FAKULTI KEJURUTERAAN DAN ALAM BINA

JABATAN KEJURUTERAAN MEKANIK DAN BAHAN (JKMB)

INTEGRATED PROJECT

KKKM 3944 System Design

KKKM 3344 Control Engineering

KKKM 3124 Fluid Mechanic II

KKKM 3144 Heat Transfer

Semester 6 2012/2013

TITLE :UTILIZATION OF WASTE HEAT BY USING THERMOELECTRIC GENERATOR (TEG)

TEAM 2

MUHAMMAD SYAFIQ BIN MEGT JIWA A133083

NUR UMMIRAH BINTI HUSIN A133016

NORHIDAYAH BINTI MAT TAIB A131793

YIN MUN KIT A132489

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INTEGRATED PROJECT

2012/2013

MUHAMMAD SYAFIQ BIN MEGT JIWA

NUR UMMIRAH BINTI HUSIN

NORHIDAYAH BINTI MAT TAIB

YIN MUN KIT

A TASK SUBMITTED TO FULFILL THE REQUIREMENTS FOR

INTEGRATED PROJECT

FACULTY OF ENGINEERING AND BUILT ENVIRONMENT

UNIVERSITI KEBANGSAAN MALAYSIA

BANGI

2013

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CONTENT PAGES

ACKNOWLEDGEMENT 4

INTRODUCTION 5

OBJECTIVES

METHODOLOGY

PROBLEM STATEMENT

CHAPTER I SYSTEM DESIGN ANALYSIS

CHAPTER II CONTROL ENGINEERING

ANALYSIS

CHAPTER III FLUID MECHANICS

ANALYSIS

CHAPTER IV HEAT TRANSFER

ANALYSIS

DISCUSSION 72

REFERENCES 73

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ACKNOWLEDGEMENT

Firstly, we have to acknowledge and present our heartily and highly appreciation to

Gods, for giving us energy and encouragement through the tough times that made the

completion of this project possible.

In preparing this report, it is our pleasure to express our sincere gratitude to all our

lecturers who are involved in this Integrated Project especially Prof. Dr. Ja`afar bin Sahari,

Prof. Dr. Dzuraidahbinti Abdul Wahab, Prof. Madya. Dr. Rozli Bin Zulkifli, Prof. Madya Dr.

Shahrirbin Abdullah, Dr. MohamadRasidi Bin Mohammad Rasani, Prof. Dr-Ing. Nik

Abdullah bin Nik Mohamed, and Dr. Sallehuddin Bin Mohamed Haris. For their support,

guidance, carefully reviewing our proposal, and giving us an inspiring example through their

characters, their academic capabilities and experiences, that what we all appreciate.

Also, we would like to express our great thanks to our friends in the same faculty, as

they share their thoughts and suggestions which enlighten us in our project.

Last but not least, we would like to express appreciation to our team members for

valuable contributions, cooperation and every effort that has been made to ensure the

smoothness of this project report.

Since this list is too long to mention, it is hoped that those who have given help in this

manner will accept this anonymous recognition. Obviously we are still learning, and we

welcome any suggestions and comments from the lecturers.

Thank you.

Yours sincerely,

Muhammad Syafiq Bin Megt Jiwa

Yin Mun Kit

Norhidayah Binti Mat Taib

Nur Ummirah Binti Husin

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INTRODUCTION

An internal combustion engine (ICE) is any engine that operates by burning its fuel

inside the engine. The most common internal combustion engine type is gasoline powered.

Other types of fuels that can be used for ICE are diesel, hydrogen, methane, propane, and

others. Engines typically can only run on one type of fuel and require adaptations to adjust the

air/fuel ratio or mix to use other fuels. During the operation of an internal combustion engine

(ICE), an amount of heat will be produced due to the process of combustion of natural gas.

The radiator and exhaust gas systems are the main heat output of an internal combustion

engine. The radiator system is used to pump the coolant through the chambers in the heat

engine block to avoid overheating and seizure. Conversely, the exhaust gas system of an

internal combustion engine is used to discharge the expanded exhaust gas through the exhaust

manifold. Exhaust gas is emitted as a result of the combustion of fuels inside the internal

combustion engine. According to the type of engine, exhaust gas is discharged into the

atmosphere through an exhaust pipe.

In order to reduce the heat waste and convert the heat as a reusable heat, there must be

some ways to utilise the waste heat generated. One of the options to utilize the waste heat

from an internal combustion engine is by designing a system called thermoelectric generator

(TEG). TEG is a generator device that will be able to recover waste heat from internal

combustion engine. TEG is mostly installed in the exhaust gas system (exhaust manifold) due

to its simplicity and low influence on the operation of the engine. Furthermore, TEG system

including the heat exchanger is commonly installed in the exhaust manifold suitable for its

high temperature region. Basically, a practical automotive waste heat energy recovery system

consists of an exhaust gas system, a heat exchanger, a TEG system, a power conditioning

system (power converter), and a battery pack.

Being one of the promising device for an automotive waste heat recovery, TEG will

become one of the most important and outstanding devices in the future. TEG is used to

convert thermal energy from different temperature gradients existing between hot and cold

ends of semiconductor into electric energy. This phenomenon was called as “Seebeck effect”.

TEG offers the conversion of thermal energy into electric current in a simple and reliable

way. There are so many advantages when using TEG, such as free maintenance, silent

operation, high reliability and involving no moving and complex mechanical parts as

compared to Rankine cycle system. By converting the waste heat into electricity, engine

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performance and efficiency of gasoline powered, diesel and hybrid electric vehicles (HEVs)

that utilize the power generation of internal combustion engine is as low as 25% and

conversely, as much as 40% of fuel energy can be lost in the form of waste heat through an

exhaust pipe.

Thermoelectric modules construction consists of pairs of p-type and n-type

semiconductor materials with a high thermoelectric coefficient. Although many different

materials can be used a bismuth telluride alloy is the most common material in use today. This

material is sliced into small blocks, one forms the p-type conductor and the other the n-type

conductor. Each pair forms a thermoelectric couple (TEC). These thermocouples are most

often connected electrically forming an array of multiple thermocouples

(thermopile).Basically, the thermoelectric couples are sandwiched between two pieces of non-

electrically conductive materials. It is also necessary for this material to be thermally

conductive to ensure a good heat transfers and usually two thin ceramic wafers are used.

Types of ceramic wafers or substrates that can be used are Aluminium Nitride and Silicon

Nitride. This now forms what is called a thermoelectric module.

The temperature difference between the two surfaces of the thermoelectric modules

generates electricity using the Seebeck Effect. When hot exhaust from the engine passes

through a TEG system, the charge carriers of the semiconductors within the generator diffuse

from the hot side heat exchanger to the cold side exchanger. The build-up of charge carrier

results in a net charge, producing an electrostatic potential while the heat transfer drives a

current. With exhaust temperatures of 700°C (~1300°F) or more, the temperature difference

between exhaust gas on the hot and cold side is several hundred degrees. This temperature

difference is capable of generating 500 to 750 W of electricity.

Figure 1.1 : Thermoelectric modules concept.

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The operation of the thermoelectric generator waste heat recovery system can be summarized

as below:

Figure 1.2 : Operation principle of thermoelectric generator system.

1. During the normal operation of an internal combustion engine, the produced waste

heat released through the exhaust manifold (exhaust gas system) is captured by the

heat exchanger which is mounted on the catalytic converter of the exhaust gas system.

2. A catalytic converter is a vehicle emissions control device which converts toxic by

product of combustion in the exhaust of an internal combustion engine to less toxic

substances by way of catalysed chemical reactions.

3. After the waste heat released enters the heat exchanger, electricity is then generated

from the thermal energy captured by the heat exchanger after it is transferred to the

TEG system.

4. TEG will convert thermal energy from different temperature gradients existing

between hot and cold ends of a semiconductor into electric energy.

5. Power conditioning is performed by the power converter to achieve maximum power

transfer. Then, the power converted will contribute to vehicle operation.

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OBJECTIVES

The main objective of this project is to design a product by utilizing the waste heat

from internal combustion engine operation. We have chosen to develop a Thermoelectric

Generator (TEG) system. There are a few sub-related objectives involve and should be

achieved with our product.

1. To analyze and improve the Thermoelectric Generator (TEG) system by integrate

it with TEG system by applying the knowledge of System Design, Fluid

Mechanics, Heat Transfer and Engineering Control.

