1. Mixing

2. Mixing
Definition:
The process of randomization of dissimilar particles with in a system.
an operation in which two or more components are treated so that each particle lies as near as possible in contact with a particle of each of the other ingredient.
Types of Mixture
Positive Mixture
Negative Mixture
Neutral Mixture
Positive Mixture:
These are formed from materials such as gases or miscible liquids, in this case irreversible mixing take place, by diffusion, without the expenditure of work provided time is unlimited. Generally such material do not present any problems in mixing.

3. Liquid Mixing 2. Negative Mixing:
Suspension of solids in liquids is example of such type of mixtures that require work for their formation and the components of which separate unless work is continuously expended on them. These are more difficult to form and maintained.
3. Neutral Mixing:
These are static in their nature the components are hard to mix spontaneously, nor do they segregate when mixed. Examples include pastes, ointments, and mixed powders.
Liquid Mixing
The liquid mixing operation has two requirements.
Localized Mixing: Required to apply shear to the particles of fluid.
2. General/bulk Mixing: Required to take all parts of the bulk of the material through the shearing (localized mixing) zone and ensure that a uniform final product is obtained.

4. The movement of the liquid at any point in the mixing vessel will have three velocity components and the complete flow pattern will depend on variations in these three components in different parts of the vessel. The three velocity components are,
1. Radial Component: Acting in a direction vertical to the impeller shaft.
2. Longitudinal Component: Acting parallel to the impeller shaft.
3. Tangential component: acting in a direction that is a tangent to the circle of rotation round the impeller shaft.

5. Requirements for liquid mixing:
Liquid mixing is usually performed in a vessel provided with mixing element, commonly a rotational device, which provides necessary shear force and produce appropriate flow pattern.
Nomenclature
Where: D = Impeller Diameter C = Impeller off Bottom Clearance B = Baffle Z = liquid Depth T = Vessel Diameter

6. OPTIMUM MIXER SELECTION CRITERIA
A full and accurate specification of the mixing vessel, the process parameters, and the required mixer performance is the first crucial step to arriving at an optimum mixing operation. Some of the many other variables that can affect mixer performance and so need to be considered in arriving at the optimum mixer design are noted on these pages.
Impeller Type
The function of any mixing impeller is to convert the rotational energy of the mixer shaft into the correct combination of flow, shear and turbulence to achieve the required process result.
As no one-impeller design is capable of providing optimum performance under every process condition, optimum process performance is dependent upon selecting an impeller design that has the specific characteristics required by a given process.

7. Number of Impellers
The use of a single impeller is the usual preferred option on the basis of cost. However, changes in the ratio of liquid level (Z) to vessel diameter (T) can have an adverse effect on the flow patterns generated within the vessel. This can result in the need to consider the use of multiple impellers in order to achieve an economic solution.
Z/T ratio alone is not the only consideration when determining the number of impellers required. Multiple impellers may also need to be considered for other reasons including, when high viscosity fluids are involved, for mixing at low level during filling and emptying or where draw down from the liquid surface is a requirement.
Impeller Positioning
Whether utilizing a single or a multiple impeller configuration the positioning of the impellers within the process fluid can have a significant effect on the overall process performance. Incorrect positioning can lead to staged flow patterns, poor dispersion of additives and impellers being out of the liquid at crucial stages of the process.

8. D/T Ratio
The ratio of mixing impeller diameter (D) to vessel diameter (T) has a very significant effect on the performance of most fluid mixers and the optimum D/T is a function of both process conditions and process requirements.
Normally the optimum D/T will be in the range 0.2 < D/T < 0.5. Some special applications however, sometimes operate outside this range.
Bottom Clearance
The impeller bottom clearance (C/T ratio) can also have a very significant effect on the overall performance of a mixer, effecting both power draw and pumping efficiency. The optimum C/T ratio is essentially dependent upon impeller type but can also be effected by process conditions.
Normally, the optimum C/T will be in the range: 0.1 < C/T < 0.3.
Vessel Geometry
When designing a vessel for mixer duty it is important to understand the role that tank geometry plays in determining the final mixer design. Poor aspect ratios and or inappropriate bottom shapes can both result in increase mixer cost and in certain circumstances make it impossible to optimize the mixer design.

