skp engineering collegeskpec.edu.in/wp-content/uploads/2017/11/basic-civil-and...difference in...

S.K.P. Engineering College, Tiruvannamalai II SEM

Mechanical Engineering Department 1 Basic Civil and Mechanical Engineering

SKP Engineering College

Tiruvannamalai – 606611

A Course Material

on

BASIC CIVIL AND MECHANICAL ENGINEERING

By

A.Jayaveeran

Assistant Professor

Mechanical Engineering Department



Quality Certificate

This is to Certify that the Electronic Study Material

Subject Code:GE 6251

Subject Name: Basic Civil and Mechanical Engineering

Year/Sem: I year/ II semester

Being prepared by me and it meets the knowledge requirement of the University

curriculum.

Signature of the Author

Name: A.Jayaveeran

Designation: Assistant Professor

This is to certify that the course material being prepared by Mr.A.Jayaveeran is of the

adequate quality. He has referred more than five books and one among them is from

abroad author.

Signature of HD Signature of the Principal

Name: Dr.J.Kuberan Name: Dr.V.Subramania Bharathi

Seal: Seal:



GE6251 BASIC CIVIL AND MECHANICAL ENGINEERING L T P C 4 0 0 4

A – CIVIL ENGINEERING

UNIT I SURVEYING AND CIVIL ENGINEERING MATERIALS 15

Surveying: Objects – types – classification – principles – measurements of distances –

angles –leveling – determination of areas – illustrative examples.

Civil Engineering Materials: Bricks – stones – sand – cement – concrete – steel

sections.

UNIT II BUILDING COMPONENTS AND STRUCTURES 15

Foundations: Types, Bearing capacity – Requirement of good foundations.

Superstructure: Brick masonry – stone masonry – beams – columns – lintels – roofing

– flooring–plastering – Mechanics – Internal and external forces – stress – strain –

elasticity – Types of Bridges and Dams – Basics of Interior Design and Landscaping.

TOTAL: 30 PERIODS

B – MECHANICAL ENGINEERING

UNIT III POWER PLANT ENGINEERING 10

Introduction, Classification of Power Plants – Working principle of steam, Gas, Diesel,

Hydroelectric and Nuclear Power plants – Merits and Demerits – Pumps and turbines –

working principle of Reciprocating pumps (single acting and double acting) – Centrifugal

Pump.

UNIT IV IC ENGINES 10

Internal combustion engines as automobile power plant – Working principle of Petrol

and Diesel Engines – Four stroke and two stroke cycles – Comparison of four stroke

and two stroke engines – Boiler as a power plant.

UNIT V REFRIGERATION AND AIR CONDITIONING SYSTEM 10

Terminology of Refrigeration and Air Conditioning. Principle of vapour compression and

absorption system – Layout of typical domestic refrigerator – Window and Split type

room Air conditioner.

TOTAL: 30 PERIODS

REFERENCES:

1. Shanmugam G and Palanichamy M S, “Basic Civil and Mechanical Engineering”, Tata McGraw Hill Publishing Co., New Delhi, (1996).

2. Ramamrutham S., “Basic Civil Engineering”, Dhanpat Rai Publishing Co. (P) Ltd.



(1999).

3. Seetharaman S., “Basic Civil Engineering”, Anuradha Agencies, (2005). 4. Venugopal K. and Prahu Raja V., “Basic Mechanical Engineering”, Anuradha Publishers, Kumbakonam, (2000).

5. Shantha Kumar S R J., “Basic Mechanical Engineering”, Hi-tech Publications,

Mayiladuthurai, (2000)



CONTENTS

S.No Particulars Page

1 Unit – I -

2 Unit – II -

3 Unit – III 6

4 Unit – IV 23

5 Unit – V 50



Unit – III

Power Plant Engineering

Part – A

1 Mention any four types of power plant. (CO3-L1-MAY 2013) Thermal powerplant Hydroelectric powerplant Nuclear powerplant Gasturbine powerplant 2. How Turbines are classified ?(CO3-L1-MAY 2014) General Classification of Turbines

According to the energy used 1. Impulse turbine 2. Reaction turbine

Direction of water flow 1. Axial flow - Radial in axial out 2. Inward flow - Outward flow

According to the head available to the inlet of turbine 1. High Head Turbine (250-1800m), Pelton Wheel 2. Medium Head Turbine (50-250m), Francis Turbine 3. Low Head Turbine ( <50m), Kaplan Turbine

According to the specific speed 1. Low specific speed ( <50) Pelton wheel 2. Medium specific speed (50 < Ns< 250) Francis 3. High Specific speed ( >250) Kaplan

According to the fluid used 1. Water Turbine (Pelton Wheel, Francis, Kaplan) 2. Gas TurbineSteam Turbine.

3. What are the main components of the gas turbine power plants ?(CO3-L1-

MAY2014) 1. L.P air compressor 2. Intercooler 3. H.P. Compressor 4. Regenerator 5. Combustion chamber



4.List the types of dams.(CO3-L1-NOV 2009)

1. Earth Dams

2. Rock-fill Dams

3. Gravity Dams

4. Arch Dams

5. Steel Dams

6. Buttress Dams

7. Timber Dams

5.Give the classification of power plants.(CO3-L1-NOV 2009)

6. Give two examples for positive displacement pumps(CO3-L1-JUNE 2010)

1. Screw pumps 2. Gear pumps 3. Plunger pumps



PART-B

1.Explain with neat sketch of thermal(steam) power plant.(CO3-H1-MAY 2014)

The layout of the steam power plant is shown in figure below. It consists of four main circuits. These are:

Coal and ash circuit. Air and flue gas circuit Water and steam circuit and Cooling water circuit

Coal and ash circuit: Coal from the storage yard is transferred to the boiler furnace by means of coal handling equipment like belt conveyor, bucket elevator, etc., ash resulting from the combustion of coal in the boiler furnace collects at the back of the boiler and is removed to the ash storage yard through the ash handling equipment.

http://3.bp.blogspot.com/-F5WRm_ji9l4/TsJINYANAiI/AAAAAAAAAW0/eKkBY9AbxOQ/s1600/power.jpg



Ash disposal : The indian coal contains 30% to 40% ash. A power plant of 100MW 20 to 25 tonnes of hot ash per hour. Hence sufficient space near the power plant is essential to dispose such large quantities of ash. Air and flue gas circuit: Air is taken from the atmosphere to the air preheater. Air is heated in the air preheater by the heat of flue gas which is passing to the chimney. The hot air is supplied to the furnace of the bolier. The flue gases after combustion in the furnace, pass around the boiler tubes. The flue gases then passes through a dust collector, economizer and pre-heater before being exhausted to the atmosphere through the chimney. By this method the heat of the flue gases which would have been wasted otherwise is used effectively. Thus the overall efficiency of the plant is improved. Air pollution: The pollution of the surrounding atmosphere is caused by the emission of objectable gases and dust through the chimney. The air pollution and smoke cause nuisance to people surrounding the planet. Feed water and steam circuit: The steam generated in the boiler passes through super heater and is supplied to the steam turbine. Work is done by the expansion of steam in the turbine and the pressure of steam is reduced. The expanded steam then passes to the condenser, where it is condensed. The condensate leaving the condenser is first heated in a l.p. water heater by using the steam taken from the low pressure extraction point of the turbine. Again steam taken from the high pressure extraction point of the turbine is used for heating the feed water in the H.P water heater. The hot feed water is passing through the economizer, where it is further heated by means of flue gases. The feed water which is sufficiently heated by the feed water heaters and economizer is then fed into the boiler. Cooling water circuit:



Abundant quantity of water is required for condensing the steam in the condenser. Water circulating through the condenser may be taken from various sources such as river or lake, provided adequate water supply is available from the river or lake throughout the year. If adequate quantity of water is not available at the plant site, the hot water from the condenser is cooled in the cooling tower or cooling ponds and circulated again. Advantages of thermal power plants

1. Initial cost is low compared with hydro-plant. 2. The power plant can be located near load center, so the transmission losses are

considerably reduced. 3. The generation of power is not dependent on the nature‟s mercy like hydro plant. 4. The construction and commissioning of thermal plant requires less period of time

than a hydro plant.

2.Explain the working principle of a single acting reciprocating compressor. ( CO3-H1-MAY 2013)

In single stage reciprocating compressor the entire compression is carried out in a single cylinder. If the compression is affected in one end of the piston & cylinder then it is known as single acting & if the compression is affected in both ends of piston & cylinder then it is known as double acting reciprocating air compressor.

The opening & closing of simple check valve (plate or spring valve) is depend upon difference in pressure, if mechanically operated valves are used for suction & discharge then their functioning is controlled by cams.

The weight of air in the cylinder will be zero when the piston is at top dead center, if we neglect clearance volume. When piston starts moving downwards, the pressure inside the cylinder falls below atmospheric pressure& suction valve/inlet valve opens. The air is drawn into the cylinder through suction filter element. This operation is known as suction stroke.

When piston moves upwards, compresses the air in cylinder & inlet valve closes when pressure reaches to atmospheric pressure. Further compression follows as the piston moves towards the top of its stroke until, when the pressure in the cylinder exceeds that in the receiver. This is compression stroke of compressor. At the end of this stroke discharge/delivery valve opens & air is delivered to receiver.When it is double acting

http://www.engihub.com/?p=32





reciprocating air compressor, suction stroke is in process at one end of piston while at same time discharge stroke is in process at other end of piston. In simple word we can say that suction & compression took place on both end of piston & cylinder in double acting reciprocating air compressor.

Applications

The reciprocating compressor generally seen where there is requirement of high pressure and low flow(or discontinuous flow up to 30 bars).Mostly where the air is used for hand-tools,cleaning dust,small paint jobs,commercial uses,etc.

Advantages

Relatively Cheap Easy maintenance Suitable for high pressure

Disadvantages

Sounds too much.You have to arrange a room for it or put it into isolating box. High outlet temperature of compressed air. High oil content in air piping.




3.Draw and name the parts of centrifugal pump and explain its working. ( CO3-H1-NOV 2011)

A centrifugal pump is of very simple design. The only moving part is an impeller

attached to a shaft that is driven by the motor.

The two main parts of the pump are the impeller and diffuser.

The impeller can be made of bronze, stainless steel, cast iron, polycarbonate, and a variety of other materials. A diffuser or volute houses the impeller and captures the water off the impeller.

Water enters the eye of the impeller and is thrown out by centrifugal force. As water leaves the eye of the impeller a low pressure area is created causing more liquid to flow toward the inlet because of atmospheric pressure and centrifugal force. Velocity is developed as the liquid flows through the impeller while it is turning at high speeds on the shaft. The liquid velocity is collected by the diffuser or volute and converted to pressure by specially designed passageways that direct the flow to discharge into the piping system; or, on to another impeller stage for further increasing of pressure.



The head or pressure that a pump will develop is in direct relation to the impeller diameter, the number of impellers, the eye or inlet opening size, and how much velocity is developed from the speed of the shaft rotation. Capacity is determined by the exit width of the impeller. All of the these factors affect the horsepower size of the motor to be used; the more water to be pumped or pressure to be developed, the more energy is needed.