2. To explore the steps in a product development process by following the guideline

from System Design subject.

3. To analyse the behavior of exhaust gas which flow inside the exhaust pipe and

heat exchanger part by applying the knowledge of fluid mechanics subject.

4. To analyse and calculate the amount of heat transfer in TEG system by using three

types of methods of heat transfer process (conduction, convection, radiation).

5. To identify governing equations that will identify inputs and outputs of the

systems by applying the knowledge of engineering control.

6. To understand the internal function of Thermoelectric Generator system and able

to undertake problem identification, formulation and solution.

7. To build a good teamwork amongst team members by completing every problems

and difficulties together.

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METHODOLOGY

This Integrated Project is to design a product with the theme of domestic hot water application

that is chosen based on four courses:

1. KKKM 3944 System Design

2. KKKM 3124 Fluid Mechanics II

3. KKKM 3144 Heat Transfer

4. KKKM 3344 Engineering Control

For System design, we will do our need assessment for strength, weakness and

constraint from customers. Then, we breakdown problem into objectives, and develop general

method based on experience, technical knowledge, creativity and input from others. We come

out with a few concepts and determine which design is the best technically, economically,

stratifies customers.The product design specification is refined from the winning design

concept. Benchmarking is done with other available water dispenser in market nowadays.

For Fluid Mechanics, we analyze the exhaust gas flow in exhaust pipes and TEG heat

exchanger. Laminar or turbulent flow is determined and effect of flow inside the pipes and

heat exchanger can be analyse. Pattern of flow is generated through usage of CFD software

which is Star CCM software.

For Heat Transfer, we will analyse on the amount of heat transfer across the heat

exchanger wall and thermoelectric modules. In order to calculate the value of rate of heat

transfer, some data such as temperature distribution inside the exhaust system can be

determined from fluid mechanic analysis.

For Engineering Control, we will analyze the internal circuit of system which

comprise of heat exchanger and thermoelectric generator system. We develop the output

(temperature difference between hot and cold side of TEG system) from input (exhaust gas

flow). Mathematical modeling is the process through which the response of the system is

obtained. We could describe the behavior of the system which is governed by a differential

equation, an integral equation or combination of both.

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PROBLEM STATEMENT

In automotive engineering field, engineer put a lot of effort to acquire batter efficiency

system of automotive due to the deplete of fossil fuel. The first thing engineer have look into

to increase the whole system efficiency was focus on the waste of the system. Engineer had

do alot of research to find a way to make use of the waste of the automotive system which is

heat energy. To restore the waste heat energy and convert to a form of usefull energy,

engineer had utilize the theory and knowledge which found by previous engineer to come up

with thermoelectric generator (TEG) which can generate electrical power when there are

temperature different in the TEG which is see back effect. With this invention, efficiency of

the system can be increase up to 10% depend on the system designed. Beside that by

recovering the waste heat, the heat expel to the environment can be reduce which also help to

prevent global warming.

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CHAPTER I

1.0 System Design Analysis

Engineering Design is a subject, represented by a particular body of knowledge that

covers the activity of engineering designing. The discipline of design engineering involves

studying and learning about engineering design.

System Design is the process of defining the architecture, components, modules,

interfaces, and data for a system to satisfy specified requirements.

To complete this project, we have plan a proper work flow and time line to ensure the final

product can be prepare before the due date assign. Below is the schematic diagram of our

work flow :

In define problem part, we need to analyze the problem which we encounter so that a

proper solution can be made.

During gathering information section, we had gather information from external and

internal source where external information were acquire from third party and internal

information gather from group member.

In evaluation of concepts, we will utilize the concept generated to give proper

evaluation to decide to continue to put effort in which concept.

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In product architecture, a sketch of the design was drawn.

Once we finalize the drawing, a more detail drawing were drawn which is

configuration of drawing.

1.1 Concept development

External source :

Market survey :

Q1 : Do you understand the role or thermoelectric generator in hybrid vehicle?

Q2 : Do you spend most of your time driving in city?

Q3 : Do you willing to spend extra capital to buy more efficient vehicle?

Q4 : Would you willing to spend extra money on vehicle maintainance to extend lifespan and

condition of your vehicle?

Q5 : Do you always maintain your vehicle on time?

Q6 : Would you consider buying more sustainable vehicle with higher capital?

Q7: Please rate the importance based on scale 1(not important) to 5 (most important) based on

your personal need your vehicle with thermoelectric generator integrated (maximum 2 same

scale) :

1. Save fuel :

2. Cheap maintainance :

3. Integrated with sustainable development concept :

4. Shorter time for the maintaince process :

5. Lighter weight to decrease load on suspension :

6. Price of the vehicle :

7. Long lasting of the vehicle part :

8. Do not required maintain frequently :

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Q1 Q2 Q3 Q4 Q5 Q60

2

4

6

8

10

12

14

16

18

20

result of survey

yesno

a b c d e f g h0

2

4

6

8

10

12

14

16

Q7 result

1 2 3 4 5

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1.2 Internal source

After carried out the survey and interview to converge the needs of the market to increase the

efficiency of future automobile, each of our group members had brainstorming to contribute

idea to satisfy customer need as much as possible. The following are the result of our concept:

1. Thermoelectric generator:

The thermoelectric generator were install in series with the exhaust of the vehicle to

allow waste heated air to be extracted and be converted to electrical energy. To

achieve batter efficiency system, we have come up with idea of our design as below:

a) Prefer the thermoelectric module to arrange in parallel rather than series. This will

reduce the electrical resistance long the circuit because connect in series will increase

the impedance of the circuit which reduce the efficiency of the system.

b) The surface area of the heat conducting side of the system is made as large as possible

to increase the heat transfer so that harvesting heat energy can be done more

efficienly.

c) The cold side of the thermoelectric generator is expose to the ambient air so can heat

energy can be dessipated so that the cold plate side can maintain optimum

temperature.

d) The hot and cold plate were made of highly thermo conductive material to ensure

batter efficiency in term of harvesting and dissipating heat energy.

e) The automotive can be integrated with sensor to sense the engine temperature so that

the TEG only will start operating once the engine warm up. If not the secondary load

like headlamp, air condition will not have sufficient energy generated by the TEG to

operate due to low temperature gradient between hot and cold plate of the TEG.

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1.3 Functional Decomposition of TEG

1.4 Regenerative brake

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The regenerative braking system main source of energy coming from the flywheel of

the tyre. The system will be activated once brake pad of the vehicle were compress. The

idea of regenerative brake is to regenerate the kinetic energy of the vehicle to electrical

energy by installing generator on the braking system. The mean time the electrical energy

is harvest, the vehicle can be decelerate. The concept that can be integrated with this

system as below:

a. The generator must not occupy much space because the space is limited in each of the

tyre.

b. The mass of the generator must not be heavy because it will render less efficiency due

to the extra load since the brake was not apply all the time.

c. The system must be integrated with sensors which only play its role when the brake

pad applies. If not the system will increase the load of the engine all the time just to

harvest electrical energy.

d. The system must have proper braking system since the decelerate effect of the system

would not be sufficient in certain scenario.

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1.5 Functional Decomposition of Regenerative Brake System

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1.6 Concept evaluation

We have brainstormed the pros and cons of each concept and continued further discussions

and research. Here are our results:

a) Pugh Chart

i) Concept screening:

1) Thermoelectric generator

2) Regenerative brake

No. Selection Criterion 1 2

1 Affordable s s

2 Readily Available s s

3 Electric Conversion Rate + -

4 Easy to install s s

5 Space used + -

6 Sustainability - +

7 Weight + -

pluses 3 1

same 3 3

minuses 1 3

net 2 -2

rank 1 2

Continue yes no

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i) Concept

scoring

1 2

selection criterion

weigh

t

ratin

g

weighted

score

ratin

g

weighted

score

Affordable 30% 2 0.60 2 0.60

Readily Available 15% 3 0.45 3 0.45

Electric Conversion Rate 35% 4 1.40 1 0.35

Easy to install 5% 4 0.20 4 0.20

Space used 5% 3 0.15 5 0.25

Sustainability 5% 3 0.15 4 0.20

Weight 5% 3 0.15 2 0.1

total score 3.1 2.15

Rank 1 2

Continue Develop no

Based on the reasons above, we concluded that the Thermoelectric Generator is most suited to

be develop as our system.

