partech cover to cover

Pertains to the science and technology related to the

handling and processing of particles (bulk solids, crystals,

granules, powders).

Particle Technology

It includes study of solid particles, liquid drops, emulsions

and bubbles.

Particle Technology

Also referred to as powder technology, particle science or powder science.

Particle Technology

In general, __ are more difficult to handle than liquids and gases.

solids

Solids in various industries are most commonly in form of __.

particles

Better control and understanding of material behavior and quality

Measurement of particle properties

Can influence other properties, such as reaction or dissolution rates, ease of flow or mix and compressibility

Measurement of particle properties

Particle properties

Particle size, Particle shape, Surface properties, Mechanical properties

the shape of a single particle is determined based on its __

sphericity

ratio of the surface area of a sphere having the same volume as the particle to the actual surface area of the particle

sphericity

for a spherical particle, sphericity is

1

For non-spherical or irregularly shaped particles, sphericity is also defined using the __ diameter

equivalent

Most important physical property of particulate samples because it has direct influence on many material properties

Particle Size

Characterized by equivalent diameter (Dp)

Particle Size

is a single dimension used to characterize the size of a solid particle, which is especially useful when the particle is not a perfect sphere

Equivalent Diameter

Regular, __ Particles: For shapes like spheres or cubes, Dp​ is described by a __, characteristic dimension

Non-equidimensional, single

Regular, __ Particles: For particles like needles or plates where one dimension differs significantly, Dp​ is often defined as the __ longest major dimension

Non-equidimensional, second

The equivalent diameter is typically considered the nominal size based on screen or microscopic analysis

Fine Particles

Dp​ is obtained through the method of equivalent spheres or statistical diameters derived from microscopic analysis

Irregularly-Shaped Particles

focuses on the individual fractions of a mixture within specific size ranges

Differential Screen Analysis (DSA)

A mixture of particles is sorted into fractions of approximately equal size, typically using a series of serial screens with decreasing mesh sizes

Differential Screen Analysis (DSA)

The analysis measures the mass (or weight fraction) of particles retained on each individual screen. The data is tabulated as the weight fraction (or percentage) versus the average particle size or mesh number (ΔΦn​)

Differential Screen Analysis (DSA)

provides a running total of the particle distribution across the entire size range

Cumulative Screen Analysis (CSA)

It is derived by summing the mass fractions obtained from the differential analysis

Cumulative Screen Analysis (CSA)

This consists of the mesh number versus the total fraction of particles that are larger than that specific opening (Φn​)

Cumulative Fraction Larger than Dp​ (CSA larger)

This consists of the mesh number versus the total fraction of particles that are smaller than that specific opening (1−Φn​)

Cumulative Fraction Smaller than Dp​ (CSA smaller)

a physical property defined as the total surface area of a sample of particles per unit mass. It is a critical parameter for characterizing fine and ultra-fine materials, where it is often expressed in units such as square metres per gram (m2/g) or square millimetres per gram (mm2/g)

Specific surface (Aw​)

The diameter of the hypothetical sphere having the same volume-to-surface ratio

Volume-surface mean diameter (𝑫𝒔)

represents the average linear size of the particles.

Arithmetic mean diameter (𝑫𝑵)

a weighted average diameter that represents the average size of particles based on their mass

Mass mean diameter (𝑫𝒘)

takes into account which particle size is present in higher mass over the other

Mass mean diameter (𝑫𝒘)

diameter of the average volume of particles found in the mixture, and is found by dividing the total volume of the sample by the number of particles in the mixture

Volume mean diameter (𝑫𝑽)

the diameter of a particle whose volume, if multiplied by the total number of particles, will equate all of the sample's volume

Volume mean diameter (𝑫𝑽)

In general, the volume of any particle is __ to its diameter cubed.

proportional

Standard screens are used to measure the size and size distribution of particles in the size range between about 76 mm and 38 μm.

Screen analysis

A set of screens is arranged serially in decreasing order of mesh size.

Sample is placed on the top screen and stack is shaken mechanically.

The particles retained on each screen are weighed and each increment are converted to mass fraction or percent.

Screen analysis

method of separating particles according to size alone.

Screening

Separation of mixture of particles of various sizes into two or more fractions by a screening surface.

Screening

The holes on the screen

Mesh

Defined as the number of holes per linear inch

Mesh number

The higher the mesh number, the __ is the screen opening

smaller

Clear opening in the screen surface

Maximum clear space between the edges of the screen opening. It is usually given in inches or millimeter

Screen aperture

Formula for aperture

1 in./mesh no. - Dwire

Mixture of differently-sized particles

Feed

Smaller than screen opening

Passes through the screen

Undersize

smaller than smallest screen

Fines

•Larger than screen opening

•Retained on the screen

Oversize

larger than largest screen

Tails

A single screen can make a single separation into two fractions, i.e., undersize and oversize.

Unsized function

When a solid mixture is divided into many fractions by passing through a series of screens.

Sized function

A measure of success of the completeness of the separation.

Screen Effectiveness (E)

Irregularly sized materials could cause blind screens which __ the screen effectiveness

lowers

are obtained with spherical particles on standard testing screens.

Closest separations

Needle-like or fibrous or where the particle tend to aggregate into __ that act as large particles.

clusters

may strike the screen surface endwise and pass through easily.