A centrifugal pump is not positive acting. As the depth to water increases, it pumps less and less water. Also, when it pumps against increasing pressure it pumps less water. For these reasons it is important to select a centrifugal pump that is designed to do a particular pumping job. For higher pressures or greater lifts, two or more impellers are commonly used; or, a jet ejector is added to assist the impellers in raising the pressure.



4.Draw the layout of diesel power plant. State the subsystems and components of the plant and explain each one of them.( CO3-H1-NOV 2011)

Fuel Supply System

It consists of storage tank, strainers, fuel transfer pump and all day fuel tank. The fuel oil is supplied at the plant site by rail or road. The oil is stored in the storage tank. From the storage tank, oil is pumped to smaller all day tank at daily or short intervals. From this tank, fuel oil is passed through strainers to remove suspended impurities. The clean oil is injected into the engine by fuel injection pump.

Air Intake System

This system supplies necessary air to the engine for fuel combustion. It consists of pipes for the supply of fresh air to the engine manifold. Filters are provided to remove dust particles from air which may act as abrasive in the engine cylinder. Because a diesel engine requires close tolerances to achieve its compression ratio, and because most diesel engines are either turbocharged or supercharged, the air entering the engine must be clean, free of debris, and as cool as possible. Also, to improve a turbocharged or supercharged engine‟s efficiency, the compressed air must be cooled after being compressed. The air intake system is designed to perform these tasks. Air intake systems are usually one of two types, wet or dry. In a wet filter intake system, as shown in the Figure 4.1, the air is sucked or bubbled through a housing that holds a bath of oil such that the dirt in the air is removed by the oil in the filter. The air then flows through a screen-type material to ensure any entrained oil is removed from the air. In a dry filter system, paper, cloth, or a metal screen material is used to catch and trap dirt before it enters the engine. In addition to cleaning the air, the intake system is usually designed to intake fresh air from as far away from the engine as practicable, usually just outside of the engine‟s building or enclosure. This provides the engine with a supply of air that has not been heated by the engine‟s own waste heat. The reason for ensuring that an engine's air supply is as cool as possible is that cool air is denser than hot air. This means that, per unit volume, cool air has more oxygen than hot air. Thus, cool air provides more oxygen per cylinder charge than less dense, hot air. More oxygen means a more efficient fuel burn and more power. After being filtered, the air is routed by the intake system into the engine's intake manifold or air box. The manifold or air box is the component that directs the fresh air to each of the engine‟s intake valves or ports. If the engine is turbocharged or supercharged, the fresh air will be compressed with a blower and possibly cooled before entering the intake manifold or air box. The intake system also serves to reduce the air flow noise.



Exhaust System

This system leads the engine exhaust gas outside the building and discharges it into atmosphere. A silencer is usually incorporated in the system to reduce the noise level. The exhaust system of a diesel engine performs three functions. First, the exhaust system routes the spent combustion gasses away from the engine, where they are diluted by the atmosphere. This keeps the area around the engine habitable. Second, the exhaust system confines and routes the gases to the turbocharger, if used. Third, the exhaust system allows mufflers to be used to reduce the engine noise. Cooling System

The heat released by the burning of fuel in the engine cylinder is partially converted into work. The remainder part of the heat passes through the cylinder wall, piston, rings etc. and may cause damage to system. In order to keep the temperature of the engine parts within the safe operating limits, cooling is provided. The cooling system consists of a water source, pump and cooling towers. The pump circulates water through cylinder and head jacket. The water takes away heat form the engine and it becomes hot. The hot water is cooled by cooling towers and re circulated for cooling.



Lubricating System

The system minimises the wear of rubbing surfaces of the engine. It comprises of lubricating oil tank, pump, filter and oil cooler. The lubrication oil is drawn from the lubricating oil tank by the pump and is passed through filter to remove impurities .The clean lubrication oil is delivered to the points which require lubrication. The oil coolers incorporated in the system keep the temperature of the oil low. An internal combustion engine would not run for even a few minutes if the moving parts were allowed to make metal-to-metal contact. The heat generated due to the tremendous amounts of friction would melt the metals, leading to the destruction of the engine. To prevent this, all moving parts ride on a thin film of oil that is pumped between all the moving parts of the engine. The oil serves two purposes. One purpose is to lubricate the bearing surfaces. The other purpose is to cool the bearings by absorbing the friction- generated heat. The flow of oil to the moving parts is accomplished by the engine's internal lubricating system.



Oil is accumulated and stored in the engine's oil pan where one or more oil pumps take suction and pump the oil through one or more oil filters as shown in the figure. The filters clean the oil and remove any metal that the oil has picked up due to wear. The cleaned oil then flows up into the engine's oil galleries. A pressure relief valve(s) maintains oil pressure in the galleries and returns oil to the oil pan upon high pressure. The oil galleries distribute the oil to all the bearing surfaces in the engine. Once the oil has cooled and lubricated the bearing surfaces, it flows out of the bearing and gravity-flows back into the oil pan. In medium to large diesel engines, the oil is also cooled before being distributed into the block. This is accomplished by either internal or external oil cooler. The lubrication system also supplies oil to the engine‟s governor. Engine Starting System

This is an arrangement to rotate the engine initially, while starting, until firing starts and the unit runs with its own power. Small sets are started manually by handles but for larger units, compressed air is used for starting. In the latter case, air at high pressure is admitted to a few of the cylinders, making them to act as reciprocating air motors to turn over the engine shaft. The fuel is admitted to the remaining cylinders which makes the engine to start under its own power.

5.Explain the components and working of nuclear power plant.( CO3-H1-JUNE

2010)

Heavy elements such as Uranium (U235) or Thorium (Th232) are subjected to nuclear

fission reaction in a nuclear reactor. Due to fission, a large amount of heat energy is

produced which is transferred to the reactor coolant. The coolant may be water, gas or

a liquid metal. The heated coolant is made to flow through a heat exchanger where

water is converted into high-temperature steam. The generated steam is then allowed to

drive a steam turbine. The steam, after doing its work, is converted back into the water

and recycled to the heat exchanger. The steam turbine is coupled to an alternator which

generates electricity. The generated electrical voltage is then stepped up using a

transformer for the purpose of long distance transmission.

The image below shows basic components and layout of a nuclear power station.



Basic components of a nuclear power plant

Nuclear Reactor

A nuclear reactor is a special apparatus used to perform nuclear fission. Since the

nuclear fission is radioactive, the reactor is covered by a protective shield. Splitting up of

nuclei of heavy atoms is called as nuclear fission, during which huge amount of energy

is released. Nuclear fission is done by bombarding slow moving neutrons on the nuclei

of heavy element. As the nuclei break up, it releases energy as well as more neutrons

which further cause fission of neighboring atoms. Hence, it is a chain reaction and it

must be controlled, otherwise it may result in explosion. A nuclear reactor consists of

http://2.bp.blogspot.com/-4PmiU5kPC9o/VfLS6nW83MI/AAAAAAAABb0/3XoPr1KTaJA/s1600/nuclear+power+plant.jpg



fuel rods, control rods and moderator. A fuel rod contains small round fuel pallets

(uranium pallets). Control rods are of cadmium which absorb neutrons. They are

inserted into reactor and can be moved in or out to control the reaction. The moderator

can be graphite rods or the coolant itself. Moderator slows down the neutrons before

they bombard on the fuel rods.

Two types of nuclear reactors that are widely used -

1. Pressurised Water Reactor (PWR) - This type of reactor uses regular water as coolant. The coolant (water) is kept at very high pressure so that it does not boil. The heated water is transferred through heat exchanger where water from secondary coolant loop is converted into steam. Thus the secondary loop is completely free from radioactive stuff. In a PWR, the coolant water itself acts as a moderator. Due to these advantages, pressurised water reactors are most commonly used.

2. BoilingWater Reactor (BWR) - In this type of reactor only one coolant loop is present. The water is allowed to boil in the reactor. The steam is generated as it heads out of the reactor and then flows through the steam turbine. One major disadvantage of a BWR is that, the coolant water comes in direct contact with fuel rods as well as the turbine. So, there is a possibility that radioactive material could be placed on the turbine.

Heat exchanger

In the heat exchanger, the primary coolant transfers heat to the secondary coolant

(water). Thus water from the secondary loop is converted into steam. The primary

system and secondary system are closed loop, and they are never allowed to mix up

with each other. Thus, heat exchanger helps in keeping secondary system free from

radioactive stuff. Heat exchanger is absent in boiling water reactors.

Steam Turbine

Generated steam is passed through a steam turbine, which runs due to pressure of the

steam. As the steam is passed through the turbine blades, the pressure of steam

gradually decreases and it expands in volume. The steam turbine is coupled to an

alternator through a rotating shaft.



Alternator

The steam turbine rotates the shaft of an alternator thus generating electrical energy.

Electrical output of the alternator is the delivered to a step up transformer to transfer it

over distances.

Condenser

The steam coming out of the turbine, after it has done its work, is then converted back

into water in a condenser. The steam is cooled by passing it through a third cold water

loop.

Advantages of Nuclear Power Station

1. As we said, the fuel consumption in this power station is quite low and hence, cost for generating single unit of energy is quite less than other conventional power generation method. Amount of nuclear fuel required is also less.

2. A nuclear power station occupies much smaller space compared to other conventional power station of same capacity.

3. This station does not require plenty of water, hence it is not essential to construct plant near natural source of water. This also does not required huge quantity of fuel; hence it is also not essential to construct the plant near coal mine, or the place where good transport facilities are available. Because of this, the nuclear power station can be established very near to the load centre.

4. There are large deposits of nuclear fuel globally therefore such plants can ensure continued supply of electrical energy for coming thousands years.

Disadvantages of Nuclear Power Plant

1. The fuel is not easily available and it is very costly. 2. Initial cost for constructing nuclear power station is quite high. 3. Erection and commissioning of this plant is much complicated and sophisticated

than other conventional power station. 4. The fission by products is radioactive in nature, and it may cause high radioactive

pollution. 5. The maintenance cost is higher and the man power required to run a nuclear

power plant is quite higher since specialist trained people are required. 6. Sudden fluctuation of load cannot be met up efficiently by nuclear plant.



7. As the by products of nuclear reaction is high radioactive, it is very big problem for disposal of this by products. It can only be disposed deep inside ground or in a sea away from sea shore.

6.Explain the working of hydro electric power plant.( CO3-H1-NOV 2009)

Dam and Reservoir:

The dam is constructed on a large river in hilly areas to ensure sufficient water

storage at height. The dam forms a large reservoir behind it. The height of water level

(called as water head) in the reservoir determines how much of potential energy is

stored in it.

Control Gate:

Water from the reservoir is allowed to flow through the penstock to the turbine.

The amount of water which is to be released in the penstock can be controlled by a

control gate. When the control gate is fully opened, maximum amount of water is

released through the penstock.



Penstock:

A penstock is a huge steel pipe which carries water from the reservoir to the

turbine. Potential energy of the water is converted into kinetic energy as it flows down

through the penstock due to gravity.

Water Turbine:

Water from the penstock is taken into the water turbine. The turbine is

mechanically coupled to an electric generator. Kinetic energy of the water drives the

turbine and consequently the generator gets driven. There are two main types of water

turbine; (i) Impulse turbine and (ii) Reaction turbine. Impulse turbines are used for large

heads and reaction turbines are used for low and medium heads.

