67880901 Automobile Ac by Utilising Waste Heat Gases

7/28/2019 67880901 Automobile Ac by Utilising Waste Heat Gases

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A

SEMINAR REPORT

ON

Automobile Ac by Utilising Waste Heat & Gases

SUBMITED IN THE PARTIAL FULFILLMENT OF THE

REQEUTREMENT FOR THE AWARD OF DEGREE OF

BACHELOR OF TECHNOLOGY

IN

MECHANICAL ENGINEERING

SUBMITTED TO: SUBMITTED BY:

YUDHISTAR SAINI ASHWANI DUBEY

HEAD OF DEPARTMENT ROLL NO. 09ESTME013

MECHANICAL ENGINEERING IV YEAR VIII SEMESTER

DEPARTMENT OF MECHANICAL ENGINEERING

STANI MEMORIAL COLLEGE OF ENGINEERING & TECHNOLOGY

SESSION- 2012 2013


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PREFACE

A very important element in curriculum of an Engineering student is the SEMINAR.

This is a part of the curriculum of the STANI MEMORIAL COLLEGE OF ENGINEERING &

TECH.ForB.Tech. course.

As we are the students of Mechanical Engineering so the SEMINAR at Automobile-Ac-

by-Utilising-Waste-Heat-Gases has been particularly beneficial for us.

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ACKNOWLEDGEMENT

The Seminar Report on Automobile-Ac-by-Utilising-Waste-Heat-Gaseshasbeen a unique

experience for me instead of routine and momentary exercise. It has leap to new field of

acquiring knowledge andlearning.

I am deeply in debuted to Mr. T.C.JAIN (Principal ) whose guidance and

feedback during the course of the study helped me not only in bringing out his report

successfully but also provided a real insight into student matter. I am also thankful for being sohelpful and providing us with valuable instructions and study material and also for kind

cooperation and help and all other employers who help me in providing various data andinformation that were needed to accomplish the end result.

My heartily thanks to Mr. YUDHISTAR SAINI, HEAD OF DEPARTMENT

MECHANICAL SMCET, JAIPURfor all kind of help they have Granted in absence of which

the report would have not been possible.

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ABSTRACT

It is the established fact that only about 30% of heat supplied by the fuel is converted

into useful work, in case of internal combustion (I.C) engines and the rest is going waste to the

atmosphere in the form of coolant losses (35%) and exhaust gas losses (35%). The conventional

air conditioning system which most of the A/C vehicles use is the vapour Compression

refrigeration system , in which the compressor needs mechanical work that is Higher-grade

energy is then taken directly from the engine crankshaft. Thus it ultimately reduces the brake

power (B.P.) available and increasing brake specific fuel consumption.

The vapour absorption refrigeration system utilizes the waste heat as it does not

involve any compressor and hence not require great mechanical work instead of that it works

directly on the heat energy i.e. .low grade energy.

Thus by making proper use of lost heat (about 60 70% of total heat). The conventional

air conditioning can be replaced with this system and the same effect can be experienced. The

common vapour absorption refrigeration systems, which are in practice, are

1. Aqua Ammonia system and

2. Lithium Bromide water system

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2.EXISITING AIR-CONDITIONING SYSTEM

The use of air conditioner for transport purpose may be a luxury in India but it is

commonly used in foreign countries .In comparison to domestic air-conditioning a very large

amount of air-conditioning capacity is required for a car. This is due to metal construction of the

car, the flow of air around moving car and relatively large glass area in the passenger

compartment. Typically, a car A/C system capacity may be between 1 to 4 tons. The system

works on Vapour Compression Refrigeration System (VCRS) and the compressor consumes

large amount of engine brake power (1 to 10 h.p.) as it is directly driven by the engine. This

affects the fuel economy severely. A loss in economy level of the order of 1 to 1.5 km/liter can

occur due to the use A/C. Maximum power is required when the car is running at maximum

speed under high ambient temperature conditions. Apart far from this VCRS has got certain

drawback, which limits its extensive use among common car owner.

DRAWBACKS

1.High initial cost.

