project report final
TRANSCRIPT
Project Report 2013
SSET, KARUKUTTY DEPARTMENT of EEE
TABLE OF FIGURES
FIG.NO TITLE PAGE NO
2.1 Seebeck arrangement 5
2.2 Generation of electricity 7
2.3 Peltier effect 8
2.4 Thermocouple measuring circuit 10
2.5 Block diagram 12
2.6 Thermoelectric module 13
2.7 Thermoelectric generator 14
2.8 Principle of thermoelectric generator 14
2.9 Schematic diagram of thermoelectric generator 16
2.10 Basic inverter schematic 18
4.1 Performance characteristics 22
4.2 Wooden stove 23
4.3 Heat sink and cooling system 24
4.4 Module connection 25
4.5 Battery 25
4.6 Circuit diagram of inverter 26
4.7 Pin configuration of IC3525 27
4.8 MOSFET 29
4.9 MOSFET working 30
4.10 Transformer 31
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CHAPTER 1
INTRODUCTION
Electricity is no longer a luxury; it has become a necessity in our everyday lives. Have you ever
imagined the life without electricity for an extended period of time? Every year thousands, even
millions have been in this position when a winter storm knocked out power over large areas.
Solar panels are a great alternative energy source, but they only produce electricity during
daylight hours and their output is significantly reduced during winter months and cloudy days.
Using a TEG can provide your home’s energy needs and depending on what state you live in,
you will begetting a check from the electric company instead off a bill in the future!!
A thermoelectric generator is a system that exploits the Seebeck effect to convert heat energy into
electricity. Utilizing several semi-conductors in series, a thermoelectric module exploits a
difference in temperature to capture energy from thermally excited electrons. It is an attractive
option for providing small amounts of electricity to homes in the developing world that
are not connected to the power grid. Generally, household’s use biomass stoves for their
cooking needs. Such stoves can be equipped with a thermoelectric. Subsequently, the generator
converts waste heat to electricity, providing a household with enough electricity.
The generator system consists of a thermoelectric module, a hot sink, and a cold sink. Heat from
the stove is captured by the hot sink and transferred to the hot side of the thermoelectric module.
The thermoelectric module converts a fraction of this heat energy into electricity. The remainder
of the heat is rejected to the environment, by the cold sink. The electricity produced by the
module flows to the load via two leads on the thermoelectric module.
The ultimate aim of this project is to convert the waste heat into the useful electrical energy. The
Existing wooden stove is modified into multifunctional wooden stove which can be used both for
cooking and also for generating of the electricity.
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CHAPTER2
LITERATURE SURVEY
Paper1:‘Study of thermoelectric generator incorporated onto a
multifunction wooden stove’
Author: Doctor Daniel Champier, Associate Professor, UPP
Abstract: Replacing traditional open firestoves, characterized by low efficiency, with improved
ones is an important challenge for the developing countries. Adding thermoelectric generators
can provide electricity that permits not only the use of an electric fan increasing the ratio of air to
fuel to achieve a complete combustion in the stoves but also the satisfaction of the basic needs:
lights, phones and the other electronic devices. T test the thermoelectric modules, an
experimental device has been carried out in the laboratory where gas heater simulates stove. The
performance of the generator mainly depends on the heat transfer through the modules and
especially on thermal contact resistances. The study of temperature and electrical power
measurements is compared to a theoretical analysis using thermoelectric and heat transfer
equations. The thermo electric generator has produced up to 9.5w.
Paper2:‘Performance of Stove Mounted Thermoelectric Generator’
Author: Harry O’Hanley. Prof. Derek Rowell
Abstract: A prototype cook stove has been fabricated with a thermoelectric generator mounted in
the chimney. This device produces both heat and electricity and is intended for use in
developing-world households that are not connected to the electrical grid. It is equipped with a
hot sink located in the flue to collect heat, a thermoelectric module to generate electricity, and
a cold sink with a cooling fan to reject heat to the environment. Three aspects of this
configuration were investigated: the correlation between temperature difference across the
module and power output, the impact of the cooling fan on the thermal resistance of the cold
sink, and the effect of matching load impedance to source impedance. Results confirmed
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the theoretical correlation, in which power output is approximately proportional to the
square of temperature difference. The thermal resistance of the cold sink was determined
to decrease exponentially with an increase of impinging airflow. Lastly, maximum power
was extracted from the thermoelectric module when the load and source impedances were
equal. These results were used to optimize the stove configuration and it was experimentally
calculated that the stove will operate best with matched impedances and the cooling fan
sub-maximally powered with 10.9V. These findings can be used to better design a power
generating cook stove. Additionally, the experimental procedure is repeatable for other cook
stove prototypes.
