3-unit - v - refrigeration & air conditioning

7/30/2019 3-Unit - V - Refrigeration & Air Conditioning

1/57

UNIT V

REFRIGERATION AND AIRCONDITIONING


2/57

For Support notes, please visit: www.arpradeep.tk

Refrigeration

It is defined as the process of providingand maintaining a temperature wellbelow that of surrounding atmosphere.

In other words refrigeration is the processof cooling substance.


3/57


Refrigerators and heat pumps

If the main purpose of the machine is tocool some object, the machine is named asrefrigerator.

If the main purpose of machine is to heata medium warmer than the surroundings,the machine is termed as heat pump.


4/57


Refrigerator and Heat pump

HeatPump

Warm Space

Cold Space

Refrigerator

Work Input

QR

Work Input

QR


5/57


Terminologies of Refrigeration

Refrigerating Effect (N):It is defined as the

quantity of heat extracted from a cold body orspace to be cooled in a given time.

N= Heat extracted from the cold space

Time taken

Specific Heat of water and ice : It is the quantity ofheat required to raise or lower the temperature ofone kg of water (or ice), through one kelvin or (10

c) in one second.Specific heat of water, Cpw = 4.19 kJ/kg K

Specific heat of ice, Cpice = 2.1 kJ/kg K.


6/57



Capacity of a Refrigeration Unit :

Capacity of a refrigerating machines are expressed by theircooling capacity.

The standard unit used for expressing the capacity ofrefrigerating machine is ton of refrigeration.

One ton of refrigerationis defined as, the quantity of heatabstracted (refrigerating effect) to freeze one ton of waterinto one ton of ice in a duration of 24 hours at 0oc.

Heat extracted from at oo c = latent heat of ice

Latent heat of ice = 336 kJ/kgi.e., 336 kJ of heat should be extracted one kg of water at 0o C

to convert it into ice.


7/57For Support notes, please visit: www.arpradeep.tk


One ton of refrigeration = 336x1000 kJ/24 hrs.

= 336x1000 kJ/min

24x60

One ton of refrigeration = 233.333 kJ/min

= 3.8889 kJ/sec




Co efficient of Performance: It is defined as the ratio

of heat extracted in a given time (refrigeratingeffect) to the work input.

Co efficient of performance = Heat extracted in evaporator

Work Input

Co efficient of performance = Refrigerating EffectWork Input

Co efficient of performance = N

W

The COP is always greater than 1 and known as theoreticalcoefficient of performance.


9/57

Refrigerants

Refrigerant: Any substance that absorbs heatthrough expansion and vaporisation process andloses heat condensation is a refrigeration processis called refrigerant.

Some examples of refrigerants are, Air

Ammonia (NH3)

Carbon dioxide (CO2)

Sulphur dioxide (SO2) Freon12

Methyl Chloride

Methylene chloride.


10/57

Classification of Refrigerants

Refrigerants are classified as,

(a) Primary Refrigerants:It is a working mediumwhich is used for cooling the substance byabsorption of latent heat.

E.G Ammonia (NH3), Carbon dioxide (CO2), Sulphur

dioxide (SO2), Freon 12, etc.,

(b) Secondary Refrigerants: Secondary refrigerant is asubstance already cooled by primary refrigerantand then employed for cooling purposes.

E.g Ice, solid carbon dioxide.

These refrigerants cool the substance by absorption oftheir sensible heat.



Types of Refrigerators

Ice Refrigerators :Ice is kept in the cabinetof refrigerators and this acts as therefrigerating means.

Air Refrigerators :Air is used as workingagent in these types of refrigerators.

E.g., Bell Coleman Cycle.

Vapour Refrigerators: The working agentsemployed in this type of refrigerators areammonia, CO2, SO2, freons etc.,



Applications of Refrigeration

In chemical industries, for separating and liquefyingthe gases.

In manufacturing and storing ice.

For the preservation of perishable food items in coldstorages.

For cooling water. For controlling humidity of air manufacture and heat

treatment of steels.

For chilling the oil to remove wax in oil refineries.

For the preservation of tablets and medicines inpharmaceutical industries.

For the preservation of blood tissues etc.,

For comfort air conditioning the hospitals, theatres,

etc.,



Properties of Refrigeration

A good refrigerant should have high latent heat ofvapourisation.

It should have low boiling and low freezing point.

It should be non toxic and should non corrosiveness

It should be non flammable and non explosive.

It should have high thermal conductivity

It should be easy to handle

It should have low specific volume of vapour. It should have high co efficient of performance


14/57


Vapour Compression Refrigeration System


15/57


Vapour Compression Refrigeration System -Construction

This system consists of a compressor,condenser, a receiver tank, an expansion valveand an evaporator.