Generator:

A generator is mounted in the power house and it is mechanically coupled to the

turbine shaft. When the turbine blades are rotated, it drives the generator and electricity

is generated which is then stepped up with the help of a transformer for the

transmission purpose.

Surge Tank:

Surge tanks are usually provided in high or medium head power plants when

considerably long penstock is required. A surge tank is a small reservoir or tank which is

open at the top. It is fitted between the reservoir and the power house. The water level

in the surge tank rises or falls to reduce the pressure swings in the penstock. When

there is sudden reduction in load on the turbine, the governor closes the gates of the

turbine to reduce the water flow. This causes pressure to increase abnormally in the

penstock. This is prevented by using a surge tank, in which the water level rises to

reduce the pressure. On the other hand, the surge tank provides excess water needed

when the gates are suddenly opened to meet the increased load demand.

http://www.electricaleasy.com/2014/03/electrical-transformer-basic.html



UNIT 4

INTERNAL COMBUSTION ENGINES

Part A

1. State any four difference between two stroke and four stroke engine? (CO4-

H1-MAY 2014)

S.No. Four stroke engine Two stroke engine

1. It has one power stroke for every

two revolutions of the crankshaft.

It has one power stroke for each

revolution of the crankshaft.

2. Engine is heavy Engine is light

3. More cost. Less cost than 4 stroke.

4. Engine is water cooled. Engine is air cooled.

5. Less fuel consumption and

complete burning of fuel.

More fuel consumption and fresh charge

is mixed with exhaust gases.

6. Engine requires more space. Engine requires less space.

7. Complicated lubricating system. Simple lubricating system.

8. More thermal efficiency. Less thermal efficiency.

2. Function of fuel injection pump in a diesel engine? (CO4-H1-MAY 2013)

It is a pump, which delivers metered quantity of fuel to each cylinder at appropriate time under high pressure. Tractor engines may use two types of fuel injection pump:

http://www.mechanicalbooster.com/2014/02/what-are-main-parts-of-automobile-engine.html



(i) Multi-element pump and (ii) Distributor (Rotary) type pump.

3. Function of flywheel in engines? (CO4-H1-NOV 2012)

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have an inertia called the moment of inertia and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed.

4. What are main components of I.C. engine? (CO4-H1-NOV 2011) 1. Cylinder 2. Cylinder head 3. Piston 4. Valves 5. Piston rings 6. Connecting rod 7. Crank shaft 8. Cam shaft

5. What is the purpose of lubrication system in an I.C. engine? (CO4-H1-JUNE 2010)

A lubricating oil with the necessary properties and characteristics will (1) provide a film of proper thickness between the bearing surfaces under all conditions of operation, (2) remain stable under changing temperature conditions, and (3) not corrode the metal surfaces. If the lubricating oil is to meet these requirements, the engine operating temperature must NOT exceed a specified limit.

6. Difference between S.I and C.I engine? (CO4-H1-NOV 2009)

S.no Aspect Spark Ignition Engine Compression Ignition

Engine



.

PART B

1. Explain the working principle of 4 stroke diesel engine with neat

sketch.(CO4-H1-MAY 2014)

PRINCIPLES OF OPERATION OF IC ENGINES: FOUR-STROKE CYCLE DIESEL ENGINE In four-stroke cycle engines there are four strokes completing two revolutions of the crankshaft. These are respectively, the suction, compression, power and exhaust strokes. In Fig. 3, the piston is shown descending on its suction stroke. Only pure air is drawn into the cylinder during this stroke through the inlet valve, whereas, the exhaust valve is closed. These valves can be operated by the cam, push rod and rocker arm. The next stroke is the compression stroke in which the piston moves up with both the

1 Engine speed SI engines are high speed

engines.

CI engines are low speed

engines.

2 Cycle efficiency SI engines have low thermal

efficiency

CI engines have high

thermal efficiency.

3 Fuel used

Petrol is used as fuel, which

has high self ignition

temperature.

Diesel is used as fuel, it has

low self ignition temperature.

4 Cycle operation SI engine works on otto

cycle.

CI engine works on diesel

cycle.

5

Constant

parameter during

cycle

Constant volume cycle. Constant pressure cycle.

http://me-mechanicalengineering.com/otto-cycle/

http://me-mechanicalengineering.com/otto-cycle/

http://me-mechanicalengineering.com/diesel-cycle/

http://me-mechanicalengineering.com/diesel-cycle/



valves remaining closed. The air, which has been drawn into the cylinder during the suction stroke, is progressively compressed as the piston ascends. The compression ratio usually varies from 14:1 to 22:1. The pressure at the end of the compression stroke ranges from 30 to 45 kg/cm2. As the air is progressively compressed in the cylinder, its temperature increases, until when near the end of the compression stroke, it becomes sufficiently high (650-800 oC) to instantly ignite any fuel that is injected into the cylinder. When the piston is near the top of its compression stroke, a liquid hydrocarbon fuel, such as diesel oil, is sprayed into the combustion chamber underhigh pressure (140-160 kg/cm2), higher than that existing in the cylinder itself. This fuelthen ignites, being burnt with the oxygen of the highly compressed air. During the fuel injection period, the piston reaches the end of its compression stroke and commences to return on its third consecutive stroke, viz., power stroke. During this strokethe hot products of combustion consisting chiefly of carbon dioxide, together with thenitrogen left from the compressed air expand, thus forcing the piston downward. This is onlythe working stroke of the cylinder. During the power stroke the pressure falls from its maximum combustion value (47-55 kg/cm2), which is usually higher than the greater value of the compression pressure (45 kg/cm2), to about 3.5-5 kg/cm2 near the end of the stroke. The exhaust valve then opens,usually a little earlier than when the piston reaches its lowest point of travel. The exhaustgases are swept out on the following upward stroke of the piston. The exhaust valve remainsopen throughout the whole stroke and closes at the top of the stroke. The reciprocating motion of the piston is converted into the rotary motion of the crankshaft by means of a connecting rod and crankshaft. The crankshaft rotates in the main bearings, which are set in the crankcase. The flywheel is fitted on the crankshaft in order to smoothen out the uneven torque that is generated in the reciprocating engine.



2. Discuss the working of otto cycle petrol engine with the help of neat sketch.(CO4-H1-MAY 2013)

Otto cycle is a gas power cycle that is used in spark-ignition internal combustion engines (modern petrol engines). This cycle was introduced by Dr. Nikolaus August Otto, a German Engineer.

An Otto cycle consists of four processes:

1. Two isentropic (reversible adiabatic) processes 2. Two isochoric (constant volume) processes

These processes can be easily understood if we understand p-V (Pressure-Volume) and T-s (Temperature-Entropy) diagrams of Otto cycle.

p-V Diagram T-s Diagram

http://mechteacher.com/thermal-engineering/introduction-to-gas-power-cycles

http://mechteacher.com/internal-combustion-engine/

http://mechteacher.com/internal-combustion-engine/



Note:

In the above diagrams,

p → Pressure

V → Volume

T → Temperature

s → Entropy

Vc → Clearance Volume

Vs → Stroke Volume

Processes in Otto Cycle:

As stated earlier, Otto cycle consists of four processes. They are as follows:

Process 1-2: Isentropic compression

In this process, the piston moves from bottom dead centre (BDC) to top dead centre (TDC) position. Air undergoes reversible adiabatic (isentropic) compression. We know that compression is a process in which volume decreases and pressure increases. Hence, in this process, volume of air decreases from V1 to V2 and pressure increases from p1 to p2. Temperature increases from T1 to T2. As this an isentropic process,

http://mechteacher.com/fluid-mechanics/properties-of-fluids#Pressure

http://mechteacher.com/fluid-mechanics/properties-of-fluids#Temperature

http://mechteacher.com/thermal-engineering/otto-cycle#c1



entropy remains constant (i.e., s1=s2). Refer p-V and T-s diagrams for better understanding.

Process 2-3: Constant Volume Heat Addition:

Process 2-3 is isochoric (constant volume) heat addition process. Here, piston remains at top dead centre for a moment. Heat is added at constant volume (V2 = V3) from an external heat source. Temperature increases from T2 to T3, pressure increases from p2 to p3 and entropy increases from s2 to s3. (See p-V and T-s diagrams above).

In this process,

Heat Supplied = mCv(T3 – T2)

where,

m → Mass

Cv → Specific heat at constant volume

Process 3-4: Isentropic expansion

In this process, air undergoes isentropic (reversible adiabatic) expansion. The piston is pushed from top dead centre (TDC) to bottom dead centre (BDC) position. Here, pressure decreases fro p3 to p4, volume rises from v3 to v4, temperature falls from T3 to T4 and entropy remains constant (s3=s4). (Refer p-V and T-s diagrams above).

Process 4-1: Constant Volume Heat Rejection

The piston rests at BDC for a moment and heat is rejected at constant volume (V4=V1). In this process, pressure falls from p4 to p1, temperature decreases from T4 to T1 and entropy falls from s4 to s1. (See diagram above).

In process 4-1,

Heat Rejected = mCv(T4 – T1)

Thermal efficiency (air-standard efficiency) of Otto Cycle,

http://mechteacher.com/thermal-engineering/otto-cycle#diagrams






Total Cylinder Volume:

It is the total volume (maximum volume) of the cylinder in which Otto cycle takes place. In Otto cycle,

Total cylinder volume = V1 = V4 = Vc + Vs (Refer p-V diagram above) where,

Vc → Clearance Volume Vs → Stroke Volume Clearance Volume (Vc): At the end of the compression stroke, the piston approaches the Top Dead Center (TDC) position. The minimum volume of the space inside the cylinder, at the end of the compression stroke, is called clearance volume (Vc). In Otto cycle, Clearance Volume, Vc = V2 (See p-V diagram above) Stroke Volume (Vs):

http://mechteacher.com/otto-cycle-air-standard-efficiency-derivation/#diagrams

http://mechteacher.com/otto-cycle-air-standard-efficiency-derivation/#diagrams



In Otto cycle, stroke volume is the difference between total cylinder volume and clearance volume.

Stroke Volume, Vs = Total Cylinder Volume – Clearance Volume = V1 – V2 = V4 – V3

Compression Ratio:

Compression ratio (r) is the ratio of total cylinder volume to the clearance volume.

Now that we know the basic terms, let us derive expressions for T2 and T3. These expressions will be useful for us to derive the expression for air-standard efficiency of otto cycle. For finding T2, we take process 1-2 and for finding T3, we take process 3-4. Process 1-2: This process is an isentropic (reversible adiabatic) process. For this process, the relation between T and V is as follows:

Process 3-4:



This is also an isentropic process. The relation between T and V in this process is similar to the relation between T and V in process 1-2:

Here,

Air-standard efficiency of Otto cycle:

It is defined as the ratio between work done during Otto cycle to the heat supplied during Otto cycle.

Air-Standard Efficiency (thermal efficiency) of Otto cycle,

From my previous article,

http://mechteacher.com/otto-cycle/#air-standard-efficiency



Mean Effective Pressure

Mean effective pressure is the ratio of work done (W) during the working stroke(s) of a cycle to the stroke volume or swept volume (Vs) of the cylinder. It is denoted by „pm„ and its unit is N/m2.

In order to derive an expression for mean effective pressure of Otto cycle, we have to find out an expression for work done and stroke volume of Otto cycle.

