Future train (electricity generated from heat loss) report
1. 0
FUTURE TRAIN (ELECTRICITY GENERATION FROM HEAT LOSS)
PROJECT I
SUBMITTED IN PARTIAL FUFILLMENT OF THE REQUIREMENT
FOR THE AWARD OF THE DEGREE
BACHELOR OF TECHNOLOGY
(MECHANICAL ENGINEERING)
SUBMITTED BY
RISHABH (2812493)
RAJ KISHOR (2812485)
RAVI PANDEY (2812489)
SHAHZAIB (2812484)
RISHI KUMAR (2812494)
RAVI KUMAR (2812235)
KURUKSHETRA UNIVERSITY, KURUKSHETRA
NOVEMBER, 2015
2. 1
FUTURE TRAIN (ELECTRICITY GENERATION FROM
HEAT LOSS)
PROJECT I
SUBMITTED IN PARTIAL FUFILLMENT OF THE REQUIREMENT
FOR THE AWARD OF THE DEGREE
BACHELOR OF TECHNOLOGY
(MECHANICAL ENGINEERING)
SUBMITTED BY
RISHABH (2812493)
RAJ KISHOR (2812485)
RAVI PANDEY (2812489)
SHAHZAIB (2812484)
RISHI KUMAR (2812494)
RAVI KUMAR (2812235)
PANIPAT INSTITUTE OF ENGINEERING & TECHNOLOGY,
SAMALKHA
NOVEMBER 2015
KURUKSHETRA UNIVERSITY KURUKSHETRA
3. 2
DECLARATION
We hereby certify that the work which is being presented in the project entitled “Future train (electricity
generated from heat loss)” by “Rishabh (2812493), Rajkishor (2812485), Ravi pandey
(2812489), Shahzaib (2812484), Rishi (2812494), Ravi (2812235)” in partial fulfillment of
requirements for the award of degree of B.Tech (Mechanical Engineering) submitted in the
department of mechanical engineering at PANIPAT INSTITUTE OF ENGINEERING &
TECHNOLOGY, SAMALKHA afflicated to KURUKSHETRA UNIVERSITY,
KURUKSHETRA is carried out during a period from AUG 2015 to NOV 2015 under the
supervision of Er. Ajay Chokker of project guide. The matter presented in the project has not
been submitted by us in any other university / institute for the award of B.Tech degree.
RISHABH (2812493)
RAJ KISHOR (2812485)
RAVI PANDEY (2812489)
SHAHZAIB (2812484)
RISHI KUMAR (2812494)
RAVI KUMAR (2812235)
This is to certify that the above statement made by the candidate is correct to the best of my / our
knowledge.
(Er. Ajay singh) Er. Amit Dubey
A.P. Mech Deptt. A.P. Mech. Deptt.
GUIDE PROJECT CO- ORDINATOR
The B.Tech viva voice Examination of Rishabh (2812493), Rajkishor (2812485), Ravi pandey
(2812489), Shahzaib (2812484), Rishi (2812494), Ravi (2812235) has been held on future train
(electricity generated from heat loss) and accepted.
(Er. SUNIL DHULL)
H.O.D. Signature of External Examiner
4. 3
ABSTRACT
Economic liberalization is finding good roots and globalization of economy is becoming a
worldwide phenomenon, thus the present scenario calls for the optimum utilization for the best
possible resources. With the growing environmental concerns and need of clean energy resources
which don’t put nature at risk ( i.e., eco-friendly). In such a scenario our Future train with
thermocouple module (Peltier chip) can be very advantageous for both humans and nature. From
this we can generate electricity from heat loss and natural air. It is technique of future and can be
very useful when coupled with technologies. Once established this technology will likely
become common place due to increasing energy and environmental concerns and the ease of
integration. Such Future Train will help our country to develop and prosper by less investment
and more output of electricity as it is also clean and cheap from other technologies.
5. 4
ACKNOWLEDGEMENT
Words are inadequate and out of place at time particularly in the context of expressing sincere
feeling in the contribution of this work, is no more than a mere ritual. It is our privilege to
acknowledge with respect and gratitude, the keen valuable and ever-available guidance rendered
to us by Er. Ajay singh ( Project Guide) without the wise counsel and able guidance, it would
have been impossible to complete the project in this manner.
We shall always be highly grateful to Dr. K.K PALIWAL, Director, Panipat Institute of
Engineering & Technology, samalkha, for providing this opportunity to carry out the present
work. The constant guidance and encouragement received from Er. SUNIL DHULL, Asstt.
Prof. & Head, Department of mechanical Engineering has been of great help field carrying out
the present work and is acknowledged with reverential thanks.
