A RESEARCH PROJECT
ON THE
DESIGN AND ANALYSIS OF WASTE HEAT ENERGY RECOVERY
SYSTEM USING THERMOELECTRICITY
BY
AKAN, DENNIS ITEM
AK17/ENG/MAE/001
IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE
AWARD OF BACHELOR IN ENGINEERING (B. ENG) IN MARINE
ENGINEERING
JUNE, 2023
A RESEARCH PROJECT
ON THE
DESIGN AND ANALYSIS OF WASTE HEAT ENERGY RECOVERY
SYSTEM USING THERMOELECTRICITY
BY
AKAN, DENNIS ITEM
AK17/ENG/MAE/001
A RESEARCH PROJECT SUBMITTED TO THE DEPARTMENT OF
MARINE ENGINEERING, FACULTY OF ENGINEERING, AKWA
IBOM STATE UNIVERSITY, IKOT AKPADEN, MKPAT ENIN LOCAL
GOVERNMENT AREA, AKWA IBOM STATE, NIGERIA
IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE
AWARD OF BACHELOR IN ENGINEERING (B. ENG) IN MARINE
ENGINEERING.
SUPERVISOR: ENGR. HOPE IKUE-JOHN
JUNE, 2023
i
ABSTRACT
Engine running on fossil fuel has been known to constitute a greater amount of pollution to the
environment. 70-90% of ships today run of either diesel engines alone or combine power plant
systems. This diesel engine during operating emits harmful substances as well as energy to the
environment. This has triggered various campaigns on environmental pollutions from carbon
formed by exhaust gases discharged from ship's engines due to the rising worries of the
worldwide community on the environmental effect of the waste heat generated from ships and
other maritime structures. This study focused on the design and analysis of a waste heat energy
recovery system using thermoelectricity. The system was designed to recover waste heat from
industrial processes and convert it into useful electrical energy. Thermoelectric effect are the
way electrical potential is generated, by presence of temperature difference and vice versa, and
this result depend on material properties of thermocouples and their size, such as areas and
lengths; Bismuth telluride (Bi2Te3) has been selected in this research project as the
thermoelements materials. Thermoelectric generator (TEG) was used as the main component
to convert waste heat into electricity. The major components considered in this research is the
semi-conditions (p-type and n-type), ceramic substrates, heat sink for cooling, heat source. The
performance of the TEG was analysed under different operating conditions, such as
temperature gradient, flow rate, and material properties. Matlab 2016a software was employed
for the simulation of the various parameter considered and solidworks 2017 software used for
designing the CAD model of this TEG system. The results showed that the TEG had a
maximum efficiency of 10.5% and generated a maximum power output of 5.4 W per
thermoelectric device. The result also showed that the figure of merit (ZT) is a principal
parameter when selecting semi-conductor materials for the TEG. A higher ZT factor will result
in an improvement of the efficiency of the system. Overall, the results suggest that a waste heat
energy recovery system using thermoelectricity has the potential to be a viable and sustainable
solution for industrial energy recovery.
ii
ACKNOWLEDGEMENT
I thank the Almighty God for His guidance, inspiration, knowledge and provisions throughout
the period of my studies and during this research work. I owe a great debt of appreciation to
the dynamic leadership of the Head of Department of Marine Engineering, Dr. Emmanuel
Antai, for his leadership and support during my studentship. I want to appreciate my amiable
supervisor, Engr. Hope Ikue-John for his patience and for painstakingly supervising for this
research project work. I also express my heartfelt gratitude to Prof. Ezenwa Ogbonnaya, Mr
Joyful Iwoette, Engr. Anietie Udo, Engr. Yireobong Akpaba (General project coordinator) and
all other lecturers/staff for their technical inputs and knowledge impacted to me during my
studies. Indeed, thank you is not enough in expressing my gratitude to the entire staff members
of the department of Marine Engineering for their effort and contribution towards making the
department conducive for learning purposes.
iii
DECLARATION
I, Akan, Denis Item (AK17/ENG/MAE/001), declare that this project represents my original
work and has not been previously submitted elsewhere or to any other University for the award
of a degree of any type.
…………………………………….
Akan, Denis Item
Signature of Student
Date:…………………………….
iv
CERTIFICATION
This is to certify that this project on “DESIGN AND ANALYSIS OF WASTE HEAT
ENERGY RECOVERY SYSTEM USING THERMOELECTRICITY” was
undertaken by Akan, Denis Item (AK17/ENG/MAE/001) of the department of Marine
Engineering, Akwa Ibom State University, under supervision and has been approved by the
Department.
…………………………………….
Date: ………………………………
Engr. Hope Ikue-John
Supervisor
…………………………………….
Date: ………………………………
Engr. Dr. Emmanuel Antai
Head of Department
…………………………………….
Date: ………………………………
Prof. Thaddeus C. Nwaoha
External Examiner
v
DEDICATION
This work is dedicated to God Almighty for His grace towards the completion of this research
project work.
vi
TABLE OF CONTENTS
Title Page
i
Abstract
ii
Acknowledgement
iii
Declaration
iv
Certification
v
Dedication
vi
Contents
vii
List of Figures
ix
List of Tables
x
Nomenclature
xi
CHAPTER ONE: INTRODUCTION
1
1.1
Background of the study
1
1.2
Aim
3
1.3
Objectives of the Research
3
1.4
Definition of Problem
3
1.5
Research Goals
3
1.6
Scope /Limitation of research
3
1.7
Contribution
3
CHAPTER TWO: LITERATURE REVIEW
2.1
Introduction
5
5
2.2
5
Exhaust Gas Heat Recovery Technology
2.2.1 Organic Rankine Cycle
6
2.2.2 Turbocharging
8
2.2.3 Turbocompounding
9
2.2.4 Exhaust Gas Recirculation (EGR) system
9
2.3
History of Thermoelectric Generators (TEGs)
10
2.4
Working principles
11
2.5
Material properties of Thermoelectric Generators (TEGs)
12
2.6
Different application in the maritime industries and others
12
vii
CHAPTER THREE: RESEARCH METHODOLOGY
13
3.1
Introduction
13
3.2
Principle of operation of the TEGs
13
3.3
Energy Generation processes
15
3.4
Methods
16
3.5
Energy analysis for the diesel engine
16
3.6
Design parameters
18
3.7
Thermoelectric Device
19
3.8
Heat loss calculation
20
3.9
Thermoelectric materials for TEG
21
3.10
Analysis of Thermoelectric generator (TEG)
23
3.11
Energy balance
24
CHAPTER FOUR: RESULTS AND DISCUSSION
28
4.1
Result
28
4.2
Discussion
31
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
33
5.1
Conclusions
33
5.2
Recommendations
34
REFERENCES
35
viii
LISTS OF TABLES
Table
Caption
Page
3.1
Summary of Energy losses in the engine
27
3.2
Design parameter for the TEG
28
3.3
properties of the exhaust gas
29
4.1
Matlab simulation results
38
ix
LIST OF FIGURES
Figure
Caption
Page
1.1
Energy balance diagram showing energy distribution in an internal
combustion engine
2
2.1
Schematic diagram of a thermoelectric generator
7
3.5
Schematics of the Organic Rankine Cycle
7
3.5
Turbocharging technology
8
3.6
A schematic diagram of EGR system
9
3.7
A thermoelectric generator
10
2.1
Schematic diagram of a thermoelectric generator
11
2.2
Power data of TEG module
12
3.1
Contact resistance with a thermoelectric module
15
3.2
Energy generation process using the TEG
15
3.3
Energy balance diagram showing the distribution of energy from
the engine
18
3.4
Thermoelectric module
22
3.5
Schematics of TEG showing heat transfer
23
3.6
CAD model of TEG device
26
3.7
Arrangement of fin cooling system on the thermoelectric system
27
3.8
Complete CAD model of TEG retrofited to an exhaust system
27
4.1
The relationship between the efficiency and the hot side temperature
4.2:
The relationship between power output and the temperature difference
29
4.3
The relationship between voltage output and the temperature difference
29
4.4
The relationship between voltage output and the temperature difference
30
4.5
Temperature profile across thermoelectric generator
(Temperature vs Thermocouples)
4.6
30
Temperature profile across thermoelectric generator
(Voltage vs Thermocouples)
31
x
NUMENCLATURE
𝐴:
Area (m 2)
𝐼:
Electrical current (A)
𝐾:
Thermal conductance (WK -1)
𝑘:
Thermal conductivity (Wm -1 K -1)
𝐿:
Length (m)
𝑁:
Number of pairs of p-type and n-type semiconductors
𝑅:
Heat flow rate (W)
𝑆:
Electrical resistance (Ω)
𝛼:
Seebeck Coefficient (VK -1)
𝑇:
Temperature (K)
𝑊:
Power output (W)
𝑍𝑇:
Figure of merit of the TEG
Greek Letters
𝜂:
Efficiency
𝜌:
Electrical resistivity (Ωm)
Subscripts:
𝑐old: Cold junction
ℎot:
Hot junction
𝑖𝑛:
Input
𝑗:
Joule heat
𝑜𝑢𝑡:
Output
𝑛:
N-type semiconductor leg
𝑝:
P-type semiconductor leg
TEG: thermoelectric generator
xi
CHAPTER ONE
INTRODUCTION
1.1
Background of the Study
Thermoelectric device is an energy converting device that is used in modern days to harvest
heat energy from a heat source and it has found wide application. The device converts the waste
heat from the exhaust gases emitted from the internal combustion engine directly to electricity
using the Seeback effect. The electricity is generated in between two metals or semiconductors
due to a temperature difference (Srithar, et al., 2014). Due to the growing concerns of the
international community regarding the environmental impact of the waste heat generated from
ships and other ocean structures, there has several campaigns on environmental pollutions from
carbon generated from exhaust gases emitted from ship’s engines. There has been lots of
breakthrough towards reducing the amount of carbon emitted but none of these prove to
decrease the carbon emission due to the increasing amount of seagoing vessels and their power
plants systems on daily basis and the increasing demands of ship owners to improve the
performance of the ships.
There has been shortage of fuel and energy resources which has caused constant increase in
prices of liquid petroleum fuel every year. This is due to the shortage of the natural resources
used in their productions. This research safely seeks to solve these challenges of environmental
hazards as the marine fleet constantly increases on daily basis by increasing the economics of
the ship power plants.
The internal combustion engine is one of the major consumptions of fossil fuel which is the
primary source of the CO2 emission. In an internal combustion engine energy analysis, 25% to
40% of heat is converted to useful mechanical work (brake power), 20% - 45% lost to the
environment through exhaust heat, 10% to 35% of heat lost through coolant, lubricant and other
Heat loss and other means of energy losses as can be illustrated in figure 1.1.
1
Figure 1.1: Energy balance diagram showing energy distribution in an internal combustion
engine (Srithar, et al., 2014)
The thermoelectric device which is a waste heat recovery system seeks to utilize the high
temperature combustion exhaust gases which carry approximately half of the rejected heat
energy from an engine. It is also useful to note here that although it has been stated that
approximately two-thirds of the fuel energy is converted into ‘waste’ heat, much of this rejected
thermal energy is the result of the limitations of the thermodynamic cycle of a heat engine.
Thus, it is impossible to reclaim all of this heat energy for useful work without contravening
the laws of thermodynamics (Srithar, et al., 2014). According to the Oak Ridge Laboratory and
the United State Department of Energy, it is possible to recover about 14% of the exhaust gas
energy for useful work using the idea of availability from the 2nd Law of Thermodynamics.
The solution to these problems is the use of the thermoelectric effect for converting the energy
of the heat of exhaust gases from marine diesel engines into electric energy. Thanks to the latest
advances in the development of thermoelectric materials and systems, interest in the use of
Theremoelectric Generator (TEG) in the grid has been renewed (Hoang & Vinogradov, 2018).
The thermoelectric generator is installed on the exhaust manifold similar to other waste heat
recovery systems but it does not increase the back-pressure while recovering energy from the
exhaust gases.
Advantages of Thermoelectric Generator (TEG)