After concluding to which concept to be taken, we are required to set specification of the

product. To do so, we need to refer to the internal source of the concept to tackle the market

needs. During the survey was carried out, we have tried to communicate with customer to

understand more on market needs on their vehicle. To do so, we need to start with the

customer need statement to finalize product specification which the below statement as most

frequent ask or quote when the survey carried out.

Customer Statement Needs Statements

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“I want to save fuel” The system have to be high efficiency

“I want cheap maintainance cost” The maintainance cost of the system

must be cheap.

“I want the car to be able to be

decompose and the part can be

recycle”

The System need to make with

sustainable material.

“I don’t want to wait too long to wait

my car to maintain”

Part easy to install and remove.

“The product would not bare much

weight to the suspension”

Weight of the part must be light

“Is this going to be expensive?” The cost of manufacturer must not be

high

“How long does it work until

replace?”

The life span of the part

“Do i have to maintain frequently Maintainance rate

1.7 Customer need

Based on the survey we had done, we had rated the importance of the needs as the survey

result which shown below:

No. Needs Imp

1 high efficiency 5

2 low maintaining rate 3

3 with maximum sustainable material build 2

4 easy to replace in case of failure 1

5 cheap maintenance fee 4

6 low in cost 4

7 light weighted 3

8 long lasting 5

Metric and unit:

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After rating the importance of the needs, a metric must be assign to measure the specification

of the product which related with the customer needs. The metric and unit table are

constructed as below:

No Metric Unit

1 See back coefficient of the thermoelectric module V/K

2 Electric conductivity of the thermoelectric module Ω-1.m-1

3 Total number of thermoelectric module -

4 Maintaining period apart Month

5 Remove time needed S

6 Time needed to install S

7 Sustainability index -

8 Price of the generator RM

9 Mass of the thermoelectric generator Kg

10 Electrical impedance of the circuit along the generator Ω

11 Temperature of the cold side of the module K

12 The temperature of the hot side of the module K

13 Thermal shock parameter Rt

Matching customer need with metric

After constructing the metric table, we need to match the metric with the customer needs to

ensure all the needs can be measure and be improve with our design with batter specification.

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See

back

coe

ffic

ient

of t

he th

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Elec

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e

ther

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Tota

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f the

rmoe

lect

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Mai

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iod

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t

Rem

ove

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Tim

e ne

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Sust

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Pric

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the

gene

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r

Mas

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he th

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oele

ctric

gen

erat

or

Elec

trica

l im

peda

nce

of

the

circ

uit

alon

g t

he

Tem

pera

ture

of t

he c

old

side

of t

he m

odul

e

The

tem

pera

ture

of t

he h

ot si

de o

f the

mod

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Ther

mal

shoc

k pa

ram

eter

high

efficiency

x x x x x x x

low

maintainin

g rate

x

with

maximum

sustainabl

e material

build

x

easy to

replace in

case of

failure

x x

low in cost x

light x

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weighted

long

lasting

x x

No Needs Metric Unit

1 1 See back coefficient of the thermoelectric module V/K

2 1 Electric conductivity of the thermoelectric module Ω-1.m-1

3 1 Total number of thermoelectric module -

4 2,8 Maintaining period apart Month

5 4 Remove time needed min

6 4 Time needed to install min

7 3 Sustainability index -

8 6 Price of the generator RM

9 1,7 Mass of the thermoelectric generator Kg

10 1 Electrical impedance of the circuit along the generator Ω

11 1 Temperature of the cold side of the module K

12 1 The temperature of the hot side of the module K

13 8 Thermal shock parameter Rt

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Assigning Marginal Values

In this part, the marginal and ideal value were assign to ensure the specification have to at

least reach the marginal value and to get as close value as the ideal value.

No Metric Unit Marginal

value

Ideal value

1 See back coefficient of the thermoelectric

module

V/K >250µ >750µ

2 Electric conductivity of the thermoelectric

module

Ω-1.m-1 >1.68×10−8 > 2.0×10−8

3 Total number of thermoelectric module - >70 >80

4 Maintaining period apart month >3 >6

5 Remove time needed min <30 <20

6 Time needed to install min <30 <20

7 Sustainability index - >0.01 >1

8 Price of the generator RM >7000 <5000

9 Mass of the thermoelectric generator kg >100 <70

10 Electrical impedance of the circuit along the

generator

Ω <10000 <1000

11 Temperature of the cold side of the module K >750 >800

12 The temperature of the hot side of the

module

K <300 <200

13 Thermal shock parameter Rt >1 >10

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Benchmarking on customer needs

In this step, we need to give rating on other thermoelectric generator which already in market

as a guide for us to decide the final specification of our product.

Imp

TEG

1-12

63-4

.3

tPO

D1

G2-

30-0

313

1 high efficiency 5

2 low maintaining rate 3

3 with maximum sustainable material build 2

4 easy to replace in case of failure 1

5 cheap maintenance fee 4

6 low in cost 4

7 light weighted 3

8 long lasting 5

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Customer Needs

Benchmark on metric:

After benchmarking the customer needs, we need to benchmark the metric of the

market product to finalize our specification to ensure our product to be competitive

compare to other which already in market:

No Needs Metric Imp Unit

TEG

1-12

63-

4.3

tPO

D1

G2-

30-0

313

1 1 See back coefficient of

the thermoelectric

module

5 V/K 500µ 700µ 350µ

2 1 Electric conductivity of

the thermoelectric

module

5 Ω-1.m-

1

1.5×10−8 1.7×10−8 1.5×10−8

3 1 Total number of

thermoelectric module

5 - 76 82 48

4 2,8 Maintaining period

apart

3 Month 6 12 3

5 4 Remove time needed 1 min 30 30 30

6 4 Time needed to install 1 min 30 30 30

7 3 Sustainability index 3 - 0.001 0.004 0.001

8 6 Price of the generator 4 RM 3000 8000 5000

9 1,7 Mass of the

thermoelectric

generator

4 Kg 140 120 150

10 1 Electrical impedance

of the circuit along the

generator

5 Ω 1600 1200 1500

11 1 Temperature of the

cold side of the module

5 K 500 800 600

12 1 The temperature of the 5 K 300 400 400

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hot side of the module

13 8 Thermal shock

parameter

5 Rt 15 16 15

1.8 Final specification:

After knowing the marginal and ideal value, a final specification had to be assign which can

cope with the used of the product.

No Metric Unit Value

1 See back coefficient of the thermoelectric module V/K 500µ

2 Electric conductivity of the thermoelectric module Ω-1.m-1 1.8×10−8

3 Total number of thermoelectric module - 74

4 Maintaining period apart month 6

5 Remove time needed min 25

6 Time needed to install min 25

7 Sustainability index - 0.1

8 Price of the generator RM 6000

9 Mass of the thermoelectric generator kg 80

10 Electrical impedance of the circuit along the generator Ω 1000

11 Temperature of the cold side of the module K 800

12 The temperature of the hot side of the module K 350

13 Thermal shock parameter Rt 15

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1.9 Parametric Design

Assembly Drawing of Thermoelectric Generator

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Detail Drawing of Heat Exchanger

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Detail Drawing of Thermoelectric Modules

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1.10 Material selection

In this section, we had take great concern in selecting the best material to build the system.

This is to ensure that the result of the product can reach the requirement that we set

previously.

As shwon below is a TEG system which consist of the thermoelectric element, ceramic wafer

where heat transfer is significant in that part and also the bridge which connect the N and P

conductor.

So in our material selection part, we have decided to concentrate on the 3 element in our

design.

Thermoelectric element

Bismuth telluride :

The role of thermoelectric element in our system are singnificant. It is they key to

convert thermal energy to electric energy. If this material does not fullfill the requirement, the

system not be able to generate sufficient electrical power to provide the vehicle secondary

load needs(aircondition, headlamp, etc).

To be able to generate sufficient electrical power, the thermoelectric element must have high

value of seebeck coefficient which indicate how sensitive the element to respond when heat

energy absorbed.

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For Bismuth telluride, it posses seeback coefficient of −287 μV/K at 54 Celsius. This element

were predict to have more than 700 μV/K in magnitude when operating above 500K which is

our operating temperature. Beside that this element had relatively high electric conductivity

which is 1.1×105 S·m/m2 compare to other thermoelectric element which can go up to micro

scale.