2. High operating cost, since fuel economy is affected, high maintenance cost, costly

refrigerant.

3.CFCs (Chlorofluorocarbon) if leaks out of the system causes great damage to the ozone layer.

4.If the cars reserve power is less, it can affect its acceleration.

5.Overloading and overheating of the engine takes place.

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ENGINE

The internal combustion engine is an engine in which the combuston of fuel and an oxidizer

(typically air) occurs in a confined space called a combustion chamber. This exothermic reaction

creates gases at high tempreture and, pressure which are permitted to expand. Internalcombustion engines are defined by the useful work that is performed by the expanding hot gases

acting directly to cause the movement of solid parts of the engine.

The term Internal Combustion Engine (ICE) is often used to refer to an engine in which

combustion is intermittent, such as a Wankel engine or a reciprocating piston engine in which

there is controlled movement of pistons, cranks, cams, or rods. However, continuous

combustion engines such as jet engines, most rockets, and many gas turbines are also classified

as types of internal combustion engines. This contrasts with external combustion engines such

as steam engines and stirling engines that use a separate combustion chamber to heat a separate

working fluid which then in turn does work, for example, by moving a piston or a turbine.

A huge number of different designs for internal combustion engines exist, each with different

strengths and weaknesses. Although they're used for many different purposes, internalcombustion engines particularly see use in mobile applications such as cars, aircraft, and even

handheld applications: all where their ability to use an energy-dense fuel (especiallyfossil fuels)

to deliver a high power-to-weight ratio is particularly advantageous.

Applications

The motion of internal combustion engines is usually performed by the controlled movement of

pistons, cranks, rods, rotors, or even the entire engine itself.

Internal combustion engines are most commonly used for mobile propulsion in vehicles and

portable machinery. In mobile equipment, internal combustion is advantageous since it can

provide high power-to-weight ratios together with excellent fuelenergy density. Generally using

fossil fuel(mainly petroleum), these engines have appeared in transport in almost all vehicles

(automobiles, trucks, motorcycles, boats, and in a wide variety of aircrafts and locomotives).

These vehicles, when they are not hybrid, are called All-Petroleum Internal Combustion Engine

Vehicles (APICEVs) or All Fossil Fuel Internal Combustion Vehicles (AFFICEVs).

Internal combustion engines appear in the form of gas turbines as well where a very high power

is required, such as injet aircraft, helicoptores, and large ships. They are also frequently used for

electric generator and by industry.

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Operation

Four-stroke cycle(or Otto cycle)

1.Intake

2.compression

3.power

4. exhaust

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http://en.wikipedia.org/wiki/Four-stroke_cyclehttp://en.wikipedia.org/wiki/Four-stroke_cyclehttp://en.wikipedia.org/wiki/Image:4-Stroke-Engine.gifhttp://en.wikipedia.org/wiki/Four-stroke_cycle


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Basic process

Internal combustion engines have 4 basic steps:

Intake

Combustible mixtures are emplaced in the combustion chamber

Compression

The mixtures are placed under pressure

Combustion/Expansion

The mixture is burnt, almost invariably a deflagration, although a few systems involve

detonation. The hot mixture is expanded, pressing on and moving parts of the engine andperforming useful work.

Exhaust

The cooled combustion products are exhausted

Many engines overlap these steps in time, jet engines do all steps simultaneously at different

parts of the engines. Some internal combustion engines have extra steps.

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Combustion

All internal combustion engines depend on the exothermic chemical process ofcombustion: the

reaction of afuel, typically with oxygen from the airalthough other oxidizers such as nitrous

oxide may be employed. The combustion process typically results in the production of a great

quantity of heat, as well as the production of steam and carbon dioxide and other chemicals at

very high temperature; the temperature reached is determined by the chemical make up of the

fuel and oxidisers .

The most common modern fuels are made up of hydrocarbons and are derived mostly fromfossil

fuels. Because of this, vehicles that uses this energy are called All-Fossil Fuel Internal

Combustion Engine Vehicles (AFFICEVs). Fossil fuels include dieselfuel, gasoline and

petrolieum gas, and the rarer use ofpropane. Except for the fuel delivery components, most

internal combustion engines that are designed for gasoline use can run on natural gas or

liquefied petroleum gases without

major modifications. Liquid and gaseousbiofuels such as ethanol and biodiesel (a form of dieselfuel that is produced from crops that yield triglycerides such as soybean oil), can also be used.

