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Unit Operation: CHD 228
Instructor: Dr. Pratibha Biswal
Lecture 2
Particle Size, Screen analysis
20-11-2018 1Shiv Nadar University

• Large quantities of particles are handled on the industrial scale
• It is frequently necessary to define the system as a whole.
• It is necessary to know the distribution of particle sizes in the
mixture.
• It is necessary to define a mean size which in some way
represents the behaviour of the particulate mass as a whole in
the system.
Why we need Particle Size Distribution?
20-11-2018 Shiv Nadar University 2
Particle Size Distribution: Need

• In general, "diameters" may be specified for any equidimensional particle.
• Particles that are not equidimensional, i.e., that are longer in one direction than in others,
are often characterized by the second longest major dimension.
• For needle like particles, for example, size would refer to the thickness of the particles, not
their length.
• Conventionally, particle sizes are expressed in different units depending on the size range
involved.
• Coarse particles are measured in inches or millimetres.
• Fine particles in terms of screen size; very fine particles in micrometers or nanometers.
• Ultrafine particles are described in terms of their surface area per unit mass.
Particle Size

Particle Size Range
Particle size is characterized
using these terms:
i. Very coarse
ii. Coarse
iii. Moderately coarse
iv. Fine
v. Very fine

Wood Chips
Urea
Granulated
Sugar
Flour
Ceramic
Powder
Magnetic
Pigment
Organic
Pigment
Carbon Black
Particle Size Range

Particle size can influence variety of
important factors:
• Dissolution rate
• Suspendability
• Uniform distribution
• Penetrability
• Chemical Reaction
• Heating and Combustion etc.
Effects of Particle Size

Screen Analysis: Nomenclature
• Particles at a specified size range can
be measured by screens or testing
sieves.
• Testing sieves (screens) are
constructed with square openings of
woven wires.
• Mesh: A single opening measured from
the center of each wire.
• Screen Aperture: Minimum clear space
between the wires
• Coarse Screens: “Mesh size” refers to
the distance between adjacent wires.
• Fine Screen: “Mesh number or sieve
number” is the number of openings per
linear inch.
Mesh
Mesh Number: Number of
meshes in 1 inch length from
the center of a wire
Screen Aperture

Screen Analysis: Standard Screens
• Sieves (Screens) are available in a number of standard series. (See Table 1.1 in Coulson
and Richardson; Appendix 20 in Mccabe, Smith and Harriot)
• The screen type is dependent on the diameter of the wire and mesh number.
Tyler Standard
Screen Series
Mostly used
US Sieve Series
Almost similar to
Tyler screen series
with slight
modifications
UK British
Standard
Smaller and
fragile
Institute of
Mining and
Metallurgy
Robust and
Expensive

Screen Analysis: Standard Screens
• Wire Diameter is 0.0053
mm (0.0021 in)
• Screen Aperture: 0.0029
in
 In general, when screens are in
series,
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑆𝐴 𝑜𝑓 𝑙𝑎𝑟𝑔𝑒𝑟 𝑠𝑐𝑟𝑒𝑒𝑛
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑆𝐴 𝑜𝑓 𝑠𝑚𝑎𝑙𝑙𝑒𝑟 𝑠𝑐𝑟𝑒𝑒𝑛
=2
𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑆𝐴 𝑜𝑓 𝑙𝑎𝑟𝑔𝑒𝑟 𝑠𝑐𝑟𝑒𝑒𝑛
𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑆𝐴 𝑜𝑓 𝑠𝑚𝑎𝑙𝑙𝑒𝑟 𝑠𝑐𝑟𝑒𝑒𝑛
=√2
 Intermediate screens are also
available for closer size
distribution (As shown in table).

Screen Analysis
 Screens are stacked with the coarsest screen at the
top and finest screen at the bottom.
 The sieves are shaken either manually or
mechanically for a fixed time.
 Material retained in each screen is removed and
weighed separately. Amount of material in each
screen is expressed as weight fraction.
 Any particles that pass the finest screen are caught
in a pan at the bottom of the stack.
 The results of a screen analysis are tabulated to
show the relationship between mass fraction and
mesh size.

 Tabulate this increment as a
function of the average particle
size.
Differential Screen Analysis
6
8
10
200
Pan
Mixture

 Plotting the cumulative sums against
the maximum particle diameter or
screen opening
Cumulative Screen Analysis
6
8
10
200
Pan
Mixture

Mixed Particle Sizes And Size Analysis
• In a sample mass ms, density ρt and uniform particles of diameter Dp, total volume of the sample is
• Number of particles in the sample is
• The total surface area of the sample is
𝑉𝑠 =
𝑚 𝑠
𝜌𝑡
Mass of the sample
Density of the sample
(Equals Density of total mixture)
….(2)
𝑁 =
𝑉𝑠
𝑉𝑝
Total Volume of the Sample
Volume of Single Particle in the Sample
𝑁 =
𝑚 𝑠
𝜌𝑡 𝑉𝑝 …(3)
𝐴 𝑠 = 𝑁𝑆 𝑝 = 𝑁𝐴 𝑝 =
6𝑚 𝑠
Φ 𝑠 𝜌𝑡 𝐷 𝑝 …(4)
Surface Area of Single Particle in the Sample

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