Significant motor resources

Lack of moving parts

Quiet operation
2

Ecological purity

Versatility with respect to the methods of supply

Removal of heat and the possibility of recovering the waste thermal energy.
Disadvantage of Thermoelectric Generator

Low efficiency of 1 – 10%.
1.2
Aim
To design and analyze a waste heat recovery system that utilizes thermoelectric device as an
alternative means of generating electricity.
1.3
Objectives of the Research
a)
Review of related literature in waste heat recovery systems.
b)
Review a case study vessel and its onboard power consumption.
c)
Review several data from thermoelectric devices.
d)
Carry out mathematical modeling of the thermoelectric device and heat transfer across
the exhaust manifold.
e)
CAD modelling of the thermoelectric generator.
1.4
Definition of Problem
Fuel consumption in the marine sector is directly connected to emissions in the atmosphere and
the worldwide shipping fleet is considered to contribute considerably to greenhouse gas
emissions. Due to increased energy consumption, efficiency is a key issue that must be
addressed in the marine industry and across all industries. By conserving fuel and improving a
ship’s energy efficiency, the amount of greenhouse gases released into the environment is
reduced. Reduced fuel consumption in ship engines is a focus in the marine sector.
Shipboard waste-heat recovery systems are a cost-effective way to improve the sustainability
of marine transportation. It creates a safe working environment, helps to meet decarbonization
goals, and reduces the maritime carbon footprint. It is also simple to connect with onboard
power supply systems. The high-temperature potential exists in some areas, notably aboard
ships.
Thermoelectric Generators (TEG) applications can reliably and practically help with energy
conversion, and TEGs are considered one of the most potential energy technologies of the
3
twenty-first century. The surface of the main engine, where the ship’s waste heat is extracted,
can provide the temperature differential required for Peltier to produce electrical energy shall
be considered. As a result of the mathematical calculations on thermoelectric generators shall
be carryout to show the alternative energy source at the point of waste recovery aboard.
1.5
Research Goals
The following are the goals that are expected to be achieved at the completion of this research
project.
a) Review several literatures on different thermoelectric generator (TEG).
b) Understand the working principles of the thermoelectric generator (TEG).
c) Develop a model for calculating the electrical energy development by the TEG.
d) Based on the analysis, propose a viable solution to help mitigate the effect of exhaust
heat energy to the environment.
1.6
Scope /Limitation of Research
a) This research project shall be concerned with the design and modelling of the
thermoelectric generator.
b) Matlab software shall be used to develop the mathematical modelling of the system
c) Data for the analysis shall be obtained from a case study vessel
1.7
Contribution
(a) This research project when completed may be used as referendum researchers.
(b) This research project when completed may also be used as teaching/learning aid.
(b) This research carryout to promote greener environment.
4
CHAPTER TWO
LITERATURE REVIEW
2.1
Introduction
Man has for many years depend on petroleum and it is estimated that approximately 13,511million-ton equivalent of this petroleum energy has been consumed. The industrial sector has
consumed approximately 2,852 MTEP as a result of the fast industrial growth in most
developing nations. From statistics, it is estimated that the energy consumption statistics will
continue to increase by about 30% on or before 2035 (BP, 2018).
About 34% of the total energy consumed in the maritime industries is rejected as residual heat,
this constitutes a major challenge. Most of this rejected energy has been identified as lowquality residual heat (Fleurial, 2009). This quality of waste heat can be harvested using
advanced thermoelectric materials for electricity generation onboard a ship (UNEP, 2006).
Concurrently with the concern for global warming and the issues of diminishing oil
consumption, there is a strong incentive for the development of more efficient and clean
technologies for heat recovery and energy conversion systems using waste heat (Luis, et al.,
2015).
Among several waste heat recovery technologies available such as the turbo-compound,
bottoming cycles, and turbocharger, thermal power technology such as the thermoelectric
generator has caught the attention of researcher and manufacturers worldwide (Nour, et al.,
2016). The major technical constraint that prevents implementation of ways to heat recovery
system is due to its intermittent and time mismatched demand and availability of energy
(Sanjeev, et al., 2018).
2.2
Exhaust Gas Heat Recovery Technology.
Waste heat recovery (WHR) is the utilization of the thermal energy that would have otherwise
been lost the surrounding. WHR has found several applications in the internal combustion
engines such as the use of engine coolant for cabin heat, turbocharging to increase power
density, bottoming cycles to produce additional work from exhaust gas, integrated exhaust
manifold to facilitate engine warm-up (Hannu, 2019). If the heat source is of high quality,
larger portion of the waste heat may be converted to work. Out of the total energy generated in
an internal combustion engine during operation, approximately, 30% to 40% is converted into
5
useful mechanical work. Others are lost the the environment through exhaust gases, engine
cooling system which results into pollution (Jadhao & Thombare, 2013) as shown in figure 2.3.
Figure 2.3: Energy flow diagram for an internal combustion engine (Avaritsioti, 2016)
SAE, (2015), investigated the possible utilization of waste heat recovered from a Heavy Duty
Diesel Engine as a was of reducing the cost of fuel consumed. The study aimed at
understanding the utilization of a WHRS as a strategy for thermal management of an aftertreatment system in reducing NOx levels. Jadhao & Thombare, (2013), also opined that the
recovery and utilization of waste heat will not conserve fuel, but has the potential of reducing
the among of waste heat and greenhouse gases damped to environment.. Vvarious technologies
have been developed for waste heat recovery such as turbocompounds, Rankine bottoming
cycles, and thermoelectric generators that reduce fuel consumption and CO2 emissions (Habib
& Hans-Erik, 2015).
2.2.2 Organic Rankine Cycle
In recent years, Organic Rankine Cycle (ORC) has become a field of intense researcn and
appears as a promising technolgo y for conversion of low grade heat into useful work or
electricity . Organic rankine cycle (ORC) rely on the same principle as conventional
steam/water rankine cycles used for primary thermal power generation purposes except that
the organic rankine cycles uses organic working fluids which have lower boiling points than
steam/water at the same pressure, which allow them to be driven by low-grade waste heat
(Alison, et al., 2013). Organic Rankine Cycle (ORC)-based power units fed by the exhaust
gases are promising and technologically ready, but they have a significant impact on the
6
exhaust line and engine behavior (Di Battista, et al., 2015). According to Alessandro, et al.,
(2019) , the organic rankine cycle is more efficient that steam cycle due to its ability to extract
heat from a low temperature source. Several research carried out by Roy, et al., (2010) to
investigate the optimal ORC configuration and working fluid for an ORC system powered by
waste flue gas from 4x20MW power station and reported that the approach was not appropriate
for flue gas as there is a limit to the cooling of flue gas to prevent corrosion of components.
The ORC also find its application as a bottoming cycle in any industries where the waste gases
are at temperature between 400OC to 200OC (Edibon, 2020). The economics of a Rankine
system is entirely linked to the thermodynamics properies of the working fluid and requires the
use of good working fluid to avoid low efficiency (Mohammed, et al, 2013). Properies of a
good fluid are: low specific volumes, high efficiency, moderate pressures in the heat
