This document discusses mixing in industrial processes. It defines mixing as manipulating a heterogeneous system to make it more homogeneous by intermingling two or more separate components. The types of mixing covered include different materials like solids, liquids, and gases. The mechanisms of mixing include shear, diffusive, and convective mixing. Common mixers are tumbling mixers, convective mixers, ribbon blenders, and others. Factors that impact mixing include mixer selection, mixing time, power consumption, and degree of mixing achieved. Agitation is also discussed and compared to mixing.

1. MIXING
By: The University of Faisalabad

2. Definition
 In industrial process engineering, mixing is
a unit operation that involves manipulating a
heterogeneous physical system, with the
intent to make it more homogeneous.
OR
 Mixing is a phenomena in which two or
more separate components are intermingled
to form more or less uniform product.

3. Types of Mixing
 Mixing of cohesive solids
 Mixing of noncohesive solids
 Mixing of liquids

4. Cont…
 Single phase liquid mixing
 Mixing of immiscible liquids
 Gas liquid mixing
 Liquid solid mixing
 Solid liquid gas mixing
 Solid solid mixing

5. Types of Mixture

6. Mechanism of Mixing
 Shear Mixing;
 In shear mixing, shear stresses give rise to slip zones
and mixing takes place by interchange of particles
between layers within the zone.
 Diffusive Mixing;
 Diffusive mixing occurs when particles roll down a
sloping surface.
 Convective Mixing.
 Convective mixing is by deliberate bulk movement of
packets of powder around the powder mass.

7. Types of Mixer
 Tumbling mixers.
 Closed vessel rotating about its axis
 Shapes of vessels include v-mixer, double cone, rotating cube
 Mechanism is diffusive mixing.
 Quality of mixture is limited.
 Baffles may be installed in an attempt to reduce segregation

8. Types of Mixer
 Convective mixers
 Circulation patterns are set up within a static shell by
rotating blades or paddles
 Mechanism is convective mixing
 Accompanied by some diffusive and shear mixing
 Ribbon blender in which helical blades or ribbons rotate
on a horizontal axis in a static cylinder
 Rotational speeds are typically < 60 rpm

9. Ribbon Blender

10. Conical Screw Mixer

11. Muller mixer

12. Pug mill

13. Pan mixer

14. Change can mixer

15. Banbury mixer

16. Mixer Selection
 Choice of impeller can also affect mixing time
 Propellers typically require longer mixing times
compared to turbines
 Propellers have lower power consumption
 Gas bubbles, liquid drops, or solid particles also
increase blending time
 No direct relation between power consumed and
amount or degree of mixing.

17. Degree of the Mixing
 Difficult to quantify the degree of mixing
 If dealing with the solid particles, the statistical
variation in composition among withdrawn at
any time from a mix is commonly used a
measure of the degree of mixing
 Standard deviation S or the variance s2
is
generally used.
 No amount of mixing will lead to the formation of
a uniform mosaic but only to a condition, where
there is an overall uniformity but not point
uniformity.

18. Agitation vs. Mixing
 Agitation – induced motion of a material in a
specified way
 Usually a circulatory pattern inside a container
 Mixing – random distribution, into and
through one another, of two or more initially
separate phases
 Various degrees of homogeneity

19. Purposes of Agitation
 Suspending solid particles
 Blending miscible liquids
 Dispersing a gas through a liquid in the form
of small bubbles
 Dispersing a second liquid, immiscible with
the first, to form an emulsion or suspension of
fine drops
 Promoting heat transfer between the liquid
and a coil or jacket

20. Agitation Equipment
 Tank or vessel
 Cylindrical in form with a vertical axis
 Rounded tank bottom
 Depth ≅ diameter
 Impellers
 Axial-flow – generate currents parallel with the
axis of the impeller shaft
 Radial-flow – generate currents in a tangential or
radial direction
 Propellers, Turbines & High-efficiency Impellers

21. Measurements of Design for Turbine

22. “Standard” Turbine Design
 Type and location of impeller, proportions of
vessel, number and proportions of baffles
 No. of baffles – 4
 No. of impeller blades – 4-16 (usually 6-8)
3
1
3
1
=
=
t
t
a
D
E
D
D
5
1
1
=
=
a
t
D
W
D
H
4
1
12
1
=
=
a
t
D
L
D
J

23. 3-blade marine propeller
Simple straight-blade turbineDisk turbine
Concave-blade
CD-6 impeller
Pitched-blade turbine
Types of Blades

24. cont.

25. Flow Patterns
 Depends on type of impeller, characteristics
of fluid, size and proportions of tank, baffles,
and agitator
 Swirling – stratification at various levels with
no longitudinal flow between levels

27. Power Consumption

28. THANKS