Paper3: ‘High Efficiency Thermoelectric Generator: Integration’
Author: Dr. Lon E. Bell, BSST LLC.25 February 2011
Abstract: Thermoelectric generator efficiency is one of the key metrics for assessment of
technology viability in particular applications. It provides an important indication of the
progress made in development of thermoelectric materials having improved performance
compared to state of the art materials. BSST has conducted a worldwide survey of
thermoelectric material development efforts, identifying and sampling the most promising
developments. These materials were assessed by their assembly and incorporation in
demonstration power generation devices. Experimental methods were employed to assembly
device components consisting of multiple types of thermoelectric material to optimize
performance. Experimental generator designs were developed and employed to incorporate the
thermoelectric components and provide a demonstration of the best possible performance that
could be obtained from the materials selected. Bulk segmented materials were used in both n-
and p-legs of tested couples and
prototype generators. A compact cylindrical TEG, comprised of an axial heat source (electrical
heater in a demo device), radial segmented TE elements, and a cold side with air or water
cooling was developed and used to demonstrate material performance. The inner volume of the
device operated in an Argon atmosphere. The design was adaptable to a variety of practical heat
sources.
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2.1 THERMOELECTRICITY
Thermoelectricity is a two-way process. It can refer either to the way a temperature difference
between one side of a material and the other can produce electricity, or to the reverse: the way
applying an electric current through a material can create a temperature difference between its
two sides, which can be used to heat or cool things without combustion or moving parts.
The fundamental problem in creating efficient thermoelectric materials is that they need to be
good at conducting electricity, but not at conducting thermal energy. That way, one side can get
hot while the other gets cold, instead of the material quickly equalizing the temperature. But in
most materials, electrical and thermal conductivity go hand in hand. New nano-engineered
materials provide a way around that, making it possible to fine-tune the thermal and electrical
properties of the material.
2.2 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 and vice versa. At the atomic scale, an applied temperature gradient causes charge
carriers in the material to diffuse from the hot side to the cold side. This effect can be used to
generate electricity, measure temperature or change the temperature of objects. Because the
direction of heating and cooling is determined by the polarity of the applied voltage. The term
"thermoelectric effect" encompasses three separately identified effects: the Seebeck effect,
Peltier effect and Thomson effect.
2.2.1 SEEBECK EFFECT
The Seebeck effect is a phenomenon in which a temperature difference between two dissimilar
electrical conductors or semiconductors produces a voltage difference between the two
substances.When heat is applied to one of the two conductors or semiconductors, heated
electrons flow toward the cooler one. If the pair is connected through an electrical circuit, direct
current (DC) flows through that circuit.
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The voltages produced by Seebeck effect are small, usually only a few microvolts (millionths of
a volt) per kelvin of temperature difference at the junction. If the temperature difference is large
enough, some Seebeck-effect devices can produce a few millivolts (thousandths of a volt).
Numerous such devices can be connected in series to increase the output voltage or in parallel to
increase the maximum deliverable current. Large arrays of Seebeck-effect devices can provide
useful, small-scale electrical power if a large temperature difference is maintained across the
junctions.
The Seebeck effect is responsible for the behavior of thermocouples, which are used to
approximately measure temperature differences or to actuate electronic switches that can turn
large systems on and off. This capability is employed in thermoelectric cooling technology.
Commonly used thermocouple metal combinations include constantan/copper, constantan/iron,
constantan/chromel and constantan/alumel.
Fig 2.1: Seebeck arrangement
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The voltage V developed can be derived from:
Where and are the Seebeck coefficients of metals A and B as a function of temperature
and and 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:
The Seebeck effect is caused by charge-carrier diffusion. Charge carriers in the materials will
diffuse when one end of a conductor is at a different temperature from 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, and vice versa. 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 a heat
current and an electric current as charge carriers are moving.
In a system where both ends are kept at a constant temperature difference, there is a constant
diffusion of carriers. If the rate of diffusion of hot and cold carriers in opposite directions is
equal, there is no net change in charge. The diffusing charges are scattered by impurities,
imperfections, and lattice vibrations or phonons. If the scattering is energy dependent, the hot
and cold carriers will diffuse at different rates, creating a higher density of carriers at one end of
the material and an electrostatic voltage.
