CHAPTER : Refrigeration and Air Conditioning 1 Subject : Basic Mechanical Engineering ... · 2020. 4. 6. · BASIC MECHANICAL ENGINEERING (3110006) Working • Low pressure and low

1CHAPTER : Refrigeration and Air Conditioning

BASIC MECHANICAL ENGINEERING (3110006)

Subject : Basic Mechanical EngineeringChapter : Refrigeration and Air Conditioning

Prepared by, MEHUL CHHOWALA



Content• Refrigeration, Refrigeration effect

• Refrigerant, Commonly used refrigerant & it’s Properties

• Performance Assessment Parameter

• Co-efficient of Performance

• Ton of Refrigeration

• Specific Power Consumption

• Energy Efficient Ratio

• Classification of Refrigeration Cycle

• Vapor compression refrigeration system

• Vapor absorption refrigeration system

• Domestic Refrigerator

• Air conditioning & its Application

• Components of Air Conditioning System

• Classification of Air Conditioning System

• Window Air Conditioner

• Split Air Conditioner



Refrigerator and Heat Pump



What is

Refrigeration?

Refrigeration is process in which the transfer of heat from a low temperature level

to a high temperature level by using a refrigerant.

It is also defined as the process of removing heat from a substance (i.e. process of

cooling a substance).

OR

What is

Refrigeration

Effect?

It is define as the amount of heat absorbed by refrigerant from the space to be

cooled. The capacity of refrigeration system is expressed in tons of refrigeration

which is unit of refrigeration.



What is

Refrigerants ?

Refrigerant is a compound typically found in either a fluid or gaseous state. It readily

absorbs heat from the environment and can provide refrigeration or air conditioning.

The refrigerant is a heat carrying medium which absorbs heat from space (desired to

cool) and rejects heat to outside the refrigerator (in atmosphere).

OR



Properties of a Ideal Refrigerant

The high specific heat of vaporization

The critical temperature and the triple point are far beyond the operating range

Chemically stable, compatible with construction materials and mixtures containing lubricants

Non-corrosive, non-toxic and non-flammable

High dielectric strength

Environmentally friendly

Low cost



• Properties : Highly toxic, flammable, good thermal properties, highestrefrigerating effect per kg of refrigerant.

• Uses : It is widely used in large industrial and commercial refrigerationsystem. It is mostly used with Vapour absorption refrigeration cycle likeice plants, cold storage, packing plants etc.

NH3 (Ammonia)

• Properties : Colorless, non-toxic, non-flammable and non-corrosivegas. It gives low refrigeration effect.

• Uses : It is used in marine refrigeration system.CO2 (Carbon dioxide)

• Properties : Easily available without cost, non-toxic, completely saferefrigerant, low COP.

• Uses : It is used in aircraft air-conditioning system.Air

Common used Refrigerants and Properties



• Properties : Non-toxic, Non-flammable and Non-corrosive.

• Uses : It is used in Small office buildings and factories for refrigeration.

R-11 (Trichloro monofluoromethane) OR Freon-11

• Properties : Non -toxic, Non-flammable, Non-explosive, high COP andmost suitable refrigerant..

• Uses : It is used in domestic vapour compression refrigeration.

R-12 (Dichlaro - difluromethane) OR Freon -12

• Properties : Non-toxic, Non-flammable, Non-explosive Required lesscompressor displacement.

• Uses : It is used in commercial and industrial low temperatureapplications (in air conditioning).

R-22 (Monochloro - difluromethane) OR Freon -22

Common used Refrigerants and Properties



Coefficient of Performance

It is the ratio of cooling capacity in kW to the total power

input in kW, at any given set of rating conditions.

The Theoretical Coefficient of Performance(Carnot)

• COPcarnot - a standard measure of refrigeration efficiency of an ideal

refrigeration system- depends on two key system temperatures, namely,

evaporator temperature (Te) and condenser temperature (Tc).

COP(carnot) = Te / (Tc - Te)

• This expression also indicates that higher COPcarnot is achieved with higher

evaporator temperature and lower condenser temperature.

Performance

Assessment

Parameter



Tons of Refrigeration (TR)

It is defined as the rate of heat transfer that results in the

freezing of 1 short ton of pure ice at 0 °C in 24 hours.

1 TR of refrigeration = 3024 kCal/hr heat rejected

= 12,000 BTU/h

= 3.5 kW

The refrigeration TR is assessed as TR = Q x Cp x (Ti – To) / 3024

Where Q is mass flow rate of coolant in kg/hr

Cp is coolant specific heat in kCal /kg deg C

Ti is inlet, temperature of coolant to evaporator (chiller) in °C

To is outlet temperature of coolant from evaporator (chiller) in °C.