Some engines with appropriate modifications can also run on hydrogengas.

All internal combustion engines must achieve ignition in their cylinders to create combustion.

Typically engines use either a spark ignition(SI)method or a compression ignition(CI) system.

In the past, other methods using hot tubes or flames have been used.

Gasoline Ignition Process

Gasoline engine ignition systems generally rely on a combination of a lead-acid battery and an

induction coil to provide a high-voltage electrical spark to ignite the air-fuel mix in the engine's

cylinders. This battery is recharged during operation using an electricity-generating device such

as an alternator or generator driven by the engine. Gasoline engines take in a mixture of air and

gasoline and compress it to not more than 185 psi, then use a spark plug to ignite the mixture

when it is compressed by the piston head in each cylinder.

Diesel Ignition Process

Diesel engines and HCCI engines, rely solely on heat and pressure created by the engine in its

compression process for ignition. The compression level that occurs is usually twice or more

than a gasoline engine. Diesel engines will take in air only, and shortly before peak

compression, a small quantity of diesel fuel is sprayed into the cylinder via a fuel injector thatallows the fuel to instantly ignite. HCCI type engines will take in both air

and fuel but continue to rely on an unaided auto-combustion process, due to higher pressures

and heat. This is also why diesel and HCCI engines are more susceptible to cold-starting issues,although they will run just as well in cold weather once started. Light duty diesel engines in

automobiles and light trucks employ glow plugs that pre-heat the combustion chamber just

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before starting to reduce no-start conditions in cold weather. Most diesels also have a batteryand charging system; nevertheless, this system is secondary and is added by manufacturers as a

luxury for the ease of starting, turning fuel on and off (which can also be done via a switch or

mechanical apparatus), and for running auxiliary electrical components and accessories. Most

new engines rely on electrical and electronic control systems that also control the combustion

process to increase efficiency and reduce emissions.

Measures of engine performance

Engine types vary greatly in a number of different ways:

Energy effeciency

fuel/propellant consumption (brake specific fuel consumtion for shaft engines, thrust

specific fuel consumption for jet engines)

power to weight ratio

thrust to weight ratio

torque curves(for shaft engines)

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Energy Efficiency

Once ignited and burnt, the combustion productshot gaseshave more available thermalenergy than the original compressed fuel-air mixture (which had higherchemical energy). The

available energy is manifested as high tempreture and pressure that can be translated into work

by the engine. In a reciprocating engine, the high-pressure gases inside the cylinders drive the

engine's pistons.

Once the available energy has been removed, the remaining hot gases are vented (often by

opening a valve or exposing the exhaust outlet) and this allows the piston to return to itsprevious position (top dead center, or TDC). The piston can then proceed to the next phase of its

cycle, which varies between engines. Any heat that isn't translated into work is normallyconsidered a waste product and is removed from the engine either by an air or liquid cooling

system.

Engine efficiency can be discussed in a number of ways but it usually involves a comparison of

the total chemical energy in the fuels, and the useful energy abstracted from the fuels in the formof kinetic energy. The most fundamental and abstract discussion of engine efficiency is the

thermodynamic limit for abstracting energy from the fuel defined by a thermodynamic cycle.

The most comprehensive is the empirical fuel economy of the total engine system for

accomplishing a desired task; for example, the miles per gallon accumulated.

Internal combustion engines are primarily heat engines and as such the phenomenon that limits

their efficiency is described by

thermodynamic cycles. None of these cycles exceed the limit defined by the Carnot cycle which

states that the overall efficiency is dictated by the difference between the lower and upperoperating temperatures of the engine. A terrestrial engine is usually and fundamentally limited

by the upper thermal stability derived from the material used to make up the engine. All metals

and alloys eventually melt or decompose and there is significant researching into ceramic

materials that can be made with higher thermal stabilities and desirable structural properties.