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Fig2.2: Generation of electricity
This electric field opposes the uneven scattering of carriers, and 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. This means the thermo power of a material depends greatly on
impurities, imperfections, and structural changes that vary with temperature and electric field;
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 connectors.
Semiconductor junctions are common in power generation devices. Charge flows through the n-
type element, crosses a metallic interconnect, and passes into the p-type element. When a heat
source is provided, the thermoelectric device functions as a power generator. The heat source
drives electrons in the n-type element toward the cooler region, creating a current through the
circuit. Holes in the p-type element then flow in the direction of the current. Therefore, thermal
energy is converted into electrical energy.
2.2.2PELTIER EFFECT
The Peltier effect is the presence of heat at an electrified junction of two different metals. The
Peltier effect is a temperature difference created by applying a voltage between two electrodes
connected to a sample of semiconductor material. This phenomenon can be useful when it is
necessary to transfer heat from one medium to another on a small scale. In a Peltier-effect
device, the electrodes are typically made of a metal with excellent electrical conductivity. The
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semiconductor material between the electrodes creates two junctions between dissimilar
materials, which, in turn, creates a pair of thermocouple voltage is applied to the electrodes to
force electrical current through the semiconductor, thermal energy flows in the direction of
the charge carriers.
Peltier effect, the cooling of one junction and the heating of the other when electric current is
maintained in a circuit of material consisting of two dissimilar conductors; the effect is even
stronger in circuits containing dissimilar semiconductors. In a circuit consisting of a battery
joined by two pieces of copper wire to a length of bismuth wire, a temperature rise occurs at the
junction where the current passes from copper to bismuth, and a temperature drop occurs at the
junction where the current passes from bismuth to copper.
Fig 2.3: Peltier effect
Peltier-effect devices are used for thermoelectric cooling in electronic equipment and computers
when more conventional cooling methods are impractical.
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2.3THERMOELECTRIC GENERATOR
Thermoelectric generators (also called Seebeck generators) are devices which convert heat
(temperature differences) directly into electrical energy, using a phenomenon called the
"Seebeck effect" (or "thermoelectric effect"). Their typical efficiencies are around 5-8%. Older
Seebeck-based devices used bimetallic junctions and were bulky while more recent devices use
semiconductor p-n junctions made from bismuth telluride (Bi2Te3), lead telluride (PbTe),calcium
manganese oxide, or combinations depending on temperature. These are solid state devices and
unlike dynamos have no moving parts, with the occasional exception of a fan or pump.
2.3.1THERMOCOUPLES
A thermocouple consists of two conductors of different materials (usually metal alloys) that
produce a voltage in the vicinity of the point where the two conductors are in contact. The
voltage produced is dependent on, but not necessarily proportional to, the difference of
temperature of the junction to other parts of those conductors. Thermocouples are a widely used
type of temperature sensor for measurement and control and can also be used to convert a
temperature gradient into electricity. Commercial thermocouples are inexpensive,
interchangeable, are supplied with standard connectors, and can measure a wide range of
temperatures. In contrast to most other methods of temperature measurement, thermocouples are
self powered and require no external form of excitation. The main limitation with thermocouples
is accuracy; system errors of less than one degree Celsius (C) can be difficult to achieve.
Any junction of dissimilar metals will produce an electric potential related to temperature.
Thermocouples for practical measurement of temperature are junctions of specific alloys which
have a predictable and repeatable relationship between temperature and voltage. Different alloys
are used for different temperature ranges. Properties such as resistance to corrosion may also be
important when choosing a type of thermocouple. Where the measurement point is far from the
measuring instrument, the intermediate connection can be made by extension wires which are
less costly than the materials used to make the sensor. Thermocouples are usually standardized
against a reference temperature of 0 degrees Celsius; practical instruments use electronic
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methods of cold-junction compensation to adjust for varying temperature at the instrument
terminals. Electronic instruments can also compensate for the varying characteristics of the
thermocouple, and so improve the precision and accuracy of measurements.
Thermocouples are widely used in science and industry; applications include temperature
measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes.
Fig 2.4: A thermocouple measuring circuit with a heat source, cold junction and a measuring
instrument.
The principle of operation of the thermocouple is the seebeck effect i.e. the voltage is developed
based on the temperature difference between the hot and the cold junctions of the thermocouple.