Compressor :Reciprocatingcompressors generally used.

For very big plants centrifugal

compressors directly coupledwith high speed rotating

engines (gas turbine) are used.


16/57



Compressor:For very big plants

Centrifugal compressorsdirectly coupled with high

speed rotating engines

(gas turbine) are used

f


17/57



Condenser :It is a coil of tubes made ofcopper.

Receiver tank:It is the reservoir of liquidrefrigerant.

Expansion Valve:This is a throttle valve.High pressure refrigerant is made to flow ata controlled rate through this valve.

Evaporator :It is the actual cooler and keptin the space to be cooled. The evaporator isa coil of tubes made of copper

f


18/57


Vapour Compression Refrigeration System -Working

Working :1. The low pressure refrigerant vapour coming out of the

evaporator flows into the compressor.

2. The compressor is driven by a prime mover.

3. In the compressor the refrigerant vapour is compressed.4. The high pressure refrigerant vapour from the

compressor is then passed through the condenser.

5. The refrigerant gives out the heat it had taken in the

evaporator (N)

i f i i


19/57


Vapour Compression Refrigeration System- Working

Working :

6. The heat equivalent of work done on it (w) on thecompressor.

7. This heat is carried by condenser medium which may beair or water.

8. The high pressure liquid refrigerant then enters theexpansion valve.

9. This valve allows the high pressure liquid refrigerant toflow at a controlled rate into the evaporator.

10. While passing though this valve the liquid partiallyevaporates.

V C i R f i i S


20/57


Vapour Compression Refrigeration System- Working

Working :

11.Most of the refrigerant is vapourised only in theevaporator, at a low pressure.

12. In the evaporator the liquid refrigerant absorbsits latent heat of vapourisation from the material

which is to be cooled.

13. Thus the refrigerating effect (N) is obtained.

14. Then the low pressure refrigerant enters the

compressor and the cycle is repeated.


21/57


Vapour Absorption Refrigeration system

In this system compression process of vapourcompression cycle is eliminated. Instead of thatthe following three processes are carried out.

1.Absorbing ammonia vapour into water.

2. Pumping this solution to a high pressure cycle

3. Producing ammonia vapours from ammonia solution

by heating.


22/57


Vapour Absorption Refrigeration system


23/57


Vapour Absorption Refrigeration system -Construction

Construction:

The vapour absorption system consists of acondenser, an expansion valve and an

evaporator. They perform the same as they do in vapour

compression method.

In addition to these, this system has an absorber,a heat exchanger, an analyser and a rectifier.


24/57


Vapour Absorption Refrigeration system Working

Working:

1. Dry ammonia vapour at low pressure passes in to theabsorber from the evaporator.

2. In the absorber the dry ammonia vapour is dissolved in

cold water and strong solution of ammonia is formed.

3. Heat evolved during the absorption of ammonia isremoved by circulating cold water through the coils keptin the absorber.

4. The highly concentrated ammonia (known as AquaAmmonia) is then pumped by a pump to generatorthrough a heat exchanger.


25/57



Working:

6. In the heat exchanger the strong ammoniasolution is heated by the hot weak solution

returning from the generator to the absorber.7. In the generator the warm solution is further

heated by steam coils, gas or electricity and theammonia vapour is driven out of solution.

8. The boiling point of ammonia is less than that ofwater.

9. Hence the vapours leaving the generator are

mainly of ammonia.


26/57



Working:

9. The weak ammonia solution is left in thegenerator is called weak aqua.

10. This weak solution is returned to the absorber

through the heat exchanger.11. Ammonia vapours leaving the generator may

contain some water vapour.

12. If this water vapour is allowed to the condenserand expansion valve, it may freeze resulting inchocked flow.

13. Analyser and rectifiers are incorporated in the

system before condenser.


27/57



Working:14. The ammonia vapour from the generator passes

through a series of trays in the analyser and ammonia isseparated from water vapour.

15. The separated water vapour returned to generator.16. Then the ammonia vapour passes through a rectifier.

17. The rectifier resembles a condenser and water vapourstill present in ammonia vapour condenses and the

condensate is returned to analyser.

18. The virtually pure ammonia vapour then passesthrough the condenser.


28/57



Working:

19. The latent heat of ammonia vapour is rejected tothe cooling water circulated through thecondenser and the ammonia vapour is condensed

to liquid ammonia.20. The high pressure liquid ammonia is throttled

by an expansion valve or throttle valve.

21. This reduces the high temperature of the liquidammonia to a low value and liquid ammoniapartly evaporates.

22. Then this is led to the evaporator.

23. In the evaporator the liquid fully vaporizes.


29/57



Working:

24. The latent heat of evaporation is obtained fromthe brine or other body which is being cooled.

25. The low pressure ammonia vapour leaving the

evaporator again enters the absorber and thecycle is completed.