Higher thermal stability allows for greater temperature difference between the lower and upper

operating temperaturesthus greater thermodynamic efficiency.

The thermodynamic limits assume that the engine is operating in ideal conditions. A

frictionless world, ideal gases, perfect insulators, and operation at infinite time. The real world is

substantially more complex and all the complexities reduce the efficiency. In addition, real

engines run best at specific loads and rates as described by their power curve. For example, a car

cruising on a highway is usually operating significantly below its ideal load, because the engine

is designed for the higher loads desired for rapid acceleration. The applications of engines are

used as contributed drag on the total system reducing overall efficiency, such as wind resistance

designs for vehicles. These and many other losses result in an engines' real-world fuel economy

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that is usually measured in the units of miles per gallon (or kilometers per liter) for automobiles.The miles in, "MPG" represents a meaningful amount of work and the volume of hydrocarbon

implies a standard energy content.

Most steel engines have a thermodynamic limit of 37%. Even when aided with turbochargers

and stock efficiency aids, most engines retain an average efficiency of about 18%-20%.

There are many inventions concerned with increasing the efficiency of IC-Engines. In

general, practical engines are always compromised by trade-offs between different properties

such as efficiency, weight, power, heat, response, exhaust emissions, or noise. Sometimes

economy also plays a role in not only in the cost of manufacturing the engine itself, but also

manufacturing and distributing the fuel. Increasing the engines' efficiency brings better fuel

economy but only if the fuel cost per energy content is the same.

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Seebeck effect

The See beck effect is the conversion of temperature differences directly into electricity.

Seebeck discovered that a compass needle would be deflected when a closed loop wasformed of two metals joined in two places with a temperature difference between the junctions.

This is because the metals respond differently to the temperature difference, which creates a

current loop, which produces a magnetic field. Seebeck, however, at this time did not recognize

there was an electric current involved, so he called the phenomenon the thermomagnetic effect,

thinking that the two metals became magnetically polarized by the temperature gradient. The

Danish physicist Hans Christia rsted played a vital role in explaining and conceiving the term

"thermoelectricity".

The effect is that a voltage, the thermoelectric EMF, is created in the presence of a temperature

difference between two different metals or semiconductors. This causes a continuous current in

the conductors if they form a complete loop. The voltage created is of the order of several

microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck

coefficient of 41 microvolts per kelvin at room temperature.

In the circuit:

(which can be in several different configurations and be governed by the same equations), the

voltage developed can be derived from:

SA and SB are the Seebeck coefficients (also called thermoelectric power or thermopower) of the

metals A and B as a function of temperature, and T1 and T2 are the temperatures of the two

junctions. The Seebeck coefficients

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are non-linear as a function of temperature, and depend on the conductors' absolute temperature,material, and molecular structure. If the Seebeck coefficients are effectively constant for the

measured temperature range, the above formula can be approximated as:

The Seebeck effect is commonly used in a device called a thermocouple (because it is made

from a coupling or junction of materials, usually metals) to measure a temperature differencedirectly or to measure an absolute temperature by setting one end to a known temperature.

Several thermocouples when connected in series are called a thermopile, which is sometimes

constructed in order to increase the output voltage since the voltage induced over each

individual couple is small.

This is also the principle at work behind thermal diodes and thermoelectric generators (such as

radioisotope thermoelectric generators or RTGs) which are used for creating power from heat

differentials.

The Seebeck effect is due to two effects: charge carrier diffusion and phonon drag (described

below). If both connections are held at the same temperature, but one connection is periodically

opened and closed, an AC voltage is measured, which is also temperature dependent.

This application of the Kelvin probe is sometimes used to argue that the underlying physics only

needs one junction. And this effect is still visible if the wires only come close, but do not touch,

thus no diffusion is needed.

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Thermopower

The thermopower, or thermoelectric power, or Seebeck coefficient of a material measure the

magnitude of an induced thermoelectric voltage in response to a temperature difference across

that material. The thermopower has units of (V / K), though in practice it is more common to

use microvolts per kelvin. Values in the hundreds of V/K, negative or positive, are typical of

good thermoelectric materials. The term thermopower is a misnomer since it measures the

voltage or electric field induced in response to a temperature difference, not the electric power.

