COVERS VTU EME SYLLABUS

1. ELEMENTS OF MECHANICAL ENGINEERING
(18ME25)
Refrigeration and Air conditioning
Module-3
Prof. Rajashekar Matpathi
Email : bkit.rcm@gmail.com
DEPARTMENT OF MECHANICAL ENGINEERING
BHEEMANNA KHANDRE INSTITUTE OF TECHNOLOGY,BHALKI

2. OUTLINE
 Defn: Refrigeration, Air-conditioning Refrigeration effect,
Ton of refrigeration, Ice making capacity,
Coefficient Of Performance(COP), Relative COP
 Desirable properties of a Good Refrigerant
 Refrigerants List- Properties and Applications
 Parts of Refrigerator and its Functions
 Differentiate between VCR & VAR
 Differentiate b/w Refrigeration & Air Conditioning

3. DEFINITIONS
REFRIGERATION: It is a method of reducing the temperature of system below that of the
surroundings and maintain it at the lower temperature by continuously abstracting the heat from it
AIR CONDITIONING: Providing a cool indoor atmosphere at all times regardless of weather
conditions needed either for human comfort or industrial purposes by artificially cooling,
humidifying or dehumidifying ,cleaning and recirculation the surrounding air is called air
conditioning.
CONCEPTS OF REFRIGERATION
• Heat transfer is possible from a high temperature region to a low temperature
region.
• Heat transfer is possible from a lower temperature system to higher temperature
surroundings by some external means as per the 2nd law of thermodynamics.
• The working fluid changes from vapor phase to liquid phase after heat rejection
and from liquid phase to vapor phase after heat absorption.
• The change of phase of the working fluid from liquid phase to vapor phase
results in cooling effect.

4. • Refrigeration effect: The rate at which the heat is absorbed in a cycle from the
interior space to be cooled is called refrigeration effect. It is defined as the quantity of heat
removed to the time taken. It is also called as the capacity of a refrigerator.
• Ton of refrigeration: A ton of refrigeration is defined as the quantity of heat absorbed in
order to form one ton of ice in 24 hours when the initial temperature of water is zero degree
centigrade. 1 Ton of refrigeration = 210 kJ/min = 3.5 kW
• COP[ Co-efficient of Performance] : The Co-efficient of Performance is defined as the
ratio of heat absorbed in a system to the work supplied.
• Relative COP: It is the ratio of actual COP to the theoretical COP of a refrigerator.
Actual COP is measured during a test and theoretical COP is obtained by applying the laws of
thermodynamics.
• Ice making capacity: It is the ability of the refrigeration system to make ice. In other
words, it is the capacity of refrigeration system to remove heat from water to make ice.
• Principle of refrigeration: It states that based on second law of thermodynamics, heat
does not flow from a low temperature body to a high temperature body without the
help of an external work. Hence, in a refrigeration system, external power is to be
supplied to remove heat continuously from the refrigerator to keep it cool at a temperature
less than the surroundings.

5. Desirable properties of a Good Refrigerant
• Boiling point: An ideal refrigerant must have a low boiling point at atmospheric pressure.
• Freezing point: The refrigerant must have a very low freezing point because the refrigerant
should not freeze at low evaporator temperatures.
• Latent heat of evaporation: It should be very high so that a minimum amount of
refrigerant will accomplish the desired result.
• Specific volume: should be very low and it reduces the size of the compressor.
• Specific heat of liquid and vapour: A good refrigerant must have a low specific heat
in liquid state for sub cooling & high specific heat in vapour state for decreasing its
superheat.
• Viscosity: Very low as it improves the heat transfer rate and reduces the pumping pressure.
• Non-toxic: should be non-toxic because any leakage increases the suffocation & poisons
the atm.
• Non-corrosive: to prevent corrosion of the metallic parts
• Chemical stability: should not decompose under operating conditions
• Odourless: otherwise food preserved will loose their taste.
• Leakage tests: Any leakage must be easily detected by simple tests
• Action with lubricating oil: should not react with lubricating oil

