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Nitin Joshi B Tech Mechanical
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TERM
PAPERREPORT
Refrigeration in
Automobiles
NITIN JOSHIBTECH MECHANICAL
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Nitin Joshi B Tech Mechanical
CONTENTS:-
Acknowledgement Introduction
Vapor-compression refrigeration
Refrigeration of transportation systems
Refrigeration & air conditioning in automobiles
The ventilation circuit in the automobile
Air conditioning control system
Carbon dioxide as a refrigerant in automobiles
References
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ACKNOWLEDGEMENT:-
Firstly I would like to thank my teacher for giving me such a good topic for
my term paper and give me the chance to express my views on this topic.
This topic will help me to increase my knowledge about the particular topic. I
also want to thank my teacher for his suggestion and guidance during the
each stage. I would also like to thanks my friends for their kind support and
suggestions which helps me to make this report properly.
INTRODUCTION:-
My topic of term paper is to tell about the refrigeration in automobiles. Firstly
I would explain that what is the refrigeration & air conditioning. After this I
will discuss the type of refrigeration system & vapor compression system.
After this I will tell about the refrigeration in transport. After this we will
discuss about the use of carbon dioxide as a refrigerant & the new trends inautomobile air conditioning. Air conditioning is the method to cool the indoor
air for the thermal comfort, it is also refer as the cooling, heating, ventilation
that modify the condition of air. Refrigeration is defined as the cooling of a
particular space by means of heat rejection & the device which performs this
is known as heat pump. As we all know refrigeration is the essential part of
an automobile because it gives the thermal comfort during the summer
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days. For refrigeration we use different refrigeration cycles & refrigerants.
Here we discuss only about the vapor compression cycle & the refrigerant
carbon dioxide.
VAPOR-COMPRESSION REFRIGERATION:-
Vapor-compression refrigeration is one out of the refrigeration cycles which
are available for use. It is the widely used method for air conditioning of
large public buildings, hotels, automobiles etc. it uses a circulating liquidrefrigerant for the purpose of removal & absorbsion of heat from a place
which has to be cooled. Figure beside shows the single stage vapor
compression system. The main components of this system are compressor,
condenser, expansion valve and evaporator. First of all the circulating
refrigerant in the saturated vapor state enters into the compressor and
compressed to a high pressure & temperature. Then this compressed vapor
in the super heated vapor state at same temperature & pressure is
condensed with available amount of cooling water or cooling air. That hot
vapor passes through the condenser where it is cooled and condensed intoliquid by flowing through a coil or tube with cool water or cool air flowing
across the tubes or coil. At this place circulating refrigerant rejects the heat
from the system & this rejected heat is carried away by the water or air. This
condensed vapor in saturated liquid state then passes through the expansion
valve where its pressure gets reduced. This reduction in pressure results in
the flash evaporation of a part of the refrigerant. It causes the auto
refrigeration which reduced the temperature of the mixture of the liquid &
vapor refrigerant. Then this cold mixture passes through the coil or tubes in
the evaporator. A fan circulating the warm air in the enclosed space across
the coil or tube carrying the mixture of vapor & cold refrigerant. That airevaporates the liquid part of the cold refrigerant mixture. At the same time
the circulating air is cooled and lowers the temperature of the enclosed
space to the desired temperature. To complete the refrigeration cycle the
refrigerant vapor from the evaporator is again routed into the compressor.
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The refrigerant mainly used into this is Freon. These
refrigerant used commonly because they have superior stability & safety
properties. These are non flammable & not toxic.
REFRIGERATION OF TRANSPORTATION SYSTEMS:-
Refrigeration of Trucks and Trailers:-
Refrigerated transport is the main link of the cold food chain. This is the
other application of refrigeration of automobiles it commonly consist of
refrigeration of trucks & trailers because these are used for transportation of
food. These vehicles are refrigerated to maintain temperature between 1.5
to 4c for cold food and -18C for frozen foods. The types of refrigeration
systems used are given below.