26. This cycle is repeated again to provide the

refrigerating effect.


30/57

Applications of refrigeration system

Preservation of food items like vegetables,milk and eggs.

Preservation of medicines.

Preservation of blood, tissues, etc., Preservation and cooling of cool drinks.

Preservation of chemicals (Chemicalindustries)

Cooling of water. Industrial and comfort airconditioning.

Processing of dairy products.

C i b t V i & V Ab ti


31/57


Comparison between Vapour compression & Vapour Absorptionrefrigeration systems

S.No. Vapour Compression System Vapour Absorption System

1 This system has more wear andtear and produces more noisedue to the moving parts of thecompressor.

Only moving part in this system isan aqua pump. Hence the quieterin operation and less wear andtear

2. Electric power is needed to

drive the system

Waste of exhaust steam may be

used. No need of electric power3. Capacity of the system drops

rapidly with loweredevaporator pressure

Capacity of the system decreaseswith the lowered evaporativepressure, by increasing the steampressure in generator.

4. At partial loads performance ispoor.

At partial loads performance is notaffected.

5. Mechanical energy is suppliedthrough compressor

Heat energy is utilised

6. Energy supplied is to ofthe refrigerating effect Energy supplied is about one andhalf times the refrigerating effect


32/57


Comparison between Vapour compression &Vapour Absorption refrigeration systems

S.No. Vapour Compression System Vapour Absorption System

7. Charging of the refrigerating to

the system is easy

Charging of refrigerant is difficult

8. Preventive measure is needed,since liquid refrigerantaccumulated in the cylindermay damage to the cylinder

Liquid refrigerant has no badeffect on the system.


33/57


Layout of Domestic Refrigerator


34/57


AIR CONDITIONING

AIR CONDITIONING:

Air Conditioning is the processof conditioning the air according to thehuman comfort, irrespective of externalconditions.


35/57


AIR CONDITIONING

Applications of Air Conditioning

Used in offices, hotels, buses, cars.,etc

Used in industries having tool roommachines.

Used in textile industries to controlmoisture.

Used in printing press.

Used in Food industries, Chemical plants.


36/57


CLASSIFICATION OF AIR CONDITIONING

Air conditioning systems are classified as

1) According to the purpose

a) Comfort Air conditioning.b) Industrial Air conditioning.

2) According to Season of the year

a) Summer Air conditioning.b) Winter Air conditioning.

c) Year round Air conditioning.


37/57


AIR CONDITIONING

Types of Air conditioners

a) Room Air conditioners

b) Winter Air conditioners

c) Central Air conditioners

Functions of Air conditioners

a) Cleaning air.

b) Controlling the temp of air.c) Controlling the moisture content.

d) Circulating the air.


38/57


BASIC CONCEPTS

1) Dry air: The atmospheric air which nowater vapour is called dry air.

2) Psychrometry: Psychrometry is the studyof the properties of atmospheric air.

3) Temperature: The degree of hotness(or) Coldness is called the temperature.

4) Moisture: Moisture is the water vapourpresent in the air.


39/57


BASIC CONCEPTS

5) Relative humidity: Relative humidity isthe ratio of actual mass of water vapour ina given volume to the mass of watervapour.

6) Dry bulb temperature: The temperatureof air measured by the ordinary

thermometer is called dry bulbtemperature:


40/57


BASIC CONCEPTS

9) Wet bulb Temperature:The temperature ofair measured by the thermometer when it iscovered by the wet cloth is known as wet bulb

Temperature.

10) Dew point Temperature: The temperature atwhich the water vapour starts condensing is

called dew point Temperature:

Wi d T Ai C diti


41/57


Window Type Air Conditioner

Wi d T Ai C diti


42/57


Window Type Air Conditioner

Wi d T Ai C diti W ki


43/57


Window Type Air Conditioner - Working

The low pressure vapour refigerant from the

evaporator is sucked by compressor throughthe open inlet valve.

The compressor compresses the vapourrefrigerant.

The high pressure and high temperaturevapour refrigerant then flows to thecondenser through the open outlet valve.

In the condenser, the outside atmospherictemperature in summer being around 42o C,air is circulated by fan.

After condensation, the high pressure liquidrefrigerant formed passes through anexpansion valve which reduces its pressure

Wi d T Ai C diti W ki


44/57


Window Type Air Conditioner - Working

The low pressure refrigerant then enters

the evaporator and evaporates, thusabsorbing latent heat of vapourisationfrom the room air.

The equipment which is used for

evaporating the refrigerant is calledevaporator.

After evaporation, the refrigerant becomesvapour.