We express gratitude to other faculty members of Mechanical Engineering Department, PIET,
Samalkha for this intellectual support throughout the course of this work.
Finally, we are indebted to our family and for their ever available help in accomplishing this task
successfully. Above all we are thankful to the Almighty God for giving strength to carry out the
present work.
RISHABH (2812493)
RAJ KISHOR (2812485)
RAVI PANDEY (2812489)
SHAHZAIB (2812484)
RISHI KUMAR (2812494)
RAVI KUMAR (2812235)
Mechanical Engg. 7th sem
6. 5
CONTENTS
Page no.
Declaration 2
Abstract 3
Acknowledgement 4
List of figures 6
CHAPTER - 1
Introduction 7
Research & Development 11
CHAPTER-2
Components used 26
Summary 27
CHAPTER-3
Invention of peltier chip 29
Uses 38
Results 39
Scope of future 40
References 42
7. 6
LIST OF FIGURES
FIGURE No. DESCRIPTION PAGE No.
1.1 Power generation from heat loss 8
1.2 How our train looks like 9
1.3 Harvesting energy 9
1.4 Thermal electric module 10
1.5 Emergency break 11
1.6 Deustsche shell 12
1.7 Industrial Reuse 13
1.8 Discarded heat 14
1.9 Fourth coming markets 13
1.10 Thermoelectric device 15
1.11 Thermoelectric material and application 16
1.12-1.13 Comparison 17
1.14 Mg2Si Cycle 18
1.15 Performance of Mg2Si 19
1.16 Si wafer fabrication system 20
1.17 Solar cell fabrication system 21
1.18 Reuse process 22
1.19 Conversion of waste silicon 23
1.20-1.21 Development status 23, 24
1.22 Mg2Si elements and module 25
1.23 Solar Thermal Power Generation 26
2.1-2.9 Components used 27
3.1 Charge carrier diffusion 34
8. 7
3.2 Three peltier module 36
3.3-3.4 Inside of module 36, 37
3.5 Electric current produce 38
3.6 Generation of electricity 38
3.7 Home power Station 40
9. 8
CHAPTER-1
INTRODUCTION
AIM OF PROJECT:
To harvest free energy for train bogies by exhaust heat energy loses from train engine.
PRINCIPLE USED IN PROJECT:
Our project is based on thermo coupling temperature difference principle.
We divided our project in two sections:
1. Power generation from heat losses
2. Emergency brake applied in case of fire.
SECTION-1
POWER GENERATION FROM HEAT LOSSES
Fig-1.1 (Power generation from heat loss)
10. 9
HOW OUR TRAIN ENGINE LOOKS LIKE
Fig-1.2 (Train engine looks)
We will apply the thermocouple peltier setup on the train engine from there we can use the loss
heat in the atmosphere and generate electricity by the temperature difference produced due to
cool natural wind and engine heat.
HARVESTING ENERGYUSE FOR LIGHT, COOLING (FAN ONLY) AND
MOBILE, LAPTOP CHARGING
Fig1.3 (Harvesting energy)
Generating electricity from waste heat and free natural wind and using for human needs like
mobile charging, laptop charging, lights, fans etc. This setup will decrease the cost.
11. 10
THERMOELECTRIC MODULE PLACEMENT
Fig1.4 (Thermoelectric moudle)
Thermoelectric module is placed between the engine and the fins so that the temperature
difference can be created easily and we can genetrate electricity. We can also put nitogen gas
into fins as nitrogen is a cool gas and more temperature difference will be created and hence
more electricity is produced.
12. 11
SECTION-2
EMERGENCYBRAKE APPLIED IN CASE OF FIRE
Fig1.5 (Emergency brake)
We also added a extra feature in our future train model that is emergency brake system. In this
we put a thermister it’s a heat sensing device , whenever there is fire produced in the coaches of
train it will sense the heat and stop the train there only by applying emergency brakes.
13. 12
RESEARCHAND DEVELOPMENT
Development of the direct thermal-to-electric Power generator using environmentally,
semiconducting material Solid-state power generation from waste heat and solar heat
Fig1.6 (Primary energy source)
This figure shows the range of primary energy sources that are anticipated in the near future
(except for water power generation) as predicted by Deutsche Shell. In order to reduce CO2
emissions to counteract greenhouse effects, the accelerated introduction of renewable energies
such as a solar cells and fuel cells based on pure hydrogen sources, seems to be very important to
replace the use of fossil fuels. We believe that atomic power generation is not an eternal solution
because of radioactive waste and resource abundance. On the other hand, since we cannot
abandon the use of fossil fuels immediately, a positive attitude towards the use of waste heat is
urgently required to sustain the huge growth in energy consumption on a world scale.