Product Subcooling:-
With the use of improved insulating materials, it is possible to drastically cutthe transmission load of vehicles. In that case, use may be made of the
storage capacity of the product itself for cold by subcooling it to as low a
temperature as possible before transporting for shorter distances. Thus even
after reaching the destination, the temperature of the product is below the
temperature of the storage requirement. Examples are tankers for milk,
orange juice, etc.
Using Water Ice:-
The top of the product can suitably be iced. It is also a satisfactory method
for short distances & for some products only. The refrigerating effect
produced by the melting of the ice is 335.4kj/kg.
Using Dry Ice:-
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It is mainly used in small retail trucks for the delivery of frozen food, such as
ice cream. The blocks of the dry ice is usually put in the ceiling. The cooling
is done by natural convection. In case of forced convection the dry ice act as
the water ice. The temperature of refrigeration is about -78.5C. The
refrigerating effect produced by the sublimation of dry ice is 605.5kj/kg.
While using dry ice care must be taken to avoid burns due to low
temperatures, and suffocation due to lack of oxygen.
Using Liquid Nitrogen:-
During the manufacturing of oxygen by liquefaction of atmospheric air, liquid
nitrogen has become available almost as a bi product. Therefore it is used for
the transport of frozen food. The boiling point of liquid nitrogen is -195.6C. It
is an extremely low temperature from the point of view of COP %
refrigeration economy. The refrigerant is introduced into the vehicle through
nozzles in case of liquid nitrogen & liquid carbon dioxide, and the flow is
controlled by thermostats & solenoid valves. The storage vessels for the
refrigerants are kept within the refrigerated space. Liquid nitrogen vessels
do not require any pressure as in case of liquid carbon dioxide to prevent
from blockage due to snow formation during pressure drop.
Eutectic Plates With Station Charging:-
The channels formed by these plates are placed all around the body of
vehicle. They contain a eutectic solution which can be frozen by a refrigerant
flowing in a coil immersed in the solution. The coil is connected to a
mechanical refrigeration system at the charging station. Cooling is done by
the evaporation of the primary refrigerant in the coil. These plates are made
in many sizes varying from 45 to 90 cm in width. A plate of size 76
1686.65 cm has a refrigerating capacity of 17935 kj. The operating
temperature of plates is -51 to -3.5C.
Refrigerated Railway Cars:-
These cars use ice bunkers with water ice or ice & salt mixture. Therecharging of ice is required at intermediate stations on the route. The
mechanical refrigeration system is being increasingly adopted nowadays. It
is provided with an independent diesel-generator set so that refrigeration is
independent of car movement. The normal generator capacity is 20kwW.
Marine Refrigeration:-
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A special feature of marine transport is the varying climate. The insulation &
fittings should be suitable both for warm & coldwater routes. Thus a vapor
barrier for moisture should be provided on both sides of the insulation.
Refrigeration is used in ships for cargo & stores of passenger ships. It is also
use for transportation of fishes. In case of cargo, the refrigeration system
should be capable of providing temperature between -23.5-12.5C. R 12 with
reciprocating compressor is presently used as a refrigerant. R 22 is not used
because of its critical oil miscibility. On other hand ships must have their own
stores. These stores have to be much bigger for passenger vessel. They also
have the ventilated area for some of the items. Fishing vessels use ice, but
deep sea fishing use mechanical refrigeration because they have to stay
away for months.
REFRIGERATION IN AIR TRANSPORT: -
Refrigerated air transport of some commodities can be justified on the basisof saving in the time & preservation of quality. The cargo compartments are
cooled by air conditioning system itself in some of passenger air craft. For
transit refrigeration, if necessary, refrigerant packages of water ice, dry ice
or other substances are used.
REFRIGERATION & AIR CONDITIONING IN
AUTOMOBILES:-
Automobile refrigeration has become more & more commonplace. The
refrigeration system ensures the thermal comfort for passengers. Figure
given below gives the refrigerant circuit in the automobile.