Note: The above TR is also called as chiller tonnage.

Performance

Assessment

Parameter



Specific power consumption(kW/TR)

It is defined as the ratio of energy consumption in kW to the

rate of heat removal in tons at the rated condition.

In a centralized chilled water system, apart from the compressor unit,

power is also consumed by the chilled water (secondary) coolant pump as

well condenser water (for heat rejection to cooling tower) pump and

cooling tower fan in the cooling tower.

• Compressor kW/TR

• Chilled water pump kW/TR

• Condenser water pump kW/TR

• Cooling tower fan kW/TR

The overall kW/TR is the sum of the above.

Performance

Assessment

Parameter



Energy Efficiency Ratio (EER)

It is defined as the ratio of net cooling capacity of a refrigeration

compressor, a packaged unit, or other device, in BTU/h, to the

electric power input to that device, in W, under designated

operating conditions.

Performance

Assessment

Parameter



Refrigerators

(A machine produce cooling effect)

Natural refrigerator

(The cooling effect produced by evaporation of liquid or sublimation of solids)

Mechanical refrigerator

(The cooling effect produced by external source of mechanical

energy or heat energy)

Vapour compression refrigerator

Vapour absorption refrigerator

Air refrigerator



Refrigeration System

Vapour Compression Refrigeration System(VCR)

VCR uses mechanical energy as the driving force for refrigeration

Vapour Absorption Refrigeration System (VAR)

VAR uses thermal energy as the driving force for refrigeration



Vapour Compression Refrigeration (VCR)

1-2 CompressorIsentropic compression

s = constantWṫ n = Ṅ (ℎ2 −̇ℎ1)

2-4 Condenser Isobaric condensation Qḣ = Ṅ (ℎ3 −̇ℎ2)

4-5 Expansion valve Isenthalpic expansion ℎ4 = ℎ3

5-1 Evaporator Isobaric evaporation Qṙ = Ṅ (ℎ1 −̇ℎ4)



Compressor

• The type of compressor may be either reciprocating, rotary, or centrifugal.

• Its function is to receive refrigerant at a particular temperature and pressure and todeliver it after compression at higher temperature and pressure.

• The temperature of the refrigerant delivered will be higher than the temperature of the cooling fluids used; so that heat will flow from the refrigerant to the cooling fluid which is at higher temperature than that of refrigerating space.

Condenser

• The high pressure and high temperature compressed vapour is discharged into the condenser where heat is transferred to the cooling fluid which is normally water or air.

• The vapour cools and then condenses, at saturation temperature which corresponds to the pressure in the condenser.

• The vapour after condensing, the high pressure liquid then enters the throttle valve or expansion valve.



Expansion valve

• This is a throttle valve in which throttling process is carried out.

• It is a valve with narrow passage through which high pressure liquid passes andexpands from high pressure to a low pressure at constant enthalpy.

• The liquid after expansion becomes low temperature wet vapour and is transferred to the receiver from where it passes to the evaporator through a control valve.

Evaporator

• In the evaporator, liquid vapour absorbs heat from the space to be cooled for itsvaporization.

• The evaporator is in the form of a coil or bare pipe or tubes, as the case may be,through which liquid vapour flows.

• The evaporated vapour is sucked by the compressor from the evaporator anddelivered to the condenser. Thus, the cycle is completed.



Process 1-2: Inlet of compressor (at point 1), low pressure and low temperature vapour enters the compressor.Compressor compresses the vapour at high temperature and pressure.

The condition of refrigerant at exit to compressor (at point 2) is high pressure and high temperature vapour.

Process 2-3: High pressure, high temperature vapour coming from compressor condenses in the condenser by the rejectingheat to cooling medium.

Cooling medium is usually air or water.

The condition of refrigerant at exit to condenser (at point 3) is low temperature saturated liquid.

Process 3-4: The saturated liquid coming from condenser passes through expansion device (throttling valve) wherepressure of saturated liquid decreases from condenser pressure to evaporator pressure.

The condition of refrigerant after throttling is low temperature and low pressure liquid.

Process 4-1: Liquid refrigerant coming from expansion device enters into evaporator where it absorbs latent heat ofevaporation from space to be cooled (refrigerator compartment).

Due to absorption of heat liquid refrigerant converted into saturated vapor or superheated vapour at lowpressure and low temperature.

Again this vapour enters into compressor and the cycle is repeated.



Domestic vapour compression Refrigerator



Domestic vapour compression Refrigerator

Construction

• It consists of an evaporator installed in the freezing compartment of the

refrigerator.

• One end of evaporator connected to the suction side of the compressor and

other end connected to condenser through throttle valve.

