CH 2040 – Course Synopsis

*References mentioned correspond to Unit operations Of Chemical Engineering (7th

Ed.)

by Warren L. McCabe, Julian C. Smith, Peter Harriott.

Shape & Size Analysis:

Steps to be followed for assessing shape

o Data Collection: (by digitizing the particle using equipments)

o Data processing: (Fit curves accordingly using Fourier analysis)

o Judgment.

Sphericity of particles. (Chapter – 28, page - 967)

Resolution of generally used equipments are

o human eye: Up to 200µm

o Optical microscope: up to 0.5µm

o Electron Microscope: ranges from 0.5µm-0.005µm

Disadvantage using electron microscope being damage of surface due to electron

bombardment and hence sputtering is done which changes the morphology.

By using AFM (Atomic Force Microscopy) sub nanometric resolution and 3D

morphology of the surface can be obtained.

Light Scattering techniques fails beyond the µm range and the intensity of the scattered

light is a function of size which being proportional to (diameter)6

For detecting sizes of solids in liquids like slurries, emulsions, lubricants etc… Light

Extinction Techniques are widely used.

Example being turbid meter which works on the principle of Beer-Lambert’s law.

For individual particle size analysis Acoustic Attenuation Spectroscopy is used, where in

waves interact with both the particles and the medium, by knowing the properties, stress-

strain relations between the particles and the interacting medium the attenuation is found

and hence the particle size.

Data Analysis:

Number mean: Ʃ nidi/Ʃ ni (d- diameter of the particle) used in finding semi-conductor

defects.

Areal mean: Ʃ sidi/Ʃ si (s- given surface area) used in catalysis, surface area separation

process.

Volume mean: Ʃ nidi3di/Ʃ ni di

3 in nanoscopic polymers.

Variance V =Ʃ(di-dm)2/(N-1) dm – mean diameter

V=σ2 σ – Standard Deviation

Size Reduction: (Chapter – 28, page - 984)

Can be done via Impaction, attrition, cutting etc….

Crushing & Mechanical Efficiency

Energy laws – Kick’s law, Rittinger’s law, Bond’s law.

Bond’s Work Index.

Practical Efficiency is the ratio of actual efficiency to efficiency evaluated under

controlled conditions.

Theoretical Efficiency is the ratio of actual efficiency to ideal efficiency (1).

Calculation of Sphericity of particles.

Ball mills, High Energy ball mills.

Critical speed of ball mill.

Crushers (Cone Crushers, Gyratory Crushers) (Chapter-28 page – 988)

Impingers

o Impingement is used as a method for the collection of particulate matter from

a fluid stream on arresting surfaces and also generally involves particles

travelling at high velocities hitting the filter media/impinger.

o It is applicable to aerosol separation as well as separations from liquid, such as

that which occurs in a deep bed filter.

Generally after “Crushing” operation for even more finer particles grinding operation is

used which

o Increase of the surface area of a solid.

o Manufacturing of a solid with a desired grain size

Hammer mills, Roller mills, Attrition mills, tumbling mills are generally used for

grinding operation.

For producing ultra-fine powders Ultra – fine grinders are used:

o Hammer Mills with Internal Classification

o Fluid Energy Mills

o Agitated Mills

o Colloid Mills

Separation of particles into various groups based on sizes can be done with

o Filters

o Screens/Sieves (Chapter – 29 page - 1001)

o Settlers

Mixing: Intermingling of two or more separate components to form a more or less

uniform product. (Chapter – 28, page - 977)

Industrial Mixers and Blenders are used to mix or blend a wide range of materials used in

different industries.

Driers – flash drier, spray drier, ring drier, rotary drier, steam tube drier, fluid bed drier.

Used in food preservations, detergent manufacturing etc…

Filtration:

Calculating effectiveness of Screens. (Chapter – 29, page - 1001)

Expression for thickness of cake and volume of filtrate for filtration

(chapter – 29 page - 1019)

At constant rate

At constant pressure filtration

HEPA filters (High Efficiency Particulate Air)

ULPA filters (Ultra Low Penetration Air)

Ribbon Blender, tumbling mixers (V-blender, Double cone blender)

Solid – Gas Separation (chapter – 29 page - 1006)

o Removal of solid particles from a fluid by passing the fluid through a filtering

medium on which solids are deposited.

o Cake filters

o Clarifying filters

o Cross filters

Solid – Liquid Separation

o Vacuum filters

o Pressure filters (Centrifugal filters)

Storage of solids: (Reference- chapter-28, page 975.)

The storage facilities must be designed such that they do not impair product quality.

Hence factors to be considered are

o Physical and chemical stability of the product.

o Interaction with environment.

Variations in storing may arise for various reasons, most of which fall into the three

general classes:

o Non Uniformity: Due to segregation.

o Inconsistency: Due to seasonal or process variations.

o Stability: Due to time, temperature, attrition or through natural degradation.

General Methods of storage:

o Bulk Storage:

Applied for coarse solids, unprotected from the weather.

Advantageous and most economical.

E.g.: coal, gravel etc…

o Bin Storage:

Used for solids that is too valuable or too soluble to be exposed in outdoor

piles.

Different equipment in bin storage

Silos (tower silos, bunker silos and bag silos)

Bins

Hoppers

Transportation of solids:

Flowability of powders is a surface property which depends on the physical properties of

the powder.

o Indicated using Hausner Index and Carr Index.

o Carr Index ( < 15 Good Flowability & > 25 Poor Flowability)

Phoretic field – the field force that predominantly affects the flow of particles in fluid.

o Electrophoresis

o Magnetophoresis

o Thermophoresis

o Gravitational & Inertial/drag effects

Total flux of particles = Convective flux + Phoretic flux + Diffusive flux

Mean free path ( λ)

Knudsen number – to characterize flow (continuum or free molecular flow )

Fick’s laws of diffusion

Brownian Diffusivity.