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The basic components of this circuit are compressor, condenser, refrigerant
cartridge, expansion valve and the evaporator. In the figure at position 1
there is a compressor at 2 there is electromagnetic coupler at 3 there is
condenser at 4 there is accessory fan at 5there is refrigerant cartridge at 6there is evaporator at 7 there is evaporator fan and at 8 there is an
expansion valve. The work of compressor is to ensure that vapor refrigerant
removes from the evaporator in such a way that both temp. & pr. is
maintained at desired level. Compressor runs by the engine of the vehicle
which will impact the refrigerant capacity because engine has to operate at
different speeds. The condenser is cooled by the stream of air induced by the
fan. The liquid refrigerant cartridge act as an equalizing & reserve unit. The
amount of refrigerant depends upon the operating conditions. The drying
pad absorbs the water or impurities which may occur. The safety device
turns on the condenser fan when there is excessive refrigerant temperature& turns off when there is excess exit pressure. The expansion valve lowers
the pressure of the liquid refrigerant. Evaporator evaporates this low
pressure liquid refrigerant.
THE VENTILATION CIRCUIT IN THE AUTOMOBILE:-
The figure shows below
contains fresh air valve at
position 1, internal
circulation valve at 2, air
mixing chamber at 3,
ventilator at 4, air filter at
5, evaporator at 6, heater
at 7, windshield defroster
outlet valve at 8, central
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duct valve at 9, leg outlet valve at 10, anterior outlet valve at 11 and side
outlet valve at 12. The fresh air valve controls the regulation of air intake in
the open circuit. Then this air flows through the air filter into evaporator, at
this position it cools and the moisture contents is condensed out. Then this
air warmed in heat exchanger to the desired temperature.
AIR CONDITIONING CONTROL SYSTEM:-
The control system ensures the desired temperature of the inner air cabin &
also controls the air intake & its distribution. In temperature controlled
systems the chosen temperature is maintained automatically, air intake &
distribution controlled manually. Fully automatic control system ensures the
desired temperature, intake air & air distribution. The desired temperature is
maintained by using air regime or water regime. Fresh air drawn in by a fan
(1) and cooled by evaporator (2) and warmed in heater (4). The requiredtemperature is compared with the actual temperature and the difference is
converted into the control unit into regulation variable for heating & cooling
capacity. The figure shows the fan at 1, evaporator at 2, evaporator
temperature sensor at 3, heater at 4, exhaust air temperature sensor at 5,
temperature selector at 6, internal temperature sensor at 7, electronic
control unit at 8, condensed water drain at 9, compressor at 10,
electromagnetic valve at 11, fresh air at a, windshield at b, upper outlet at c,
internal circulation at d, bypass at e, lower outlet at f.
At high speeds the pressure of air increases. At thissituation the specialized device lowers the fans
revolutions. Most of the control systems function on
the basis of temperature measured near the area
around the driver.
CARBON DIOXIDE AS A
REFRIGERANT IN AUTOMOBILES:-
Test conducted on CO2 gas shows it can be used as a refrigerant in the
automobiles. These tests compared the thermal efficiency of CO2 system
with the one commonly used in automobiles. The CO2 system performed well
than the conventional systems under most of operating conditions. Current
systems are using R134a as a refrigerant. To reduce global warming & to
obtain better fuel economy, the more efficient air conditioning system isnitinjoshi.jo@gmail.com
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necessary. Energy efficient engine may not generate enough waste heat to
warm during the winter. In this case heat pump is required. R134a works
poorly as a heating fluid where as CO2 is suited for heat pump application.
To compare the systems researcher constructed identical test chambers. A
variable wind tunnel simulated. The two heat exchanger of equal volume &
same pressure drop on the air side. Compressors are of also same size. By
taking lot of information from these experiments we can reduce some of the
technical problems surrounding the ultimate limits on CO2 performance.
REFERENCES:-
I have taken the references from the following websites & books to make my term
paper report.
1. www.google.co.in
2. www.wikipedia.com
3. www.howstuffworks.com
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4. Refrigeration & air conditioning by C P Arora, TMH publisher.
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