9. Shaker Mixers
Impeller Mixers
Shaker Mixers: such mixers operates on the principle of agitation. They either oscillates (lab Scale) or rotates (large Scale). These mixers are not categorized as efficient mixers therefore their use is limited.
Impeller Mixers: These the most widely used form of mixer for liquids. These are of three types.
Propeller mixers
Turbine Mixers
Paddle Mixers
Propeller Mixers:
Propeller usually resembles ordinary marine
propellers in shape, have small diameter as
Compare to the container and operates at
high speed i.e. around 8000 RPM. These mixers promote longitudinal movement. The propeller mixers are not effective for the liquids with viscosity greater than 50P or 500 cP, which is the viscosity somewhat greater than the viscosity of glycerin or castor oil.

10. Due to promotion of longitudinal movement and high speed vortexing and aeration is the major problem associated with the propellers. To avoid these condition the propellers must be placed deep in the liquid and symmetry should be avoided. There are number of ways to avoid vortexing;
The propeller shaft may be off set from the centre.
the shaft may be mounted at an angle.
the shaft may enter the side of the vessel.
vessel other than cylindrical may be used.
Use of push pull propeller, in which two propellers are mounted on the same shaft with opposite pitches.
use of baffles.
Propellers are best suited for the suspension as they promote longitudinal currents and is not suitable for emulsification , which requires high shear.

12. 2. Turbine Mixers:
Turbine mixer uses a circular disc impeller, to which are attached a number of short, vertical blades, which my be straight or curved. The RPM and the D/T ratio is some what lower than the
propeller mixer. The blades may have a pitch
giving some axial flow, but commonly the blades
Are flat, thus there is very little axial or radial flow
flow. It means that turbine promote tangentional
flow, providing high shear forces than
Propeller mixers. These shear forces may be
increased further by fitting a diffuser ring.
Diffuser ring is a stationary perforated or slotted
ring which surrounds the impeller, so that the discharged liquid must pass through the aperture. The diffuser reduces rotational swirling and vortexing. Turbine mixers are more useful with viscous liquids as compared to propeller mixer.(100 Ns/m2), approximately that of liquid glucose. Turbine are not useful for suspending heavy solids, but the high shear forces and greater viscosity range make them more useful for emulsification.

13. 3. Paddle Mixers:
These mixers use an agitator with flat blades
Attached to the vertical shaft and rotating at low
speed i.e. 100rpm.these mixers promotes radial
and tangential flow with very little longitudinal
flow which may be increased by using paddles
with slight pitch. The diameter is half to two
Third of the diameter of the vessel. An alternate
paddle mixer for viscous liquids is planetary
mixer which rotates on at axis and also with
the walls of the vessel.

14. Air Jets:
In such systems pressurized air or other gas
introduced from the bottom of the vessel, the
pressure of the air bubbles lift the liquid from the
bottom to the top of the vessel. The liquids which
is to be mixed must be
low viscous
Uncreative with the gas
Nonfoaming
Fluid jets:
In such system one liquid is pumped the
another liquid through nozzles arranged to
permit good circulation of material through out the tank .

15. Solid Mixing Factors to be considered during mixing:
A. Segregated Powder B. Ideal mixed C. Randomized Mixing A B C
Factors to be considered during mixing:
Material Density 2. Particle Size
3.Particle Shape 4. Particle Attraction
5. Mixer Volume 6. Mixing Time
7. Mixing order 8. Speed of the mixer

16. Mixing Mechanism
Convective mixing:
This mechanism may be regarded as analogous to bulk transport as in fluid mixing. Convective mixing in solids occurs by an inversion of the powder bed, by means of rotation of container, movement of blades or paddles.
2. Shear Mixing:
it is due to the forces with in the particulate mass, slip planes are set up.
3. Diffusive Mixing:
When random motion of particles with in a powder bed causes them to change their position relative to one another. Diffusive mixing occur at the interfaces of dissimilar regions that are undergoing shear.

17. Mixing Equipment:
Mixers used for solid mixing can be categorized mainly into two types
Agitator Mixers
Tumbling Mixers
Agitator Mixers:
These can be further classified as
Conventional Mixer
Planetary mixers
High Shear Mixers

20. DIFFERENT BLADE ATTACHMENT AVAILABLE
PLANETARY MIXER
DIFFERENT BLADE ATTACHMENT AVAILABLE

28. Tumbling Mixer
Application
 Mixing Powder & Granule
Theory
The eight angles shaped tumbler have baffles on each side. The granules are twisted flowing along the angle of baffles and mixed again by the center shaft baffles It can reach the best and efficient mixing result , the mixing ratio can be up to 1:10,000
Feature
1. Uniform mixing
2. Short mixing time
3. Mixing ratio up to 1:10,000
4. With safety gate and interlock
5. Option to integrate with vacuum suction system and connect to dry granulator for contained production process and continuous auto loading.