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Any attempt to measure this voltage necessarily involves connecting another conductor to the
"hot" end. This additional conductor will then also experience the temperature gradient, and
develop a voltage of its own which will oppose the original. Fortunately, the magnitude of the
effect depends on the metal in use. Using a dissimilar metal to complete the circuit creates a
circuit in which the two legs generate different voltages, leaving a small difference in voltage
available for measurement. That difference increases with temperature, and is between 1 and 70
microvolts per degree Celsius (µV/°C) for standard metal combinations.
The voltage is not generated at the junction of the two metals of the thermocouple but rather
along that portion of the length of the two dissimilar metals that is subjected to a temperature
gradient. Because both lengths of dissimilar metals experience the same temperature gradient,
the end result is a measurement of the difference in temperature between the thermocouple
junction and the reference junction.
2.3.2PROPERTIES OF THERMOCOUPLE CIRCUITS
The behavior of thermoelectric junctions with varying temperatures and compositions can be
summarized in three properties:
Homogeneous material—a thermoelectric current cannot be sustained in a circuit of a single
homogeneous material by the application of heat alone, regardless of how it might vary in cross
section. In other words, temperature changes in the wiring between the input and output do not
affect the output voltage, provided all wires are made of the same materials as the thermocouple.
Intermediate materials—the algebraic sum of the thermoelectric EMFs in a circuit composed
of any number of dissimilar materials is zero if all of the junctions are at a uniform temperature.
So if a third metal is inserted in either wire and if the two new junctions are at the same
temperature, there will be no net voltage generated by the new metal.
Successive or intermediate temperatures—if two dissimilar homogeneous materials produce
thermal EMF1 when the junctions are at T1 and T2 and produce thermal EMF2 when the
junctions are at T2 and T3, the EMF generated when the junctions are at T1 and T3 will be
EMF1 + EMF2, provided T1<T2<T3
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Thermocouples can be connected in series to form a thermopile, where all the hot junctions are
exposed to a higher temperature and all the cold junctions to a lower temperature. The output is
the sum of the voltages across the individual junctions, giving larger voltage and power output.
Fig 2.5: Thermoelectric wooden stove block diagram
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COLD
HOT
TEM
BATTERY
OSCILLATOR
CIRCUIT POWER CIRCUIT TRANSFORMER
LOAD
WOODEN STOVE
INVERTER
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2.4THERMOELECTRIC MODULE
Thermoelectric modules are solid-state devices (no moving parts) that convert electrical energy
into a temperature gradient, known as the "Peltier effect" or convert thermal energy from a
temperature gradient into electrical energy, the "Seebeck effect." Thermoelectric modules used
as TE generators or TEGs are rather inefficient and little power is produced.
Fig 2.6: Thermoelectric module
With no moving parts, thermoelectric modules are rugged, reliable and quiet heat pumps,
typically 1.5 inches (40 x 40mm) square or smaller and approximately ¼ inch (4 mm) thick. The
industry standard mean time between failures is around 200,000 hours or over 20 years for
modules left in the cooling mode.
Because the cold side of the module contracts while the hot side expands modules with a
footprint larger than 1.5 - 2 inches square usually suffer from thermally induced stresses, at the
electrical connection points inside the module causing a short, so they are not common. Long,
thin modules want to bow for the same reason and are also rare. Larger areas than an individual
module can maintain are cooled or have the temperature controlled by using multiple modules.
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Since the energy available from a single thermocouple is very small, arrays of thermocouples
must be used to construct thermoelectric devices capable of handing practical amounts of power.
Higher power devices can be made by connecting thermocouples in series to increase the voltage
capability and in parallel to increase the current capacity. Such an array of thermocouples is
called a thermopile. The thermocouples are connected using the conducting material and the
thermopile is given a covering using ceramic substances in order to withstand the temperature
difference applied .The unit as a whole is called as the thermoelectric module.
2.5 PRINCIPLE
OF THERMOELECTRIC GENERATION
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Fig 2.7: Thermoelectric generator (TEG)
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Fig2.8: Principle of TEG
In the thermoelectric module the metal cannot be used since the interconnections between the
thermocouples using metal may cause the voltage to be developed in the opposite direction and
as a result the net voltage produced id reduced and the output is drastically reduced.
In order to avoid the problems while using the metallic conductors we use p and n type
semiconductors connected together so that the voltage developed is aiding and the net output
produced is increased.
The operation is as follows:
The temperature at the hot side is more at the hot side than at the cold side and as a result
the electrons at the hot side of the n type semiconductor is having more energy and tends
to flow towards the cold side. The movement of the electrons from the hot side is more
faster than that from the cold side. Hence the flow of electron is from the hot side to the
cold side
Whereas when the temperature at the hot side is increased for the p type semiconductor
the holes or the positive charge particle gets more energy and flow from the hot side to
the cold side.