An applied temperature difference causes charged carriers in the material, whether they are

electrons or holes, to diffuse from the hot side to the cold side, similar to a classical gas that

expands when heated. Mobile charged carriers migrating to the cold side leave behind their

oppositely charged and immobile nuclei at the hot side thus giving rise to a thermoelectric

voltage (thermoelectric refers to the fact that the voltage is created by a temperature difference).

Since a separation of charges also creates an electric potential, the buildup of

charged carriers onto the cold side eventually ceases at some maximum value since there exists

an equal amount of charged carriers drifting back to the hot side as a result of the electric field at

equilibrium. Only an increase in the temperature difference can resume a buildup of morecharge carriers on the cold side and thus lead to an increase in the thermoelectric voltage.

Incidentally the thermopower also measures the entropy per charge carrier in the material. To be

more specific, the partial molar electronic heat capacity is said to equal the absolute

thermoelectric power multiplied by the negative of Faraday's constant.

The thermopower of a material, represented by S (or sometimes by ), depends on the

material's temperature and crystal structure. Typically metals have small thermopowers because

most have half-filled bands. Electrons (negative charges) and holes (positive charges) bothcontribute to the induced thermoelectric voltage thus canceling each other's contribution to that

voltage and making it small. In contrast, semiconductors can be doped with an excess amount of

electrons or holes and thus can have large positive or negative values of the thermopower

depending on the charge of the excess carriers. The sign of the thermopower can determinewhich charged carriers dominate the electric transport in both metals and semiconductors.

If the temperature difference T between the two ends of a material is small, then thethermopower of a material is defined (approximately) as:

and a thermoelectric voltage V is seen at the terminals.

This can also be written in relation to the electric field E and the temperature gradient , by

the approximateequation:

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In practice one rarely measures the absolute thermopower of the material of interest. This isbecause electrodes attached to a voltmeter must be placed onto the material in order to measure

the thermoelectric voltage. The temperature gradient then also typically induces a thermoelectric

voltage across one leg of the measurement electrodes. Therefore the measured thermopower

includes a contribution from the thermopower of the material of interest and the material of the

measurement electrodes.

The measured thermopower is then a contribution from both and can be written as:

Superconductors have zero thermopower since the charged carriers produce no entropy.

This allows a direct measurement of the absolute thermopower of the material of interest, since

it is the thermopower of the entire thermocouple as well. In addition, a measurement of the

Thomson coefficient, , of a material can also yield the thermopower through the relation:

The thermopower is an important material parameter that determines the efficiency of a

thermoelectric material. A larger induced thermoelectric voltage for a given temperature

gradient will lead to a larger efficiency. Ideally one would want very large thermopower values

since only a small amount of heat is then necessary to create a large voltage. This voltage can

then be used to provide power.

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THE AUTOMOBILE ENGINE

The prime mover of the automobile (I.C. engine) is a heat engine, which can convert only a

fraction of the total heat of fuel into the useful work.

20 to30 % for SI engines

30 to 36% for CI engines

The remaining heat is lost to the atmosphere through the coolant and exhaust. Heat balance is

given in the below table: -

%AGE OF FUEL ENERGY

S.I. C.I.

To power 26 31

To coolant 30 26

To exhaust 32 30

Radiation 12 13

Also refer the fig. 1

Thus we have about 60% of heat which is going waste. So, with such a small efficiency

of the heat engine. Obviously it is not worthwhile for a common man to install such an A/C in

his car.

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AN ALTERNATIVE TO THIS SYTEM

The concept is to use this otherwise going waste heat, for air-conditioning with the aid

of Vapour Absorption System (VARS) which does not affect the engine power. It need no

maintenance and is environment friendly.