exchangers, low cost, low toxicity, low ODP (Ozone Depletion Potential) and low GWP (Global
Worming Potential) among others (Tchanche, et al., 2009). The standard thermodynamic
relations can be applied in calculating the fluid conditions at each point in the cycle (Alison, et
al., 2013). The efficiency of the technology is in the range fo 20-24% for high temperature of
400OC and 8-12% in the lower range of 150OC-200OC (Edibon, 2020).
Figure 3.5: Schematics of the Organic Rankine Cycle (Edibon, 2020)
7
2.2.2 Turbocharging
The turbocharger is an air pump designed to be drived by exhaust gases from an internal
combustion what would have been lost to the environment. During basic analysis of the use of
fuel energy in combustion engine, it was discovered that about one-third of fuel energy is
converted into exhaust waste and subsequently released into the environment. According to
scientists, this waste heat energy is a potential source of useful energy (Ali Anwar, 2012).
Turbocharging device has found different application such as increasing the power output of
the engine, for scavanging purpose, increase the volumetric efficiency of the engine, cooling
the charge air inside the intake manifold, which saves fuel and reduces nitric oxide emissions
in exhaust gases, etc. It is a common practice today that the waste heat energy is utilized to
power the turbocharging device retrofited at the exhaust manifold (SAE, 2020). It is one of the
best methods to recover the waste heat (Bibin, et al, 2012). The heat energy and pressures in
the engine exhaust gas is utilized to drive the turbine wheel (Ali Anwar, 2012). According to
research carried out by Ali Anwar, (2012), to predict the effect of using this turbocharging
device, it was discovered that the temperature of the exhaust gas decreased from 570OC to
150OC which invariably decreased the pollution and saved 76.62kW of heat which also reduced
global warming.
Figure 3.5: Turbocharging technology (Ingenieria, 2019)
8
2.2.3 Turbocompounding
The turbocompounding system consists of conventional turbocharger which recovers exhaust
energy in a turbine to boost the air coming into the engine through the inlet manifolds. At the
downstream of the turbocharger turbine, the exhaust gas goes through a second turbine. The
energy recovered can be utilized to power the engine shaft, gears and fluid coupling. The
concept of turbocompounding makes the exhaust nergy recovery more efficient. The efficiency
of the turbine plays an role in the recovery of the wasted heat (Habib & Hans-Erik, 2015).
Bheshma & Annamalai, (2016), also agreed that the turbocompounding technology can further
recover more exhaust thermal energy and better fuel utilization.
2.2.4 Exhaust gas recirculation (EGR) system
Usually the internal combustion engine gives off extensive heat through exhaust gases. The
exhaust gases constitutes different chemicals that are harmful to the environments such NOx,
SOx, etc. The EGR is a nitrogen oxide emission reduction technique used in petrol/gasoline.
Diesel engine and hydrogen engines. The Environmental protection agency regulates the NOx
emission from diesel engines (Kanimozhi, et al, 2020).
EGR works by recirculating a portion of an engine’s exhast gas back to the engine cylinder.
The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber.
Reducing the among of oxyten reduces the among of fuel that can burn in the cylinder thereby
reducing peaak in-cylinder temperatures (Wikipedia, 2022).
Figure 3.6: A schematic diagram of EGR system (Mohamed, et al, 2011)
9
2.3
History of Thermoelectric Generators (TEGs)
The Seebeck effect, was discovered by Thomas Johann Seebeck in 1821. It is the fundamental
operating principle of TEG. The found that a circuit made from two dissimilar metals, with
junctions at different temperatures would deflect a compass magnet. Seebeck initially believed
this was due to magnetism induced by the temperature difference and thought it might be
related to the Earth's magnetic field. However, it was quickly realized that a "Thermoelectric
Force" induced an electrical current, which by Ampree's law deflects the magnet. More
specifically, the temperature difference produces and electric potential (voltage) which can
drive an electric current in a closed circuit. Today, this is known as the Seebeck effect. He
discovered that the voltage produced is proportional to the temperature difference between the
two junctions. The proportionality constant (S or a) is known as the Seebeck coefficient, and
often referred to as "thermopower" even though it is more related to potential than power. In
1851 Gustav Magnus discovered the Seebeck voltage does not depend on the distribution of
temperature along the metals between the junctions an indication that the thermopower is
a thermodynamic state function. This is the physical basis for a thermocouple, which is used
often for temperature measurement (Thermoelectrics, 2019).
𝑽 = ∝ (𝑻𝒉 − 𝑻𝒄 )
Where:
𝑉 is the voltage difference across the terminals of the open circuit
𝑇ℎ temperature of the hot junction
𝑇𝑐 temperature of the cold junction
Seebeck investigated different materials: elements, alloys and minerals including zine
antimonide, chalcogenide minerals such as PbS and Cobalt arsenide (Wikipedia, 2018).
10
Figure 3.7: A thermoelectric generator (Wikipedia, 2018)
2.4
Working Principles
Thermoelectric generator consists of an arrangement of small blocks of bismuth telluride
(Bi2Te3) doped with n-type and p-type, mounted alternately, electrically in series, and
thermally in parallel between two plates of good thermal conduction, as shown in Figure 2.1.
Figure 2.1: Schematic diagram of a thermoelectric generator (Luis, et al., 2015).
The energy conversion efficiency of Thermoelectric devices is measured by the figure of merit
(ZT). The thermoelectric Generator (TEG) modules operates in two modes, power generation
and heat pumping. It operates in power mode by generating a temperature gradient across the
two sides of the thermoelectric module thereby producing an electrical current (Georgios, et
al., 2022).
11
Figure 2.2: Power data of TEG module (Georgios, et al., 2022).
2.5
Material Properties of Thermoelectric Generators (TEGs)
Commercial Thermoelectric materials with ZT >1 is not available; thus, the conversion
efficiency of current Thermoelectric material is less than 5%. Te-based alloys in combination
with Bismuth (Bi), Antimony (Sb), or Selenium (Se) are referred to as low temperature
materials (up to 3000C) although lead tellurium could be used until far higher temperature.
Finding the efficient, non-costly and environmental friend thermoelectric materials for energy
conversion. Silicides, skutterudites, Sulfides and half-Heusler materials are very promising
candidates and silicon-germanium (SiGe) alloys can be operated at the highest temperatures,
up to 11000C (Nour, et al., 2016).
.
2.6
Different Application in the Maritime Industries and others
Sanjeev, et al.,( 2018), researched on the use of the exhaust heat to maintain the temperature
of the food items inside the container being heated by a copper plate during delivery for food
delivery companies. Modern ships discharge large amounts of energy into the environments
due to the heavy-duty power plants utilized for the propulsions and other purposes. Due to this
significant heat transfer and temperature difference, thermoelectric devices could be used to
harness this energy and convert it into electrical use (Georgios, et al., 2022).
12
CHAPTER THREE
METHODOLOGY
3.1
Introduction
Electricity production is an important issue for the maritime industries. Since the ships require
power plants for propulsion and electrification, waste heat is also an important topic. It is in
this context that thermoelectric generators (TEGs) are currently taking off. TEGs constitute a
set of thermoelectric (TE) modules inserted between two heat exchangers. Each TE module is
then composed of several tens to hundreds of pairs of TE couples connected together
electrically in series and thermally in parallel, which directly convert a part of the thermal
energy that passes through them into electricity (Daniel, 2017).
There are numerous benefits of using TEGs in waste heat recovery systems:

It gives direct energy conversion, unlike many heat engines that first convert thermal
energy into mechanical energy and then convert this mechanical energy into electricity
using an alternator.

It consists of no moving parts and no working fluids inside the TEG, hence no
maintenance and no extra costs.

It has a long lifespan, especially when working with constant heat sources.

It has no scale effect: TEG can be used for micro generation in very limited spaces or
to produce kilowatts.

Good noiseless operations,

Suitable for any working position is possible, making TEGs well suited for embedded
systems.
3.2
Principle of Operation of the TEGs
The temperature differential between surfaces is directly converted into electrical energy
utilizing thermoelectric generators (TEGs), a type of renewable energy technology composed
of a semiconductor. The thermoelectric generator (TEG) is a device that converts heat input at
low temperatures (below 1000K) into electrical energy. It is the best technique for recovering
heat from exhaust. It may be used to a variety of things, including cars, boilers, wood stoves,
etc. The thermoelectric components of a TEG determine its efficiency. The main research of
the world is to use the renewable energy. The usage of green energy is TEG's key benefit. The
Seebeck effect theory serves as the foundation for the TEG. A thermoelectric generator has an
13
efficiency of about 5%. The heat is produced by a heat source, which then moves via a
thermoelectric converter to a heat sink that is kept at a lower temperature than the source.
The basic building blocks of thermoelectric power generators or coolers are called modules.
Modules are made up of a grid of semiconductor thermoelectric couples that are thermally and
electrically interconnected in series. Sandwiched between two ceramic substrates are
thermoelectric couplings and their electrical interconnects. The positioning of the various
components of a thermoelectric module is shown in Figure 3.1. Thermoelectric elements (or
legs), Ceramic substrates, conductor, and (4) External Electrical loads are the basic components
of a thermoelectric module.
The couples used in thermoelectric modules to generate electricity are known as the
thermoelectric elements (or legs). This research project utilizes the bismuth-telluride materials
for the production of this legs. The application area and operating temperature range influence
the material choice. Figure 3.1 depicts the module's regular matrix arrangement of the
thermoelectric legs. The thermoelectric module is electrically isolated from the exterior
mounting surfaces using ceramic substrates. In order to transport heat with the least amount of
thermal resistance, the substrates must also have excellent thermal conductance. Aluminum
oxide is a typical ceramic substrate (Al2O3). The thermoelectric legs are connected by the metal
conductor, which operate as electrical contacts. All of the legs are electrically linked in series
thanks to the contacts' configuration. To connect the module to an electrical load while
producing electricity or to an electrical source when using thermoelectric cooling, external
electrical connections are used.
The interface between two solid materials is never perfectly smooth. There will always be
microscopic roughness on the surfaces, even though they appear to be completely smooth,
which will cause air-filled gaps to emerge when the surfaces are forced together. The amount
that these voids reduce the surface area that is really in contact depends on the materials'
softness, surface roughness, and contact pressure. Possible surface coatings like oxides or other
contaminants were assumed to be used in this research. Though it may have an impact on an
interface's thermal and electrical conductivity. By reducing the area of the voids, either by
smoothing or softening the surfaces, or by raising contact pressure, the magnitude of the
thermal contact resistances can be reduced.
14
Figure 3.1: Contact resistance with a thermoelectric module
3.3
Energy Generation Processes
As the p-type element is electrically connected to the n-type element, the mobile holes in the
p-type element “see” the mobile electrons in the n-type element and migrate just to the other
side of the junction as shown in figure 3.2.
For every hole that migrates into the n-type element, an electron from the n-type element
migrates into the p-type element. Soon, each hole and electron that “switch sides” will be in
equilibrium and act like a barrier, preventing more electrons or holes from migrating. This is
called the depletion zone.
Figure 3.2: Energy generation process using the TEG
15
3.4
Methods
Generally, the waste heat from the ICE comes from exhaust gases at high temperature. As a
result, the available positions for the TEG device to operate is after the combustion chamber.
For purpose of this research purpose, a CAT C18 diesel engine with an exhaust gas for a typical
6-cylinder ICE with engine power 12MW are used and the temperature of the exhaust gases is
around 370OC. This turbocharged engine series operates in typical commercial ships and its
overall power depends on the number of cylinders, rotational speed (124 RPM) and engine
configuration. It has a 500 mm bore, 2010 mm stroke and a length of 7.34 m for 6 pistons.
There are different available positions that the TEG can be installed, such as the cylinder
exhaust port, engine bypass system, engine manifold, and ship chimney. For this study, the
manifold is chosen because the manifold had two circular flat surfaces at its ends. Other
installation positions are possible and can be explored using the procedure developed in this
paper. However, the manifold position is chosen since it is the least intrusive to the ICE system,
which leads to simpler modifications for the installation. Taking into consideration the exhaust
gases temperature and the temperature losses, a conservative approach is used and the
temperature on the outside surface of the manifold is set to be 300OC, where the hot side of the
TEG will be installed.
3.5
Energy Analysis for the Diesel Engine
To perform an energy analysis of the diesel engine based on the provided information, we need
to determine the amount of waste heat that can be recovered from the exhaust gases and the
potential power output of the thermoelectric generator (TEG).
𝑄𝑡𝑜𝑡𝑎𝑙 = 𝑚̇𝑓 𝑥 𝐿𝐶𝑉
3.1
Where LCV is the Lower Calorific Value and 𝑚̇𝑓 is the mass flow rate of the fuel
𝑄𝑡𝑜𝑡𝑎𝑙 = 0.223 𝑥 42,000
𝑄𝑡𝑜𝑡𝑎𝑙 = 9,366𝑘𝐽/𝑠
16
The waste heat available for the TEG can be estimated by considering the exhaust gas
temperature and flow rate. Assuming a constant exhaust gas flow rate of 10 kg/s and an exhaust
gas temperature of 370°C, the heat available for the TEG can be calculated using the following
equation:
𝑄 = 𝑚̇𝐶𝑝 (𝑇𝑖𝑛 − 𝑇𝑜𝑢𝑡 )
3.2
where:
𝑚̇ is the mass flow rate of exhaust gas = 10 kg/s
𝐶𝑝 represents the specific heat of exhaust gas = 1.1 kJ/kg-K (approximate value for diesel
engine exhaust gas)
𝑇𝑖𝑛 is the temperature of exhaust gas entering the TEG = 370°C
𝑇𝑜𝑢𝑡 is the temperature of exhaust gas leaving the TEG = 300°C (assumed based on the
information provided)
Submitting the values
𝑄 = 10 𝑥 1.1 (370 − 300)
𝑄 = 770𝑘𝑊
This means that the TEG can potentially generate up to 770 kW of power from the waste heat
of the diesel engine.
Table 3.1 below shows the summary of the energy expanded by the engine during operations
Table 3.1: Summary of Energy losses in the engine
Energy
Parameters
Symbols
consumption (kW)
Exhaust gas heat
𝑄𝑔
2,613
27.9
Cooling water heat
𝑄𝑐𝑜
1,321
14.1
Intercooler heat
𝑄𝑖𝑛𝑡
862
9.2
Radiation heat
𝑄𝑟𝑎𝑑
10
1.0
Rated Power
𝑊𝑏
3,437
36.7
Lubricating heat
𝑄𝑙𝑢𝑏
1,040
11.1
17
% Rep.
Using the energy diagram to show the distribution of the energy in the engine
Figure 3.3: Energy balance diagram showing the distribution of energy from the engine
3.6
Design Parameters for the TEG
For the purpose of this research project, the design parameters were obtained from a case study
vessel where the engine parameters, electrical power consumptions and the fuel consumption
were obtained. Application of mathematical modeling to analyze the design process in order to
obtained the behviour and characteristics.
Three main factors were taken into account while developing a thermoelectric generator:

Specifications: the needed power output P, operating temperatures TC, TH, and (and or
output voltage, V or current, I).

Material characteristics: the module’s electrical and thermos contact qualities, as well as
the thermoelectric properties of thermoelement materials Z (∝, 𝜎, 𝛾).

The cross-sectional area A, the number of thermocouples N, and the length L of the
thermoelement are the design parameters.
Table 3.2 show summary of design data obtained from the TEG materials.
18
Table 3.2: Design parameter for the TEG
Parameters
Values
Temperature
300 OC hot side
30 OC Cold side
Semi-conductor material
Bi2Te3
Figure of merit
0.04
Seebeck coefficient
0.0015
Length
60mm
Width
60mm
Thermal conductivity
1.2 W/mK
Electrical conductivity
0.06 S/m
Density
7.8x103 kg/m3
Specific heat capacity
200kJ/kg
3.7
Thermoelectric Device
Thermoelectric effects are reversible processes that directly convert heat energy to electrical
energy. Direct energy conversion is based on the thermoelectric materials’ physical transport
qualities (thermal conductivity, electric conductivity, and Seebeck coefficient) and their energy
conversion efficiency (figure-of-merit). The Seebeck effect is employed in thermoelectric
generators, often used to convert heat energy to electrical energy. Charge carriers travel from
the hot to the cold side of a conductive substance when a temperature gradient is introduced.
Charge build-up causes an electric potential difference in the case of an open circuit. TEGs
have several benefits, including design simplicity, the lack of moving parts, a long lifespan,
minor maintenance, and environmental friendliness (no chemical compounds). To boost the
output power, TEGs is normally made up of numerous coupled thermopiles. Each thermopile
comprises a few thermocouples (TCs) electrically linked in series and thermally associated in
parallel. The thermocouple consists of two materials with opposing Seebeck coefficients
connected at their ends. Due to the Seebeck effect, the appearance of a temperature gradient
between the two TCs ends generates an electric voltage defined by equation 3.1.
𝑽𝒐𝒖𝒕 = 𝑵𝜶∆𝑻
3.3
where 𝑵 is the number of connected thermocouples, 𝜶 is the Seebeck coefficients of the two
joined materials forming the thermocouple, and ∆𝑻 is the temperature gradient.
19
3.8
Heat Loss Calculation
Two points between the exhaust gas manifold was selected as the source of heat for the
thermoelectric generator and the heat between the point were calculated using equation 3.4.
Table 3.1 show the properties of the exhaust gas, assuming steady state flow condition.
𝑄ℎ = 𝐶𝑃 𝑥 𝑉 𝑥 𝜌 𝑥 𝐴 𝑥 𝑇𝑥
3.4
Where:
𝑄ℎ is the heat loss across the selected location
𝐶𝑃 is the specific heat capacity of air (J/kgK)
𝑉 is the exhaust gas velocity (m/s)
𝜌 is the density of air taken to be 1.223kg/m3
𝜇 is the dynamic viscosity of the exhaust gas
𝐴 is the cross-sectional area of the exhaust pipe (m2)
𝑇 is the temperature of the exhaust gas at any location (K)
𝜗 is the kinematic viscosity of the exhaust gas (m2/s)
Table 3.3: properties of the exhaust gas
𝜌 (kg/m3)
𝐶𝑃 (kJ/kgK)
𝜇𝑥106 (Pas)
𝜗𝑥106 (m2/s)
273 (0OC)
1.295
1.042
15.8
12.20
373 (100OC)
0.950
1.068
20.4
21.54
473 (200OC)
0.748
1.097
24.5
32.80
573 (300OC)
0.617
1.122
28.2
45.81
T (K)
In this calculation, the exhaust gas flow was assumed to be laminar, the internal lining of the
exhaust pipe is smooth, 20hermos-convention of the exhaust gas is equal to the conduction
through the thickness, mean losses were considered and uniformly distributed in all direction.
The output voltage of the TEG is directly proportional to the temperature change, which is the
principle of a TEG using the phenomenon characteristics known as the seebeck effect and
displayed as the following equation:
𝑉 = 𝛼∆𝑇
3.5
Where 𝛼 is the Seebeck coefficient ((𝑉𝐾 −1 ) and ∆𝑇 is the temperature difference of two sides
of the surface in K.
20
3.9
Thermoelectric Materials for TEG
The performance of thermoelectric devices strongly depends on the efficiency of the materials
of which they are made, the material used in the construction of a TEG plays an important role
in controlling the performance of these devices. The efficiency is evaluated by the
thermoelectric figure of merit (Z), which expresses the combination between Seebeck
coefficient (𝑆), electrical resistivity (𝜎), and thermal conductivity (𝐾) in equation 3.2 (Truong,
2019). There are many features that describe the performance of these materials to make them
suitable for use in TEG device manufacture. The potential of a material for thermoelectric
applications s determined in large part to a measure of the material’s figure of merit.
The maximum efficiency of a thermoelectric material for thermoelectric power generation and
cooling is determined by the dimensionless figure of merit ZT, which can be experiences using
equation 3.2
𝑍𝑇 =
𝑇=
𝑆2𝜎
𝐾
𝑇
3.6
𝑇𝐻 − 𝑇𝐶
3.7
2
where S denotes the Seebeck coefficient, 𝜎 denotes the electrical resistivity, 𝐾 denotes the
thermal conductivity, and 𝑇 is the material’s absolute temperature. For the most part, the figure
of merit (ZT) is a temperature-dependent material parameter determined from the temperaturedependent material properties.
A thermoelectric material exhibits maximum ZT at a certain temperature, which can be
optimized to peak at different temperatures by adjusting the carrier concentration through
doping. This means that different TE materials are suitable for various operating temperature
ranges.
TE materials can be categorized on many different levels, such as crystal structure, conversion
efficiency, cost and temperature range. Conventional TE materials can be classified into three
groups in terms of the temperature range of their operation: low temperature materials (200500 K), medium temperature materials (500-800 K), and high temperature materials (800 K).
for this purpose of this research project, the Bismuth telluride (𝐵𝑖2 𝑇𝑒3 ) shall be used.
The alloys of 𝐵𝑖2 𝑇𝑒3 – 𝑆𝑏2 𝑇𝑒3 are low temperature state-of-the-art Thermoelectric materials
operating in the temperature range of 200-400K. Due to their relatively high ZT values of
around 1 compared to other bulk materials around room temperature, 𝐵𝑖2 𝑇𝑒3 – 𝑆𝑏2 𝑇𝑒3 alloys
21
have been the material of choice in a variety of commercial TE devices with applications in
refrigeration and temperature regulation of scientific instrumentation, drinking fountains, and
car seats. Additional applications of Bi2Te3 – based materials lie in the recovery of low-quality
waste heat from combustion processes or even from electronic circuits.