Compression ratio,



Pressure ratio,

In process 1-2 (isentropic compression),

In process 3-4 (isentropic expansion),

Also from the p-V diagram above, V1 = V4 and V2 = V3

http://mechteacher.com/otto-cycle-mean-effective-pressure-derivation/#diagram



Let Vc = V2 = V3 = 1 Work done during Otto cycle,

W = Work done during isentropic expansion (process 3-4) – Work done during isentropic compression (process 1-2)



This is the expression for work done (W) in terms of r, k, γ and p1. Now, let us derive an expression for stroke volume Vs in terms of r. We know that in Otto cycle,



Vs = V1 – V2 (See p-V diagram above)

Now, Mean effective pressure,

The above expression can be written as

http://mechteacher.com/otto-cycle-mean-effective-pressure-derivation/#diagram



3. Write briefly about the fuel supply system used in S.I. engine.(CO4-H1-NOV 2012) FUEL SUPPLY SYSTEM IN SPARK IGNITION ENGINE The fuel supply system of spark ignition engine consists of: (i) Fuel tank (ii) Fuel filter (iii) Sediment bowl (iv) Fuel lift pump (v) Carburettor (vi) Fuel pipes (vii) Inlet manifold In some spark ignition engine, the fuel tank is placed above the level of the carburettor. The fuel flows fromthe fuel tank to the carburettor under the action of gravity. There are one or two filters between the fueltank and the carburettor. A transparent sediment bowl is also provided to hold the dust and dirt of the fuel.If the tank is below the level of the carburettor, a lift pump is provided in between the tank and the carburettor for forcing fuel from the tank to the carburettor of the engine. The fuel comes from the fuel tank to the sediment bowl and then to the lift pump. From there the fuel goes to the carburettor through suitable pipe. From the carburettor, the fuel goes to the engine cylinder, through the inlet manifold of the engine.



CARBURETTOR: The process of preparing an air-fuel mixture away from the cylinders of an engine is called carburetion and the device in which this process take place is called carburettor. Principle of carburettor: The basic principle of all carburettor design that when air flows over the end of a narrow tube or jet containing liquid, some liquid is drawn into the air stream. The quantity of liquid drawn into the air stream increases as the speed of air flow over the jet increases and also the quantity is greater if the jet is made larger.



Carburettor with pump feed to fuel reservoir

Diaphragm type fuel pump In practice, the fuel level in the jet is maintained by a float chamber. The fuel levels in the jet and in the float chamber are always the same. As the fuel is consumed, the level in the float chamber goes down. The float in the float chamber also goes down and the needle valve comes off its seat allowing more fuel into the chamber from the fuel tank. When the fuel level rises to its correct level, the float presses the needle valve back to its seat and cuts off the fuel flow. The velocity of the air flowing over the jet is increased by a constriction in the induction pipe known as venturi. A throttle butterfly valve



provides an adjustable obstruction in the induction pipe. It is used to control the flow of air-fuel mixture to the engine. As the butterfly valve is turned into the accelerate position, the airflow over the jet increases and more fuel is drawn out into the air stream, keeping the mixture strength constant. A second butterfly valve called choke is used to provide a richer mixture for the engine to start in cold condition. The choke controls the volume of air entering into the venturi. A second jet is fitted near the throttle butterfly, which is used when the engine is idling. Fuel is delivered to the float chamber through fuel pipe either by gravity or by a pump. The float chamber is connected with the mixing chamber (venturi) via fuel nozzle equipped with fuel jet. Function of Carburettor: The main functions of the carburettor are: (i) To mix the air and fuel thoroughly (ii) To atomise the fuel (iii) To regulate the air-fuel ratio at different speeds and loads and (iv) To supply correct amount of mixture at different speeds and loads.

4. Compare two stroke and four stroke engine. (CO4-H1-NOV 2012)

Difference between two stroke and four stroke engines



S.No. Four stroke engine Two stroke engine

1. It has one power stroke for every

two revolutions of the crankshaft.

It has one power stroke for each

revolution of the crankshaft.

2. Heavy flywheel is required and

engine runs unbalanced because

turning moment on the crankshaft

is not even due to one power

stroke for every two revolutions of

the crankshaft.

Lighter flywheel is required and engine

runs balanced because turning moment

is more even due to one power stroke for

each revolution of the crankshaft.

3. Engine is heavy Engine is light

4. Engine design is complicated due

to valve mechanism.

Engine design is simple due to absence

of valve mechanism.

5. More cost. Less cost than 4 stroke.

6.

Less mechanical efficiency due to

more friction on many parts.

More mechanical efficiency due to less

friction on a few parts.

7. More output due to full fresh

charge intake and full burnt gases

exhaust.

Less output due to mixing of fresh charge

with the hot burnt gases.

8. Engine runs cooler. Engine runs hotter.

9. Engine is water cooled. Engine is air cooled.

10. Less fuel consumption and More fuel consumption and fresh charge

http://www.mechanicalbooster.com/2014/02/what-are-main-parts-of-automobile-engine.html



complete burning of fuel. is mixed with exhaust gases.

11. Engine requires more space. Engine requires less space.

12. Complicated lubricating system. Simple lubricating system.

13. Less noise is created by engine. More noise is created by engine.

14. Engine consists of inlet and

exhaust valve.

Engine consists of inlet and exhaust

ports.

15. More thermal efficiency. Less thermal efficiency.

16. It consumes less lubricating oil. It consumes more lubricating oil.

17. Less wear and tear of moving

parts.

More wear and tear of moving parts.

18. Used in cars, buses, trucks etc. Used in mopeds,

scooters, motorcyclesetc.

5. Write in detail about working principle of two stroke cycle engine. (CO4-H1-JUNE 2010)

TWO-STROKE CYCLE DIESEL ENGINE: The cycle of the four-stroke of the piston (the suction, compression, power and exhaust strokes) is completed only in two strokes in the case of a two-stroke engine. The air is drawn into the crankcase due to the suction created by the upward stroke of the piston. On the down stroke of the piston it is compressed in the crankcase, The compression pressure is usually very low, being just sufficient to enable the air to flow into the cylinder through the transfer port when the piston reaches near the bottom of its down stroke.

http://www.mechanicalbooster.com/2014/01/top-5-most-expensive-cars-in-world.html

http://www.mechanicalbooster.com/2013/12/top-5-cheapest-motorcycles-in-world.html



The air thus flows into the cylinder, where the piston compresses it as it ascends, till the piston is nearly at the top of its stroke. The compression pressure is increased sufficiently high to raise the temperature of the air above the self-ignition point of the fuel used. The fuel is injected into the cylinder head just before the completion of the compression stroke and only for a short period. The burnt gases expand during the next downward stroke of the piston. These gases escape into the exhaust pipe to the atmosphere through the piston uncovering the exhaust port. Modern Two-Stroke Cycle Diesel Engine The crankcase method of air compression is unsatisfactory, as the exhaust gases do not escape the cylinder during port opening. Also there is a loss of air through the exhaust ports during the cylinder charging process. To overcome these disadvantages blowers are used to precompress the air. This pre-compressed air enters the cylinder through the port. An exhaust valve is also provided which opens mechanically just before the opening of the inlet ports

Principle of two-stroke cycle diesel engine

6. Briefly discuss boiler as power plant. (CO4-H1-NOV 2009)



Definition of Boiler: Steam boiler or simply a boiler is basically a closed vessel into which water is heated

until the water is converted into steam at required pressure. This is most basic

definition of boiler.

Working Principle of Boiler The basic working principle of boiler is very very simple and easy to understand. The

boiler is essentially a closed vessel inside which water is stored. Fuel (generally coal) is

bunt in a furnace and hot gasses are produced. These hot gasses come in contact with

water vessel where the heat of these hot gases transfer to the water and consequently

steam is produced in the boiler. Then this steam is piped to the turbine of thermal power

plant. There are many different types of boiler utilized for different purposes like running

a production unit, sanitizing some area, sterilizing equipment, to warm up the

surroundings etc.

Steam Boiler Efficiency The percentage of total heat exported by outlet steam in the total heat supplied by the

fuel (coal) is called steam boiler efficiency.

It includes with thermal efficiency, combustion efficiency & fuel to steam efficiency.

Steam boiler efficiency depends upon the size of boiler used. A typical efficiency of

steam boiler is 80% to 88%. Actually there are some losses occur like incomplete

combustion, radiating loss occurs from steam boiler surrounding wall, defective

combustion gas etc. Hence, efficiency of steam boiler gives this result.

Types of Boiler There are mainly two types of boiler – water tube boiler and fire tube boiler. In fire tube

boiler, there are numbers of tubes through which hot gases are passed and water

surrounds these tubes. Water tube boiler is reverse of the fire tube boiler. In water tube

boiler the water is heated inside tubes and hot gasses surround these tubes. These are

the main two types of boiler but each of the types can be sub divided into many which

we will discuss later.

http://www.electrical4u.com/steam/

http://www.electrical4u.com/water-tube-boiler-operation-and-types-of-water-tube-boiler/

http://www.electrical4u.com/fire-tube-boiler-operation-and-types-of-fire-tube-boiler/



Fire Tube Boiler

As it indicated from the name, the fire tube boiler consists of numbers of tubes through

which hot gasses are passed. These hot gas tubes are immersed into water, in a closed

vessel. Actually in fire tube boiler one closed vessel or shell contains water, through

which hot tubes are passed. These fire tubes or hot gas tubes heated up the water and

convert the water into steam and the steam remains in same vessel. As the water and

steam both are in same vessel a fire tube boiler cannot produce steam at very high

pressure. Generally it can produce maximum 17.5 kg/cm2 and with a capacity of 9

Metric Ton of steam per hour.

Types of Fire Tube Boiler There are different types of fire tube boiler likewise, external furnace and internal

furnace fire tube boiler. External furnace boiler can be again categorized into three

different types-

1. Horizontal Return Tubular Boiler.

2. Short Fire Box Boiler.

3. Compact Boiler.

Again, internal furnace fire tube boiler has also two main categories such as horizontal tubular and vertical tubular fire tube boiler. Normally horizontal return fire tube boiler is used in thermal power plant of low capacity. It consists of a horizontal drum into which there are numbers of horizontal tubes. These tubes are submerged in water. The fuel (normally coal) burnt below these horizontal drum and the combustible gasses move to the rear from where they enter into fire tubes and travel towards the front into the smoke box. During this travel of gasses in tubes, they transfer their heat into the water and steam bubbles come up. As steam is produced, the pressure of the boiler developed, in that closed vessel.

Advantages of Fire Tube Boiler

1. It is quite compact in construction.



2. Fluctuation of steam demand can be met easily.

3. It is also quite cheap.

Disadvantages of Fire Tube Boiler

1. As the water required for operation of the boiler is quite large, it requires long time for

rising steam at desired pressure.

2. As the water and steam are in same vessel the very high pressure of steam is not

possible.

3. The steam received from fire tube boiler is not very dry.

Water Tube Boiler

A water tube boiler is such kind of boiler where the water is heated inside tubes and the

hot gasses surround them.

This is the basic

definition of water tube boiler. Actually this boiler is just opposite of fire tube boiler

where hot gasses are passed through tubes which are surrounded by water.



