refrigeration in automobiles

8/9/2019 Refrigeration in Automobiles

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Nitin Joshi B Tech Mechanical

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TERM

PAPERREPORT

Refrigeration in

Automobiles

NITIN JOSHIBTECH MECHANICAL
mailto:[email protected]:[email protected]


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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 [email protected]


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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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http://www.google.co.in/http://www.wikipedia.com/http://www.howstuffworks.com/mailto:[email protected]://www.google.co.in/http://www.wikipedia.com/http://www.howstuffworks.com/mailto:[email protected]


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4. Refrigeration & air conditioning by C P Arora, TMH publisher.

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refrigeration in automobiles

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