𝐵𝑖2 𝑇𝑒3 alloys are obtained through a slight change of its stoichiometric composition, n-type or
p-type 𝐵𝑖2 𝑇𝑒3. This can be achieved by applying various methods such as doping composition
optimization, or device engineering. The modules investigated in this study were made of “hotpressed” Bi-Te based semiconductors as shown in figure 3.4.
Figure 3.4: Thermoelectric module
3.10
Analysis of Thermoelectric Generator (TEG)
The efficiency of the Thermoelectric generator depends on the Z factor and resistance ratio
(m). Schematic illustrations of the arrangement of the p-type and n-type semi-conductors in a
thermoelectric system is shown in figure 3.5.
Figure 3.5: Schematics of TEG showing heat transfer
22
To carry out this analysis, the energy balance of the TEG must be first considered in terms
Joule heat, Conduction heat, and Peltier heat
(a) Joule heat (𝑸𝒋 )
𝑄𝑗 = 𝐼 2 𝑅
3.8
Where R is the electrical resistance represented with 𝑅 =
𝜌𝐿
𝐴
𝜌 is the resistivity of the conducting material
𝐿 is the length of the conductor
𝐴 is the area of the conductor
𝑄𝑗 = 𝐼 2 [
𝜌𝑝 𝐿𝑝
𝐴𝑝
+
𝜌𝑛 𝐿𝑛
𝐴𝑛
]
3.9
(b) Conduction heat (𝑸𝒄𝒐𝒏𝒅 )
𝑄𝑐𝑜𝑛𝑑 = (𝑇ℎ𝑜𝑡 − 𝑇𝑐𝑜𝑙𝑑 ) [
𝐾𝑝 𝐴𝑝
𝐿𝑝
+
𝐾𝑛 𝐴𝑛
𝐿𝑛
]
3.10
Where 𝐾𝑝 and 𝐾𝑛 are the thermo-conductance of both the p-type and n-type semi-conductor
respectively and 𝐴𝑝 and 𝐴𝑛 are area of conduction material for both p-type and n-type
semi-conductor respectively.
𝐾= [
𝐾𝑝 𝐴𝑝 𝐾𝑛 𝐴𝑛
+
]
𝐿𝑝
𝐿𝑛
𝑄𝑐𝑜𝑛𝑑 = (𝑇ℎ𝑜𝑡 − 𝑇𝑐𝑜𝑙𝑑 )𝐾
3.11
(c) Peltier heat (𝑸𝒑 )
𝑄𝑝 = 𝜋𝑃−𝑁 𝐼𝑇
3.12
Where T can be 𝑇ℎ𝑜𝑡 𝑜𝑟 𝑇𝑐𝑜𝑙𝑑 depending on the junction
𝜋𝑃−𝑁 is the seebeck coefficient of the p-type and n-type semi-conductor
23
3.11
Energy Balance
For the hot junction:
𝑄𝑖𝑛 +
1
𝑄 = 𝑄𝑐𝑜𝑛𝑑 + 𝑄𝑝
2 𝑗
𝑄𝑖𝑛 = 𝑄𝑐𝑜𝑛𝑑 + 𝑄𝑝 −
1
2
𝑄𝑗
3.13
Submitting their respective formulars
𝑄𝑖𝑛 = (𝑇ℎ𝑜𝑡 − 𝑇𝑐𝑜𝑙𝑑 )𝐾 + 𝜋𝑃−𝑁 𝐼𝑇 −
1 2 𝜌𝑝 𝐿𝑝
𝐼 [𝐴
2
𝑝
+
𝜌𝑛 𝐿𝑛
𝐴𝑛
]
3.14
For the cold junction:
𝑄𝑜𝑢𝑡 −
1
𝑄 = 𝑄𝑐𝑜𝑛𝑑 + 𝑄𝑝
2 𝑗
𝑄𝑜𝑢𝑡 = 𝑄𝑐𝑜𝑛𝑑 + 𝑄𝑝 +
1
2
𝑄𝑗
3.15
Submitting their respective formulars
𝑄𝑜𝑢𝑡 = (𝑇ℎ𝑜𝑡 − 𝑇𝑐𝑜𝑙𝑑 )𝐾 + 𝜋𝑃−𝑁 𝐼𝑇 +
1 2 𝜌𝑝 𝐿𝑝 𝜌𝑛 𝐿𝑛
𝐼 [
+
]
2
𝐴𝑝
𝐴𝑛
𝑄𝑜𝑢𝑡 = (𝑇ℎ𝑜𝑡 − 𝑇𝑐𝑜𝑙𝑑 )𝐾 + 𝜋𝑃−𝑁 𝐼𝑇 +
1 2
𝐼 𝑅
2
3.16
Amount of electrical work
𝑊 = 𝑉𝐿 𝐼 = 𝑄𝑖𝑛 − 𝑄𝑜𝑢𝑡
𝑉𝐿 𝐼 = 𝛼𝑃−𝑁 𝐼(𝑇𝑖𝑛 − 𝑇𝑜𝑢𝑡 ) − 𝐼 2 𝑅
𝑉𝐿 [ = 𝐼𝑅𝐿 ] = 𝛼𝑃−𝑁 (𝑇𝑖𝑛 − 𝑇𝑜𝑢𝑡 ) − 𝐼 (𝑅𝑝 − 𝑅𝑛 )
𝐼=
𝛼𝑃−𝑁 (𝑇𝑖𝑛 −𝑇𝑜𝑢𝑡 )
3.17
𝑅𝐿 + 𝑅𝑝 +𝑅𝑛
Efficiency of the TEG
𝜂𝑇𝐸𝐺 =
𝑊𝐿
3.18
𝑄𝑖𝑛
The resistance ratio of this conducting materials is given by m
𝑅𝐿
𝑚=
3.19
𝑅𝑝 +𝑅𝑛
Therefore;
𝐼=
𝛼𝑃−𝑁 (𝑇𝑖𝑛 − 𝑇𝑜𝑢𝑡 )
(1 + 𝑚)𝑥 (𝑅𝑝 + 𝑅𝑛 )
𝑊𝐿 = 𝐼 2 𝑅𝐿 =
𝑊𝐿 =
𝑚
(1+𝑚)2
𝛼 2 𝑃−𝑁 (𝑇𝑖𝑛 − 𝑇𝑜𝑢𝑡 )2
𝑥 𝑚 (𝑅𝑝 + 𝑅𝑛 )
(1 + 𝑚)2 𝑥 (𝑅𝑝 + 𝑅𝑛 )2
𝑥
𝛼2 𝑃−𝑁 (𝑇𝑖𝑛 −𝑇𝑜𝑢𝑡 )2
3.20
(𝑅𝑝 +𝑅𝑛 )
24
The efficiency of the TEG can be written as
𝜂𝑇𝐸𝐺
𝛼 2 𝑃−𝑁 (𝑇𝑖𝑛 − 𝑇𝑜𝑢𝑡 )2
𝑚
𝑥
2
(1 + 𝑚)
(𝑅𝑝 + 𝑅𝑛 )
𝑊𝐿
=
=
1
𝑄𝑖𝑛
(𝑇ℎ𝑜𝑡 − 𝑇𝑐𝑜𝑙𝑑 )𝐾 + 𝜋𝑃−𝑁 𝐼𝑇 − 2 𝐼 2 𝑅
𝜂𝑇𝐸𝐺 =
𝑚
1 (𝑇𝑖𝑛 −𝑇𝑜𝑢𝑡 )
𝑅𝐾
(1+𝑚)−
+ 2
2
𝑇𝑖𝑛
𝛼 𝑃−𝑁
(1+𝑚)2
𝑥
𝑇𝑖𝑛
𝑥
(𝑇𝑖𝑛 −𝑇𝑜𝑢𝑡 )
𝑇𝑖𝑛
3.21
Where;
𝑍𝑇 =
𝛼2 𝑃−𝑁
3.22
(𝐾𝑝 +𝐾𝑛 )(𝑅𝑝 +𝑅𝑛 )
This equation 3.20 is known as the figure of merit (Z) used to describe the function of materials
properties and geometry.
𝜂𝑇𝐸𝐺 =
(𝑇𝑖𝑛 −𝑇𝑜𝑢𝑡 )
𝑇𝑖𝑛
𝑥
𝑚
3.23
1 (𝑇𝑖𝑛 −𝑇𝑜𝑢𝑡) (1+𝑚)2
(1+𝑚)−
+
2
𝑇𝑖𝑛
𝑍𝑇𝑖𝑛
The total power output for an n number of thermoelectric devices can therefore be expressed
as:
𝑃𝑇𝑜𝑡𝑎𝑙 = 𝑃𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙 𝑥 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡ℎ𝑒𝑟𝑚𝑜𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑑𝑒𝑣𝑖𝑐𝑒 𝑐𝑜𝑛𝑠𝑖𝑑𝑒𝑟𝑒𝑑
3.24
The proposed thermoelectric device consists of the following three main parts: the heat
expansion plate, thermoelectric modules, and the water cooled heatsink, as shown in Figure
3.2. The area between the TEG modules is assumed to be static air. To achieve a high
temperature difference between the hot and the cold side of the modules, the modules are
sandwiched between the cooling heatsink and the heat expansion plate. The expansion is in
direct contact with the outside surface of the manifold. The device has a square profile, its
overall dimensions are 360 × 360 mm and it includes a total of 236 modules arranged in a 20
× 11 pattern. These dimensions allow for an 8 mm gap between the modules and a 10 mm
empty space at each end. These gaps are necessary for electrical connections and cables that
run from each module to the outside connections of the TEG.
25
Figure 3.6: CAD model of TEG device
The cooling heatsink is an enclosed rectangular tube that allows the flow of the water in order
to extract heat and create a low temperature on the cold side of the modules. The lower surface
of the heatsink is in contact with the modules. The inside area of the heatsink includes
longitudinal fins that increase the overall heat transfer area and, therefore, the heat transferred
from the modules to the water. The configuration of the heatsink is shown in Figure 6. The fins
can have a variable height and width that will be determined later using the parametric studies.
In addition, the number of fins or gap between the fins is variable. Initially, the heatsink has an
overall height of 60 mm and 15 fins.
Fin
Heat sink
TEG
Module
Figure 3.7: Cut section showing the arrangement of fin cooling system on the thermoelectric
system
26
TEG
Module
Figure 3.7: Arrangement of TEG module on the Exhaust manifold
Heat sink
Exhaust
gas inlet
Figure 3.8: Complete CAD model of TEG on an exhaust system
27
CHAPTER FOUR
RESULTS AND DISCUSSIONS
4.1: Result
Matlab software was used to develop a programme to simulate the result obtained using
equation 3.1 – 3.21. The hot side temperature was varied over a range of 573K to 303K to
under the effect of temperature on power output, voltage, current and efficiency of the system.
Table 4.1 shows a summary of the result obtained. See appendix 1 for the complete simulated
results.
Table 4.1: Matlab simulation results
Temperature
(K)
573
568
563
558
553
548
543
538
533
Efficiency
Power (W)
Voltage (V)
5.1105
5.0964
5.0823
5.0681
5.054
5.04
5.0259
5.0118
4.9977
0.28017
0.27981
0.27945
0.27909
0.27873
0.27837
0.27801
0.27765
0.27729
Current (A)
18.241
18.214
18.186
18.159
18.132
18.105
18.078
18.051
18.024
10.5125
10.5022
10.4919
10.4815
10.4712
10.4608
10.4504
10.4400
10.4296
Figure 4.1: the relationship between the efficiency and the hot side temperature
28
Figure 4.2: the relationship between power output and the temperature difference
Figure 4.3: the relationship between voltage output and the temperature difference
29
Figure 4.4: the relationship between voltage output and the temperature difference
Figure 4.5: Temperature profile across thermoelectric generator (Temperature vs
Thermocouples)
30
Figure 4.6: Temperature profile across thermoelectric generator (Voltage vs Thermocouples)
