SIZE ENLARGEMENT Flashcards
What is size enlargement?
The process by which smaller particles are put together to form larger masses in which the original particles can still be identified.
Size enlargement is a critical step involving particulate solids in various process industries.
What are the industries in which size enlargement is used?
- Pharmaceutical
- Food
- Agricultural
These industries utilize size enlargement for various applications.
What are the objectives of size enlargement?
- Reduction of dust hazard
*Reduction of caking and lump formation - Improve flow properties
- Increase bulk density for storage
- Create non-segregating mixtures of ingredients of differing original size
*Provide a defined metered quantity of active ingredient - Control of surface to volume ratio
These objectives help in optimizing material handling and processing.
What are Van der Waals forces?
Weak intermolecular forces that are dependent on the distance between atoms or molecules, arising from the interactions between uncharged atoms/molecules.
These forces play a significant role in particle interactions.
What are electrostatic forces?
A result of interparticle friction or through the generation of opposite charges.
Electrostatic forces can affect particle behavior during size enlargement.
What are liquid and solid bridges in the context of size enlargement?
Dispersion of liquid into a powder mass generally results in a significant increase in the strength of particle-particle agglomerates.
These bridges enhance the cohesion between particles.
What are the size enlargement rate processes?
- Compaction
- Granulation
- Encapsulation
- Pelletizing
- Agglomeration
Each of these processes plays a unique role in size enlargement.
What is granulation?
The process of forming grains or granules from a powdery or solid substance, producing a granular material.
Granulation is widely used in the chemical and pharmaceutical industries.
What are the reasons for granulation?
- To prevent segregation of powder mix
- To improve flow characteristics
- For improving compression ability
Granulation enhances the handling and processing of powders.
What is wet granulation?
A method of granulation that involves the addition of a liquid to a powder to form granules.
This technique is essential in producing uniform granules.
What is the first step in the mechanism of wet granulation?
Nucleation, where granulation starts with particle to particle contact and adhesion due to liquid bridges.
Nucleation is crucial for the formation of granules.
What are the three states describing the distribution of liquid between particles in wet granulation?
- Pendular State
- Funicular State
- Capillary State
These states illustrate the varying degrees of liquid presence between particles.
What is the process of wetting in granulation?
The process by which air within the voids between particles is replaced by liquid, governed by surface tension and contact angle.
Wetting influences the efficiency of granulation.
What is granule breakage?
The fracture of a granule to form two or more pieces.
Breakage can impact the quality of the final granules.
What is attrition in the context of granulation?
The reduction in size of a granule by loss of primary particles from its surface.
Attrition can lead to undesirable changes in granule characteristics.
Fill in the blank: The size enlargement process that transforms a powder material into large entities is called _______.
Granulation
True or False: The capillary state is when all air has been displaced from between the particles.
True
Fill in the blank: _______ is the process of compressing or molding a material into the shape of a pellet.
Pelletizing
At what level of spray flux will show drop footprints will not overlap and each drop will form separate nucleus granule
low
What is the PENDULAR STATE?
Usually at low moisture level, particles are held together by lens-shaped rings of liquid, with mainly air between the particles.
This state indicates low moisture content in the material.
What characterizes the FUNICULAR STATE?
It is an intermediary state where air starts to displace from between particles.
This state indicates a transition from low moisture to higher moisture levels.
What occurs in the CAPILLARY STATE?
All air has been displaced from between the particles; liquid penetrates the pores and forms a solid bridge between particles, resulting in the strongest adhesion when the liquid evaporates.
This state signifies maximum moisture content and strong particle adhesion.
there will be significant overlap of drops hitting the
powder bed
At high spray flux
when spray flux is high, spray flux is
𝝍𝒂 ≈ 𝟏
At low spray flux
𝝍𝒂 ≪ 𝟏
The parameter that determines whether coalescence will occur is
Stokes number
a measure of the ratio of collisional kinetic energy to energy dissipated through viscous dissipation
Stokes number
For coalescence to occur, Stokes number must be
less than the
critical value Stk*
What type of motion is imparted to particles in tumbling granulators?
A tumbling motion
This motion occurs in an inclined cylinder or a pan.
What is a key operational characteristic of tumbling granulators?
Operate in continuous mode and can handle large throughputs
This allows for efficient processing of materials.
What does the tumbling action in granulators lead to?
Natural classification of contents according to size
This helps in sorting particles during the granulation process.
How is the motion of particles achieved in mixer granulators?
By an agitator rotating at low or high speed
The axis of rotation can be vertical or horizontal.
What is the range of rotation speeds for horizontal pug mixers used for fertilizer granulation?
50 rpm to over 3000 rpm
This varies depending on the application and equipment used.
What is the impeller speed range for vertical axis mixers in the pharmaceutical industry for mixers less than 30 cm in diameter?
500 to 1500 rpm
Larger mixers, over 1 m in diameter, have lower speeds of 50–200 rpm.
What sets particles in motion in fluidized bed granulators?
Fluidizing air
This can create either a bubbling or spouted bed.
What operational modes can fluidized bed granulators operate in?
Batch or continuous mode
This flexibility allows for various production processes.
What are some advantages of fluidized bed granulators?
Good heat and mass transfer, mechanical simplicity, ability to produce small granules from powder feeds
These advantages make them suitable for various applications.
What must happen for two colliding primary granules to coalesce?
Their kinetic energy must be dissipated
This is crucial for forming a strong bond.
What must the strength of the resulting bond be able to resist?
External forces exerted by the agitation of the powder mass
This is important to maintain granule integrity during processing.
