Solid Mixing Mechanisms and Equipment
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MIXING
Lab 7
DEFINITION
Solid Mixing and their mechanisms
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:
1- Particle size and particle size distribution
2- Particle density, elasticity, surface
roughness and shape.
NOTE:
Free flowing powders tend to segregate
during or after mixing.
Highly cohesive powders are difficult to
mix owing to agglomeration.
MIXING
MECHANISMS
Solid mixing proceeds by the
combination of one or more
mechanism:
1.
Convective mixing
2.
Shear mixing
3.
Diffusive mixing
1. CONVECTIVE MIXING
(NON- SEGREGATING)
Mechanism analogous to bulk transport
Convective (bulk) mixing occurred by:
Inversion of powder bed
By the aid of:
A- Blades or paddles
B- Revolving screw
C- Any method of moving large mass of
material from one part of powder bed to
another.
As a result of forces within mass
slip planes
Depending on the flow characteristic of
powder, that can occur in such a way to
give rise to
[laminar flow]
When shear occurs between regions of
different composition and parallel to their
interface.
Reduce the scale of segregation by
thinning the dissimilar layers
3- Diffusive mixing
(segregating)
Random motion of particles within a powder
bed
Change position by single particles relative to
one another
Reduction intensity of segregation
It occurs at the
interface of dissimilar
particles
in
shear mixing
or any form of
agitation that cause random motion of
individual particles.
EQUIPMENTS FOR SOLID
MIXING
Batch Mixing
1-
tumbling mixers
Mixers consist of containers of one or several
geometric forms (mounted and rotated about an
axis).
Tumbling motion by baffles or by virtue of shape
of container
TWIN-SHELL BLENDER
(FORM V-SHAPE MIXERS)
Effective because it’s mechanism of mixing
is:
Bulk transport and shearing.
Efficiency is dependent on speed of rotation.
Optimum rotation (30 - 100 rpm).
Used for dry solid mixing.
2- STATIONARY
CONTAINER TYPE:
Employs stationary container to
hold the material and bring mixing
by moving screws, paddles or
blades.
Useful in mixing solids that have
been wetted and therefore are in
sticky or plastic state.
WELL KNOWN STATIONARY
MIXERS INCLUDE:
A.
Ribbon blender
Consist of horizontal
cylindrical tank usually opening
at the top and fitted with helical
blades.
Blades mounted on the shaft
through the long axis of tank
and have both right and left
hand twist.
B.
Helical flight
mixers
Powders are lifted by a
centrally located
vertical screw and
allowed to cascade to
the bottom of the tank.
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:
1- Measuring degree of mixing
[according to the
uniformity of powder bed
that indicates the function of
mixer ].
2- Power requirements
[power required to produce good mixture with appropriate time].
NOTE:-
Unmixing and segregation might result from:
1- Improper mixing operation or wrong mixer or both,
2- After prolong mixing the milling occur because of abrasion of particles.
3- Powder properties that affecting solid mixing process.
FOR MORE INFORMATIONS, FOLLOW THE
UNDERLYING LINKS
https://www.youtube.com/watch?v=WRhCYNoIq-4
https://www.youtube.com/watch?v=jRkRLPnAWh0
https://www.youtube.com/watch?v=Aja9xbzcuG0
https://www.youtube.com/watch?v=DFUheo3biIc
Solid mixing involves processes like convective, shear, and diffusive mixing which randomize dissimilar particles in a system. Factors affecting solid mixing include particle size, distribution, and properties like density and elasticity. Various mechanisms like tumbling mixers are used for solid mixing to achieve homogenous mixtures.
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Presentation Transcript
MIXING Lab 7
A process that results in a randomization of dissimilar particles within a system. Mixing DEFINITION
The variables The variables effecting solid effecting solid mixing: mixing: NOTE: 1- Particle size and particle size distribution Free flowing powders tend to segregate during or after mixing. Highly cohesive powders are difficult to mix owing to agglomeration. 2- roughness Particle density, elasticity, and surface shape.
Solid combination mechanism: mixing proceeds of one by the more or MIXING MECHANISMS 1.Convective mixing 2.Shear mixing 3.Diffusive mixing
1. CONVECTIVE MIXING (NON- SEGREGATING) Mechanism analogous to bulk transport Convective (bulk) mixing occurred by: Inversion of powder bed By the aid of: A- Blades or paddles B- Revolving screw C- Any method of moving large mass of material from one part of powder bed to another.
2. SHEAR MIXING (segregating) As a result of forces within mass slip planes Depending on the flow characteristic of powder, that can occur in such a way to give rise to [laminar flow] When shear occurs between regions of different composition and parallel to their interface. Reduce the scale of segregation by thinning the dissimilar layers
3- Diffusive mixing (segregating) Random motion of particles within a powder bed Change position by single particles relative to one another Reduction intensity of segregation It occurs at the interface of dissimilar particles in shear mixing or any form of agitation that cause random motion of individual particles.
EQUIPMENTS FOR SOLID MIXING Batch Mixing 1- tumbling mixers Mixers consist of containers of one or several geometric forms (mounted and rotated about an axis). Tumbling motion by baffles or by virtue of shape of container
TWIN-SHELL BLENDER (FORM V-SHAPE MIXERS) Effective because it s mechanism of mixing is: Bulk transport and shearing. Efficiency is dependent on speed of rotation. Optimum rotation (30 - 100 rpm). Used for dry solid mixing.
2- STATIONARY CONTAINER TYPE: Employs stationary container to hold the material and bring mixing by moving screws, paddles or blades. Useful in mixing solids that have been wetted and therefore are in sticky or plastic state.
WELL KNOWN STATIONARY MIXERS INCLUDE: A. Ribbon blender Consist cylindrical tank usually opening at the top and fitted with helical blades. of horizontal Blades mounted on the shaft through the long axis of tank and have both right and left hand twist.
B. Helical flight mixers Powders are lifted by a centrally located vertical screw and allowed to cascade to the bottom of the tank.
MIXER SELECTION MIXER SELECTION Mixer selection and evaluation depend on: 1- Measuring degree of mixing [according to the uniformity of powder bed that indicates the function of mixer ]. 2- Power requirements [power required to produce good mixture with appropriate time]. NOTE:- Unmixing and segregation might result from: 1- Improper mixing operation or wrong mixer or both, 2- After prolong mixing the milling occur because of abrasion of particles. 3- Powder properties that affecting solid mixing process.
FOR MORE INFORMATIONS, FOLLOW THE UNDERLYING LINKS https://www.youtube.com/watch?v=WRhCYNoIq-4 https://www.youtube.com/watch?v=jRkRLPnAWh0 https://www.youtube.com/watch?v=Aja9xbzcuG0 https://www.youtube.com/watch?v=DFUheo3biIc