Long, thin particles

Other particles of the same size and shape may strike the screen __ and be retained.

sideways

Amechanical screeningmachine consisting of a perforated cylindrical drum that is normally elevated at an angle at the feed end.

Rotary Trommel Screen

in a rotary trommel, physical size separation is achieved as the feed material spirals down the rotating drum, where the __ material smaller than the screen apertures passes through the screen, while the __ material exits at the other end of the drum.

undersized, oversized

Any process whereby small particles are agglomerated, compacted, or otherwise brought together into larger, relatively permanent masses in which the original particles can still be distinguished.

Size Enlargement

In size enlargement, a particulate feed is introduced to a process vessel and is __ – either batchwise or continuously, to form a __ product.

agglomerated, granulated

The formation of aggregates through the sticking together of the feed material

Agglomeration

Size enlargement without application of pressure (tumble growth)

Moisture/Binders is added in the process to facilitate enlargement

Non-Pressure Agglomeration

Forming of particles into desired shape and size by applying various levels of pressure

Pressure Agglomeration

Unit operation that will convert large sized particles into smaller one of desired size and shape with the help of external forces.

Size Reduction (Comminution)

particle disintegration by two rigid forces (nutcracker)

Compression

particle concussion by a single rigid force (hammer)

Impact

produced when a particle is compressed between the edges of two hard surfaces moving tangentially (scissor)

Cutting/Shear

arising from particles scraping against one another or against a rigid surface (a file)

Attrition

Uses compressive force (nutcracker)

Product size: coarse (150-250 mm) and fine (6 mm)

Crushers

Uses impact mechanism (hammer)

Product size: intermediate (40-mesh) and fine (200-mesh)

Grinders

Product size: 1-5 microns (feed size: <6 mm)

Ultrafine Grinders

Uses shear force (scissors); gives particles definite size and shape

Product size: 2-10 mm

Cutting Machine

major expense in crushing and grinding

Power cost

When a material fractures, a new surface area is created. Each new unit area of surface requires a certain amount of energy.

Some of the energy added is used to create the new surface, but a large portion of it appears as heat.

Power cost

The work required in crushing is proportional to the new surface created raised to n

Power Requirement

It is based on the fact that particles do not deform before breaking (i.e., highly brittle).

Rittinger’s Law

Better prediction for fine grinding (for feed size < 0.05 mm) where a large increase in surface area results.

Rittinger’s Law

In Rittinger’s Law, the energy requirement is proportional to the __ created due to particle fragmentation.

new surface

Predicts more accurately for coarse particles (feed size > 50 mm) reduction wherein the energy is mainly used in causing fractures along existing cracks.

Kick’s Law

In Kick’s Law, the energy requirement is proportional to the __ ratio

size reduction

Applicable for a variety of materials undergoing coarse, medium and fine size reduction (feed size of 0.05 – 50 mm).

Bond’s Law

The energy required for size reduction is proportional to the square root of the __ ratio.

surface-to-volume

the gross energy required in KWH per ton of feed to reduce a very large feed to such a size that 80% of the product passes a 100 μm screen

Wi = work index

used to separate particulate solids from a liquid phase

Fluid Motion

To separate solids from each other according to particle size or density

Fluid Motion

This may be due to gravity, centrifugal forces, or electric and magnetic fields.

External force (Fe)

The upward force that acts on a particle that is wholly or partially immersed in a fluid.

It is parallel to the motion of the settling particle but opposite in direction.

Buoyant force (Fb)

The resistance force resulting from the motion of a particle through a fluid.

Drag force (FD)

The behavior of a particle under free settling can be described by __

Newton’s Law of Motion

the maximum constant velocity attained by a solid particle moving through a fluid medium. This state is reached when the forces acting on the particle are in equilibrium, meaning the particle is no longer accelerating (du/dt=0)

Terminal velocity (ut​)

Due to GRAVITY(e.g. sedimentation)

Due to CENTRIFUGAL FORCE

Acceleration due to external force (ae)

The tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier.

SEDIMENTATION

A process involving the use of centrifugal force to separate heterogeneous mixtures.

CENTRIFUGATION

the area formed by projecting the shape of a particle onto a plane that is normal (perpendicular) to its direction of motion through a fluid

Particle projected area (Ap​)

A dimensionless constant used to relate the complex dependencies, such as shape and flow conditions, of drag force by a particle moving through a fluid.

Drag Coefficient (CD)

It is a function of Reynold’s Number (Re) and usually obtained from a graph/equation.

Drag Coefficient (CD)

is a dimensionless parameter used to determine the flow region (Stokes’, Intermediate, or Newton’s Law) of a particle moving through a fluid

Criterion K

Its primary advantage is that it is calculated using known variables of the particle and fluid system, meaning terminal velocity (ut​) is not required to determine the regime

Criterion K

Particle has sufficient distance from the container and other particles.

Its fall is not affected by other particles.

Free settling velocity is the terminal velocity (ut)

FREE SETTLING

When particles are too crowded, a particle’s motion is impeded by other particles present in the container.

Exists when particles are very near each other even if there is no actual collision.

Particles settle at a lower rate.

HINDERED SETTLING