4.2
Discussion
The matlab code in appendix 2, simulates the thermoelectric generator using a Bi2Te3 material
with dimensions of 60x60x4mm. The generator is assumed to have a hot side temperature of
573 K and a cold side temperature of 303 K. An electrical load of 2 kW is applied to the
generator. The power, voltage, and current output of the thermoelectric generator at various
temperatures between the hot and cold sides was calculated using the programme developed in
matlab. This was obtained by iteratively calculating the Seebeck coefficient, electrical
resistivity, and thermal resistance based on the mean temperature of the generator. The figure
of merit and maximum theoretical efficiency based on the Seebeck coefficient, electrical
resistivity, and thermal conductivity were also calculated. Finally, the maximum theoretical
efficiency was used to calculate the power output of the generator.
From table 4.1, it can observe that as temperature increases, so does power, voltage, and
current. However, the efficiency of the system decreases with increasing temperature. This
inverse relationship between temperature and efficiency is common in many systems and is
often attributed to increased losses due to higher temperatures.
It can also be observed from table 4.1 that the changes in power, voltage, and current are
relatively small as the temperature increases, especially when compared to the change in
31
efficiency. This suggests that the efficiency is more sensitive to changes in temperature than
the other parameters.
The results are also plotted in three figures (Figure 4.1 – 4.3) that shows the power, voltage,
and current output of the generator as a function of temperature. As the hot side temperature
decreases from 573 K to 303 K (the cold side temperature), the power output, voltage output,
and current output of the thermoelectric generator also decrease. This is because the
temperature difference between the hot and cold sides, which is a driving force for the
thermoelectric effect, decreases. As a result, the Seebeck coefficient, which is a measure of the
magnitude of the thermoelectric effect, decreases as well. Additionally, the electrical resistivity
of the material increases with decreasing temperature, which further reduces the power output
of the generator.
The plots show that the power output, voltage output, and current output of the generator all
decrease in a similar fashion with decreasing temperature difference. However, the rate of
decrease is not constant, as can be seen from the non-linear shapes of the curves in the plots.
This is due to the temperature dependence of the material properties and the thermoelectric
effect itself.
This results above demonstrate the importance of maintaining a high temperature difference
between the hot and cold sides of a thermoelectric generator in order to achieve a high-power
output. The Figure 4.4 shows the temperature profile across the thermoelectric generator, with
the x-axis representing the thermocouple number and the y-axis representing the temperature
in Kelvin. As we move from the cold side to the hot side of the generator, it can seen that the
temperature increases gradually in steps. This is because the generator consists of a series of
thermocouples, each of which generates a small voltage based on the temperature difference
between the hot and cold sides. Figure 4.5 shows the voltage profile across the thermoelectric
generator, with the x-axis representing the thermocouple number and the y-axis representing
the voltage output in volts. As we move from the cold side to the hot side of the generator, it
can also be seen that the voltage output increases in steps. This is because each thermocouple
generates a small voltage based on the temperature difference between the hot and cold sides.
This voltage profile is important because it helps us understand how the voltage output changes
across the generator and how it affects the overall performance of the generator.
By examining both plots together, it can be seen that the temperature and voltage profiles are
related. The temperature profile shows us how the temperature changes across the generator,
32
which in turn affects the voltage output of each thermocouple. The voltage profile shows us
how the voltage output of each thermocouple changes across the generator, which is affected
by the temperature difference across each thermocouple. Therefore, by analyzing figure 4.4
and 4.5, we can better understand the relationship between temperature and voltage output,
which is important for optimizing the performance of the thermoelectric generator.
33
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
5.1
Conclusions
Waste heat from industrial generating system, when not captured, are useless and contribute to
global warming, there are a lot of methods to recover the waste heat generated from local
industries. This research project utilizes thermoelectric generator to extract this waste heat;
which is the renewable energy source.
Thermoelectrics effect are the way electrical potential is generated, by presence of temperature
difference and vice versa, and this result depend on material properties of thermocouples and
their size, such as areas and lengths; Bismuth telluride (Bi2Te3) has been selected in this
research project as the thermoelements materials. The CAD design and modelling of this device
consists of 32 thermogenerator devices mounted on a exhaust system with a heat sink mounted
on the cold side to maintain a high temperature difference.
Based on the analysis conducted, it can be concluded that the performance of the thermoelectric
generator is heavily dependent on the temperature difference between the hot and cold sides.
As the temperature difference increases, the voltage output and electrical power also increase,
while the electrical resistance decreases. However, it was also observed that the number of
thermocouples does not have a significant impact on the performance of the generator. The
analysis also showed that the Seebeck coefficient, which is a measure of the ability of the
thermoelectric material to generate a voltage in response to a temperature difference, is a key
factor in determining the performance of the generator. The thermal conductivity of the
material is also important, as it affects the rate of heat transfer and hence the temperature
difference between the hot and cold sides.
Finally, it is important to note that the efficiency of the thermoelectric generator is still