14. 13
Fig1.7 (Reuse )
We now believe that the industrial reuse of “Waste Heat” and “Waste Si” is definitely required
for a sustainable society.
In the case of “Waste Heat” from caloric systems, this brings about an increase in CO2
emissions, and consequently to rises in atmospheric temperatures, which is becoming serious.
On the other hand, for “Waste Si” from the semiconductor industry, there are problems related
to increases in Si waste, and, simultaneously, a lack of Si resources, as we are now beginning to
recognize.
With increases in the production of LSI devices and solar cells, we will generate significant
amounts of “Wandering Si waste” due to a lack of landfill capacity and associated environmental
contamination by Si waste. This is also becoming a serious issue.
15. 14
Fig1.8 (Greenhouse effect)
The value of 11294.9 Mtoe (million tonnes oil equivalent : Mtoe) represents the total amount of
primary energy consumption of the world last year.(BP statistical review of world energy 2009)
Of this huge primary energy consumption, please consider that about 70 % of the installed
primary energy is discarded as heat, resulting in increases in CO2 emissions and atmospheric
temperature rises.
By using a direct thermal-to-electric energy conversion technique, we would like to reuse this
discarded heat energy in order to reduce CO2 emissions as soon as possible.
Fig1.9 (Fourthcoming market)
A major portion of this huge global primary energy consumption is consumed by two dominant
countries, the United States and China, who consume about 20 % and 18 %, respectively. In
these two countries, about 90 % of the primary energy is supplied by fossil fuels. From this point
of view, these two countries will become the main target markets for new thermoelectric power
plants
16. 15
Fig1.10 (Thermoelectric device)
This figure is a schematic illustration of the thermal-to-electric energy conversion; the so-called
thermoelectric device.
One side of the thermoelectric device is heated by waste heat from such as industrial furnaces
and automobile engines. The temperature difference between the hot-side and the cool -side can
be used to generate electrical power. This is the mechanism for thermoelectric power generation.
As you can understand, the device structure is very simple and there are no moving parts, as
compared with other competitive power generators such as gas turbines and the Stirling engine.
These are remarkable advantages for thermoelectric power generation.
17. 16
Fig1.11 (Thermoelectric material and application)
This viewgraph shows various thermoelectric materials and their applications. Formerly,
thermoelectric power generation was performed using Pb-Te, but, as you know, these days
regulations such as ROHS and REACH in the EU prohibit the development of Pb-Te
thermoelectric devices.
As alternative materials, Co-Sb, Zn-Sb and TAGS have been developed, but I should point out
that these materials still contain harmful substances, so they are not really solutions in terms of
ROHS and REACH regulations.
From this point of view, we have been trying to fabricate environmentally benign thermoelectric
materials from Mg2Si. The constituent elements of Mg and Si are abundant and are non-toxic.
Additionally, Mg2Si itself and its by-products are not included in the scope of regulations
covering harmful substances.
19. 18
Fig1.14(Cycle of magnesium silicate)
The above tables show comparisons of the conversion efficiency, abundance, material cost, and
toxicity for Mg2Si and other related materials. The expected value for the conversion efficiency
of Mg2Si is 9.5 % for each “element” (Japanese NEDO target value), where an “element”
consists of a device structure equipped with an electrode, a thermal contact and associated
electronics. Compared with other materials, Mg2Si exhibits comparable or slightly higher energy
conversion efficiency. Since Mg2Si is a very light material, if we refer to the value of efficiency
divided by material density, the index that we obtain exhibits much higher values.
In a comparison of relative abundance, material cost, and the need for environmentally
hazardous substances, Mg2Si is exemplary. Its constituent elements Si and Mg are readily
available, it has sufficient energy conversion efficiency, and its non-toxic nature means it can be
discarded safely after its lifetime.
20. 19
Fig1.15 (Performance of mg2si)
This figure shows the measured performance of fabricated Mg2Si devices at elevated operating
temperatures.
Typically, we consult the value of the figure of merit, ZT, to quantify the available material
conversion efficiency. ZT = 1 stands for about 10% material conversion efficiency.
In the case of Mg2Si, we have already obtained a ZT value of 1.1, indicating greater than 11 %
material conversion efficiency. We can therefore say that environmentally benign Mg2Si is a
very promising material on which to base a system for reusing waste heat.
21. 20
Fig1.16 (Wafer fabrication process)
This is a schematic illustration of the silicon (Si) wafer fabrication process.
In general, Si wafer fabrication begins with polycrystalline Si and nuggets.
After the crystal growth process by means of the Czochralski (CZ) method, we end up with a
single-crystal Si ingot. In order to obtain a Si wafer that can be used for electronic device
fabrication such as LSI, the grown Si ingot is sliced using a sawing machine, and then mirror-
like polishing is carried out.