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Thus in effect the cold side portion of the n type semiconductor contains the negative
charge and act as the negative terminal and the cold side portion of the p type
semiconductor has the positive charge hence it will be acting as the positive terminal.
By connecting the adjacent n type and p type semiconductors at each side alternately the
effective output increases since they are aiding.
2.6THERMOELECTRIC MATERIALS
Bismuth Telluride (BizTe3) is the most semiconductor material that often used in the
thermoelectric module construction. The crystals of bismuth telluride have the layers of atoms
forming the sequence as:
The bismuth and tellurium layers are connected by strong covalent ionic bonds. There are 2 ways
to fabricate thermoelectric materials which are either by using directional crystallization from a
melt or pressed powder metallurgy. By using the directional crystallization, typically Bismuth
Telluride material is fabricated in ingot or boule form and then sliced into wafers of various
thicknesses. Then the wafer is diced into blocks that may be assembled into thermoelectric
cooling modules after the wafer's surfaces have been properly prepared. The blocks of Bismuth
Telluride material, usually are called elements or dice.
Beside Bismuth Telluride (Bi2Te3), other thermoelectric materials including Lead Telluride
(PbTe), Silicon Germanium (SiGe), Bismuth-Antimony (Bi-Sb), Mercury Telluride and Silver
Telluride alloys may be used in specific situations.
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2.7 WOOD BURNING STOVE
A wood-burning stove is a heating appliance capable of burning wood fuel and wood-
derived biomass fuel, such as wood pellets. Generally the appliance consists of a solid metal
(usually cast iron or steel) closed fire chamber, a fire brick base and an adjustable air control.
The appliance will be connected by ventilating stove pipes to a suitable chimney orflue, which
will fill with hot combustion gases once the fuel is ignited. The chimney or flue gases must be
hotter than the outside temperature to ensure combustion gases are drawn out of the fire chamber
and up the chimney. Many wood-burning stoves are engineered such that they can be converted
to multi-fuel stoves with the addition of a grate.
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Fig 2.9: Schematic diagram of thermoelectric generator
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2.8 INVERTER
An inverter, is an electrical power converter that changes direct current (DC) to alternating
current (AC); the converted AC can be at any required voltage and frequency with the use of
appropriate transformers, switching, and control circuits.
Solid-state inverters have no moving parts and are used in a wide range of applications, from
small switching power supplies in computers, to large electric utility high-voltage direct
current applications that transport bulk power. Inverters are commonly used to supply AC power
from DC sources such as solar panels or batteries.
The inverter performs the opposite function of a rectifier. The electrical inverter is a high-
power electronic oscillator. It is so named because early mechanical AC to DC converters were
made to work in reverse, and thus were "inverted", to convert DC to AC.
The square wave output has a high harmonic content, not suitable for certain AC loads such as
motors. Square wave units were the pioneers of inverter development.
2.8.1 BASIC DESIGNS
In one simple inverter circuit, DC power is connected to a transformer through the centre tap of
the primary winding. A switch is rapidly switched back and forth to allow current to flow back to
the DC source following two alternate paths through one end of the primary winding and then
the other. The alternation of the direction of current in the primary winding of the transformer
produces alternating current (AC) in the secondary circuit.
The electromechanical version of the switching device includes two stationary contacts and a
spring supported moving contact. The spring holds the movable contact against one of the
stationary contacts and an electromagnet pulls the movable contact to the opposite stationary
contact. The current in the electromagnet is interrupted by the action of the switch so that the
switch continually switches rapidly back and forth. This type of electromechanical inverter
switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar
mechanism has been used in door bells, buzzers and tattoo guns.
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Fig 2.10: Basic inverter schematic
As they became available with adequate power ratings, transistors and various other types
of semiconductor switches have been incorporated into inverter circuit designs. Certain ratings,
especially for large systems (many kilowatts) use thyristors (SCR). SCRs provide large power
handling capability in a semiconductor device, and can readily be controlled over a variable
firing range.
