What is a Refrigerant | Desired properties of a Refrigerant | Important Refrigerant.

What is a Refrigerant ?

1) A refrigerent is a substance that carries heat from the refrigerated space or body to the outside surrounding.

2) Therefore a refrigerent may be defined as any substance that absorbs heat either by expansion or vapourisation and rejects it through condensation.

3) In Mechanical refrigeration systems refrigerant is subjected to cyclic thermodynamic processes, so that it is forced to vapourise in the evaporator by absorbing heat from refrigerated space and it is forced to condense and convert into liquid in the condenser by rejecting heat to surrounding.

4) The blood of any Refrigerating system is the refrigerant circulating inside the system.

Desirable Properties of a Good Refrigerant

1) Thermodynamic Properties :-

a) Boiling Point :- It should have Low Boiling Point.

b) Freezing Point :- It should be below the Evaporator temperature.

c) Evaporative Pressure :- It should be above Atmospheric pressure.

d) Condensing Pressure :- It should have LOW Condensing pressure.

e) Latent Heat of Vapourisation :- It should have HIGH Latent heat of Vaporisation.

f) Critical Temperature & Pressure :- It should be above the condensing Temperature & Pressure.

2) Chemical Properties :-

a) Toxicity :- It should not be Poisonous or injurious . It should not be non-irritating to eyes.

b) Corrosiveness :- It should not be corrosive & should not have any effect on materials used in equipment.

c) Leak Detection :- It should have less tendency to leak & if it is leaking it should be easily detectable.

d) Flammability :- It should not be Inflammable.

e) Miscibility with Oil :- It should be immiscible with oil & should not have any effect on the properties of Oil used for Lubrication.

f) Effect on Foodstuff :- It should not affect on food articles Or make them poisonous or unportable.

g) Stability :- It should be capable of withstanding high pressure & temperature.

3) Physical Properties :-

a) Specific Volume :- It should be LOW in Vapour state.

b) Viscosity :- It should have LOW viscosity.

c) Thermal Conductivity :- It should have HIGH Thermal Conductivity.

d) Di-Electric Strength :- It should have High strength.

4) Other Properties :-

a) Handling & Maintainance :- It should be easy & safe to handle.

b) Cost & Availability :- It should be readily available at LOW cost.

c) Performance of the System :- It should have high COP & LOW power requirement.

Important Refrigerants

1) Water :-

i) Working temp. :- above 3 degree celcius.

ii) It is the cheapest, less corrosive & have high specific heat.

2) Brines :-

i) They are the solutions of Nacl & Cacl2 .

ii) Used below the freezing point of water.

3) Ethylene glycol & Propylene glycol :-

i) Used as anti-freeze mixtures.

ii) Mixture with water makes colourless & odourless.

iii) Capacity to lower freezing point.

4) Halocarbon compounds :-

i) These contains one or more of 3 halogens i.e., chlorine, bromine or fluorine. These are sold under names Freon, Genetron, Isotron, Aretron etc.

ii) Have low freezing points.

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What are Ceramics | Their Classification | Structure | Properties

Ceramics

The word "ceramics" is derived from an ancient Greek word "keramos",

which refers to potter's clay and the objects made from it.

What are ceramics ???? 

Defination :-

1) Ceramics are Inorganic, Non-Metallic compounds for which Interatomic Bonds may be either of the following two types :-

a) Ionic, but with some Covalent character or

b) Covalent in some cases.

2) Ceramics are prepared by heating inorganic , nonmetallic solids and then cooling them to retain the given shape.

Classification of Ceramics :-

Ceramics can be classified on the basis of their Industrial applications and structure as follows :-

i) Functional Classification :- Abrasives, Fireclay products, Cementing products, Glass, Rocks, Minerals, Clay, Refractories etc.

ii) Structural Classification :- Crystalline ceramics & Non-Crystalline ceramics.

Structure :-

1) Ceramics have crystal structure which is similar to a metal structure.

2) Atoms of ceramics are ionically bonded or covalently bonded.

3) Ionically bonded ceramics are hard ,rigid and posses high chemical stability. Example:- Nacl.

4) Covalently bonded ceramics are also hard,rigid and posses high electrical resistance. Example:- SiO

5) Combinedly bonded ceramics are similar in properties and show better characteristics than both. Example :- MgO.

Properties :- The following properties of ceramic materials make them useful for Engineering Applications :-

1) Mechanical Properties :-

i) Ceramic materials have low tensile strength.

ii) They generally fail due to stress concentration on cracks, pores etc.

iii) Ceramics posses great hardness and resistance to wear and can be used for grinding.

iv) Ceramics posses high compressive strength.

v) Most ceramics posses low fracture strength and fail in a brittle manner.

vi) Values of Modulus of Elasticity for ceramics ranges from 7 x 10¹⁰

N/m² to 40 x 10¹⁰ N/m² .

2) Electrical Properties :-

i) Ceramics are often used for electric insulation.

ii) Some ceramics conduct electrically well and are used as Semiconductors i.e N.T.C & P.T.C resistors.

iii) Many ceramics have a dielectric constant value upto 100 and very low dielectric losses.

iv) Some ceramics also exhibit piezoelectric properties and can transfer mechanical deformations in to voltage changes.

3) Chemical Properties :-

i) Majority of ceramics are highly resistant to all chemicals and organic solvents.

ii) Ceramics are completely resistant to oxidation even at high temperature.

iii) Glazed porcelain ceramics is used for chemical vessels.