Bridge between N and P pole

Brazable brass(sand-cast) :

The role of the bridge is to complete the electrical circuit and serve as a bridge for the

electron to move along the circuit. To optimize the efficiency of the system, the material

selected must posses high electrical conductivity which mean low electrical resistivity. Beside

that, this material also must have high melting point and high resistance from oxidation when

operated in high temperature because the TEG is operated at temperature of about 700Co.

Copper is well known as high electric conductivity material which are widely use as wiring in

electrical appliance. But to select a material which have high melting point and would not

oxidize at temperature up to 700Co would not be easy.

After go through a couple of copper made alloy, we had found that brazable brass posses the

required property to play that role in our system. Thie material consist of low electrical

resistivity which is 5.89 - 6.92µohm.cm and also melting point as high as 1010Co. Beside that,

the durability on oxidation at 500Co was good compare to most of the other bronze made

material. This had conclude that brazable brass as our material to form the bridge between the

N and P pole.

Ceramic wafer

ALN230 (aluminium nitride and silicon nitride ceramic substrate materials)

In this section, a very high thermal conductivity material is needed because the role of

this material is to transfer the heat energy from the heat source to the thermoelectrical

material. The amount of heat energy can be extracted depend on the thermal conductivity of

this material. Beside that the thermal expansion of the material should be considerably low to

avoid failure in system when it expend.

In this part of the system, we have consider a few thermal conductive ceramic substrate as

shown table below. Due to the significant distinct of the thermal conductivity property of

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ALN230, and since the thermal expansion different between each other are not significant,

ALN230 had conclude our material selection in this part.

As shown as table above, the thermal conductivity of ALN230 is about 30% more compare to

other ALN material. On the other hand the thermal expansion were maintain the same. Since

the material were not be conjected on any physical loading function, so the mechanical

property were not take into account.

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CHAPTER II

2.0 Control System Analysis

TEG is a device to produce electric power from heat source by absorb the heat from the surface and convert the heat through the medium thermoelectric to produce the electrical power. In TEG progress, Now our main part in concerned on the heat exchanger where the TEG system were attached to Heat exchanger to absorbed the heat that flow across the heat exchanger.

Below are the block diagram of controlling part in order to produce the maximum value output of temperature difference. The maximum voltage can produced by TEG is proportional to the temperature difference. the output of the system analysis produced delta T as the output since TEG need the temperature difference to produce voltage output. However, since the electrical measurement does not put as priority in the analysis. The output of the system is the temperature difference produce from the heat exchanger.

The relation between the temperature absorbed by TEG is inversely proportional to the speed of fluid. Therefore, to control the speed of the gas inside the exhaust pipe before entering the heat exchanger, a pinch valve is use to control the speed. A sensor and a controller is entered to the system to control the pressure exerted on the pinch to control the valve opening and allow the air to flow based on suitable temperature required in heat exchanger in order to produce maximum temperature difference.

The cooling system is the ambient air from the surrounding. Ambient air is the outdoor air in which humans and other organisms live and breathe. Ambient air temperature is normally under standard pressure at 1 atm is 25 C. However since the ambient air use to cooling the exhaust gas, it is surrounded the car body and the temperature of ambient air is much higher than standard temperature since it is under the car body and near the engine system. Therefore the temperature is assumed as 27 C. In the system, the ambient air is assumed as an uncontrollable situation since the temperature is naturally from the outside temperature. Therefore, the temperature from cooping system is called as disturbance, Td. It is appear in between the process of heat exchanger and TEG since TEG and heat exchanger need ambient air as the input to produce the temperature difference.

Heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The heat exchanger is designed to allow the hot temperature gases to flow inside it and give the heat near the wall of the heat exchanger. From the gases path flow, the temperature analysis shows the maximum temperature is transferred near the wall of the heat exchanger. The temperature is then absorbed by TEG system that attached to all the surface of the heat exchanger to maximize the total area of heat absorber. The temperature absorbed by TEG predicted to be as high as possible to produce the maximum temperature difference since the outside temperature ambient air is 27 C.

However to control the suitable temperature on the surface, a thermostat is use to control the temperature to be adjustable depend on the ability of the TEG absorption because the overheat

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of the TEG can cause damage to the electrical part of the element in producing the voltage. Therefore aome insulator is put in between the TEG so that the temperature is control to make sure the material can withstand the temperature. Since, there will be some heat loss to surrounding, the thermostat is able to measure and control the temperature needed. A thermostat is a component of a control system which senses the temperature of a system so that the system's temperature is maintained near a desired set point. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature.

2.1 Block diagram

2.2 Block Diagram Analysis

In order to simplifying the block diagram, the heat from exhaust and the temperature difference are considered as the input and the output of the system.

Y(s) = output

R(s) = input

Deleting the first feedback

Y(s) = G2. G3.E(s)

E(s) = G1 – H1 . Y(s)

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Exhaust

heat, R(s)

Heat exchangerG2

TEG , G3

∆T (Y

(S))

Sensor, H2

Valve , G1-

+

Td

Thermostat, H1

+-

+

+

Td

Y(s) [1 + H1.G2.G3] = G1.G2.G3

Y(s) = [G2. G 3

1+ H 1.G2. G 3] *G1

Y(s) = [G2. G 3

1+ H 1.G2. G 3]. G1 . E(s)

E(s) = R(s) – H2. Y(s)

Y(s) [1+H 2.G1. G 2.G 31+H 1. G 2.G 3

¿=R .G 1. G2.G31+ H 1.G2. G 3

Y(s) = G 1.G 2. G3

1+ H 1. G2. G 3+H 2. G1. G 2.G 3. R(s)

Since the system consist the disturbance from the surrounding, therefore the system with the disturbance is

From Td(s)

Y (s )R (s)

= G 31+H 1.G 2. G3+H 2. G1. G 2.G 3

= T(s)

E(s) = G3

1+ H 1. G2.G 3+H 2.G 1.G 2. G3 . Td(s)

The real output from the disturbance is

Y(s) = Y(s) + E(s) from the disturbance

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R(s) G1 Y(s)

H1

+-

R(s)

Y(s)

Y(s) = G 1.G 2.G 3. R

1+ H 1.G2. G 3+H 2.G 1.G 2.G3+ G 3.Td

1+H 1. G2. G 3+H 2.G 1.G 2.G 3

Y(s) = G 3

1+ H 1.G2. G 3+H 2.G 1. G 2.G 3[G 1.G2. R+Td ]

The sensitivity of the system also can be determined by

S = δTδG

. GT

T(s) = G3

1+ H 1. G2.G 3+H 2.G 1.G 2. G3

∂ T∂G 3 =

(1+ H 1.G2.G 3+H 2.G 1.G 2.G3 ) (G 1.G 2 )−(G 1.G 2. G3 )(H 1.G 2+H 2. G1. G 2)(1+H 1.G2.G 3+H 2.G 1.G 2.G 3)2

S = 1

1+ H 1. G2. G 3+H 2.G 1.G 2. G3

2.3 Component of block diagram

From each component, the transfer function of each component can be determined from the input and output of the component

2.3.1 Pinch valve Pinch valve is controlled by the sensor and electronic detector and controller called as PID controller

Free body diagram of the valve

Diagram 1 Free body diagram of the valveFrom the diagram above, the pressure were applied on both side of the valve to control the flow rate of the fluid flow. Therefore, from the equation of conservation of the momentum where,

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F1F2

V1

V2

∑ F=∑ ṁV ∈−∑ṁV outSince there are some external force exerted on the valve, so the force is change in term of f(t)

From the flow, the assumption from the flow is steady flow incompressible flow inviscid

The equation of the valve isf(t) = ṁV1 -ṁV2 since the flow is steady, mass flow rate inlet is constant to the mass flow rate outlet and the input of the valve is the mass flow rate from the engine. Therefore,

ṁ (V1-V2) = f(t)d mdt

(V 1−V 2 )=f (t )

Transform to laplace function,s M(s) (V1-V2) = F(s)

G1 = M (s)F(s)

= 1(V 1−V 2 ) s

In controlling the valve, the sensor from feedback controller is use to control the valve opening depend on the required flow across the heat exchanger. Therefore, PID system is the best way in determining the controller valve from sensor or PID in order to control the flow. The input from the sensor were transmitted to the valve as passing through the controller of PID. PID controller is called Proportional-Integral-Derivatives controller. A PID controller calculates an "error" value as the difference between a measured process variable and a desired set point. The controller attempts to minimize the error by adjusting the process control inputs.