CHAPTER3
OBJECTIVES
The main objectives of this project are:
The main objective is to find a substitute for general source of electricity
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Remedy for rural area electrification
Incorporation of thermo electric module onto the wooden stove
Generation of electricity from the waste heat of the stove
Study of the inverter design
CHAPETR4
PROJECT PHASES
Collection and
analysis of TEM
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Making of the
wooden stove
Incorporation of the
TEM on wooden
stove
Electrical
connections
Inverter
Design
Observations
4.1 PHASE1: COLLECTION AND ANALYSIS OF THE TEM
4.1.1COMPARING DIFFERENT MODULES
Different thermoelectric modules characteristics were compared and the availability of the
modules were studied. The modules compared include TEC12704,TEC12705,TEC12706 etc.
Table 4.1: Comparison of different modules
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Among the different thermo electric modules the available one was the TEC12704.
The following are the specifications of the TEC12704
Table 4.2: TE module dimension
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Table 4.3: TE module parameter
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The performance characteristics of the TEC12704 with the variation in the
temperature are given below:
Fig 4.1: Performance characteristics
4.2 PHASE2: MAKING OF THE WOODEN STOVE
The wooden stove is to be built in order to integrate the thermo electric module to it. The
following steps were used in the construction of the multifunctional wooden stove:
The wooden frame for the construction of the stove was built. The frame was built in two
layers.
5 holes were made on either side of the frame in order provide the provision for the
incorporation of the thermo electric modules to the stove.
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4 bolts were used in order to make the frame a rigid structure.
The 0.25 inch iron rods were made into L shape and were placed inside the frame.
The plantain stem was placed inside the holes before filling the cement.
The cement, sand and water were made into a mixture and was filled in to the frame
made earlier.
The stove was covered with cloths to prevent the loss of the moisture. The arrangement
was made wet regularly for 4 days.
The cover for the stove consist of 2 layers:- the topmost layer is of aluminium and the
bottom layer made of particular type of ceramic material made to withstand high
temperature.
After 4 days the plantain stem shrinked and was taken out.
A wooden layer was provided on both sides in order to prevent the flames from coming
through the holes.
Fig 4.2: Wooden stove
4.3 PHASE3: INCORPORATION OF TEM ON WOODEN STOVE
4.3.1HEAT SINK
The heat applied to all the thermo electric modules must be equal and the modules must not be
directly subjected to the flames. In order to provide the equal heat to all the cells and to keep it
away from the flame heat sink was provided. Al was chose to build the heat sink since it
provides equal distribution of the heat on the surface.
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The construction and placement of the sink is as follows:
The 5 pieces of the Al with length 15cm and width 4cm were bend into L shape.
These 5 pieces were riveted onto a thick rod of Aluminium.
The arrangement of the heat sink is placed onto the wooden stove by inserting the 5 fins
to the five holes of the stove.
4.3.2COOLING SYSTEM
The cooling system is made in order to provide the cooling at the cold junction of the
thermocouples in the thermo electric module. The cold water was supplied through the cooling
system in order. The steps involved are:-
The hollow rod of aluminium was cut into the 2 pieces of the required length.
Four small hollow tubes were cut and they were placed at the ends of the hollow rod.
The two ends of the tubes were connected using a plastic pipe and among the remaining
tubes one was given to the water inlet and the other for the outlet of the water.
Fig 4.3: Heat sink and cooling system
4.4 PHASE4: ELECTRICAL CONNECTIONS
4.4.1 MODULE CONNECTION
The output voltage obtained from each cell was 2.25volt and to get an output voltage of about
20volt the cells were all connected in series so that the voltage developed by each cell gets added
up. The series connection was made by connecting the red and the blue wires of the consecutive
modules.
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The 20 volt was desired in order to withstand the voltage drop occurring while loading to the
battery. The connections are made as shown in the figure below.
Fig 4.4: Module connection
4.4.2 BATTERY
A battery is a device consisting of one or more electrochemical cells that convert stored
chemical energy into electrical energy. The secondary batteries (rechargeable batteries), which
are designed to be recharged and used multiple times are used. The 12v 7Ah battery is used in
order to store the electric charge generated from the stove.
Fig 4.5: Battery
4.5 PHASE5: INVERTER DESIGN
The inverter was made in order convert the DC energy stored in the battery to the AC to make it
suitable for the house hold appliances.
The inverter was made for the conversion from 12v DC to 230v AC with a frequency of 50Hz.
For the simplicity square wave inverter was made. The inverter circuit has mainly 3 parts :
The oscillatory part using IC3525
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The power part
The transformer and load part
Fig 4.6: Circuit diagram of inverter
4.5.1THE OSCILLATORY PART: IC 3525
The oscillatory part consists mainly of the IC3525. The oscillatory part is to provide the
necessary frequency of the output square wave.