The low pressure vapour is again passedto the compressor. Thus the cycle isrepeated.

A partition separates high temperature

side of condenser, compressor and lowtem erature side of eva orator

Wi d T Ai C diti


45/57


Window Type Air Conditioner -

Working

The quantity of air circulated can becontrolled by the dampers.

10. The moisture in the air passing overthe evaporator coil is dehumidified and

drips into the trays. The unit automatically stops when the

required temperature is reached in theroom. This is accomplished by the

thermostat and control panel. Generally, the refrigerant monochloro

diluloro mehane (CHCLF2) is used in airconditioner. It is called Freon 22.

Merits and Demerits of Window type air


46/57

Merits and Demerits of Window type airconditioner

Merits :

A separate temperature control is provided in eachroom.

Ducts are not required for distribution.

Cost is less.

Skilled technician is required for installation.

Demerits:

It makes noise.

Large hole is made in the external wall or a largeopening to be created in the window panel. This leadsto insecurity to inmates.

Air quantity cannot be varied.

Split Type Air Conditioner


47/57


Split Type Air Conditioner -Construction

Split Type Air Conditioner Layout


48/57


Split Type Air Conditioner - Layout


49/57

Split Type Air Conditioner - Layout

In split air type air conditioner noise makingcomponents like compressor and condenserare mounted outside or away from room.

Split type air conditioning system has two

main components.(i) Outdoor Unit (ii) Indoor unit.

The outdoor unit consists of compressor and

condenser. The indoor unit consists of power cables,

refrigerant tube and an evaporator mountedinside the room.

Split Type Air Conditioner - Working


50/57

Split Type Air Conditioner Working

Compressor is used to compress the refrigerant.

The refrigerant moves between the evaporator andcondenser through the circuit of tubing and fins in thecoils.

The evaporator and condenser are usually made ofcoil of copper tubes and surrounded by aluminium

fins. The liquid refrigerant coming from the condenser

evaporates in the indoor evaporator coil.

During this process the heat is removed from the

indoor unit air and thus, the room is cooled. Air return grid takes in the indoor air.

Water is dehumidified out of air is drained throughthe drain pipe.

Split Type Air Conditioner Working


51/57

Split Type Air Conditioner - Working

The hot refrigerant

vapour is passed to thecompressor and then tothe condenser where itbecomes liquid.

Thus the cycle isrepeated.

A thermostat is used to

keep the room at aconstant, comfortabletemperature avoiding thefrequent turning on off.

Merits and Demerits of Split type air


52/57

Me ts a d e e ts o Sp t type aconditioner

Merits :

It is compact

Upto four indoor AHUs may be connected toone outdoor unit.

It is energy and money saving. Duct is not used.

Easier to install.

It is noiseless, because rotary air compressor

used is, kept outside. It is more efficient and powerful.

It has the flexibility for zoning.

Merits and Demerits of Split type air


53/57

p ypconditioner

DeMerits :

Initial cost is higher than window airconditioner

Skilled technician is required for installation.

Each zone or room requires thermostat tocontrol the air cooling.

Applications of air conditioning


54/57

pp g

Used in houses, hospitals, offices, computer

centres, theatres, departmental stores etc.,

Air-conditioning of transport media such asbuses, cars trains, aeroplanes and ships.

Wide application in food processing, printing,chemical, pharmaceutical and machine tool,etc.,


55/57


References

www.phac-aspc.gc.ca/.../section3-eng.php

Shanmugam G and Palanichamy M S, Basic Civil and

Mechanical Engineering,Tata McGraw Hill Publishing

Co., New Delhi, (1996). Ramamrutham. S, Basic Civil Engineering, Dhanpat Rai

Publishing Co. (P) Ltd. (1999).

Seetharaman S. Basic Civil Engineering, Anuradha

Agencies, (2005). Venugopal K and Prahu Raja V, Basic Mechanical

Engineering, Anuradha Publishers, Kumbakonam,

(2000).

f
http://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.php


56/57


References

www.phac-aspc.gc.ca/.../section3-eng.php Shanmugam G and Palanichamy M S, Basic Civil and

Mechanical Engineering,Tata McGraw Hill PublishingCo., New Delhi, (1996).

Ramamrutham. S, Basic Civil Engineering, DhanpatRai Publishing Co. (P) Ltd. (1999).

Seetharaman S. Basic Civil Engineering, AnuradhaAgencies, (2005).

Venugopal K and Prabu Raja V, Basic MechanicalEngineering, Anuradha Publishers, Kumbakonam,(2000).
http://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.phphttp://www.phac-aspc.gc.ca/.../section3-eng.php


57/57

3-unit - v - refrigeration & air conditioning

Documents