During these wafer-fabrication processes, about 60 % of the initial Si source is discarded as Si
sludge. Since the production of 1 kg of Si wafers requires ~1000 kWh electricity, a large amount
of energy is used to produce discarded Si sludge. This is an awful state of affairs.
22. 21
Fig1.17 (Solar cell fabrication system)
This is a schematic illustration of the LSI-fabrication and the cast solar-cell fabrication
processes.
Back-grinding of LSI embedded wafers and sawing of cast Si ingots also produce Si sludge.
During the device fabrication process, ~60 to 70 % of the Si from the initial ingot is discarded.
As we are recognizing, the increase in discarded Si from wafers and from device fabrication
processes is becoming serious in terms of the lack of land fill capacity and environmental
contamination.
Last year we experienced a serious lack of semiconductor-grade and solar-cell-grade Si source
material, while huge amounts of Si sludge were emitted as industrial waste in concurrence. This
seems to be an inconsistent situation. I would like to attain a “reuse-Si cycle” using waste Si as a
new angle on the Si problem in the semiconductor industry.
23. 22
Fig1.18 (Reuse process)
One interesting approach of our Mg2Si development is the introduction of waste Si as a starting
source material. The waste Si sludge is provided from an LSI fab producing CPUs, memories,
power IC devices, and baseband chips for mobile phones.
In addition, solar cell factories also emit Si waste which is of utility value for Mg2Si synthesis.
Recently, we have developed a low-cost purification process for the waste Si sludge, in order to
improve the fabrication process for Mg2Si.
The thermal-to-electric conversion performance of Mg2Si devices fabricated using purified
‘reuse-Si’ and less pure Mg sources exhibits practically the same power generation ability
compared with other Mg2Si devices synthesized from pure Si and Mg sources.
24. 23
Fig1.19 (Conversion of wested silicon)
By means of “Waste Si”, we would like to produce a “Waste Heat” reuse system based on the
environmentally begin semiconductor material Mg2Si. We believe that this approach could serve
as an aid for the restrain to the greenhouse effect and the global energy crisis. “The future must
be wonderful”. Such a strong statement is a source of motivation toward making these
improvements.
Fig1.20 (Development status)
For the past few decades, Mg2Si has been recognized as a good TE material, but it also has been
identified as very difficult to synthesize with good crystalline quality. This is mainly due to the
dangerous process temperature required for the melt growth of Mg2Si.
25. 24
The melting point of Mg2Si is 1085°C, and thus ~1150°C or slightly higher temperature is
needed for obtain good crystalline quality.
However, this desirable process temperature is beyond the “boiling temperature (1090°C)” of
Mg. This is why Mg2Si has not been pursued extensively, even though Mg2Si is anticipated as a
candidate for thermo electric material. We provocatively inaugurated a plan to develop a possible
growth method for Mg2Si back in the year 2000.
Fig1.21 (Development status)
In 2000, as our first action, we tried to fabricate single crystal Mg2Si, and we successfully
developed a synthesis technique for this material. For the grown Mg2Si, the measured
thermoelectric performance and durability at elevated temperature were sufficient for practical
use. In 2003, we then tried to reduce the fabrication cost to establish commercial Mg2Si material
using refined synthesis methods.
Starting from 2005, we examined the introduction of Si sludge and recycled Mg-alloy as source
materials for Mg2Si fabrication by developing a low-cost purification process. We have now
achieved a “Mg2Si for waste heat reuse device” using waste Si and recycled Mg sources. So far,
our approach to making Mg2Si has been epochal. From 2009, we have started to fabricate Mg2Si
thermoelectric power generation modules, and have executed field tests of the modules at various
industrial moderate-temperature heat sources.
26. 25
Fig1.22 (Element and module)
The fabricated Mg2Si thermoelectric elements and modules are shown here. Since the measured
power generation ability of Mg2Si is large enough, we have just started the development of
specific modules for solar heat power generation.
The typical current power generation density of this material is about 2.5 to 3 kW/m2, and
tentative life tests (hot side: 600 °C, cool side: 100 °C, in the air) have lasted for more than
15,000 hrs with neither remarkable power drop nor surface degradation.
27. 26
Fig1.23 (Solar thermal power generation)
Since the current power density of these Mg2Si thermoelectric elements is large enough, we
have been able to examine the development a specific Mg2Si modules for solar thermal power
generation.
An SES solar thermal power generator using a Stirling engine already exists in California, as
shown in the picture below.
This type of power generator is also available for Mg2Si solid-state thermoelectric power-
generation by replacing the Stirling engine with a thermoelectric device.