29. Double Cone Mixer Theory
The core shaped mixer is wide in the middle and narrow at the both ends. Inside have baffles in the middle, when the powder or granules are rolling up and down in the drum and hit the middle baffles , the best mixing result can be reached.
Feature
1. Uniform mixing.
2. Simple structure.
3. With safety gate and interlock.
4. Option to integrate with vacuum suction system and connect to dry granulator for contained production process and continuous auto loading.

30. V-Mixer/twin Shell Mixer
Application
Mixing Powder & Granules 
Theory
The mixing method of the V-shaped mixer is through rotating the granules rapidly and this enables the product separating into two cones then two merge into one again, By repeating the procedure , the granules will then be separated and merged again and again to reach the best mixing result.
Feature
1. Excellent mixing effect.
2. Simple structure
3. Easy cleaning
4. With safety gate and interlock
5. Option to integrate with vacuum suction system and connect to dry granulator for contained production process and continuous auto loading.

31. Mixing of Semisolids
The mixing mechanism depends upon the nature of material, semisolids show considerable variation in their consistency. The rheological properties of non-Newtonian materials have an important effect on the mixing operation. The dilatant or plastic materials are usually difficult more to mix than the Newtonian materials, but thixtropy may make the mixing easier.
Theory:
In mixing an insoluble powder to a liquid , a number of stages can be observed as the liquid content is increased.
Pellet and powder state:
Addition of small amount of liquid to the bulk of dry powder causes the solid to ball up and form small pellet. The pellets are embedded in matrix of dry powder which has cushioning effect and makes the ball difficult to break up.
2. Pellet State:
Further addition of liquid results in the conversion of more dry powder to pellet state, until all the material is in this state. The mass has coarse granular appearance, but the pellets do not cohere and agitation will cause aggregates to break down. Into smaller granules.

32. 3. Plastic State:
As the liquid content is further increased, the character of mixture changes markedly, the aggregates adhere, the granular appearance is lost, the mixture becomes more or less homogeneous and of clay like consistency. Plastic properties are shown and the material is difficult to shear.
4. Sticky state:
Increase in the liquid content causes the mixture to attain this state, the appearance become paste like, the surface is shiny and the mass adheres to solid surface.
5. Liquid State:
Further addition of liquid results in a decrease consistency until a fluid state is reached. In this state the mixture flows under its own weight.

33. Mixers for semisolids: Agitator Mixers
Planetary Mixer
Sigma Mixers
Shear Mixers
Roller Mills
Colloidal mills
homogenizers
Ultrasonic Mixers

34. Poise
Named after the physicist Poiseuille this is the CGS derived unit of dynamic viscosity of a fluid. When a force of 1 dyne maintains unit rate of shear of a film of unit thickness between surfaces of unit area dyne sec cm-2
Conversions 1 poise=0.10 kg m-1s-1
1poise=0.1 N s m-2
1 poise= lbf s ft-2
1poise= Poundal s ft-2
1 poise= reyn
1poise= slugs ft-1s-1
1 poise=100 centipoise
1 poise=1.0 dyne s cm-2

35. Pitch: Is the displacement a propeller makes in a complete spin of 360° degrees.

36. BLENDING / HOMOGENISATION OF MISCIBLE LIQUIDS Chemical Reactions
• Polymerization
• Simple blending of miscible fluids
• Make-Up Tanks
• Storage, Feed, or Holding Tanks
Information Required for Mixer Selection
• Viscosity
• Density
• Pressure & Temperature
• Blend Time
• Volume (s)
• Any specific process requirement
SOLIDS SUSPENSION
Principally there are five degrees of suspension as follows
Solids Just Suspended
• Off Bottom Suspension
• Moderate Uniformity
• Nearly Uniform Suspension
• Uniform Suspension

37. Information Required for Equipment Selection
• SG of Liquid
• SG of Solid
• Solids size or distribution of range
• Percent solids by Weight
• Slurry viscosity
• Degree of Suspension required

38. MIXING MECHANISMS Mixing is achieved by a number of different mechanisms, as summarized in the following table.
Convection
Induced by pumping action of the impeller, Fluid moves through the different parts of vessel, preventing stratification.
Macro-mixing
Caused by turbulent flow a wide range of vortices. Smallest in the impeller region where dissipation is the highest. Separates bulk of fluid into smaller elements.
Laminar shear
Below the scale of macro mixing fluid elements are further dispersed by laminar shearing. Elements are stretched, distorted and folded.
Micro-mixing
Final smallest scale mixing. Diffusion of reactants takes place and is driven only by concentration gradient.