VARS is a heat operated refrigeration machine in which the compressor is replaced

by the combination of absorber and generator. A solution known as the absorbent (e.g. water in

case of A qua-ammonia system) which has an affinity for the refrigerant used (i.e. ammonia) is

circulated between the absorber and the generator by a pump (solution pump). I n this system,

the low pressure ammonia vapour living the evaporator, enters the absorber where it is absorbed

by the low temperature water in the absorber .The water has the ability to absorb very large

quantity of ammonia vapour and the solution thus formed, is known as Aqua-ammonia. The

absorption of ammonia vapour lowers the pressure in the absorber, which in turn draws more

ammonia vapour from the evaporator and thus raises the temperature of solution. Some form of

cooling arrangement (usually water-cooling) is employed in the absorber to remove the heat of

solution evolved there. This is necessary in order to increase the absorption capacity of water.

The liquid pump pumps the strong solution thus formed in the absorber to the generator. The

pump increases the pressure of the solution upto 10bar. The strong solution of ammonia in

generator is heated by heat of coolant and the exhaust gases, which are waste in atmosphere

without any use and the heat, wasted in cooling of engine. During the heating process, the

ammonia vapour is driven of the solution at high pressure leaving behind the hot weak ammonia

solution in the generator. The weak ammonia solution flows back to the absorber at low pressure

after passing through the reducing valve. But then also the ammonia vapour contains some

particles of water. If these unwanted water particles are not removed before entering into the

condenser, they will enter into the expansion valve where they freeze and choke the pipeline. In

order to remove these unwanted

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particles flowing to the condenser, an analyzer is used. The analyzer may be built as an integral

part of the generator or made as a separate piece of equipment. It consists of a series trays

mounted above the generator. The strong solution from the absorber and the aqua from the

rectifier are introduced at the top of analyzer and flow downward over the trays and into the

generator. In this way, considerable liquid surface area is exposed to the vapour rising from the

generator. The vapour is cooled and most of the water vapour condenses. So, that mainly

ammonia vapour, leaves the top of the analyzer. Since the aqua is heated by the vapour, less the

generator is condensed in the condenser to high-pressure liquid ammonia. This liquid ammonia

is passed to the expansion valve through a receiver and then to the evaporator. This evaporator

is made up of number of tubes, which is installed in the cabin of automobile. The function of

compressor is performed by the absorbent in the absorber, and the generator performs the

function of compression and discharge. The complete system is schematically represented in the

fig. 2.

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5.OPERATING THE SYSTEM

As we know that VARS is a heat operated refrigerating machine in which heat is

supplied to the generator. So this required heat we will supply from the waste heat (coolant

loss and exhaust) which is our center of focus. So we have to distribute the exhaust gases and

the coolant to all the system whenever necessary to satisfy the cold and hot air conditioning and

flexibility of operation in various possible mode.

For this there are two types of circuits.

1) Coolant circuit

2) Exhaust circuit

1.Coolant Circuit: -

In vapour absorption refrigeration system, there is necessity of cooling of absorber and

condenser, which is achieved by water-cooling. The water is supplied to this system by radiator

and heat gained by the cooling water from the engine is utilized in generator and heater. The

systematic arrangement is shown in the given fig.

The coolant circuit in various modes of operations is given below: -

I. Normal running with A/C OFF.

Circuit: - (Radiator - V3-Engine V2 Radiator)

Valve position: -

a) V2---0-1

b) V3---0-1

II. Normal running with A/C ON.

i. For summer ( or high surrounding temperature)

Circuit :-( Radiator-V3-Condenser Absorber-Rectifier-N.R.V.-Engine-V2-Generator-

N.R.V-Radiator)

Valve position

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a) V2---0-2

b) V3---0-2

ii. For winter (or low surrounding temperature)

Circuit: - (Radiator V3 Engine-V2-Heater-N.R.V.-Radiator)

Valve position

a) V2---0-3

b) V3---0-1

2.Exhaust Circuit: -

We are using the waste exhaust gas heat to the generator and heater and then the exhaust

gas is exhausted to atmosphere. Distribution of the gas to the generator, heater and the

atmosphere is maintained by exhaust circuit whenever necessary. The exhaust gas be either fed

to the heater during winter or the generator during the summer or bypassed to the atmosphere.