30. 29
CHAPTER-3
Invention of peltire chip
Jean Charles Athanase Peltier (1785 in Ham (France) - 1845 in Paris) was a French physicist.
He discovered the calorific effect of electric current passing through the junction of two different
metals. This is now called the Peltier effect or Peltier–Seebeck effect.
The Peltier effect, where current is forced through a junction of two different metals, forms the
basis of the small 12/24 Volt heater/coolers sold for vehicle use. By switching the direction of
current, either heating or cooling may be achieved. It also forms the basis of the rather
expensive, but very stable, junction heated soldering irons, and is used for spot cooling of certain
integrated circuits.
It is important to realise that junctions always come in pairs, as the two different metals must be
joined at two points. Thus heat will be moved from one junction to the other. To make a usable
heat pump, multiple junctions are created between two plates. One side will get hot and the other
side cold. An effective heat dissipation device must be attached to the hot side to maintain a
cooling effect on the cold side. This is usually a heat sink and fan assembly.
Thermoelectric effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage
and vice versa. A thermoelectric device creates a voltage when there is a different temperature on
each side. Conversely when a voltage is applied to it, it creates a temperature difference (known
as the Peltier effect). At atomic scale (specifically, charge carriers), an applied temperature
gradient causes charged carriers in the material, whether they are electrons or electron holes, to
diffuse from the hot side to the cold side, similar to a classical gas that expands when heated;
hence, the thermally-induced current.
This effect can be used to generate electricity, to measure temperature, to cool objects, or to heat
them or cook them. Because the direction of heating and cooling is determined by the sign of the
applied voltage, thermoelectric devices make very convenient temperature controllers.
Traditionally, the term thermoelectric effect or thermoelectricity encompasses three separately
identified effects, the Seebeck effect, the Peltier effect, and the Thomson effect. In many
textbooks, thermoelectric effect may also be called the Peltier–Seebeck effect. This separation
derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and
Estonian-German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated
whenever a voltage is applied across a resistive material, is somewhat related, though it is not
generally termed a thermoelectric effect (and it is usually regarded as being a loss mechanism
due to non-ideality in thermoelectric devices). The Peltier–Seebeck and Thomson effects can in
principle be thermodynamically reversible, whereas Joule heating is not.
31. 30
Seebeck effect
The Seebeck effect is the conversion of temperature differences directly into electricity.
Seebeck discovered that a compass needle would be deflected when a closed loop was formed of
two metals joined in two places with a temperature difference between the junctions. This is
because the metals respond differently to the temperature difference, which creates a current
loop, which produces a magnetic field. Seebeck, however, at this time did not recognize there
was an electric current involved, so he called the phenomenon the thermomagnetic effect,
thinking that the two metals became magnetically polarized by the temperature gradient. The
Danish physicist Hans Christian Ørsted played a vital role in explaining and conceiving the term
"thermoelectricity".
The effect is that a voltage, the thermoelectric EMF, is created in the presence of a temperature
difference between two different metals or semiconductors. This causes a continuous current in
the conductors if they form a complete loop. The voltage created is of the order of several
microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck
coefficient of 41 microvolts per kelvin at room temperature.
In the circuit:
(which can be in several different configurations and be governed by the same equations) , the
voltage developed can be derived from:
SA and SB are the Seebeck coefficients (also called thermoelectric power or thermo power) of the
metals A and B as a function of temperature, and T1 and T2 are the temperatures of the two
junctions. The Seebeck coefficients are non-linear as a function of temperature, and depend on
the conductors' absolute temperature, material, and molecular structure. If the Seebeck
coefficients are effectively constant for the measured temperature range, the above formula can
be approximated as:
32. 31
The Seebeck effect is commonly used in a device called a thermocouple (because it is made from
a coupling or junction of materials, usually metals) to measure a temperature difference directly
or to measure an absolute temperature by setting one end to a known temperature. A metal of
unknown composition can be classified by its TE effect if a metallic probe of known
composition, kept at a constant temperature, is held in contact with it. Industrial quality control
instruments use this Seebeck effect to identify metal alloys. This is known as Thermo electric
alloy sorting. Several thermocouples when connected in series are called a thermopile, which is
sometimes constructed in order to increase the output voltage since the voltage induced over
each individual couple is small.
This is also the principle at work behind thermal diodes and thermoelectric generators (such as
radioisotope thermoelectric generators or RTGs) which are used for creating power from heat
differentials.