relatively low, with only a small fraction of the heat energy being converted into electrical
energy. Therefore, further research and development is needed to improve the efficiency and
make thermoelectric generators more practical for real-world applications.
The temperature profile is important because it helps us understand how the temperature
changes across the generator and how it affects the performance of the generator.
34
5.2
Recommendations
In order to maximize the voltage output of the thermoelectric generator, it is recommended to
increase the number of thermocouples in the generator. This is because the voltage output is
directly proportional to the number of thermocouples, as shown in the voltage profile plot.
Additionally, increasing the length of the generator can also increase the voltage output. It is
recommended to use materials with high thermal conductivity and low electrical conductivity
for the legs of the thermoelectric generator. This is because the legs need to be good thermal
conductors, but poor electrical conductors, in order to maintain the temperature gradient across
the generator and maximize the Seebeck coefficient.
It is also important to optimize the hot and cold side temperatures of the thermoelectric
generator. In this analysis, it was found that increasing the hot side temperature had a greater
effect on the voltage output than decreasing the cold side temperature. However, it is important
to ensure that the temperature difference across the generator is not too large, as this can cause
thermal stress and reduce the efficiency of the generator.
Finally, it is recommended to use a load resistance that is matched to the electrical output of
the generator, in order to maximize power output. This can be achieved by adjusting the load
resistance until the maximum power point of the generator is reached.
Overall, the recommendations above can help to maximize the voltage and power output of a
thermoelectric generator, and improve its overall efficiency.
35
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39
APPENDICES
Appendix 1: Matlab simulation results
Temperature
(K)
573
568
563
558
553
548
543
538
533
528
523
518
513
508
503
498
493
488
483
478
473
468
463
458
453
448
443
438
433
428
423
418
413
408
403
398
Efficiency
Power (W)
Voltage (V)
5.1105
5.0964
5.0823
5.0681
5.054
5.04
5.0259
5.0118
4.9977
4.9837
4.9696
4.9556
4.9415
4.9275
4.9135
4.8995
4.8855
4.8715
4.8575
4.8436
4.8296
4.8156
4.8017
4.7878
4.7738
4.7599
4.746
4.7321
4.7182
4.7044
4.6905
4.6766
4.6628
4.6489
4.6351
4.6213
0.28017
0.27981
0.27945
0.27909
0.27873
0.27837
0.27801
0.27765
0.27729
0.27692
0.27656
0.2762
0.27583
0.27547
0.27511
0.27474
0.27438
0.27401
0.27364
0.27328
0.27291
0.27254
0.27217
0.27181
0.27144
0.27107
0.2707
0.27033
0.26996
0.26959
0.26922
0.26884
0.26847
0.2681
0.26773
0.26735
40
Current (A)
18.241
18.214
18.186
18.159
18.132
18.105
18.078
18.051
18.024
17.996
17.969
17.942
17.915
17.888
17.86
17.833
17.806
17.779
17.751
17.724
17.697
17.669
17.642
17.615
17.587
17.56
17.532
17.505
17.478
17.45
17.423
17.395
17.368
17.34
17.313
17.285
10.5125
10.5022
10.4919
10.4815
10.4712
10.4608
10.4504
10.4400
10.4296
10.4191
10.4086
10.3982
10.3876
10.3771
10.3666
10.3560
10.3454
10.3348
10.3242
10.3136
10.3029
10.2923
10.2816
10.2709
10.2601
10.2494
10.2386
10.2278
10.2170
10.2062
10.1954
10.1845
10.1736
10.1627
10.1518
10.1408
393
388
383
378
373
368
363
358
353
348
343
338
333
328
323
318
313
308
303
4.6075
4.5937
4.5799
4.5661
4.5523
4.5385
4.5248
4.511
4.4973
4.4836
4.4699
4.4562
4.4425
4.4288
4.4151
4.4014
4.3878
4.3741
4.3605
0.26698
0.2666
0.26623
0.26585
0.26548
0.2651
0.26473
0.26435
0.26397
0.26359
0.26322
0.26284
0.26246
0.26208
0.2617
0.26132
0.26094
0.26056
0.26017
41
17.258
17.23
17.203
17.175
17.148
17.12
17.092
17.065
17.037
17.009
16.982
16.954
16.926
16.899
16.871
16.843
16.815
16.788
16.76
10.1299
10.1189
10.1079
10.0969
10.0858
10.0748
10.0637
10.0526
10.0414
10.0303
10.0191
10.0080
9.9968
9.9855
9.9743
9.9630
9.9517
9.9404
9.9291
Appendix 2: Matlab code for analysis of TEG
clc;
clear all;
close all;
%
%
%
%
%
%
Thermoelectric Generator Code
Dimensions: 40x40x4
Material: Bi2Te3
Hot side: 300 C
Cold side: 30 C
Electrical Load: 2 kW
% Define constants
L = 0.04; % Length (m)
A = L^2; % Cross-sectional area (m^2)
k = 1.6; % Thermal conductivity (W/mK)
rho = 7.8e3; % Density (kg/m^3)
Cp = 200; % Specific heat capacity (J/kgK)
alpha = 1e-4; % Seebeck coefficient (V/K)
sigma = 1e6; % Electrical conductivity (S/m)
% Define temperature range
T_hot = 573; % Hot side temperature (K)
T_cold = 303; % Cold side temperature (K)
T_range = T_hot:-5:T_cold;
% Initialize arrays for results
P_array = zeros(size(T_range)); % Array for power output
V_array = zeros(size(T_range)); % Array for voltage output
I_array = zeros(size(T_range)); % Array for current output
% Iterate through temperature range
for i = 1:length(T_range)
T_mean = (T_hot + T_cold) / 2; % Calculate mean temperature
T_diff = T_hot - T_cold; % Calculate temperature difference
% Calculate Seebeck coefficient based on mean temperature
alpha_mean = alpha - (alpha / (2 * T_mean)) * T_diff;
% Calculate electrical resistivity based on mean temperature
rho_e = sigma / (1 + 4 * pi^2 * (k / rho) * T_mean);
% Calculate thermal resistance based on dimensions and material
properties
Rth = (L / (A * k)) * rho * Cp;
% Calculate figure of merit
ZT = alpha_mean^2 * T_mean / (rho_e * k);
% Calculate maximum theoretical efficiency based on ZT
eta_max = (T_hot - T_cold) / T_hot * sqrt((1 + ZT)^(T_hot/T_mean) - 1)
/ (sqrt((1 + ZT)^(T_hot/T_mean) + ZT^2) - 1);
% Calculate power output
P = eta_max * (T_hot - T_cold) * A;
42
% Store results in arrays
P_array(i) = P;
V_array(i) = alpha_mean * T_diff;
I_array(i) = P / V_array(i);
% Adjust hot side temperature for next iteration
T_hot = T_hot - 0.5;
end
% Display results in table
results_table = table(T_range', P_array', V_array', I_array',
'VariableNames', {'Temperature_K', 'Power_W', 'Voltage_V', 'Current_A'});
disp(results_table)
% Plot power output vs. temperature
figure
plot(T_range, P_array)
title('Power Output vs. Temperature')
xlabel('Temperature (K)')
ylabel('Power Output (W)')
% Plot voltage output vs. temperature
figure
plot(T_range, V_array)
title('Voltage Output vs. Temperature')
xlabel('Temperature (K)')
ylabel('Voltage Output (V)')
% Plot current output vs. temperature
figure
plot(T_range, I_array)
title('Current Output vs. Temperature')
xlabel('Temperature (K)')
ylabel('Current Output (A)')
43