Exhaust Circuit: -

A. Normal running with A/C OFF.

Circuit: - (Engine V1 to atm.)

Valve position V1---0-1

B. Normal running with A/C ON

a) For summer (or high temperature of surrounding)

Circuit: - (Engine V1 generator N.R.V. to atm.)


b) For winter (or low temperature of surrounding)

Circuit: - (Engine V1 generator N.R.V. to atm.)


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AIR CONDITIONING SYSTEM

The outside air flows through the damper and mixes up with the recirculated air (which

is obtained from the conditioned space.) The mixed air passes through a filter to remove dirt,

dust and other impurities. In summer air conditioning, the cooling coil operates to cool the air to

the desired value. The dehumidification is obtained by operating the cooling coil at a temp lower

than the dew point temperature (apparatus due point). In winter the cooling coil is made in

operative and the heating coil operates to heat the air. The schematic arrangement can be shown

by fig.6

7.INSTALLATION

For the design of the complete system the requirements are:

1) Engine manual (supplied by the manufacture) containing all details about the engine

performance and characteristics, especially cooling and exhaust.

2) Determining the cooling capacity required for a particular vehicle in a particular

region, considering the year round meteorological conditions the various parameters of

the air conditioner can be defined.

The year round air conditioning can be achieved by the system which is required in the cities

like New Delhi where it is too cold in winter and quit hot in summer. Thus by knowing the

amount of waste heat available (usable) and the cooling capacity, various component of the

system can be designed. To get rough idea, let us see the heat available (usable) and the cooling

capacity, various components capacity required for a car as 2TR lets find the heat requirement

for a certain aqua ammonia system.

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Case Study of SI Engine

4-Stroke, 6-cylinder (7.5 cm bore and 9-stroke)

Rpm=3300

Fuel consumption = 0.3 kg/min

c.v. =42000 kJ/min

Jacket water flow rate Q = 65 kg/min

Temperature rise = 12/C

Ventilate air blown up = 14 kg/min

Enters at 10/C and leaves at 65/C

(Engine in insulated box)

B.P. = 42.55 kW (100%)

Heat input = 0.3 * 42000

= 12600 KJ/min

i. Heat equivalent to B.P. = 42.55 * 60

= 2553 KJ/min

ii. Heat in cooling water = (65*4.1868*12)

= 3266 KJ/min (25.9%)

iii. Heat in ventilating air = 14*1.055*55

=774 KJ/min. (6.14%)

iv. Heat to exhaust and

Other losses = 6007 KJ/min (47.66%)

So heat available for VARS = Heat in cooling water + Heat in exhaust

= 3266 + 6007

= 9273 KJ/min. (73.59%)

Let us assume that the effectiveness of heat exchangers be 0.7

Net heat available = 6491.1 KJ/min

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Case Study Of An Aqua- Ammonia System-

Now a case study of aqua-ammonia system is as-

In an aqua ammonia vapour absorption system the following data is available: -

Temperature of weak solution in generator =100degr.C

Temperature of strong solution admitted to generator =80 degr. C

Temperature of condenser = Temperature of absorber =40 degr.C

Temperature rise in evaporator =10 degr.C

Analysis for 2 tonn refrigeration capacity: -

(Mass flow of ammonia through evaporator)

m = 2*3.5/h4-h3 = 7/1600-535 = 0.00657/kg/sec.

i. Heat supplied per kg.of ammonia in the generator

= h12-ha

=1840-(-425)

=2265kj/kg(ammonia)

Q (kJ/sec) = 0.066*2265

=14.75 kJ/sec

ii. Heat rejected in the absorbed per sec.