• Normally condenser installed at the backside of refrigerator.

• The delivery side of compressor is connected to a condenser.

• Available in capacities of 65 liters, 100 liters, 165 liters, 275Iitres,360

liters,500 liters, 1000 liters etc with star rating.



Vapour Absorption Refrigeration System (VAR)



Construction

• This system is shown in figure consists of (i) evaporator, (ii) condenser, (iii) generator,

(iv) absorber, (v) pump and (vi) expansion device.

• In this system the refrigerant coming from evaporator is absorbed by absorber.

• The absorbing medium may be solid or liquid.

• In VAR system, the compressor is replaced by an absorber and generator.

• Ammonia is refrigerant has characteristic as it is easily absorbed by water at low

pressure and temperature, but at high pressure and temperature, the solubility of

ammonia in water is reduced.

• Therefore when mixture of water and ammonia is heated by generator, the ammonia

vapour is separated from water.

• This principle is used in the vapour absorption refrigeration system. Here the ammonia is

refrigerant and water is absorbent.



Working

• Low pressure and low temperature vapour ammonia coming from evaporator enters in

the absorber where ammonia is absorbed by weak solution coming from generator

through throttle valve.

• Due to absorption of NH3 in water, solution becomes strong. [In the mixture of NH3 and

water, if amount of NH3 is less than water is called weak solution and if amount of NH3

is more than the water is called strong solution.]

• During absorption process heat is released and rejected to cooling water.

• The strong solution from absorber is pumped into generator, where it is heated and NH3

vapour separated from solution.

• In generator is supplied from external source. The weak solution at point 4 is flowing

back to absorber through throttle valve.

• Again weak solution in absorber absorbs NH3 vapour coming from evaporator.

• NH3 vapour coming from generator passes through condenser and condensed in

condenser and reject heat to cooling medium. Then liquid NH3 throttled through

expansion device and it enters



Air Conditioning

Basic processes of Air Conditioning

system

Sensible cooling/heating

Humidifying

Dehumidifying

Air cleaning

Air change

Air movement

Applications of

Air Conditioning

For Human comfort

Industrial Air Conditioning



Components of Air Conditioning System

Fans For circulation of air

Filters For cleaning air

Heating elementHeating of air (It may be electric

heater, steam, hot water)

Control systemIt regulates automatically the amount of cooling or heating.

GrilleIt adjusts the direction of

conditioned air to the room.

Tray It collects condensed water



Classification of Air Conditioning System

Air conditioning system

According to arrangement of

equipment

Unitary system

Window Air Conditioner

Split Air Conditioner

Central system

According to the purpose

Comfort air conditioning system

Industrial air conditioning system

According to season of year

Winter air conditioning system

Summer air conditioning system



Window Air Conditioner



Working• The hot air coming from room is flowing on the evaporator (cooling coil), the cooling coil absorbs

heat from air.

• The moisture of air gets removed on the cooling coil surface by process of condensation of air.

Thus the air is cooled and dehumidified to meet the requirement comfort air conditioning in the

room.

• The filter clean the air coming from room before passes through the cooling coil. The tray is

provided below the cooling coil (evaporator) to collect moisture which condenses from

recirculation of air.

• The flow of hot air (from room) and cooled air (to room) is taking place by the evaporator blower.

The refrigerating unit provides cooling effect at evaporator. The condenser fan circulates air on

outside of condenser tubes, the refrigerant in condenser reject heat to outside atmospheric air.

• Necessary fresh air is allowed to mix with the recalculated room air to meet the ventilation

requirement.

• Ventilation air is controlled by ventilation damper. The room -temperature is controlled by a

thermostat using on-off power supply to compressor motor.

Limitations :

• It produce noise in the room because of compressor is very near to the room.

• It requires appropriate size of window or hole in wall to fit the conditioner.



Split Air Conditioner



ConstructionThis unit differs from window air conditioner. In terms of splits of unit into two parts. In split air

conditioner, the window air conditioner divided (split) into two parts.

• First part: Includes the evaporator, filter, evaporator fan and grille (cooling coil). They placed inside

the room.

• Second part: Includes condenser, condenser fan, and compressor. This placed outside the room.

• First part (inside of room) and second part (outside of room) is connected by small diameter tubes.

Therefore, small hole required in wall for installation of split air conditioner.

Advantages• The compressor is outside of room, therefore no compressor noise in the room.

• No window opening and fixing needed..



Thank You...

Documents

CHAPTER : Refrigeration and Air Conditioning 1 Subject : Basic Mechanical Engineering ... · 2020. 4. 6. · BASIC MECHANICAL ENGINEERING (3110006) Working • Low pressure and low