From the Proportional controller, Kp= Kp where

Y(s) = Kp .G(s)

1+G ( s ) . Kp

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2.3.2 Heat exchanger

Heat exchanger is controlled by the valve in allowing the fluid flow across it to provide required temperature. The energy transfer from the heat exchanger will absorb by Thermoelectric generator (TEG) that will change the heat into a voltage required to reuse in the automotive system.

Figure 2: Free body diagram of heat exchanger and flow of heat

From the conservation of mass where Assuming that the flow is- Incompressible- Steady flow- Move in 2D (x and y axis)- Inviscid

The heat transfer from the heat exchanger is a result of heat transfer through convection. Convection is a medium of heat transfer from a solid body to or from the moving fluid at certain velocity. Therefore, from equation of heat transfer through convection,

dQdt

=hA dT

Where,

h = coeeficient of convectionA= total surface areadt = Temperature differenceL = length of heat exchanger

transfer function of Q,

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m2

m3

T absorb

Q(s )h ( s)

= A dTs

and also from the equation of Reynold number,

Re = VLv and Re =

hc

Transform in laplace transform,

ℜ(s)V (s)

=Lv and

ℜ(s)h (s)

= 1C

Therefore, a form of chain rule created from the combination of these three equations

Q(s )V (s )

=Q(s)h(s)

. h(s)ℜ(s)

. ℜ(s )V (s)

Q ( s )V ( s )

=( A dTs )( c )( L

v)

G2 =Q(s )V (s )

= AcLdTvs = ALc DT

vs ’

Where the input of the system is the velocity of the flow and the output is the heat transfer absorbed form the surface of heat exchanger into TEG.

2.3.3 Thermoelectric Generator (TEG) system

Thermoelectric generator is a generator that converting heat energy into electrical energy by using the see beck effect. TEG system use the temperature difference produce from internal and external temperature. The higher difference of temperature will produce the maximum output of voltage. TEG is attached to all part of heat exchanger surface to absorb the temperature as much as possible.

Figure 3. Themoelectric generator design

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From the conservation of energy and since the output of TEG is the current,

dQdt

=I ( t )V

Where,

I(t) = current produce by TEG

V = voltage of TEG

The laplace transform of the Q equation produce,

sQ(s) = I(s)V

G3(s) = Q(s )I(s)

=Vs

New block diagram shows

Now assume that H1(s) = 1 since we use H1 as thermostat

Thermostat is a device that control and read the temperature required to transfer in TEG. Since the temperature does not change with any variable, we let H1(s) as 1

From the equation

Y(s) = [G2. G 3

1+ H 1.G2. G 3]

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R(s)

Y(s)

H1H2

k+ +

Td

+

+

_ _

Y(s) = ( ALdT

s )( Vs)

1+ (1 )( AldTs )( V

s)

Y(s) = ALV dT

s2+ ALdT V

Overall transfer function of the system is

Y(s) = G 1. G2.G3

1+ H 1. G2.G 3+H 2.G 1.G 2. G3

G1.G2.G3 = ALcdT V

v (V 1−V 2 ) s3

¿¿

After including the disturbance, the disturbance shows that the ambient air was entered as the uncontrolled condition, therefore the equation of overall transfer function with the disturbance is

Y(s) = G 3

1+ H 1.G2. G 3+H 2.G 1. G 2.G 3[G 1.G2. R+Td ]

G1 = M (s)F(s)

= 1(V 1−V 2 ) s

G2 =Q(s )V (s )

= AcLdTvs = ALc DT

vs ’

G3(s) = Q(s )I (s)

=Vs

From the fluid and heat transfer analysis, we assumed

V1-V2 = 1.5 m/sL = 0.5 mA = 3.6 x 10 ^-3v = 16.79 x 10^-6 at condition air 1 atmT1-T2= 329 Kc = 343.2 m/s as the speed of sound

Therefore,

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G(s)= V ALcdT +V v (V 1−V 2 ) s2

v (V 1−V 2 ) s3+ ALcdT V (V 1−V 2 ) s+ALc V dT

G(s) = (812. 97+1.02 x104 s2)2.5 x 10−5 s3+3.7 s+812.97

from the position controller, we use PID system where PID system is act as a controller of a sensor of device. In this case, we use PID system in controlling the sensor of valve motion to produce a movement of sensor depending on suitable situation. There are three types of PID controller. However, in reducing the error of the system, a proportional controller is suitable to use as controller When the k is increasing, it is able to reduce the steady state error, reduce the sensitivity of the disturbance and able to change the pole location.

Let Kp = 2

Y(s) = Kp . G(s)

1+G ( s ) . Kp

Y(s) = G 1. G2.G3. k

1+ H 1.G2. G 3+H 2.G 1.G 2.G3

Now we calculate the pole position of the root.

The equation produced is the third order equation when the denominator shows s^3

Y(s) = 812.97 k

2.4555 x 10−5 s3+1219.5ks+812.97 k

2.4555x10^-5.s^3 +1219.5(1)s +812.97(1) = 0

S1 = -0.67

S2=0.3 ±7047.2i

Since there are one of the pole that is negative, therefore the system is not fully stable since it is going towards positive direction.

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Figure 4 Graph of stability of root locus depend on k increasing

Steady state error if k=1 is

yss = lims → 0

s .( 812.97 k2.4555 x10−5 s3+1219. 5 ks+812.97 k ) .( 1

s )Yss = 1

Ess = r(t) –Yss

Ess = 1-1

= 0

Therefore, the system shows that steady state error of the system is zero. Therefore, the system have high sensitivity.

The calculation of sensistivity is,

From the formula

S = 1

1+ H 1. G2. G 3+H 2.G 1.G 2. G3

S= 1

0.982+ 145354.5s2 +31937536.8

s3

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-0.76

R

Im

S= s3

0.982 s3+145354.5 s+31937536.8

Determining the sensitivity by

lims → ∞

s . 1

0.982+ 145354.5s2 +31937536.8

s3.(1/s)

S= 1/0.982

S=1.018

Therefore, the sensitivity of the system is 1.018

CHAPTER III

3.0 Fluid Mechanics Analysis

3.1 Concept and properties of flow

3.1.1 Flow Concept

The system works in such a way that, air flow is sucked in into the air duct through the

covers, it then flows in the ducting passing through the heat exchanger transferring the energy

to the fluid generator system and then finally out to the open air.

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Figure 3.1

The predicted flow sequence is as follows:

i) An exhaust inlet, air is sucked into the duct openings.

ii) A uniform flow, air flow in duct follows duct geometry.

iii) A laminar flow, caused as flow passes through heat exchanger and fan.

iv) An exhaust outlet, air is blown out emanating out from the duct opening.

3.1.2 Properties of flow

For this project we limit the Fluid Mechanics analysis to 2 dimensional flows. The fluid

analyzed is air which we assumed to be isentropic which means it is adiabatic and is a

frictionless flow.

i) Mach Number

We first analyze whether the flow is compressible or incompressible.

Since it is an isentropic flow, ds=s2−s1=0, the speed of sound, c is calculated

as follows:

c=√kRT

Where:

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c, is the speed of sound

k, is the Boltzmann constant = 1.399

R, Gas constant = 287 J/(Kg.K)

T, Temperature of air flow = 973 K = 700 C

c=625.04 m /s

Mach Number is given by , Ma≡ M = vc

Where:

vt, maximum velocity of air flow in duct = 7.0 m/s

Ma≡ M =0.011

M ≤ 0.3

Which means, this is a Nearly-Incompressible flow with nearly symmetrical pressure

wave, changes in density is negligible (<5%) and the Bernoulli equation can be used.

ii) Reynolds Number

To determine if the flow is laminar or turbulent we need to calculate the Reynolds

Number by using this formula :

ℜ= ρVD

Where by using table properties of air at 1 atm ( Table A-19 )

ρ, is the density of air at 1atm and T=573K = 0.61762 kg m-3

D, is the hydraulic diameter of the pipe = 0.046 m

, is the dynamic viscosity of air = 2.9382 (kg/m s)x10-5

ℜ=3867.74

ℜ<4000

So , we can say the flow is a laminar flow.

