This document discusses mixing and different types of mixers. It defines mixing as the random distribution or addition of materials, as opposed to agitation which refers to induced motion without distribution. Mixing can involve solids, liquids, or gases. The key types of mixing discussed are solid mixing, liquid mixing, and gas mixing. For solid mixing, different mixers are used depending on whether the solids are cohesive or non-cohesive. Common mixers mentioned include ribbon mixers, tumbling mixers, pony mixers, and beater mixers. The document also discusses how the degree of mixing is quantified using a mixing index.

1. MIXING & MIXING INDEX

2. WHAT IS MIXING ?
 Many processing operations depends for their success on the
effective agitation and mixing of fluid or solid particles.
 Though often confused , agitation and mixing are not
synonymous of each other . both having different meaning.
 Agitation refers to induced motion of material in specified way
, usually in circulatory pattern inside in container.
 Mixing is the random distribution or addition.

3.  A single homogeneous material, such as a tankful of cold
water , can be agitated ,but it can not be mixed until some
other material is added to it.
 Hence , it should be necessary to having two material for
mixing and for agitation only one material is enough.
 The term mixing is applied to a variety of operation , differing
widely in the degree of homogeneity of mixed material.
 Consider in one case , two gases that are brought together
and thoroughly blended and in second case , sand ,gravel,
cement and water tumbled in rotating drum for long time.
 In both the case final product said to be mixed. Yet the
product are obviously not equal homogeneous.
 The machine which is used for mixing is known as mixer.

4.  Many type of mixing is available such as ,
 solid mixing
 liquid mixing
 gas mixing
 The mixing of solids, weather free flowing or cohesive ,
resembles to some extent the mixing of low-viscosity liquid.
the processes intermingle two or more separate component to
from a more or less uniform product.
 Some equipment normally used for blending liquid may, on
occasion, be used to mix solid.
 There are significant difference between the two processes.
liquid blending depends on the creation of flow currents ,
which transport unmixed material to the mixing zone adjacent
to impeller.
 In solid mixing , much more power is required .

5.  There are two types of solid such as cohesive solids and non-cohesive
solids.
 Obviously the mixer is used for both solids are different.
 Mixer for Non-cohesive solids :
Ribbon mixer and tumbling mixer are generally use for non-
cohesive solids.
1. Ribbon mixer :
 In a ribbon mixer , two counteracting ribbons are mounted on the same
shaft .
 One shaft moving the solid slowly in one direction and the other moving it
quickly.
 The ribbons may be continuous or interrupted. Some unit operate batch
wise , some are continuously.

7.  2.Tumbling mixer :
 Tumbling mixers include ball mills and tumbling drums also ,
both of which can handle dense slurries and heavy solids.
 In this mixer , the solids are filled from top side until it is 50 to
60 % full ,
then rotated about a horizontal axis for 5 to 20 min.
 Mixing in tumbling mixer is initially rapid ,but never
complete.in this type of mixer the components are never
broken in complete manner.
 And in ribbon mixer , the mixing is complete and the particles
are mix each other very well than tumbling mixer.
 Power consumption is also less in ribbon mixer than tumbling
mixer.

9.  Mixer for cohesive solids :
pony mixer and beater mixer are used for cohesive solids
mixing.
 Some of the most difficult of all mixing problems involve
cohesive solids such as pastes , plastic materials , rubber.
 In some ways , these substance resemble liquids , but their
enormously high viscosity.
 It means the equipment which is used for mixing is more
effective in this case.
 The forces generated in these mixer are large and power
consumption is high.

10.  Change can mixers blend viscous liquids or light phases, as in
food processing or paint manufacture, in a removable agitated
can or a vessel 5 -100 gallon in size .
 In a pony mixture the rotating agitator carries several vertical
blades positioned near the vessel wall. The can is driven by a
turntable in a direction opposite to that of agitator.
 In a beater mixture the can is stationary and the agitator has
planetary motion, so that as it rotates it precesses, repeatedly
visiting all parts of vessel

11. 1. Pony Mixer :
 In a pony mixer the rotating agitator carries several vertical
blades positioned near the vessel wall.
 Three type of blade is use in these mixer :
1.sigma blade
2.double-naben blade
3.disperser blade

12.  The common sigma blade shown left is used for general-
purpose kneading . its edges may be serrated to given a
shredding action.
 The double-naben ,or fishtail, blade in center is particularly
effective with heave plastic materials.
 The dispersion blade at the right develops the high shear
forces needed to disperse powders or liquid in to plastic or
rubbery masses.
 Masticator blades are even heavier than this three blades.
Sometimes being little larger in diameter than the shaft that
drive them spiral , flattened and elliptical designs of masticator
blades are used.

14.  2.Beater mixer :
in the beater mixer the can is stationary and agitator has
planetary motion , so that as it rotates it precesses , repeatedly
visiting all the part of the vessel.

15. squashing the mass flat, folding over it, and squashing it once
more.
 Most kneading machines also tear the mass apart and shear it
between a moving blade and a stationary surface.
 Considerable energy is required even for thin materials, and
as the mass becomes stiff and rubbery power requirements
become very large.
 As per the requirements various kneader can be used.
 A disperser is heavier in construction and draws even more
power then a kneader, it works additives and coloring agents
into stiff materials.
 A masticator is even heavier and draws even more power.

16. MIXING INDEX
 Mixing is harder to define with solids and pastes than it is with
liquids. Quantitative measures of mixing based on statistical
procedures are sometimes used to evaluate mixer
performance.
 For noncohesive solids, multiple small samples containing
about same particle are used. Let us have A and B component
from which N spot samples , each containing n particles are
taken and analysed. Then the standard deviation ‘s’ is
estimated from the analytical result by the eq.
 S =
𝑖=1
𝑛 𝑥𝑖−𝑥 2
𝑁−1
, here xi= number fraction of a in each sample
X= avg value of measured number fractions

17.  Now with granular solids the mixing index is based not on
conditions at zero mixing but on the standard deviation that
would be observed with a completely random, fully blended
mixture.
 For any given size of spot samples. There is a theoretical
standard deviation for a completely random mixture.
 σ e = 𝜇 1 − 𝜇
𝑛

18.  For granular solids Mixing Index I s is defined as the ration
of σe to s.
 Is = 𝜇 1−𝜇 𝑁−1
𝑛 𝑖=1
𝑛 𝑥𝑖2 −𝑥 𝑥=1
𝑛 𝑥𝑖

19. THANK YOU