Types of Water Tube Boiler There are many types of water tube boilers, such as

1. Horizontal Straight Tube Boiler.

2. Bent Tube Boiler.

3. Cyclone Fired Boiler.

Horizontal Straight Tube Boiler again can be sub - divided into two different types,

1. Longitudinal Drum Water Tube Boiler.

2. Cross Drum Water Tube Boiler.

Bent Tube Boiler also can be sub divided into four different types,

1. Two Drum Bent Tube Boiler.

2. Three Drum Bent Tube Boiler.

3. Low Head Three Drum Bent Tube Boiler.

4. Four Drum Bent Tube Boiler.

Advantages of Water Tube Boiler There are many advantages of water tube boiler due to which these types of boiler are

essentially used in large thermal power plant.

1. Larger heating surface can be achieved by using more numbers of water tubes.

2. Due to convectional flow, movement of water is much faster than that of fire tube

boiler, hence rate of heat transfer is high which results into higher efficiency.

3. Very high pressure in order of 140 kg/cm2 can be obtained smoothly.



Disadvantages of Water Tube Boiler

2. The main disadvantage of water tube boiler is that it is not compact in construction.

3. Its cost is not cheap.

4. Size is a difficulty for transportation and construction.



UNIT -5

REFRIGERATION AND AIR CONDITIONING

PART-A

1. What are the factors which affect the air conditioning?(CO5-L1-MAY 2014)

Excerpt SEER Rating Temperature Set Point Duct Conditions

2. What is tonne of refrigeration?(CO5-L1-MAY 2013)

1 tonne of refrigeration is the rate of heat removal required to freeze a

metric ton (1000 kg) of water at 0°C in 24 hours. Based on the heat of fusion

being 333.55 kJ/kg, 1 tonne of refrigeration = 13,898 kJ/h = 3.861 kW.

3. Define Relative Humidity.(CO5-L1-NOV 2012)

Relative humidity (RH) is the ratio of the partial pressure of water vapor to

the equilibrium vapor pressure of water at a given temperature. Relative

humidity depends on temperature and the pressure of the system of interest. It

requires less water vapor to attain high relative humidity at low temperatures;

more water vapour is required to attain high relative humidity in warm or hot air.

4. State the role of condenser in vapour compression in refrigeration circuit

https://en.wikipedia.org/wiki/Partial_pressure

https://en.wikipedia.org/wiki/Equilibrium_vapor_pressure



(CO5-L1-NOV 2011)

a condenser is a device or unit used to condense a substance from

its gaseous to its liquid state, by cooling it. In so doing, the latent heat is given

up by the substance, and will transfer to the condenser coolant. Condensers are

typically heat exchangers which have various designs and come in many sizes

ranging from rather small (hand-held) to very large industrial-scale units used in

plant processes.

5. Give the applications of Refrigeration.(C05-L1-JUNE 2010)

Dehumidification of air. Solidification of a solute. Removal of Heat of Reaction Control of Fermentation Preservation of Dairy Products

6. Define the term Refrigeration(CO5-L1-NOV 2009)

https://en.wikipedia.org/wiki/Condensation

https://en.wikipedia.org/wiki/Gas

https://en.wikipedia.org/wiki/Liquid

https://en.wikipedia.org/wiki/Latent_heat

https://en.wikipedia.org/wiki/Heat_exchanger



Refrigeration is a process of moving heat from one location to another in

controlled conditions. The work of heat transport is traditionally driven

by mechanical work, but can also be driven by

heat, magnetism, electricity, laser, or other means. Refrigeration has many

applications, including, but not limited to: household refrigerators,

industrial freezers, cryogenics, and air conditioning. Heat pumps may use the

heat output of the refrigeration process, and also may be designed to be

reversible, but are otherwise similar to air conditioning units.

PART-B

1.Explain the domestic refrigerator with neat diagram?(CO5-H1-MAY 2014)

The domestic refrigerator is one found in almost all the homes for storing food,

vegetables, fruits, beverages, and much more. This article describes the important parts

of the domestic refrigerator and also their working.

Parts of the Domestic Refrigerator and how they Work

The domestic refrigerator is one found in almost all the homes for storing food,

vegetables, fruits, beverages, and much more. This article describes the important parts

of the domestic refrigerator and also their working. The parts of domestic refrigerator

can be categorized into two categories: internal and external. Let see these in details

along with their images.

Parts of the Domestic Refrigerator

https://en.wikipedia.org/wiki/Heat

https://en.wikipedia.org/wiki/Mechanical_work

https://en.wikipedia.org/wiki/Magnetism

https://en.wikipedia.org/wiki/Electricity

https://en.wikipedia.org/wiki/Laser

https://en.wikipedia.org/wiki/Refrigerator

https://en.wikipedia.org/wiki/Freezer

https://en.wikipedia.org/wiki/Cryogenics

https://en.wikipedia.org/wiki/Air_conditioning

https://en.wikipedia.org/wiki/Heat_pump



Internal Parts of the Domestic Refrigerator

The internal parts of the refrigerator are ones that carry out actual working of the

refrigerator. Some of the internal parts are located at the back of the refrigerator, and

some inside the main compartment of the refrigerator. Some internal parts of the

domestic refrigerator are (please refer the figure above):



1) Refrigerant: The refrigerant flows through all the internal parts of the refrigerator. It

is the refrigerant that carries out the cooling effect in the evaporator. It absorbs the heat

from the substance to be cooled in the evaporator (chiller or freezer) and throws it to the

atmosphere via condenser. The refrigerant keeps on recirculating through all the

internal parts of the refrigerator in cycle.

2) Compressor: The compressor is located at the back of the refrigerator and in the

bottom area. The compressor sucks the refrigerant from the evaporator and discharges

it at high pressure and temperature. The compressor is driven by the electric motor and

it is the major power consuming devise of the refrigerator.

3) Condenser: The condenser is the thin coil of copper tubing located at the back of the

refrigerator. The refrigerant from the compressor enters the condenser where it is

cooled by the atmospheric air thus losing heat absorbed by it in the evaporator and the

compressor. To increase the heat transfer rate of the condenser, it is finned externally.

4) Expansive valve or the capillary: The refrigerant leaving the condenser enters the

expansion devise, which is the capillary tube in case of the domestic refrigerators. The

capillary is the thin copper tubing made up of number of turns of the copper coil. When

the refrigerant is passed through the capillary its pressure and temperature drops down

suddenly.

5) Evaporator or chiller or freezer: The refrigerant at very low pressure and

temperature enters the evaporator or the freezer. The evaporator is the heat exchanger

made up of several turns of copper or aluminum tubing. In domestic refrigerators the

plate types of evaporator is used as shown in the figure above. The refrigerant absorbs

the heat from the substance to be cooled in the evaporator, gets evaporated and it then

sucked by the compressor. This cycle keeps on repeating.

6) Temperature control devise or thermostat: To control the temperature inside the

refrigerator there is thermostat, whose sensor is connected to the evaporator. The

thermostat setting can be done by the round knob inside the refrigerator compartment.

When the set temperature is reached inside the refrigerator the thermostat stops the

electric supply to the compressor and compressor stops and when the temperature falls

below certain level it restarts the supply to the compressor.

http://www.brighthubengineering.com/hvac/61270-types-of-refrigeration-evaporators/



7) Defrost system: The defrost system of the refrigerator helps removing the excess

ice from the surface of the evaporator. The defrost system can be operated manually by

the thermostat button or there is automatic system comprising of the electric heater and

the timer.

Those were the some internal parts of the domestic refrigerator; now let us see the

external parts of the refrigerator.

The external parts of the refrigerator are: freezer compartment, thermostat control,

refrigerator compartment, crisper, refrigerator door compartment, light switch etc.

External Visible Parts of the Refrigerator

The external parts of the compressor are the parts that are visible externally and used

for the various purposes. The figure below shows the common parts of the domestic

refrigerator and some them are described below:

1) Freezer compartment: The food items that are to be kept at the freezing

temperature are stored in the freezer compartment. The temperature here is below zero

degree Celsius so the water and many other fluids freeze in this compartment. If you

want to make ice cream, ice, freeze the food etc. they have to be kept in the freezer

compartment.

2) Thermostat control: The thermostat control comprises of the round knob with the

temperature scale that help setting the required temperature inside the refrigerator.

Proper setting of the thermostat as per the requirements can help saving lots of

refrigerator electricity bills.

3) Refrigerator compartment: The refrigerator compartment is the biggest part of the

refrigerator. Here all the food items that are to be maintained at temperature above zero

degree Celsius but in cooled condition are kept. The refrigerator compartment can be

divided into number of smaller shelves like meat keeper, and others as per the

requirement.

4) Crisper: The highest temperature in the refrigerator compartment is maintained in

the crisper. Here one can keep the food items that can remain fresh even at the medium

temperature like fruits, vegetables, etc.



2) Explain the vapour compression refrigerator system with neat sketch

.compare it with absorption system? (C05-H1-MAY2013)

Vapor-Compression Refrigeration or vapor-compression refrigeration system

(VCRS),[1] in which the refrigerant undergoes phase changes, is one of the

many refrigeration cycles and is the most widely used method for air-conditioning of

buildings and automobiles. It is also used in domestic and commercial refrigerators,

large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated

trucks and railroad cars, and a host of other commercial and industrial services. Oil

refineries, petrochemical and chemical processing plants, and natural gas

processing plants are among the many types of industrial plants that often utilize large

vapor-compression refrigeration systems.

Refrigeration may be defined as lowering the temperature of an enclosed space by

removing heat from that space and transferring it elsewhere. A device that performs this

function may also be called an air conditioner, refrigerator, air source heat

pump, geothermal heat pump or chiller (heat pump).

Description of the vapour-compression refrigeration system

1.Refrigerants

Description of the vapour-compression refrigeration system[edit]

https://en.wikipedia.org/wiki/Vapor-compression_refrigeration#cite_note-1

https://en.wikipedia.org/wiki/Refrigerant

https://en.wikipedia.org/wiki/Phase_transition

https://en.wikipedia.org/wiki/Refrigeration_cycle


https://en.wikipedia.org/wiki/Oil_refinery

https://en.wikipedia.org/wiki/Oil_refinery

https://en.wikipedia.org/wiki/Petrochemical

https://en.wikipedia.org/wiki/Chemical_plant

https://en.wikipedia.org/wiki/Natural_gas_processing

https://en.wikipedia.org/wiki/Natural_gas_processing

https://en.wikipedia.org/wiki/Air_conditioner


https://en.wikipedia.org/wiki/Air_source_heat_pump

https://en.wikipedia.org/wiki/Air_source_heat_pump

https://en.wikipedia.org/wiki/Geothermal_heat_pump

https://en.wikipedia.org/wiki/Heat_pump_and_refrigeration_cycle

https://en.wikipedia.org/wiki/Vapor-compression_refrigeration#Description_of_the_vapour-compression_refrigeration_system

https://en.wikipedia.org/wiki/Vapor-compression_refrigeration#Refrigerants

https://en.wikipedia.org/w/index.php?title=Vapor-compression_refrigeration&action=edit&section=1



Figure 1: Vapor compression refrigeration

The vapor-compression uses a circulating liquid refrigerant as the medium which

absorbs and removes heat from the space to be cooled and subsequently rejects that

heat elsewhere. Figure 1 depicts a typical, single-stage vapor-compression system. All

such systems have four components: a compressor, a condenser, a thermal

expansion valve (also called a throttle valve or metering device), and an evaporator.