3.2 Flow Pattern and Properties

The flow is a laminar flow and by using Star CCM we generated the following

observations. In order to use Star CCM, we first need to create a volume mesh, shown

in figure 1 below. Secondly we set the parameters related to the flow, they are:

I) Implicit unsteady

II) Ideal Gas

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III) Segregated Flow with Segregated Fluid Temperature

IV) Gravity

V) Three Dimensional

VI) Inviscid Flow

VII) Initial condition

Temperature : 300 c

Velocity : 7 m/s

Pressure : 1 atm

VIII) Inlet Boundaries

Velocity : 7 m/s

Temperature : 700 c

IX) Outlet Boundaries

Pressure : 1 atm

Temperature : 300 c

3.2.1 Mesh scene

Base size : 30 mm

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Figure 3.2 : Volume mesh

Figure 3.3 : Velocity streamlines

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Figure 3.4 Temperature streamline

Figure 3.5 Pressure streamlines

We observe that streamlines are laminar. The resistance to flow in a liquid can be

characterized in terms of the viscosity of the fluid if the flow is smooth. The laminar

streamlines are shown above.

3.2.2 Scalar scene

Velocity, temperature and pressure represented magnitude with smooth filled colour.

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Figure 3.6 Scalar volume

Figure 3.7 Scalar velocity

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Figure 3.8 Scalar temperature

Figure 3.9 Scalar pressure

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3.2.3 Vector scene

Velocity vector represented by small arrows in the duct. The error represent the

direction flow while the colour determines its velocity magnitude. We can see that the

outlet speed is approximately 4.0 m/s with the inlet speeds varying from 7 m/s. to 5

m/s .

Figure 3.10 Vector velocity

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Figure 3.11 Vector vorticity

The local spinning motion of a fluid near some point, as would be seen by an observer located

at that point and traveling along with the fluid. The vorticity vector would be twice the

mean angular velocity vector of those particles relative to their center of mass, oriented

according to the right-hand rule. This quantity must not be confused with the angular velocity

of the particles relative to some other point.

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3.3 Flow in Heat Exchanger

Figure 3.12 Flow in heat exchanger

After a device has gone through its start up process it could enter a steady flow process.

There are few definitions that can be used to describe a steady flow process. First, a steady

flow process has the fluid flowing through the CV steadily. Since the fluid is flowing steadily,

the mass flow value through the device would be constant. Next a steady flow process has no

intensive or extensive properties that would change with time. This would mean that the

specific volume, internal energy, and others would remain constant, and for these values to

remain constant that would mean that the energy going into the device must equal the energy

coming out of the device. For a device to be considered a steady flow device it must be able to

operate under the same conditions for a long period of time under a steady flow process.

There are a number of steady flow devices. However, only a few will be discussed here. They

are Diffusers and Nozzle .

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Figure 3.13 Flow through diverging

A diffuser on the other hand is the exact opposite of a nozzle, instead of increasing the

velocity of a fluid it decreases the velocity of a fluid. Diffuser is to be our inlet boudaries. In

order to do this for subsonic flows the entrance of a diffuser is larger than its exit. While for

supersonic flow the entrance is smaller than its exit. Refer to the image above . Based on star

ccm sofware used , we defined the velocity enter around v1 is 7m/s to v2 is 4m/s .

Figure 3.14 Flow through converging

A nozzle is a device that will increase the velocity of a flow at the expense of pressure.

Nozzle becomes our outlet boundaries . For subsonic flows a nozzle will have a wider cross-

sectional area at its entrance, that will slope down to a smaller cross-sectional area at its exit.

On the other hand if the flow is supersonic, in order for the nozzle to increase the flow

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velocity the entrance cross-sectional are is smaller than the exit cross-sectional area. Refer to

the images above based on star ccm sofware , we defined the velocity pass out the nozzle

around v1 is 2m/s to v2 is 4m/s .

3.4 Comparison between different velocity

Different velocity inlet effect the flow of air pass through the heat exchanger . Lets we make

some comparison if we set up the velocity inlet with 5m/s and 12 m/s as we can control the

valve in our system .

Figure 3.15 Velocity and temperature at 5 m/s

The velocity too slow when it enter the inlet eventhough the flow is smooth but if we relates

with heat transfer , the temperature decrease when it already enter the heat exchanger because

heat loss occur at the tube is very high before enter exchanger .

Figure 3.16 Velocity and temperature at 12 m/s

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Then when we compared this simulation above , when we use a 12 m/s, the speed too fast.

Flow from the inlet directly to the outlet without generates a lot of heat causing decreasing

temperature when in the heat exchanger because the temperature cools quickly . So we decide

the best speed is 7 m/s .

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CHAPTER IV

4.0 Heat Transfer Analysis

For an automobile engine, there are two main exhaust heat gas sources which are readily

available. The radiator and exhaust gas systems are the main heat output of an internal

combustion engine. The radiator system is used to pump the coolant through the chambers in

the heat engine block to avoid overheating and seizure. Conversely, the exhaust gas system of

an IC engine is used to discharge the expanded exhaust gas through the exhaust manifold. For

this integrated project, we will concentrate on recovering the waste heat from exhaust gas

system. In order to utilise the waste heat from the exhaust gas system, we have used

Thermoelectric Generator system.

Heat transfer analysis for Thermoelectric Generator (TEG) system will cover about the

temperature distribution inside the exhaust system and how to utilise the heat inside exhaust

system. TEG is placed onto the outside surface of heat exchanger so that it will capture the

heat from heat exchanger. Temperature difference between inside and outside of the heat

exchanger will cause the TEG to generate electricity by using the seebeck effect.The higher

the temperature difference between region inside and outside of the heat exchanger, the higher

the heat transferred across the wall. As the result, TEG module can be optimised in order to

generate as much as electricity.

4.1 Exhaust Gas Properties

Engine exhaust gases are discharged into the environment through the exhaust system.

The designer of the exhaust system components must know the exhaust gas properties in

order to do analysis on the exhaust system. The largest part of most combustion gas is

nitrogen (N2), water vapor (H2O) (except with pure-carbon fuels), and carbon dioxide (CO2)

(except for fuels without carbon). A relatively small part of combustion gas is undesirable

noxious or toxic substances, such as carbon monoxide (CO) from incomplete combustion,

hydrocarbons from unburnt fuel, nitrogen oxides (NOx) from excessive combustion

temperatures, Ozone (O3), and particulate matter (mostly soot). Composition and properties

of exhaust gas is important to know because the properties of any gas vary at different

temperature. In order to get a good result for calculation part, we need to consider some

parameters such as temperature variation, pressure, velocity and others. From that, we can

59 | P a g e

determine the properties of the exhaust gas system. Table 4.1 shows the composition of

exhaust gas for combustion of petrol and diesel.

Table 4.1 : Composition of exhaust gas.

N 2 = Nitrogen CO = Carbon Monoxide

CO2 = Carbon dioxide NOX = Nitrogen oxides

H 2O = Water SO2= Sulphur dioxide

O2 = Oxygen PM = Particulate matter

CX HY= Hydrocarbons

Based on the data of components of combustion product, we can compare it to the

components of ambient air. The composition of exhaust gas and ambient air are almost

similar. As an approximation, the properties of air can be used for exhaust gas calculations.

The error associated with neglecting the combustion products is usually no more than about

2%. In a more rigorous approach, corrections must be taken to account for the actual exhaust

gas composition (increased H2O and CO2, decreased O2). In order to get the best result for

this research, many experiments need to be done so that every data and information can be

recorded. Due to time and budget constraint, we lack of information and data, therefore,

wemay use the properties of air for exhaust gas calculations. Table 4.2 shows the properties of

air respect to temperature variation.

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T ρ h s c p K µ v

260 1.340 260.0 6.727 1.006 0.0231 1.587 10.73

280 1.245 280.2 6.802 1.006 0.0247 1.785 13.20

300 1.161 300.3 6.871 1.007 0.0263 1.983 15.68

350 0.995 350.7 7.026 1.009 0.0301 2.075 20.76

400 0.871 401.2 7.161 1.014 0.0336 2.286 25.90

450 0.774 452.1 7.282 1.021 0.0371 2.484 28.86

500 0.696 503.4 7.389 1.030 0.0404 2.671 37.90

600 0.580 607.5 7.579 1.051 0.0466 3.018 51.34

800 0.435 822.5 7.888 1.099 0.0577 3.625 82.29

1000 0.348 1046.8 8.138 1.141 0.0681 4.152 117.80

1200 0.290 1278 8.349 1.175 0.0783 4.690 159.10

1400 0.249 1515 8.531 1.207 0.0927 5.170 205.50

Table 4.2 : Physical properties of air (p=101.13kpa)

T Temperature, K

ρ Density, kg /m3

h Specific enthalpy, kJ /kg

s Specific entropy, kJ /(kg .K )

c p Specific heat at constant pressure, kJ /(kg .K )

K Thermal conductivity, W /(m. K )

µ Dynamic Viscosity, kg /(m . s)×10−5

v Kinematic viscosity, (m¿¿2/s )×10−6 ¿

Table 4.2 above shows the physical properties of air at different temperature. At 1 atm,

by varying the temperature of air, the physical properties of air such as density, specific heat,

thermal conductivity, viscosity and others will changed also. Therefore, we need to do some

analysis on temperature distribution inside the exhaust system. By knowing the output exhaust

gas temperature from internal combustion engine, we can run a simulation in Star CCM

software for fluid mechanic analysis. Based on the Fluid mechanic analysis, we can calculate

the temperature variation along the exhaust pipe and inside heat exchanger.