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Fig4.7: Pin configuration of IC3525
The IC3525series of pulse width modulator integrated circuits are designed to offer improved
performance and lowered external parts count when used in designing all types of switching
power supplies. The input common-mode range of the error amplifier includes the reference
voltage eliminating external resistors. A sync input to the oscillator al lows multiple units to be
slaved or a single unit to be synchronized to an external system clock. A single resistor between
the CT and the discharge terminals provide a wide range of dead time adjustment. These devices
also feature built in soft-start circuitry with only an external timing capacitor required. A
shutdown terminal controls both the soft-start circuitry and the output stages, providing
Instantaneous turn off through the PWM latch with pulsed shut down, as well as soft-start recycle
with longer shut down commands. These functions are also control led by an under voltage
lockout which keeps the out puts off and the soft-start capacitor discharged for sub-normal input
voltages. This lockout circuitry includes approximately 500 mV of hysteresis for jitter free
operation. Another feature of these PWM circuits is a latch following the comparator. Once a
PWM pulses has been terminated for any reason the outputs will remain off for the duration of the
period. The latch is reset with each clock pulse. The output stages are totem-pole designs capable
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IC 3525
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SSET, KARUKUTTY DEPARTMENT of EEE
of sourcing or sinking in excess of 200 mA. The IC3525Aoutput stage features NOR logic, giving
a LOW output for an OFF state.
4.5.2 POWER PART: IRF44 (MOSFET)
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is
a transistor used for amplifying or switching electronic signals. Although the MOSFET is a four-
terminal device with source (S), gate (G), drain (D), and body (B) terminals, the body (or
substrate) of the MOSFET often is connected to the source terminal, making it a three-terminal
device like other field-effect transistors. Because these two terminals are normally connected to
each other (short-circuited) internally, only three terminals appear in electrical diagrams. The
MOSFET is by far the most common transistor in both digital and analog circuits, though
the bipolar junction transistor was at one time much more common.
In enhancement mode MOSFETs, a voltage drop across the oxide induces a conducting
channel between the source and drain contacts via the field effect. The term "enhancement
mode" refers to the increase of conductivity with increase in oxide field that adds carriers to the
channel, also referred to as the inversion layer. The channel can contain electrons (called an
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Table 4.4: Maximum ratings
Project Report 2013
SSET, KARUKUTTY DEPARTMENT of EEE
nMOSFET or nMOS), or holes (called a pMOSFET or pMOS), opposite in type to the substrate,
so nMOS is made with a p-type substrate, and pMOS with an n-type substrate (see article
on semiconductor devices). In the less common depletion mode MOSFET, detailed later on, the
channel consists of carriers in a surface impurity layer of opposite type to the substrate, and
conductivity is decreased by application of a field that depletes carriers from this surface layer.
Fig 4.8: MOSFET
The traditional metal–oxide–semiconductor (MOS) structure is obtained by growing a layer of
silicon dioxide (Si O 2) on top of a silicon substrate and depositing a layer of metal or
polycrystalline silicon (the latter is commonly used). As the silicon dioxide is a dielectric
material, its structure is equivalent to a planar capacitor, with one of the electrodes replaced by a
semiconductor. When a voltage is applied across a MOS structure, it modifies the distribution of
charges in the semiconductor. If we consider a p-type semiconductor a positive voltage, ,
from gate to body creates a depletion layer by forcing the positively charged holes away from the
gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile,
negatively charged acceptor ions. If is high enough, a high concentration of negative charge
carriers forms in an inversion layer located in a thin layer next to the interface between the
semiconductor and the insulator. Unlike the MOSFET, where the inversion layer electrons are
supplied rapidly from the source/drain electrodes, in the MOS capacitor they are produced much
more slowly by thermal generation through carrier generation and recombination centers in the
depletion region. Conventionally, the gate voltage at which the volume density of electrons in the
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inversion layer is the same as the volume density of holes in the body is called the threshold
voltage. When the voltage between transistor gate and source (VGS) exceeds the threshold voltage
(Vth), it is known as overdrive voltage.
Fig 4.9: MOSFET working
4.5.3 TRANSFORMER AND THE LOAD
A transformer is a static electrical device that transfers energy by inductive coupling between its
winding circuits. A varying current in the primary winding creates a varying magnetic flux in the
transformer's core and thus a varying magnetic flux through the secondary winding. This varying
magnetic flux induces a varying electromotive force (EMF), or "voltage", in the secondary
winding.