Circulating refrigerant enters the compressor in the thermodynamic state known as

a saturated vapor[2] and is compressed to a higher pressure, resulting in a higher

temperature as well. The hot, compressed vapor is then in the thermodynamic state

known as a superheated vapor and it is at a temperature and pressure at which it can

be condensed with either cooling water or cooling air flowing across the coil or tubes.

This is where the circulating refrigerant rejects heat from the system and the rejected

heat is carried away by either the water or the air (whichever may be the case).

https://en.wikipedia.org/wiki/Refrigerant

https://en.wikipedia.org/wiki/Gas_compressor

https://en.wikipedia.org/wiki/Condenser_(heat_transfer)

https://en.wikipedia.org/wiki/Thermal_expansion_valve

https://en.wikipedia.org/wiki/Thermal_expansion_valve

https://en.wikipedia.org/wiki/Throttle

https://en.wikipedia.org/wiki/Boiling_point#Saturation_temperature_and_pressure


https://en.wikipedia.org/wiki/Condensation

https://en.wikipedia.org/wiki/File:Refrigeration.png



A fictitious pressure-volume diagram for a typical refrigeration cycle

The condensed liquid refrigerant, in the thermodynamic state known as a saturated

liquid, is next routed through an expansion valve where it undergoes an abrupt

reduction in pressure. That pressure reduction results in the adiabatic flash

evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the

adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant

mixture to where it is colder than the temperature of the enclosed space to be

refrigerated.

The cold mixture is then routed through the coil or tubes in the evaporator. A fan

circulates the warm air in the enclosed space across the coil or tubes carrying the cold

refrigerant liquid and vapor mixture. That warm air evaporates the liquid part of the cold

refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the

temperature of the enclosed space to the desired temperature. The evaporator is where

the circulating refrigerant absorbs and removes heat which is subsequently rejected in

the condenser and transferred elsewhere by the water or air used in the condenser.

To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again

a saturated vapor and is routed back into the compressor.

Refrigerants



https://en.wikipedia.org/wiki/Flash_evaporation

https://en.wikipedia.org/wiki/Flash_evaporation

https://en.wikipedia.org/wiki/Evaporates

https://en.wikipedia.org/wiki/Refrigeration_cycle

https://en.wikipedia.org/wiki/File:Refrigeration_PV_diagram.svg



"Freon" is a trade name for a family of haloalkane refrigerants manufactured

by DuPont and other companies. These refrigerants were commonly used due to their

superior stability and safety properties: they were not flammable at room temperature

and atmospheric pressure, nor obviously

toxic as were the fluids they replaced, such as sulfur dioxide. Haloalkanes are also an

order(s) of magnitude more expensive than petroleum derived flammable alkanes of

similar or better cooling performance.

Unfortunately, chlorine- and fluorine-bearing refrigerants reach the upper atmosphere

when they escape. In the stratosphere, CFCs break up due to UV radiation, releasing

their chlorine free radicals. These chlorine free radicals act as catalysts in the

breakdown of ozone through chain reactions. One CFC molecule can cause thousands

of ozone molecules to break down. This causes severe damage to the ozone layer that

shields the Earth's surface from the Sun's strong UV radiation, and has been shown to

lead to increased rates of skin cancer. The chlorine will remain active as a catalyst until

and unless it binds with another particle, forming a stable molecule. CFC refrigerants in

common but receding usage include R-11 and R-12.

Newer refrigerants with reduced ozone depletion effect such as HCFCs (R-22, used in

most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC

use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by

hydrofluorocarbons (HFCs), such as R-410A, which lack chlorine. However, CFCs,

HCFCs, and HFCs all have large global warming potential.

More benign refrigerants are currently the subject of research, such

as supercritical carbon dioxide, known as R-744.[3] These have similar

efficiencies[compared to existing CFC and HFC based compounds, and have many

orders of magnitude lower global warming potential.

S.no Aspect Vapor Absorption System Vapor Compression System

https://en.wikipedia.org/wiki/Haloalkane

https://en.wikipedia.org/wiki/Haloalkane

https://en.wikipedia.org/wiki/Refrigerants

https://en.wikipedia.org/wiki/DuPont

https://en.wikipedia.org/wiki/Sulfur_dioxide

https://en.wikipedia.org/wiki/Stratosphere

https://en.wikipedia.org/wiki/UV

https://en.wikipedia.org/wiki/Catalyst

https://en.wikipedia.org/wiki/Ozone_layer

https://en.wikipedia.org/wiki/Ozone_depletion

https://en.wikipedia.org/wiki/HCFC

https://en.wikipedia.org/wiki/Chlorodifluoromethane

https://en.wikipedia.org/wiki/Hydrofluorocarbon

https://en.wikipedia.org/wiki/R-134a

https://en.wikipedia.org/wiki/Montreal_Protocol

https://en.wikipedia.org/wiki/R-410A

https://en.wikipedia.org/wiki/Chlorine

https://en.wikipedia.org/wiki/Global_warming_potential

https://en.wikipedia.org/wiki/Supercritical_fluid

https://en.wikipedia.org/wiki/Carbon_dioxide

https://en.wikipedia.org/wiki/R-744

https://en.wikipedia.org/wiki/Vapor-compression_refrigeration#cite_note-3



1 Energy Input

Vapor absorption system

takes in low grade energy

such as waste heat from

furnace, exhaust team or

solar heat for its operations.

Vapor compression system takes in high grade such as electrica

energy for

its operation of compressor used in the cycle.

2 Moving part

It uses a small pump as

moving part, which is run by

a small motor.

It uses a compressor driven by an electric motor or engine.

3 Evaporator

pressure

It can operate with reduced

evaporator pressure, with

little decrease in refrigerant

capacity.

The refrigerant capacity decreases with lowered evaporator pressu

4 Load

variation

The performance of vapor

absorption system does not

change with load variation

The performance of vapor compressing system is very poor at p

5 Evaporator

exit

In vapor absorption system,

the liquid refrigerant leaving

the evaporator does not put

any bad effect on the

system except to reduce

the refrigerant effect.

In a vapor compression system, it is desirable to superheat vapo

the evaporator

, so no liquid can enter the compressor.

6 Lowest

temperature

Since water is used as

refrigerant, thus the lowest

temperature attained is

above 0°C.

With cascading, the temperature can be lowered upto -150°C or

temperature.

http://me-mechanicalengineering.com/refrigerant-and-desired-properties-of-a-refrigerant/



Compare it with absorption system

7

Coefficient

of

Performance

The COP of the system is

poor. The COP of the system is excellent.

8 Capacity It can built in capacities well

above 1000 TR.

For a single compression system, it is not possible to have a syste

than 1000 TR

capacity.

9 Refrigerant Water or ammonia is used

as refrigerant.

Chloroflourocarbon, hydroflorocarbon and hydrochlorofluorocarb

most of the

systems.

http://me-mechanicalengineering.com/refrigerant-and-desired-properties-of-a-refrigerant/#ammonia



3) Expalin the operation of any one type of refrigeration system with schematic

line

(C05-H1-NOV 2012)

Absorption Refrigeration System

The vapor absorption refrigeration system comprises of all the processes in the vapor

compression refrigeration system like compression, condensation, expansion and

evaporation. In the vapor absorption system the refrigerant used is ammonia, water or

lithium bromide. The refrigerant gets condensed in the condenser and it gets

evaporated in the evaporator. The refrigerant produces cooling effect in the evaporator

and releases the heat to the atmosphere via the condenser.



The major difference between the two systems is the method of the suction and

compression of the refrigerant in the refrigeration cycle. In the vapor compression

system, the compressor sucks the refrigerant from evaporator and compresses it to the

high pressure. The compressor also enables the flow of the refrigerant through the

whole refrigeration cycle. In the vapor absorption cycle, the process of suction and

compression are carried out by two different devices called as the absorber and the

generator. Thus the absorber and the generator replace the compressor in the vapor

absorption cycle. The absorbent enables the flow of the refrigerant from the absorber to

the generator by absorbing it.

Another major difference between the vapor compression and vapor absorption cycle is

the method in which the energy input is given to the system. In the vapor compression

system the energy input is given in the form of the mechanical work from the electric

motor run by the electricity. In the vapor absorption system the energy input is given in

the form of the heat. This heat can be from the excess steam from the process or the

hot water. The heat can also be created by other sources like natural gas, kerosene,

heater etc. though these sources are used only in the small systems.

Simple Absorption System

1) Condenser: Just like in the traditional condenser of the vapor compression cycle, the

refrigerant enters the condenser at high pressure and temperature and gets condensed.

The condenser is of water cooled type.

2) Expansion valve or restriction: When the refrigerant passes through the expansion

valve, its pressure and temperature reduces suddenly. This refrigerant (ammonia in this

case) then enters the evaporator.

3) Evaporator: The refrigerant at very low pressure and temperature enters the

evaporator and produces the cooling effect. In the vapor compression cycle this

refrigerant is sucked by the compressor, but in the vapor absorption cycle, this

refrigerant flows to the absorber that acts as the suction part of the refrigeration cycle.



4) Absorber: The absorber is a sort of vessel consisting of water that acts as the

absorbent, and the previous absorbed refrigerant. Thus the absorber consists of the

weak solution of the refrigerant (ammonia in this case) and absorbent (water in this

case). When ammonia from the evaporator enters the absorber, it is absorbed by the

absorbent due to which the pressure inside the absorber reduces further leading to

more flow of the refrigerant from the evaporator to the absorber. At high temperature

water absorbs lesser ammonia, hence it is cooled by the external coolant to increase it

ammonia absorption capacity.

This part of the article describes how the absorption refrigeration system. The

absorption refrigeration system comprises of condenser, expansion valve, evaporator,

absorber, pump and generator. The refrigerant leaving the evaporator enter the

absorber, where it is absorbed by the absorbent. The strong solution of refrigerant-

absorber enters the generator with the help of the pump. The refrigerant then enters the

condenser while the remaining weak solution enters back to the absorber and the cycle

is repeated.

5) Pump: When the absorbent absorbs the refrigerant strong solution of refrigerant-

absorbent (ammonia-water) is formed. This solution is pumped by the pump at high

pressure to the generator. Thus pump increases the pressure of the solution to about

10bar.

6) Generator: The refrigerant-ammonia solution in the generator is heated by the

external source of heat. This is can be steam, hot water or any other suitable source.

Due to heating the temperature of the solution increases. The refrigerant in the solution

gets vaporized and it leaves the solution at high pressure. The high pressure and the

high temperature refrigerant then enters the condenser, where it is cooled by the

coolant, and it then enters the expansion valve and then finally into the evaporator

where it produces the cooling effect. This refrigerant is then again absorbed by the

weak solution in the absorber.



When the vaporized refrigerant leaves the generator weak solution is left in it. This

solution enters the pressure reducing valve and then back to the absorber, where it is

ready to absorb fresh refrigerant. In this way, the refrigerant keeps on repeating the

cycle.

The pressure of the refrigerant is increased in the generator, hence it is considered to

be equivalent to the compression part of the compressor.