The Seebeck effect is due to two effects: charge carrier diffusion and phonon drag (described
below). If both connections are held at the same temperature, but one connection is periodically
opened and closed, an AC voltage is measured, which is also temperature dependent. This
application of the Kelvin probe is sometimes used to argue that the underlying physics only
needs one junction. And this effect is still visible if the wires only come close, but do not touch,
thus no diffusion is needed.
Thermo power
The thermo power, thermoelectric power, or Seebeck coefficient of a material measures the
magnitude of an induced thermoelectric voltage in response to a temperature difference across
that material. The thermo power has units of (V/K), though in practice it is more common to use
microvolts per kelvin. Values in the hundreds of μV/K, negative or positive, are typical of good
thermoelectric materials. The term thermo power is a misnomer since it measures the voltage or
electric field induced in response to a temperature difference, not the electric power. An applied
temperature difference causes charged carriers in the material, whether they are electrons or
holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when
heated. Mobile charged carriers migrating to the cold side leave behind their oppositely charged
and immobile nuclei at the hot side thus giving rise to a thermoelectric voltage (thermoelectric
refers to the fact that the voltage is created by a temperature difference). Since a separation of
charges also creates an electric potential, the buildup of charged carriers onto the cold side
eventually ceases at some maximum value since there exists an equal amount of charged carriers
drifting back to the hot side as a result of the electric field at equilibrium. Only an increase in the
temperature difference can resume a buildup of more charge carriers on the cold side and thus
lead to an increase in the thermoelectric voltage. Incidentally the thermo power also measures
the entropy per charge carrier in the material. To be more specific, the partial molar electronic
33. 32
heat capacity is said to equal the absolute thermoelectric power multiplied by the negative of
Faraday's constant.
The thermo power of a material, represented by S (or sometimes by α), depends on the material's
temperature and crystal structure. Typically metals have small thermo powers because most have
half-filled bands. Electrons (negative charges) and holes (positive charges) both contribute to the
induced thermoelectric voltage thus canceling each other's contribution to that voltage and
making it small. In contrast, semiconductors can be doped with excess electrons or holes, and
thus can have large positive or negative values of the thermo power depending on the charge of
the excess carriers. The sign of the thermo power can determine which charged carriers dominate
the electric transport in both metals and semiconductors.
If the temperature difference ΔT between the two ends of a material is small, then the thermo
power of a material is defined (approximately) as:
and a thermoelectric voltage ΔV is seen at the terminals.
This can also be written in relation to the electric field E and the temperature gradient , by
the approximate equation.
In practice one rarely measures the absolute thermo power of the material of interest. This is
because electrodes attached to a voltmeter must be placed onto the material in order to measure
the thermoelectric voltage. The temperature gradient then also typically induces a thermoelectric
voltage across one leg of the measurement electrodes. Therefore the measured thermo power
includes a contribution from the thermo power of the material of interest and the material of the
measurement electrodes.
The measured thermo power is then a contribution from both and can be written as:
Superconductors have zero thermo power since the charged carriers produce no entropy. This
allows a direct measurement of the absolute thermo power of the material of interest, since it is
the thermo power of the entire thermocouple as well. In addition, a measurement of the Thomson
coefficient, μ, of a material can also yield the thermo power through the relation:
The thermo power is an important material parameter that determines the efficiency of a
thermoelectric material. A larger induced thermoelectric voltage for a given temperature gradient
will lead to a larger efficiency. Ideally one would want very large thermo power values since
only a small amount of heat is then necessary to create a large voltage. This voltage can then be
used to provide power.
34. 33
Charge-carrier diffusion
Charge carriers in the materials (electrons in metals, electrons and holes in semiconductors, ions
in ionic conductors) will diffuse when one end of a conductor is at a different temperature than
the other. Hot carriers diffuse from the hot end to the cold end, since there is a lower density of
hot carriers at the cold end of the conductor. Cold carriers diffuse from the cold end to the hot
end for the same reason.
If the conductor were left to reach thermodynamic equilibrium, this process would result in heat
being distributed evenly throughout the conductor The movement of heat (in the form of hot
charge carriers) from one end to the other is called a heat current. As charge carriers are moving,
it is also an electrical current.
In a system where both ends are kept at a constant temperature difference (a constant heat current
from one end to the other), there is a constant diffusion of carriers. If the rate of diffusion of hot
and cold carriers in opposite directions were equal, there would be no net change in charge.
However, the diffusing charges are scattered by impurities, imperfections, and lattice vibrations
(phonons). If the scattering is energy dependent, the hot and cold carriers will diffuse at different
rates. This creates a higher density of carriers at one end of the material, and the distance
between the positive and negative charges produces a potential difference; an electrostatic
voltage.
