The document discusses refrigeration and air conditioning. It defines refrigeration as the process of transferring heat from a low temperature region to a high temperature region to cool a substance. The principle of refrigeration is based on the second law of thermodynamics, which states that heat does not flow from a low to high temperature body without external work. It then describes the vapor compression refrigeration system, which uses a compressor, condenser, expansion valve and evaporator. Current refrigeration methods discussed are vapor compression and vapor absorption. Vapor absorption uses a heat source rather than electricity. Air conditioning alters properties like temperature and humidity of air for comfort or industrial processes, regardless of external conditions. Different types of air conditioning systems are also outlined
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Refrigeration and air conditioning
1. FROM : E L E C T R I C A L D E PA R T M E N T
S U BJECT : E L E M E N T S O F M E C H A N I C A L
E N G I N E E R I N G
Mahatma Gandhi Institute Of Technical
Education And Research Center
3. REFRIGERATION
• It can be defined as the process of
transferring heat from a low temperature
region to a high temperature region.
• In other words it is the process of cooling a
substance.
• This can be achieved only if the heat is
removed from that substance.
4. PRINCIPLE OF REFRIGERATION
The principle of refrigeration is based on
second law of thermodynamics. It states that
heat does not flow from a low temperature
body to a high temperature body without the
help of an external work.
5. PRINCIPLE
Since the heat has to be
transferred from a low
temperature body to a high
temperature body some
external work has to be done
according to the second law of
thermodynamics. This external
work is done by means of
compressor, condenser etc.
This external work is done by
means of
compressor, condenser etc.
6. TERMS IN REFRIGERATION
1. Refrigerator:
It is a machine used to extract heat from a body at low
temperature and reject this heat to a body at high
temperature. Thus it cools the body.
2. Refrigerant:
It is substance, which is used as a working fluid in
refrigerators. The refrigerant has low boiling point, which
means that it vaporizes at low temperature and takes away
the heat from a substance.
7. 3. Capacity of Refrigerator:
It is defined as the rate at which heat can be removed from
the cold body.
4. Refrigeration Effect:
It is defined as the ratio of the quantity of heat removed to
the time taken.
Refrigeration Effect = Heat removed / Time taken
5. Coefficient of Performance (COP):
It is defined as the ratio of heat absorbed in a given time
(Refrigeration Effect) to the work done
COP = Refrigeration Effect / Work done
9. 9
The Vapor-Compression Refrigeration Cycle
The vapor-compression refrigeration cycle has four components:
evaporator, compressor, condenser, and expansion (or throttle) valve.
The most widely used refrigeration cycle is the vapor-compression
refrigeration cycle. In an ideal vapor-compression refrigeration cycle,
the refrigerant enters the compressor as a saturated vapor and is
cooled to the saturated liquid state in the condenser. It is then throttled
to the evaporator pressure and vaporizes as it absorbs heat from the
refrigerated space.
The ideal vapor-compression cycle consists of four processes.
Ideal Vapor-Compression Refrigeration Cycle
Process Description
1-2 Isentropic compression
2-3 Constant pressure heat rejection in the condenser
3-4 Throttling in an expansion valve
4-1 Constant pressure heat addition in the evaporator
10. 10
The P-h diagram is another convenient diagram often used to illustrate the
refrigeration cycle.
11. WORKING PRINCIPLE
• During evaporation, the refrigerant absorbs its latent
heat of vaporization from the material that is to be
cooled. Thus the body is cooled in the evaporator .
Then the low pressure vapor refrigerant enters the
compressor and the cycle is repeated. Thus a material
is cooled in vapor compression system
14. • A vapour absorption system uses heat sources like steam,
exhaust gas, hot water etc to produce cooling. This can be
used for space cooling as well as process cooling in various
industries like food processing, beverages, chemical
processing, pharmacies, textile, breweries, semiconductor
etc.
• A compression chiller uses electricity as a power source.
• Compression cycle
Evaporator->Compressor->Condenser->Expansion Valve-
>Evaporator->...
• Absorption Cycle
Evaporator->Absorber->Pump->Generator->Condenser-
>Evaporator->...
15. In an absorption system, the evaporator is where the
refrigerant gets evaporated due to lower pressure at a
lower temperature by using the heat from the chilled
water and thus cooling the chilled water. The refrigerant
vapours are then absorbed by the working fluid (because
of its affinity towards refrigerant vapours) in the absorber.
The dilute solution is pumped to the generator where by
a heat source like steam,exhaust gas,hot water etc the
refrigerant gets boiled out (separated) from the dilute
solution. This refrigerant condenses in the condenser
(using cooling water from the cooling tower) and the
condensed refrigerant falls into the evaporator and the
cycle continues. The solution which was dilute now
becomes strong (as the refrigerant has been boiled out)
and falls into the absorber and absorbs the refrigerant
WORKING
16. If there is waste heat available (like exhaust gas, excess
steam, oil vapours, hot water from process) the cooling
produced becomes extremely economical which is a
major advantage of the vapour absorption system.
Some other advantages are low power consumption
(hence less electricty costs), less maintenance costs (as
fewer number of moving parts compared to a
compression system and good performance at part
load.
On the other hand vapour absorption systems have
higher initial costs (though lower running costs) and
require a larger cooling tower.
17. AIR CONDITIONING
• Air conditioning is the process of altering the
properties
of air (primarily temperature and humidity) to
more favorable conditions.
• The control of these conditions may be desirable to
maintain the health and comfort of the occupants, or
to meet the requirements of industrial processes
irrespective of the external climatic conditions
19. TYPE OF AIR-CONDITIONING
1) Window air-conditioning system
To install one of these units, you need the space to
make a slot in the wall, and there should also be
some open space behind the wall.
when the summer heat dies down, these units can
easily removed for storage, and you can use the
window sill for other purpose
20.
21. 2) Split Air-Conditioning System :
• The split air conditioner comprises of two parts: the
outdoor unit and the indoor unit.
• The outdoor unit, fitted outside the room, houses
components like the compressor, condenser and
expansion valve.
• The indoor unit comprises the evaporator or cooling
coil and the cooling fan.
22.
23. 3) Centralized Air-Conditioning System :
The central air conditioning plants or the systems are
used when large buildings, hotels, theaters, airports,
shopping malls etc. are to be air conditioned
completely.
24.
25. 4) Packaged Air-Conditioning System :
The packaged air conditioners are used for the
cooling capacities in between split air conditioners
and centralised air conditioners.