Working of Absoption Refrigeration System

The initial flow of the refrigerant from the evaporator to the absorber occurs because the

vapor pressure of the refrigerant-absorbent in the absorber is lower than the vapor

pressure of the refrigerant in the evaporator. The vapor pressure of the refrigerant-

absorbent inside the absorbent determines the pressure on low-pressure side of the

system and also the vaporizing temperature of the refrigerant inside the evaporator. The

vapor pressure of the refrigerant-absorbent solution depends on the nature of the

absorbent, its temperature and concentration.

When the refrigerant entering in the absorber is absorbed by the absorbent its volume

decreases, thus the compression of the refrigerant occurs. Thus absorber acts as the

suction part of the compressor. The heat of absorption is also released in the absorber,

which is removed by the external coolant.

4) Explain window air conditioner with neat diagram(C05-H1-NOV 2011)

Working of Window AC

Now that we have seen the various parts of the window air conditioner, let us see its

working. For understanding the working of the window AC please refer the figures given

below. The working of window air conditioner can be explained by separately

considering the two cycles of air: room air cycle and the hot air cycle. The

compartments of the room and hot air are separated by an insulated partition inside the

body of the air conditioner. The setting of thermostat and its working has also been

explained in the discussions below.

Room Air Cycle

http://www.brighthubengineering.com/hvac/55186-parts-of-the-window-air-conditioners-part-one/



The air moving inside the room and in the front part of the air conditioner where the

cooling coil is located is considered to be the room air. When the window AC is started

the blower starts immediately and after a few seconds the compressor also starts. The

evaporator coil or the cooling gets cooled as soon as the compressor is started.

The blower behind the cooling coil starts sucking the room air, which is at high

temperature and also carries the dirt and dust particles. On its path towards the blower,

the room air first passes through the filter where the dirt and dust particles from it get

removed.

The air then passes over the cooling coil where two processes occur. Firstly, since the

temperature of the cooling coil is much lesser than the room air, the refrigerant inside

the cooling coil absorbs the heat from the air. Due to this the temperature of the room

air becomes very low, that is the air becomes chilled.

Secondly, due to reduction in the temperature of the air, some dew is formed on the

surface of the cooling coil. This is because the temperature of the cooling coil is lower

than the dew point temperature of the air. Thus the moisture from the air is removed so

the relative humidity of the air reduces. Thus when the room air passes over the cooling

coil its temperature and relative humidity reduces.



This air at low temperature and low humidity is sucked by the blower and it blows it at

high pressure. The chilled air then passes through small duct inside the air conditioner

and it is then thrown outside the air conditioner through the opening in the front panel or

the grill. This chilled air then enters the room and chills the room maintaining low

temperature and low humidity inside the room.

The cool air inside the room absorbs the heat and also the moisture and so its

temperature and moisture content becomes high. This air is again sucked by the blower

and the cycle repeats. Some outside air also gets mixed with this room air. Since this air

is sent back to the blower, it is also called as the return room air. In this way the cycle of

this return air or the room air keeps on repeating.

Hot Air Cycle

The hot air cycle includes the atmospheric air that is used for cooling the condenser.

The condenser of the window air conditioner is exposed to the external atmosphere.

The propeller fan located behind the condenser sucks the atmospheric at high

temperature and it blows the air over the condenser.

The refrigerant inside the condenser is at very high temperature and it has to be cooled

to produce the desired cooling effect. When the atmospheric air passes over the

condenser, it absorbs the heat from the refrigerant and its temperature increases. The

atmospheric air is already at high temperature and after absorbing the condenser heat,

its temperature becomes even higher. The person standing behind the condenser of the

window AC can clearly feel the heat of this hot air. Since the temperature of this air is

very high, this is called as hot air cycle.

The refrigerant after getting cooled enters the expansion valve and then the evaporator.

On the other hand, the hot mixes with the atmosphere and then the fresh atmospheric

air is absorbed by the propeller fan and blown over the condenser. This cycle of the hot

air continues.



The hot air cycle includes the atmospheric air that is used for cooling the condenser.

The condenser of the window air conditioner is exposed to the external atmosphere.

The propeller fan located behind the condenser sucks the atmospheric at high

temperature and it blows the air over the condenser. The refrigerant inside the

condenser is at very high temperature and it has to be cooled to produce the desired

cooling effect. When the atmospheric air passes over the condenser, it absorbs the heat

from the refrigerant and its temperature increases. The atmospheric air is already at

high temperature and after absorbing the condenser heat, its temperature becomes

even higher. The person standing behind the condenser of the window AC can clearly

feel the heat of this hot air. Since the temperature of this air is very high, this is called as

hot air cycle.

Setting the Room Temperature with Thermostat

The temperature inside the room can be set by using the thermostat knob or the remote

control. If your window AC has knob, you would see some numbers or the round scale

round the knob that will enable setting the temperature desired in the room. If your AC

has come with the remote control, then you will see the room temperature on the digital

indicator placed in the control panel of the window AC. You would probably also see the

temperature on the small screen of the remote control. With the buttons provided on the

remote control you can easily set the temperature inside the room.

When the desired temperature is attained inside the room, the thermostat stops the

compressor of the AC. After some time when the temperature of the air becomes higher

again, the thermostat restarts the compressor to produce the cooling effect. One should

set the thermostat at the required temperature and not keep it at very low temperature

to avoid high electricity bills.

Setting the Speed of the Air

The Speed of the air can be set by the fan motor button provided on the control panel. If

your AC has the remote control you can see the fan speed button on it. The motor of the

blower is of multispeed that type that enable changing the speed or the flow of air inside

the room.

Important Part of the Window AC: Air Filter



The filter is a very important part of the AC since it cleans the air before it enters the

room. For proper functioning of the filter it is very important to clean it every two weeks.

If this is not done the filter will get choked and it won‟t be able to clean the air. Soon the dirt will also enter the evaporator coil and choke it. If this happens the AC will stop

functioning and cleaning the evaporator becomes a very tedious process. Cleaning the

filter hardly takes five minutes, do it regularly and enjoy the comforts of window AC on

long-term basis.

5) Draw the sketch of vapour absorption refrigeration system.and list the

components and their functions?(C05-H1-JUNE 2010)

An absorption refrigerator is a refrigerator that uses a heat source (e.g., solar energy, a

fossil-fueled flame, waste heat from factories, or district heating systems) to provide the

energy needed to drive the cooling process.

Absorption refrigerators are often used for food storage in recreational vehicles. The

principle can also be used to air-condition buildings using the waste heat from a gas

turbine or water heater. Using waste heat from a gas turbine makes the turbine very

efficient because it first produces electricity, then hot water, and finally, air-conditioning

(called cogeneration/trigeneration).

Principles


https://en.wikipedia.org/wiki/Solar_thermal_energy

https://en.wikipedia.org/wiki/Waste_heat

https://en.wikipedia.org/wiki/District_heating

https://en.wikipedia.org/wiki/Recreational_vehicle


https://en.wikipedia.org/wiki/Gas_turbine

https://en.wikipedia.org/wiki/Gas_turbine

https://en.wikipedia.org/wiki/Water_heater

https://en.wikipedia.org/wiki/Electricity

https://en.wikipedia.org/wiki/Cogeneration



Absorption cooling process

Both absorption and compressor refrigerators use a refrigerant with a very

low boiling point (less than 0 °F (−18 °C)). In both types, when this refrigerant

evaporates (boils), it takes some heat away with it, providing the cooling effect. The

main difference between the two systems is the way the refrigerant is changed from a

gas back into a liquid so that the cycle can repeat. An absorption refrigerator changes

the gas back into a liquid using a method that needs only heat, and has no moving parts

other than the refrigerant itself.

The absorption cooling cycle can be described in three phases:

Evaporation: A liquid refrigerant evaporates in a low partial pressure environment,

thus extracting heat from its surroundings (e.g. the refrigerator's compartment).

Because of the low partial pressure, the temperature needed for evaporation is also low.

Absorption: The now gaseous refrigerant is absorbed by another liquid (e.g. a salt

solution).

Regeneration: The refrigerant-saturated liquid is heated, causing the refrigerant to

evaporate out. The hot gaseous refrigerant passes through a heat exchanger,

transferring its heat outside the system (such as to surrounding ambient-temperature

air), and condenses. The condensed (liquid) refrigerant supplies the evaporation phase.

In comparison, a compressor refrigerator uses an electrically powered compressor to

increase the pressure on the gaseous refrigerant. The resulting hot, high-pressure gas

is condensed to a liquid form by cooling in a heat exchanger ("condenser") that is

exposed to the external environment (usually air in the room). The condensed

refrigerant, now at a temperature near to that of the external environment, then passes

through an orifice or a throttle valve into the evaporator section. The orifice or throttle

valve creates a pressure drop between the high pressure condenser section and the

low pressure evaporator section. The lower pressure in the evaporator section allows

the liquid refrigerant to evaporate, which absorbs heat from the refrigerator food

compartment. The now-vaporized refrigerant then goes back into the compressor to

repeat the cycle.

https://en.wikipedia.org/wiki/Vapor-compression_refrigeration

https://en.wikipedia.org/wiki/Boiling_point


https://en.wikipedia.org/wiki/Evaporative_cooling



Another difference between the two types is the refrigerant used. Compressor

refrigerators typically use an HCFC or HFC, while absorption refrigerators typically

use ammonia or water.

Simple salt and water system

A simple absorption refrigeration system common in large commercial plants uses a

solution of lithium bromide and Lithium chloride salt and water. Water under low

pressure is evaporated from the coils that are being chilled. The water is absorbed by a

lithium bromide/water solution. The system drives the water off the lithium bromide

solution with heat.[5]

Water spray absorption refrigeration

Another variant, depicted to the right, uses air, water, and a salt water solution. The

intake of warm, moist air is passed through a sprayed solution of salt water. The spray

lowers the humidity but does not significantly change the temperature. The less humid,

warm air is then passed through an evaporative cooler, consisting of a spray of fresh

water, which cools and re-humidifies the air. Humidity is removed from the cooled air

with another spray of salt solution, providing the outlet of cool, dry air.

The salt solution is regenerated by heating it under low pressure, causing water to

evaporate. The water evaporated from the salt solution is re-condensed, and rerouted

back to the evaporative cooler.

https://en.wikipedia.org/wiki/Chlorofluorocarbon

https://en.wikipedia.org/wiki/Organofluorine_chemistry#Hydrofluorocarbons

https://en.wikipedia.org/wiki/Ammonia

https://en.wikipedia.org/wiki/Water

https://en.wikipedia.org/wiki/Lithium_bromide

https://en.wikipedia.org/wiki/Lithium_chloride

https://en.wikipedia.org/wiki/Absorption_refrigerator#cite_note-5

https://en.wikipedia.org/wiki/Evaporative_cooler

https://en.wikipedia.org/wiki/File:Absorptive_refrigeration.svg



Single pressure absorption refrigeration

1. Hydrogen enters the pipe with liquid ammonia

2. Ammonia and hydrogen enter the inner compartment of the refrigerator. An increase

in volume causes a decrease in the partial pressure of the liquid ammonia. The

ammonia evaporates, taking heat from the liquid ammonia (ΔHVap) and thus lowering its

temperature. Heat flows from the hotter interior of the refrigerator to the colder liquid,

promoting further evaporation.

3. Ammonia and hydrogen return from the inner compartment, ammonia returns to

absorber and dissolves in water. Hydrogen is free to rise upwards.