6. Refrigerants - Properties and Applications
Sl.No. Name of Refrigerant Properties Applications/uses
1 Ammonia Boiling point :-33.3C, Highly toxic,
Inflammable, Irritating & Corrosive
VAR, cold storage, ice plants,
packaging plants, etc
2 Freon - 12 Boiling point :-29.8C, Non-flammable,
Non-explosive, Non.-corrosive
&Odourless
Domestic refrigerators, Water
coolers, small AC, etc
3 Freon- 22 Boiling point : -40.8C, Non-flammable,
Non-toxic
Large air conditioners, Food,
freezing, Food drying, etc
4 Carbon Dioxide Boiling point : -77.6C, Non-flammable,
Non-toxic, Low specific volume
Marine applications
5 Sulphur dioxide Boiling point :-10C, Suffocating Irritating
odour
Olden Domestic refrigerators

7. PRINCIPLE OF REFRIGERATION
• It is based on 2nd law of thermo dynamics. As per Clausius
Statement, heat cannot flow from a body at lower
temperature to a body at higher temperature unless assisted
by some external means. In refrigeration, heat is
continuously removed from the system at a lower
temperature and same heat is rejected to the surroundings at a
higher temperature. This is done by using an external source
like a compressor (or) a pump.
• Heat from a system at lower temperature is abstracted by
using a working fluid/medium called refrigerant.

8. PARTS OF A REFRIGERATOR
Evaporator: is the heart of the refrigeration system, where the
liquid refrigerant is evaporated by the absorption of the heat
from the refrigerator cabinet in which the substances to be
cooled are kept. It consists of copper tubing surrounding the
freezing and cooling compartments.
Compressor or Pump: For circulating the refrigerant in the
system, a compressor or a pump is used. They increase the
pressure and therefore the temperature of the refrigerant.
Generally, these devices are driven by electric motor.
Condenser: In a condenser, the refrigerant vapour, gives off its
latent heat to the air and consequently condenses into liquid
form so that it can be recirculated in the refrigeration cycle. It
consists of coil of tubes made of copper.
Expansion or Throttle valve: An expansion valve serves as a
device to reduce the pressure and temperature of the liquid
refrigerant before it passes to the evaporator. This also used to
control the flow of refrigerant to the evaporator.

9. • Circulate the refrigerant to undergo the refrigeration cycle
• Increase the pressure and therefore the temperature of the refrigerant
• To compress and circulate the low temperature and low pressure working fluid into high
temperature and high-pressure vapor.
They are power absorbing mechanical devices and need input power. An electrical motor
supplies power to these drives.
1. COMPRESSOR (OR) PUMP:
2. EVAPORATOR
Where the liquid refrigerant is evaporated by the absorption of heat from refrigerator
cabinet
It has cooling coils arranged in form of U – tubes.
The function of the evaporator is to reduce the temperature of the refrigerator cabinet.
The low temperature two phase mixture of refrigerant passing through the evaporator coils
absorbs heat from the cabinet and changes into vapor phase.
This effect of cooling is also known as refrigerating effect

10. 3. CONDENSER
• Heat from the refrigerant is rejected to atmosphere
• Hence it gets cooled
• i.e refrigerant gives off its latent heat and condenses into liquid
Condenser consists of a series of coils in the form of U – tubes.
The high pressure, high temperature refrigerant from the compressor enters condenser
Where the refrigerant rejects its heat to the surrounding atmosphere.
The latent heat of the refrigerant is given to the surrounding atmosphere, which results in change of
phase of the refrigerant.
4. EXPANSION VALVE
Device which reduce the pressure and temperature of the liquid before it passes to the evaporator
The high pressure and temperature liquid refrigerant expands in the expansion valve to low pressure &
low temperature two-phase mixture.
The temperature of the refrigerant drops in the expansion valve due to partial evaporation

11. Comparison between Vapour Compression and Absorption refrigerators
VCR [Vapour Compression Refrigeration] VAR[Vapour Absorption Refrigeration]
1 Refrigerant vapour is compressed Refrigerant vapour is absorbed and heated
2 More Noise due to compressor Less noise due to pump
3 Chances of leakage of refrigerant are more No leakage problem
4 Smaller in size Larger in size
5 Works using mechanical energy Works using heat energy
6 Refrigerating capacity is less than 100 tons Capacity is more than 100 tons
7 Freon - 12 or any other refrigerant Only Ammonia is used as refrigerant
8 Wear and tear are more Less
9 Maintenance and operating cost is more Less
10 COP is much higher ( 4 to 10) COP is less than 2