Qa =mr (h4-ha)

=0.0066(1600+425)

=13.3 kJ/sec

iii. Degassing C5-Cw C7-C8 = 0.46-0.4

=0.06 kg/kg of aqua

iv. Heat rejected in deflimator (cooler after generator)

=mr (h12-h1)

=0.0066(1840-1630)

=1.38

v. Heat rejected in condenser24


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Qc =mr (h1-h2)

=0.0066(1630-535)

=7.197

vi. Considering the enthalpy balance across the heat exchanger, we can write,

Heat lost by weak solution = Heat gain by strong solution

For 1kg ammonia entering into the absorber mw kg of weak solution is entering then

ms=mw+1

mw (h8-h9) =(mw+1)(h7-h6);

mw (350-120) = (mw+1)(260-70)

40 mw = 190

mw = 4.75 kg/kg of ammonia

ms (strong solution handled by the pump)= mw+1

=4.75+1

=5.75 kg/kg of ammonia

=0.0066 * 5.75

=0.037 kg/sec

vii. c.o.p. Qe/Qg = h4-h3/Q9=1600-535/2265=0.47

viii. Energetic ne is given by

Ne = Qe/Qg [Tg/Te (Te-Te/Tq-Te)]

=0.47(100+273/10+273)(40-10/100-40)

=31%

Heat supplied =4.75kj/sec.

Heat rejected in absorber =3.3kj/sec.

Heat rejected =7.197

Heat rejected in deflimator =1.38


Heat rejected =13.3+7.19725


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Heat rejected in condenser =7.197

Heat rejected in deflimator =1.38


Heat rejected =13.3+7.197

=20.49kj/sec

Heat supplied =885kj/min

Heat rejected =1229.82kj/min

Heat available =3266+6007

Considering effectiveness =0.7=2286+4204

=6490kj/min

Heat required =885kj/min.

Thus we see that a large amount of heat is available and our requirement is lesser. The

system here described is simple basic. It can be further improved and made sophisticated by

using various control systems and relays. A basic control system is shown in fig. 7

Apart from the new design of vehicles installing (VARS), the existing vehicles can also

be equipped with this system and by studying the make of particular a proper placed can be found

out for erecting the system and tracing various circuits.

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CONTROLLING THE SYSTEM

The exhaust coolant circuit is controlled by 3 valves V1, V2 and V3. The valve V1 operates the

exhaust circuit and the valves V2 &V3 operate the coolant circuit where valve V3 is two way

valves and other two V1 and V2 are three way valves. The combination of position of valve for

different conditions are as shown below: -

V1 V2 V3

A/C OFF A/C OFF 1 1 1

A/C ON Summer 2 2 2

A/C ON Winter 3 3 1

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ERECTION

By studying the manual of the particular vehicle, an appropriate place can be found out for the

erection of the system for existing vehicles and for newer design, it is to be already taken into

consideration. The condenser, expander, absorber and evaporator should be kept away from the

engine as possible because the engine evolves at high temp. The conditioned air supply and

distribution system remains the same as in the existing A/C vehicles.

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ADVANTAGES OF VARS OVER VCRS

1) No moving parts so, quiet in operation, subjected to little wear, low maintenance cost. The

pump required quite small power in comparison with compressor.

2) Large capacity.

3) Excellent part load efficiency and almost constant c.o.p. of the system over a wide range of

load.

4) Automatic capacity control is easy.

5) Smaller space per unit capacity.

6) No harm to the ozone layer.

7) Inexpensive refrigerant.

8) Leakage can be easily detected in case of aqua ammonia system.

9) It can reduce the global warming of atmosphere.

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CONCLUSION

Thus we have seen that the VARS is efficient in every respect, and can be successfully

implemented with better designs and sophistication. Now it is the task of the up coming

engineers to overcome the hurdles in the way if any and make our countrys people enjoy the

comfort and luxury of A/C and fuel will also be saved to a greater extent which would have been

consumed in excess by the (VARS) air conditioner.

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REFERENCES

Basic Refrigeration and Air conditioning- P.N. Anathnarayan

Refrigeration and air conditioning C.P. Arora

A course in Refrigeration and Air-conditioning- S.C.Arora, S.Domkundwar

Thermodynamics and Heat Engines- R.Yadav

A course in Internal Combustion Engines M.L. Mathur, R.P. Sharma

Automobile Engineering R.B. Gupta

A Text Book of Refrigeration And Air Conditioning R.S. Khurmi & S.K. Gupta

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67880901 Automobile Ac by Utilising Waste Heat Gases