4) Optical Properties :-

i) Many types of glasses are used for windows and optical lenses.

ii) They also find use in selective transmission or absorption of certain wavelengths.

5) Thermal Properties :-

i) Ceramic materials do not have enough electrons for bringing about electronic thermal conductivity.

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Heart of any CHEMICAL Plant - it's Utilities

Plant Utilities

1) Any Chemical Plant requires raw materials in order to produce final products.

2) It also requires various other services called Utilities for smoothly carrying out the processes.

3) Utility is neither a reactant nor a product, But Utilities are required for maintaining adequate conditions of a manufacturing unit.

4) Utility area is an important area of a Chemical Plant.

5) This may house various Boilers, Large Compressors, Refrigeration systems, Air Conditioning systems, Water Treatment Plants, Cooling Towers etc.

6) Utilities also include Electric Power, so Power Plants are also considered as a part of Utilities.

7) Utilities are situated outside Battery limits should not give any wrong impression that utilities are any less important than the main process,because it is the Efficient Management of Utilities that generate Profits.

8) On the other hand bad management of utilities can make even the most profitable processes unprofitable.

9) The utilities help to maintain proper process conditions like pressure,temperature etc., without which it will be impossible to carry out the process.

10) Now a days most of the Engineering practices are aimed at reducing the consumption of utilities, Because the production of utilities whether it is compressed air,steam etc., requires energy and energy is becoming costlier day by day.

11) Efficient Utility Management doesn't end at cost cutting, If utilities supply is not proper the equipments may not last their full life.

12) For eg :-

If Steam at higher temperature than desired enters Heat Exchangers,the Exchangers may get damaged.

13) Air,Water,Steam etc., are the common utilities used in Chemical Plants.

14) Some Properties of utilities :-

a) They are generally Reusable.

b) Their Composition do not change.

c) They cannot be stocked, So regular supply is must.

15) The aim of an Chemical Engineer should be to provide Utilities & other services in required quantities and of quality as required by the users.

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What are Colloids, their Properties and their Types..?

There are three major groups of mixtures,they are :-

a) Solution :-

·        A solution is a homogeneous mixture of two or more components.

·        The dissolving agent is called as solvent where as the substance which is dissolved is called as solute.

·        The components of a solution are unevenly distributed and cannot be seperated.

·        The components of a solution are smaller in size up to 10^-9 m .

Eg. Sugar and water

b) Suspension :-

·        A suspension is a heterogeneous mixture containing solid particles that are sufficiently larger than the particles found in the solutions and have a average size up to 10^-7 m .

·        The Components of a suspension can be evenly distributed by mechanical means, like shaking,stirring etc., but inspite of this the components settle down and seperate from one another.

Eg. Oil and Water.

c) Colloids :-

·        The Colloids were first discovered in 1860.

·        The credit for the discovery of Colloids can be given to a Scottish Scientist, Thomas Graham.

·        A COLLOID is a substance which is microscopically dispersed (widely spread) evenly throughout another substance.

·        Colloids when mixed remain evenly distributed without settling forming a mixture known as Colloidal Dispersion.

·        Colloids are not visible with our naked eyes, but they can be seen under microscope.

·        The Particles of colloids are intermediate in size between those found in solutions and suspensions.

·        Colloidal particles have an average size of 10^-9 to 10^-7 m .

·        The Colloidal particles form Dispersed phase and the medium used for this is called as Dispersion medium.

·        Dispersing medium is the external phase and is found in the greater extent in the colloid whereas the Dispersed phase is the internal phase and is found in the lesser extent.

·        A colloidal system can exist in any of the three forms solid, liquid or gaseous.

Eg :- Milk

Properties of Colloids

1) Tyndall Effect :-

A British Physicist John Tyndall in 1869 first observed this phenomenon and hence it is known as Tyndall Effect.

He observed that when a beam of light is passed through a colloidal solution, the light is scattered by the particles present in the colloidal solution.

This effect is often used as a measure of the existence of a colloid.

2) Brownian Movement :-

The Molecules of the Dispersion medium constantly collide with the colloidal particles thereby passing Kinetic Energy to them.

This phenomenon results into zigzag movement of the colloidal particles.

This zigzag movement of the colloidal particles is known as Brownian movement.

3) Electrophoresis :-

The movement of the colloidal particles under the influence of an applied electric potential is called as Electrophoresis.

4) Electro-Osmosis :-

When the movement of the Colloidal particles is prevented by some suitable means, it is observed that the Dispersion medium itself begins to move under the influence of an electric field. This phenomenon is known as Electro osmosis.

Types of Colloids

1) Sol :-In Sol the Dispersing medium is the Liquid whereas the Dispersed phase is the solid.

Eg :- Paint,Ink,Detergent etc.

2) Gel :- In Gels the Dispersing medium is the Solid whereas the Dispersed phase is the Liquid.

Eg :- Butter,Jelly etc.

3) Emulsion :- In the Emulsions both the Dispersing medium and the Dispersed phase are the liquids.

Eg :- Cometic lotions,Lubricants etc.

4) Foams :- In Foams the Dispersing medium is the Liquid whereas the Dispersed phase is the Gas.

Eg :- Shaving lather,whipped cream etc.

5) Aerosols :-In Aerosols the Dispersing medium is the Gas whereas the Dispersed phase is the Liquid.

Eg :- Insecticide sprays,Smog,Cloud,Fog etc.

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