This electric field, however, opposes the uneven scattering of carriers, and an equilibrium is
reached where the net number of carriers diffusing in one direction is canceled by the net number
of carriers moving in the opposite direction from the electrostatic field. This means the thermo
power of a material depends greatly on impurities, imperfections, and structural changes (which
often vary themselves with temperature and electric field), and the thermo power of a material is
a collection of many different effects.
Early thermocouples were metallic, but many more recently developed thermoelectric devices
are made from alternating p-type and n-type semiconductor elements connected by metallic
interconnects as pictured in the figures below. Semiconductor junctions are especially common
in power generation devices, while metallic junctions are more common in temperature
measurement. Charge flows through the n-type element, crosses a metallic interconnect, and
passes into the p-type element. If a power source is provided, the thermoelectric device may act
as a cooler, as in the figure to the left below. This is the Peltier effect, described below.
Electrons in the n-type element will move opposite the direction of current and holes in the p-
type element will move in the direction of current, both removing heat from one side of the
device. If a heat source is provided, the thermoelectric device may function as a power generator,
as in the figure to the right below. The heat source will drive electrons in the n-type element
toward the cooler region, thus creating a current through the circuit.
Holes in the p-type element will then flow in the direction of the current. The current can then
be used to power a load, thus converting the thermal energy into electrical energy.
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Fig3.1 (Charge carrier diffusion)
Phonon drag
Phonons are not always in local thermal equilibrium; they move against the thermal gradient.
They lose momentum by interacting with electrons (or other carriers) and imperfections in the
crystal. If the phonon-electron interaction is predominant, the phonons will tend to push the
electrons to one end of the material, losing momentum in the process. This contributes to the
already present thermoelectric field.
This contribution is most important in the temperature region where phonon-electron scattering
is predominant. This happens for
Where θD is the Debye temperature. At lower temperatures there are fewer phonons available for
drag, and at higher temperatures they tend to lose momentum in phonon-phonon scattering
instead of phonon-electron scattering.
This region of the thermo power-versus-temperature function is highly variable under a magnetic
field.
Peltier effect
The Peltier (pronounced /ˈpɛltyeɪ/) effect bears the name of Jean-Charles Peltier, a French
physicist who in 1834 discovered the calorific effect of an electrical current at the junction of
two different metals. When a current I is made to flow through the circuit, heat is evolved at the
upper junction (at T2), and absorbed at the lower junction (at T1). The Peltier heat absorbed by
the lower junction per unit time, Q is equal to .
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Where Π is the Peltier coefficient ΠAB of the entire thermocouple, and ΠA and ΠB are the
coefficients of each material. p-type silicon typically has a positive Peltier coefficient (though
not above ~550 K), and n-type silicon is typically negative.
The Peltier coefficients represent how much heat current is carried per unit charge through a
given material. Since charge current must be continuous across a junction, the associated heat
flow will develop a discontinuity if ΠA and ΠB are different.
This causes a non-zero divergence at the junction and so heat must accumulate or deplete there,
depending on the sign of the current. Another way to understand how this effect could cool a
junction is to note that when electrons flow from a region of high density to a region of low
density, they expand (as with an ideal gas) and cool.
The conductors are attempting to return to the electron equilibrium that existed before the current
was applied by absorbing energy at one connector and releasing it at the other. The individual
couples can be connected in series to enhance the effect.
An interesting consequence of this effect is that the direction of heat transfer is controlled by the
polarity of the current; reversing the polarity will change the direction of transfer and thus the
sign of the heat absorbed/evolved
.A Peltier cooler/heater or thermoelectric heat pump is a solid-state active heat pump which
transfers heat from one side of the device to the other. Peltier cooling is also called thermo-
electric cooling (TEC).
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Close-upof inside of a module:
Note: metallized connecting bars on ceramic plate on the left. These serve to connect all of the
couples in series.
Fig3.4 (View of module)
HOW IT WORKS:
TEGs are made from thermoelectric modules which are solid-state integrated circuits that
employ three established thermoelectric effects known as the Peltier, Seebeck and Thomson
effects. It is the Seebeck effect that is responsible for electrical power generation.
Their construction consists of pairs of p-type and n-type semiconductor materials forming a
thermocouple. These thermocouples are then connected electrically forming an array of multiple
thermocouples (thermopile). They are then sandwiched between two thin ceramic wafers.
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When heat and cold are applied, the device then generates electricity.
Fig3.5 (Process to generate electricity)
These thermocouples are then connected electrically in series and/or parallel forming an array of
multiple thermocouples (thermopile). When heat and cold are applied this device then generates
electricity. Almost any heat source can be used to generate electricity, such as solar heat, ocean
heat, geothermal heat, even body heat! In addition the efficiency of any device or machine that
generates heat as a by-product can be drastically improved by recovering the energy lost as heat.