4. Ammonia gas condensation (passive cooling).

5. Hot ammonia (gas).

6. Heat insulation and distillation of ammonia gas from water.

7. Heat source (electric).

8. Absorber vessel (water and ammonia solution).

A single-pressure absorption refrigerator takes advantage of the fact that a

substance's boiling point depends upon the partial pressure of the vapor above the

liquid and goes down with lower partial pressure. While having the same total pressure

throughout the system, the refrigerator maintains a low partial pressure of the refrigerant

(therefore low boiling point) in the part of the system that draws heat out of the low-

temperature interior of the refrigerator, but maintains the refrigerant at high partial

pressure (therefore high boiling point) in the part of the system that expels heat to the

ambient-temperature air outside the refrigerator.

The refrigerator uses three substances: ammonia, hydrogen gas, and water. The

cycle is closed, with all hydrogen, water and ammonia collected and endlessly reused.

The system is pressurized to the pressure where the boiling point of ammonia is higher

than the temperature of the condenser coil (the coil which transfers heat to the air

outside the refrigerator, by being hotter than the outside air) This pressure is typically

14-16atm, at which pressure the dew point of ammonia will be about 95°F (35°C).

https://en.wikipedia.org/wiki/Ammonia

https://en.wikipedia.org/wiki/Hydrogen

https://en.wikipedia.org/wiki/Water



The cooling cycle starts with liquid ammonia entering the evaporator at room

temperature. The volume of the evaporator is greater than the volume of the liquid, with

the excess space occupied by a mixture of gaseous ammonia and hydrogen. The

presence of hydrogen lowers the partial pressure of the ammonia gas, thus lowering

the boiling point of the liquid below the temperature of the refrigerator's interior.

Ammonia evaporates, taking a small amount of heat from the liquid and lowering the

liquid's temperature, until it reaches that boiling point. It then continues to evaporate,

without the liquid descending below the boiling point, while the large enthalpy of

vaporization (heat) flows from the warmer refrigerator interior to the cooler liquid

ammonia and then to more ammonia gas.

In the next two steps, the ammonia gas is separated from the hydrogen so it can be

reused.

The ammonia (gas) and hydrogen (gas) mixture flows through a pipe from the

evaporator into the absorber. In the absorber, this mixture of gases contacts water

(technically, a weak solution of ammonia in water). The gaseous ammonia dissolves in

the water, while the hydrogen, which doesn't, collects at the top of the absorber, leaving

the now-strong ammonia-and-water solution at the bottom. The hydrogen is now

separate while the ammonia is now dissolved in the water.

The next step separates the ammonia and water. The ammonia/water solution flows to

the generator (boiler), where heat is applied to boil off the ammonia, leaving most of the

water (which has a higher boiling point) behind. Some water vapor and bubbles remain

mixed with the ammonia; this water is removed in the final separation step, by passing it

through the separator, an uphill series of twisted pipes with minor obstacles to pop the

bubbles, allowing the water vapor to condense and drain back to the generator.

The pure ammonia gas then enters the condenser. In this heat exchanger, the hot

ammonia gas transfers its heat to the outside air, which is below the boiling point of the

full-pressure ammonia, and therefore condenses. The condensed (liquid) ammonia

flows down to be mixed with the hydrogen gas released from the absorption step,

repeating the cycle.

Components:


https://en.wikipedia.org/wiki/Boiling_point

https://en.wikipedia.org/wiki/Enthalpy_of_vaporization

https://en.wikipedia.org/wiki/Enthalpy_of_vaporization

https://en.wikipedia.org/wiki/Heat_exchanger



1) Condenser: Just like in the traditional condenser of the vapor compression cycle, the

refrigerant enters the condenser at high pressure and temperature and gets condensed.

The condenser is of water cooled type.

2) Expansion valve or restriction: When the refrigerant passes through the expansion

valve, its pressure and temperature reduces suddenly. This refrigerant (ammonia in this

case) then enters the evaporator.

3) Evaporator: The refrigerant at very low pressure and temperature enters the

evaporator and produces the cooling effect. In the vapor compression cycle this

refrigerant is sucked by the compressor, but in the vapor absorption cycle, this

refrigerant flows to the absorber that acts as the suction part of the refrigeration cycle.

4) Absorber: The absorber is a sort of vessel consisting of water that acts as the

absorbent, and the previous absorbed refrigerant. Thus the absorber consists of the

weak solution of the refrigerant (ammonia in this case) and absorbent (water in this

case). When ammonia from the evaporator enters the absorber, it is absorbed by the

absorbent due to which the pressure inside the absorber reduces further leading to

more flow of the refrigerant from the evaporator to the absorber. At high temperature

water absorbs lesser ammonia, hence it is cooled by the external coolant to increase it

ammonia absorption capacity.

5) Pump: When the absorbent absorbs the refrigerant strong solution of refrigerant-

absorbent (ammonia-water) is formed. This solution is pumped by the pump at high

pressure to the generator. Thus pump increases the pressure of the solution to about

10bar.



6) Generator: The refrigerant-ammonia solution in the generator is heated by the

external source of heat. This is can be steam, hot water or any other suitable source.

Due to heating the temperature of the solution increases. The refrigerant in the solution

gets vaporized and it leaves the solution at high pressure. The high pressure and the

high temperature refrigerant then enters the condenser, where it is cooled by the

coolant, and it then enters the expansion valve and then finally into the evaporator

where it produces the cooling effect. This refrigerant is then again absorbed by the

weak solution in the absorber.

When the vaporized refrigerant leaves the generator weak solution is left in it. This

solution enters the pressure reducing valve and then back to the absorber, where it is

ready to absorb fresh refrigerant. In this way, the refrigerant keeps on repeating the

cycle.

The pressure of the refrigerant is increased in the generator, hence it is considered to

be equivalent to the compression part of the compressor.

6)Write short notes on window and split a/c(CO5-H1-N0V 2009)

Window Air Conditioner

Window air conditioner is sometimes referred to as room air conditioner as well.

It is the simplest form of an air conditioning system and is mounted on windows or walls.

It is a single unit that is assembled in a casing where all the components are located.

This refrigeration unit has a double shaft fan motor with fans mounted on both sides of

the motor. One at the evaporator side and the other at the condenser side.

The evaporator side is located facing the room for cooling of the space and the

condenser side outdoor for heat rejection. There is an insulated partition separating this

two sides within the same casing.

Front Panel



The front panel is the one that is seen by the user from inside the room where it

is installed and has a user interfaced control be it electronically or mechanically. Older

unit usually are of mechanical control type with rotary knobs to control the temperature

and fan speed of the air conditioner.

The newer units come with electronic control system where the functions are controlled

using remote control and touch panel with digital display.

The front panel has adjustable horizontal and vertical(some models) louvers where the

direction of air flow are adjustable to suit the comfort of the users.

The fresh intake of air called VENT (ventilation) is provided at the panel in the event that

user would like to have a certain amount of fresh air from the outside.

Indoor Side Components

The indoor parts of a window air conditioner include:

Cooling Coil with a air filter mounted on it. The cooling coil is where the heat

exchange happen between the refrigerant in the system and the air in the room.

Fan Blower is a centrifugal evaporator blower to discharge the cool air to the room.

Capillary Tube is used as an expansion device. It can be noisy during operation if

installed too near the evaporator.

Operation Panel is used to control the temperature and speed of the blower fan. A

thermostat is used to sense the return air temperature and another one to monitor the

temperature of the coil. Type of control can be mechanical or electronic type.

Filter Drier is used to remove the moisture from the refrigerant.

Drain Pan is used to contain the water that condensate from the cooling coil and is

discharged out to the outdoor by gravity.

Outdoor Side Components



The outdoor side parts include:

Compressor is used to compress the refrigerant.

Condenser Coil is used to reject heat from the refrigerator to the outside air.

Propeller Fan is used in air-cooled condenser to help move the air molecules

over the surface of the condensing coil.

Fan Motor is located here. It has a double shaft where the indoor blower and

outdoor propeller fan are connected together.

Operations

During operation, a thermostat is mounted on the return air of the unit. This

temperature is used to control the on or off of the compressor. Once the room

temperature has been achieved, the compressor cuts off.

Usually, it has to be off for at least 3 minutes before turning on again to prevent it

from being damaged. For mechanical control type, there is usually a caution to turn on

the unit after the unit has turned off for at least 3 minutes. For electronic control, there is

usually a timer to automatically control the cut-in and cut-out of compressor.

The evaporator blower fan will suck the air from the room to be conditioned

through the air filter and the cooling coil. Air that has been conditioned is then discharge

to deliver the cool and dehumidified air back to the room. This air mixes with the room

air to bring down the temperature and humidity level of the room.



The introduction of fresh air from outside the room is done through the damper

which is then mixed with the return air from the room before passing it over the air filter

and the cooling coil. The air filter which is mounted in front of the evaporator acts as a

filter to keep the cooling coil clean to obtain good heat-transfer from the coil. Hence,

regular washing and cleaning of the air filter is a good practice to ensure efficient

operation of the air conditioner.

Heat Pump Window Air Conditioner

In temperate countries, heating of the room is required. A heat pump window air

conditioner unit is able to cool the room during summer and heat the room during

winter. A reversing valve (also known as 4-Way-Valve) is used to accomplish this.

During heating operation, it reverses the flow of the refrigerant which results in the

evaporator to act as a condenser and the condenser as evaporator.

Split Air Conditioner System

A split air conditioner consists of two main parts: the outdoor unit and the indoor

unit. The outdoor unit is installed on or near the wall outside of the room or space that

you wish to cool. The unit houses the compressor, condenser coil and the expansion

coil or capillary tubing. The sleek-looking indoor unit contains the cooling coil, a long

blower and an air filter.

How Split Air Conditioner Differs From Other A/C Units

A split air conditioner does not require major installation work because it does not

require ductwork. Rather, the indoor and outdoor units are connected with a set of

electrical wires and tubing. This is good for your wallet and the environment. The

ductwork required for many traditional A/C units generally increases energy

expenditures, as many centralized A/C units lose a lot of energy due to heat exchange

in the air duct system. So, without a duct system, there is very little opportunity for heat

or energy loss in a split air conditioner system.

Benefits of a Split Air Conditioning System

http://www.networx.com/article/electrical-upgrade

http://www.networx.com/article/electrical-upgrade



This kind of air conditioner system has many advantages over traditional air

conditioners. Perhaps the most obvious benefit is the quiet performance of a split air

conditioner system. The parts of an air conditioner that make the most noise are the

compressor and the fan that cools the condenser. In a split system, the compressor and

fan for the condenser are located outside of the room being cooled and therefore the

major sources of noise are removed - unlike with window units.

Another benefit of a split air conditioner system is that you can opt for a multi-split

system, where you can have more than one indoor unit connected to a single outdoor

unit. This makes it easy to cool multiple rooms or maintain the temperature throughout a

large room through the use of two indoor cooling units.

A split air conditioner is an efficient and cost-effective way to cool your home. It

should be noted that the initial cost of this kind of air conditioning unit is significantly

higher than a window unit and it does require professional installation. However, the

amount of money you will save on your energy bills as well as the longevity of the unit

will make it worth your while in the end.

http://www.networx.com/article/keeping-cool-tips

skp engineering collegeskpec.edu.in/wp-content/uploads/2017/11/basic-civil-and...difference in...

Documents