The transformer used is a step up transformer. The transformer steps up the voltage to 230 volt,
which is the required voltage. The transformer is having number of turns in the secondary greater
than that at the primary.
Fig4.10: Transformer
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12v
12v
Primary 12v-0-12v centre tapped secondary230v
Project Report 2013
SSET, KARUKUTTY DEPARTMENT of EEE
4.5.4: INVERTER COMPONENTS DESIGNING
The designing of the oscillatory circuit is governed by the following equation:
Fosc = 1
C(0.7RT+3RD)
To get an ac signal of ‘f’ frequency the input to the oscillatory circuit of the IC3525 should be
‘2f’.therefore to get an 50HZ signal at the output the input frequency to the oscillator should me
100HZ.
Let C=100nf and RD=470ohm
100 = 1
100*10-9(0.7RT +3*470)
Hence RT = 140.857Kohm (150Kohm standard value)
The 104micro farad is connected between Vref and Inv.input in order to give a constant input to
the error amplifier.
The capacitor connected between the soft start and the ground serves the function of controlling
the starting current and the gradual increase of the duty cycle to the desired value.
The equation governing the soft start is:
Tsec = Css *Vout
I
I = 51 micro amperes
Vout = 2.5V
To get soft start time as 0.1sec the capacitor of 2.2micro farad is chosen.
A 2.2Kohm and a 104 micro farad is connected in parallel across the ground and the shut down
pin as a filter for the noises. It should be kept low in order to generate the gate pulses for the
mosfet to get triggered.
The 33ohm resistor is connected between the output pins and the mosfets to limit if any high
current flow through it.
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4.6 OBSERVATIONS
The firewood was placed in the stove and the ignition was given. The temperature began to rise
slowly. At the same time the cold water was passed through the cooling system which was
arranged at the cold side of the modules. After sometime the temperature difference at the
thermo electric module began to build up. The multimeter showed a deflection. The voltage
began to increase rapidly for about 5 minutes. Then the rising of the voltage become slow. After
reaching a particular temperature the voltage rise stopped and it began to decrease slowly.
In order to prevent the decrease of the voltage the heat sink fins are slowly released from the
stove. The electric energy from the modules were stored in a battery. The inverter was driven
from the battery. The output from the inverter is 230volt and the wattage was 150w.
CHAPTER5
ECONOMIC ANALYSISTABLE 5.1: Economic analysis
Sl no. Item Quantity Price per Total
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unit
1 TEC12704 12 550 6600
2 Inverter
2.1 Transformer 1 625 625
2.2 MOSFET(IRF44) 2 15 30
2.3 IC 3525 1 15 15
2.4 Other
components
80
3 Battery 1 700 700
4 Stove 1 1500 1500
5 Miscellaneous
expense
520
Total expense 10070
Comparison of the LPG stove and the thermoelectric wooden stove
A study was done with the ordinary LPG gas stove and the Thermo Electric wooden stove .The
comparison period was taken as one year. The cost for the operation of the two systems were
compared and tabulated.
Table 5.2: cost comparison with LPG
ITEM QUANTITY RATE AMOUNT
LPG STOVE 1 5500 5500
THERMOELECTRIC
WOODEN STOVE
1 8100 8100
LPG WITH SUBSIDY 9 460 4140
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LPG WITHOUT
SUBSIDY
3 960 2880
HARD WOOD 12*90 KG 4 4320
By the above comparison the total cost for the LPG stove for one year is obtained as 12520 Rs.
Where as in the case of the wooden stove it costs only 12420 Rs.
The electricity generated per day while burning for 3.5 hrs in an average =105watts
Electricity generated per month = 105*30 = 3150watts
Electricity generated per year = 3000*12 = 37800 watts
Thus the thermo electric wooden stove acts as the secondary source of energy for the households.
Table 5.3: Advantage and disadvantages
ITEM LPG THERMO ELECTRIC
STOVE
ADVANTAGES Ease of use
Quick heating
Clean burning
Renewable
Low cost
Readily available
DISADVANTAGES Non renewable
High cost
Not easily available
Pollution
Slow heating
CHAPTER6
CONCLUSION
From this project we came to the conclusion that thermoelectric wooden stove can be used as a
substituent for general source of electricity for households. The construction of the
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multifunctional wooden stove is very useful since its efficiency is increased by utilizing its waste
heat to generate electricity. The thermo electric wooden stove is very useful in the rural area
electrification where electricity has not reached yet. The components used in this project are very
less and hence can be built easily and fast which is an added advantage to the thermoelectric
wooden stove.
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