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4.2 Temperature Distribution Inside Exhaust Gas System

In order to know the temperature distribution inside the exhaust gas system, we can run a

simulation by using Star CCM software. Based on the fluid mechanic analysis, we can

calculate the temperature variation along the exhaust pipe and inside the heat exchanger.

Figure 5.1 below shows the temperature distribution inside the exhaust gas system.

Figure 4.1 : Temperature distribution inside the exhaust system.

Based on our research, exhaust gas typically run between 850K and 1000K. For this

integrated project, we have chosen 973K (700°C) as the output temperature of exhaust gas

from the internal combustion engine. The temperature of exhaust gas will decrease when

flowing inside the exhaust pipe and heat exchanger part. For exhaust pipe component, we

need to make sure that it is well insulated in order to prevent any heat loss to outside when

flowing inside the pipe. Selection of material for this part is very important because by

maintaining the exhaust temperature and reducing heat loss, we can ensure the inlet exhaust

temperature of heat exchanger is maintained at high temperature. By maintaining the exhaust

gas at high temperature, we can increase the amount of heat transferred across the wall of heat

exchanger and then pass through the TEG modules.

Based on the analysis, the inlet and outlet exhaust gas temperatures of heat exchanger

are 773.14K and 573.14K respectively. Basically, the average of temperature inside the heat

exchanger can be considered with the value of 673.14K. For outside region temperature, we

assume the normal surrounding temperature of ambient air to be 303 K. The higher the

temperature difference between region inside and outside of the heat exchanger, the higher the

heat transferred across the wall. As the result, TEG module can be optimised in order to

generate as much as electricity.

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4.4 Heat Transfer Calculations

For heat transfer analysis, we need to calculate on how much heat can be transferred from inside to the outside of heat exchanger. By knowing the amount of heat being transferred to the outside, we can know the amount of heat transfer through the TEG modules. The objective of this project is to get the highest temperature difference so that the usage of TEG modules canbe optimised and generate as much as electricity. Amount of electricity generated depends on temperature difference between hot region (region inside the heat exchanger) and cold region (region outside the heat exchanger which is ambient air).

In order to calculate the amount of heat transfer for TEG system, we must calculate the value of thermal resistance of each material and also resistance due to effect of convection and radiation. These thermal resistances can be shown by forming a thermal resistance network.

4.4.1 Thermal Resistance Network

Selection of material procedure is needed in order to select the best material and to improve the amount of heat transfer throughout the heat exchanger and pass through the TEG modules. Thermoelectric modules are attached on the outside surface of heat exchanger. In order to maximize the utilization of waste heat from the exhaust gas, the exhaust pipe must be well insulated so that heat loss along the exhaust pipe can be reduced. Besides, outside surface area of heat exchanger also must be utilized by placing the thermoelectric modules. It is to ensure that all heat whichpassing through the heat exchanger wall can be absorbed by the TEG modules.

Figure 4.2 : Thermal resistance network of TEG system

Rconv , Exhaust Resistance of exhaust gas convection

Rcu Resistance of copper

R s Resistance of ceramic substrate (Aluminium Nitride)

RBT Resistance of Bismuth Telluride

Rconv , Air Resistance of air convection

Rrad , Air Resistance of air radiation

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4.4.2 Resistance of Exhaust Gas

Figure 4.3 : Cross section area of heat exchanger.

Formula of resistance of exhaust gas due to convection :

Rconv , Exhaust=1

(hconv , Exhaust)( A s)

In order to determine the value of heat transfer coefficient for convection of exhaust gas, we need to calculate the Reynold number inside the heat exchanger.

Cross section Area , Ac=0.196 m×0.036 m=0.007056 m2

Perimeter , p=2 (0.196 m )+2 (0.036 m )=0.464 m

Characteristic length for this case (rectangular cross section) is hydraulic diameter, Dh:

Dh=4 AC

p=

4 (0.007056 m2)0.464 m

=0.060828 m

Based on the fluid mechanic analysis, the average velocity (vavg¿ of exhaust gas inside the heat exchanger is 3.23 m/s.

Properties of air at T = 673.14K :

ρ=0.5270 kg/m3

c p=1068.55 J /kg . K

k=0.05066 W /m . K

v=6.209207 ×10−5m2 . s

µ=3.248734 × 10−5 kg/m . s

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Reynoldnumber :

ℜ=vavg Dh

v=

(3.23 m /s)(0.060828 m)(6.209207× 10−5 m2/s)

=3164

Prandtlnumber :

Pr=c p µk

=(1068.55 J /kg . K )(3.24873 ×10−5 kg /m. s)

0.05066 W /m . K=0.685242

Nusseltnumber :

Nu=h Dh

k=(0.023 ) ℜ0.8 Pr0.3=(0.023 ) (31640.8 ) (0.6852420.3 )=12.962673

Therefore, the value of heat transfer coefficient of exhaust gas (convection) can be calculated by using this formula:

hconv, Exhaust=kNuDh

=(0.05066 W /m .K )(12.962673)

0.060828 m=10.7959W /m2 . K

Total wall area, A s :

A s=2 A1+2 A2

Wall area, A1 :

A1=0.196 m× 0.3m=0.0588 m2

Wall area, A2 :

A2=0.036 m× 0.3 m=0.0108 m2

Therefore, the total wall area, A s :

A s=2 A1+2 A2=2 (0.0588 m2 )+2 (0.0108 m2)=0.1392 m2

After calculate the value of heat transfer coefficient of exhaust gas (convection) and total wall area, resistance of exhaust gas due to convection can be calculated :

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Rconv , Exhaust=1

(hconv , Exhaust)( A s)= 1

(10.7959 W /m2 .K )(0.1392 m2)=0.665429 K /W

4.4.3 Resistance of Heat Exchanger Wall

Formula of resistance of heat exchanger wall (copper) :

RHE(Cu)=L1

(kCu)(A s)=

(0.002 m)(386 W /m . K )(0.1392 m2)

=3.72223 ×10−5 K /W

Where,

L1=0.002 m kCu=386 W /m .K A s=0.1392m2

4.4.4 Resistance of Ceramic Substrate (Aluminium Nitride, ALN230)

Formula of resistance of ceramic substrate (ALN230) :

RS=L2

(k ALN 230)( A s)=

(0.001m)(230W /m. K )(0.1392m2)

=3.12344 ×10−5 K /W

Where,

L2=0.002 m k ALN 230=230 W /m. K A s=0.1392 m2

4.4.5 Resistance of Metal Conductor (Copper)

Formula of resistance of metal conductor, Copper:

RCu=L3

(kCu)( A s)=

(0.001 m)(386 W /m. K )(0.1392 m2)

=1.86112×10−5 K /W

Where,

L3=0.001 m kCu=386 W /m .K A s=0.1392m2

4.4.6 Resistance of Bismuth Telluride

Formula of resistance of Bismuth Telluride :

RBT=L4

(kBT )( A s)=

(0.001 m)(7.97 W /m. K)(0.1392m2)

=9.013686× 10−4 K /W

Where,

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L4=0.001 m k BT=7.97 W /m. K A s=0.1392 m2

4.4.7 Resistance of Air due to Convection

The cooling of outermost surface of TEG system is by free convection of air. The range of typical values of convection heat transfer coefficient for free convection of air is 2W /m2 K until 25W /m2 K . Before calculating the value of convection heat transfer coefficient of air, some assumptions must be made which is :

Assumptions:

a) Type of convection of air is free convection.b) The value of convection heat transfer coefficient used is 20W /m2 K .

