with only very
slight shear. See figure b
Horizontal and Vertical Trough Mixers

16. C. V-cone blender and Y-cone blender :
The V-cone blender is similar to a double cone unit, but consists of two
large diameter pipe sections cut at a 45◦-angle and welded together to
form a V. In the same way, the Y-cone blender has a third section that
extends the volume of the blender in a bisectional direction with respect
to the other pipe sections. Inlets are typically located at both ends of the
V (or of the Y); the outlet is at the V point (or at the bottom of the Y).
The unit is also mounted on trunnions to allow it to tumble and can be
equipped with a spray line for liquid addition and an agitator for de-
lumping. The units tumble end over end as in the double cone blender.
The free-falling action combined with increased frictional contact
between the material and the long vessel sides result in less gentle
mixing than in a double cone blender.See figure c or d

17. 1.Vertical Screw Mixers :
In vertical screw mixers, a rotating vertical screw is located in a cylindrical
or cone shaped vessel. The screw may be mounted centrally in the vessel or
may rotate or orbit around the central axis of the vessel near the wall.
Materials are lifted from the bottom to the top of the hopper and are then
exchanged with materials on the way up. Such mixers are schematically
shown in . A vertical screw blender may be desired for larger batches
handled in a small space, while the orbiting screw mixer (Fig. 17.4b) is used
for difficult mixes. The latter arrangement is more effective and stagnant
layers near the wall are eliminated. Vertical screw mixers are quick,
efficient, and particularly useful for mixing small quantities of additives
into large masses of material. Specialized atmospheres as well as normal
temperatures and pressures are accessible for multipurpose operations.
see figure a or b on next slide

19. 2.Fluidized Bed Mixers:
Food powders can also be mixed by aeration using a fluidized bed. The
resulting turbulence of passing air through a bed of particulate material
causes material to blend. Materials are moved upward by air jets, causing
differential movement. Stationary vessels using gas-flow agitation are used
primarily for batch mode mixing. Materials to be mixed have to be relatively
fine and fairly narrow in their size distribution, as well as not too cohesive.
Powders to be mixed can be charged to more than 70% of the vessel volume.
Mixing times required in fluidized beds are significantly lower than those
required in conventional powder mixers. The mixing is largely convective
with the circulation patterns set up by the bubble motion within the bed. An
important feature of the fluidized bed mixer is that several processing steps
(mixing reaction, coating, drying, etc. may be carried out in the same vessel.
Additional equipment can include blowers, dust collectors, and pressure
regulators, which will enlarge the system as a whole. A particular type of the
fluidized mixer is the fluidized paddle mixer . The mixer has twin troughs,
each with a center mounted rotating shaft. Flat paddles are welded to spokes
on each shaft. The paddles lift the material from the bottom and throw it into
a zero gravity, fluidized mixing zone, settling a random displacement pattern
for the material.figure seen on next slide…

20. Fluidized Bed Mixers