Can you really generate that much electricity from waste heat?
You may be surprised just how much you can! Here is a small example of how much power you
can generate. Below is a pot of hot water with 4-thermoelectric modules attached around the
sides. The output from this simple thermoelectric generator (TEG) is about 8 watt and the light is
a 12 volt auto lamp.
Fig 3.6 (Generation of electriciy)
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Thermoelectric generators have been in use for many years by NASA to power spacecraft and
the oil and gas industry to power remote monitoring stations around the globe.
Only in recent years has this technology become available to the general public and TEG Power
is at the forefront of this thermoelectric energy revolution. We are the first manufacture to
provide practical and affordable thermoelectric generators to the energy conscious consumer.
Almost any heat source can be used to generate electricity, such as solar heat, ocean heat,
geothermal heat, even body heat!
NOTE:
One 165 watt Sharp PV panel produces 0.6 kWh of electricity per day in sunny Southern
California. One 25 watt TEG also produces 0.6 kWh of electricity per day (with a continuous
heat source) day or night.
When you compare the costs of solar and our thermoelectric generators based on the amount of
electricity they actually produce per day, you find that our TEGs cost far less per kWh than
solar! The PV (photovoltaic) equivalent of 50 watts of TEG power operating on a wood stove is
330 watts of solar panels or 1.2 kWh per day. This means using just 150 watts thermoelectric
power can produce the same amount of electricity in a day as 990 watts of solar PV panels.
If comparing costs, the price range for 990 watts of solar would be as much as $5,000 depending
on the particular brand. Whereas the cost of 150 watts of thermoelectric power can be as low as
$500. Unlike solar TEGs are not dependant on the sun to producing electric power. If you have a
continuous heat source, like a wood stove, TEGs can produce power day and night, 24/7-365.
Granted you will need a cheap or free source of heat, but if you already have an existing heat
source such as a wood stove or hot flu gases there is no added fuel cost to run the TEG! Unlike
conventional electric generators powered by fossil fuels, TEGs have no moving parts to break.
They are virtually silent and rated to last more than 200,000 hours of continuous operation.
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Home Power Stations:
One possible use for thermoelectric generators is to provide supplemental or back-up electricity
for home owners who use outdoor wood/biofuel furnaces. The diagram below reflects just one of
the possible thermoelectric home power stations that could be setup using TEGs. It should be
noted that just 500 watts of thermoelectric power added to an outdoor wood/biofuel furnace like
the one below can produce 12 kWh of electricity per day, which is enough to reduce the average
household electric bill by more than one third, based on an average household usage of 30.66
kWh per day. The vast majority of wood burning furnaces today use gasification technology
which produces clean burning hydrogen gas, making them extremely efficient and clean burning.
Fig3.7 (Home power station)
The need for thermoelectric power . .
Electricity is no longer a luxury; it has become a necessity in our everyday lives. Have you ever
had to live without electricity for an extended period of time? If so then you know what it is like
to lose all the food in your refrigerator and/or chest freezer and shivering in the cold because you
have no heat.
Every year thousands, even millions have been in this position when a winter storm knocked out
power over large areas. Not to mention rapidly rising energy costs and an uncertain economic
future. Still many people have become complacent about their electrical energy needs. Solar
panels are a great alternative energy source, but they only produce electricity during daylight
hours.In addition their daily output is significantly reduced during winter months and cloudy
days. Now, using a TEG in conjunction with solar and wind, their combined output can provide
all off your home’s energy needs and depending on what state you live in, you will be getting a
check from the electric company instead off a bill.
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Results
Electricity has been generated by applying Peltier chip on the engine of the train when the train
is in motion i.e, when natural air is striking at one side of the peltier chip and hence due to temp.
difference we can generate electricity out of waste heat. It can be used for mobile charging,
laptop charging, fan and tube lights. Here in the model we used heating press element instead of
engine and blower instead of natural air and we are able to produce electricity upto 3V with the
help of generated electricity we are using a small fan.
We also used thermesters (heat sensing device) for emergency braking system in train during the
case of accidental fire. It will stop the moving train whenever it senses heat and emergency
brakes will be applied.
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Scope for future
Since it is a eco-friendly technology hence will be appreciated in all areas. The peltier chip
consist of magnesium silicate which is not costly, easily available and does not have toxicity.
With this greenhouse effect will be controlled no depletion of ozone layer. No pollution will get
into the atmosphere and can be used to generate electricity where a good temp. Difference is
present. This technology is very useful and can be used to generate electricity efficiently in a
clean manner. With the decrease in fuel percentage there is a utmost importance of this
technology to be used in many sectors for electricity generation.