For this case, we use the standard value of convection heat transfer coefficient for air which is 20W /m2 K .

hconv, Air=20W /m2 K

Resistance of convection of air :

Rconv , Air=1

(hconv , Air)( A s)= 1

(20W /m2 K )(0.1392 m2)=0.359195 K /W

4.4.8 Temperature of Surface inside the Heat Exchanger

Temperature of surface inside the heat exchanger can be calculated by using formula :

T outlet=T s 1−(T s 1−T inlet ) exp (−h A s

m c p)

h A s

mc p=

(10.7959W /m2 . K)(0.1392m2)(0.012 kg /s)(1068.55 kJ /kg . K )

=0.8895

Therefore, by arranging the formula, T s 1 value can be calculated :

T outlet=T s 1−(T s 1−T inlet ) exp (0.8895)

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Figure 4.4 : Temperature distribution inside the exhaust system

Where,

T 1=T inlet=733.14 K

T 2=T outlet=533.14 K

Therefore, the value of T s 1is :

T s 1=404.50 K

4.4.9 Resistance of Air due to Radiation

In order to calculate the value of resistance of air due to radiation, we must calculate the value of radiation heat transfer coefficient first. Before calculating the value of this radiation heat transfer coefficient, some assumptions must be made which is :

The value of temperatures inside the control volume :

T ∞ 1=673.14 K

T ∞2=303 K

T s 1=404.50 K

Assumptions:

a) Outermost TEG system surface temperature, T s 2 must be higher than surrounding temperature, T ∞ 2(303 K).

Qtotal=Q conv , Exhaust=T ∞1−T s 1

R conv ,Exhaust=403.713 W

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Outermost TEG system surface temperature, T s 2be calculated by using this formula :

Qtotal=QT ∞ 1−T s2=

T ∞1−T s 2

RT ∞1−T s2

=403.713 W

Where,

RT ∞1−T s 2=Rconv , Exhaust+RHE (Cu)+2(R¿¿S)+RBT+2(R¿¿Cu)=0.66647 K /W ¿¿

Therefore, the value of T s 2 :

T s 2=T ∞1−(403.713 W )(RT ∞1−T s 2)=404.08 K

Formula of radiation heat transfer coefficient :

hrad , Air=ɛσ (T s 22+T ∞ 2

2)(T s2+T ∞ 2)

Radiation heat transfer coefficient :

hrad , Air=ɛσ (T s 22+T ∞ 2

2 ) (T s 2+T∞ 2 )

Where,

ɛ=0.85 σ=5.67 ×10−8W /m2 K

Therefore,

hrad , Air=(0.85)(5.67 × 10−8 W /m2 K )((404.08 K )2+(303 K )2 ) (404.08 K+303 K )

hrad , Air=8.69282W /m2 K

Resistance of air due to radiation :

Rrad , Air=1

(hrad , Air )(A s)= 1

(8.69282 W /m2 K )(0.1392 m2)=0.826418 K /W

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4.4.10 Combination of Resistance of Air due to Convection and Radiation

Resistance of air due to convection and radiation is shown as parallel in the thermal network resistance.

1Rcombine , Air

= 1R conv, Air

+ 1R rad , Air

= 10.359195 K /W

+ 10.826418 K /W

Rcombine , Air=0.250373 K /W

4.5 Total Resistance of TEG System

Based on the thermal network resistance for TEG system, we can calculate the value of total resistance. Total resistance can be calculated by sum up all the series resistances.

Figure 5.5 : Thermal resistance network of TEG system

RTotal=Rconv, Exhaust+RHE (Cu)+2(R¿¿S)+RBT+2(R¿¿Cu)+2RCombine ¿¿

Where,

Rconv , Exhaust=0.66543 K /W

RHE(Cu)=3.72223 ×10−5 K /W

RS=3.12344 ×10−5 K /W

RCu=1.86112×10−5 K /W

Rcombine , Air=0.25037 K /W

Therefore, the value of total resistance is :

RTotal=0.91684 K /W

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4.6 Total Heat Transfer Rate

Total heat transfer rate can be calculated by dividing the temperature difference with total resistance of the TEG system. The value of total heat transfer rate is :

Qtotal=∆ TRtotal

=T∞1−T∞2

R total=673.14 K−303 K

0.91684 K /W=403.713W

4.7 Heat Transfer Rate Across Each Wall

Heat from the exhaust gas inside the heat exchanger will passed through the wallin 2 dimensions which is in x and y axis :

Figure 5.6 : Heat transfer across heat exchanger wall.

Wall area, A1(Top surface):

A1=0.196 m× 0.3m=0.0588 m2

Qwall ,1=0.0588 m2

0.1392m2 × 403.713 W=170.534 W

Wall area, A2(¿ side surface) :

A2=0.036 m× 0.3 m=0.0108 m2

Qwall , 2=0.0108 m2

0.1392m2 × 403.713 W=31.323 W

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Wall area, A1 (Bottom surface):

A1=0.196 m× 0.3m=0.0588 m2

Qwall ,3=0.0588m2

0.1392m2 × 403.713 W=170.534 W

Wall area, A2(¿ surface) :

A2=0.036 m× 0.3 m=0.0108 m2

Qwall , 4=0.0108 m2

0.1392 m2 × 403.713W =31.323 W

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CONCLUSION

At the end of the project, we have utilized all the knowledge from the four main course in this

semester for our long learning life. The relation of all these course, Heat transfer, Fluid

Mechanics II, Control Engineering and System design give the best description about all the

knowledge to create a system in order to reuse the waste heat from the exhaust as a main

power supply in a automotive system. Therefore, a system called TEG that able to change the

waste heat from the exhaust system is created and the analysis is made from all the course we

have learned.

For System design, from the assessment for strength, weakness and constraint from

customers. Then, we have breakdown the problems into objectives, and develop general

method based on experience, technical knowledge, creativity and input from others. We come

out with a few concepts and determine which design is the best technically, economically,

stratifies customers. The product design specification is refined from the winning design

concept. Benchmarking is done with other available water dispenser in market nowadays.

For Fluid Mechanics, we analyze the exhaust gas flow in exhaust pipes and TEG heat

exchanger. Laminar or turbulent flow is determined and effect of flow inside the pipes and

heat exchanger can be analyse. Pattern of flow is generated through usage of CFD software

which is Star CCM software. From the analysis also, we can identified the accurate

temperature and speed produced by the flow of heat in exhaust. the speed of the heat can

affect the temperature of heat convection transfer.

For Heat Transfer, we have analysed on the amount of heat transfer across the heat

exchanger wall and thermoelectric modules. In order to calculate the value of rate of heat

transfer, some data such as temperature distribution inside the exhaust system can be

determined from fluid mechanic analysis. The main point of view in this system is in the heat

exchanger where it produce bigger amount of electric power with high temperature with

controllable velocity of fluid in heat exchanger.

For Engineering Control, we will analyze the internal circuit of system which

comprise of heat exchanger and thermoelectric generator system. We develop the output

(temperature difference between hot and cold side of TEG system) from input (exhaust gas

flow). Mathematical modeling is the process through which the response of the system is

obtained. From the analysis, we are controlling the fluid flow that cause the temperature

difference to be much bigger and produce more power. From the analysis, the error produce

by the system is nearly to zero and have high sensitivity in detecting the system.

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REFERENCE

Source from books,

Yunus A. Cengel & Ashin J. Ghajar, 2011. Heat and Mass Transfer, Fundamentals

and Applications. 4th edition in SI Units. New York: McGraw-Hill, Inc.

S.N. Sridhara, S.R. Shankapal & V. Umesh Babu, 2005, “CFD Analysis of Fluid Flow

and Heat Transfer in a Single Tube-fin Arrangement of an Automotive Radiator”

Proceedings of thr International Conference on Mechanical Engineering 2005,

Dhaka, Bangladesh.

Bruce R.Munson, Donald F.Young & Therodore H.Okiishi, 2006. Fundamentals of

Fluid Mechanics. 5th edition. Asia: John Wiley & Sons (Asia) Pte Ltd.

Teoman Ayhan, Hasan Karabay & Erol Genc, 1991, “ Turbulent Flow Heat Transfer

and Fluid Friction in Helical-Graterlike Turbulator Inserted Tubes”, K.T.U. Trabzon,

Turkey.

http://en.wikipedia.org/wiki/Thermoelectric_generator

http://www.sciencedirect.com/science/article/pii/S0011227511002141-effectiveness of

heatgenerator

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node131.html-

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