UNIT-4
Contents as per syllabus:
1. Thermo-electrical Conversions
1.1. Introduction & Principle of working
1.2. Thermoelectric Power Generator
1.3. Applications of Thermoelectric Power Generation
1.4. Performance and limitations
1.5. Short Answer Questions
1.6. University asked Questions
1.7. MCQs
2. Thermionic Conversions
2.1 Introduction
2.2 Work function ()
2.3 Thermionic generators
2.4 Thermionic converter materials
2.5 University asked Questions
2.6 MCQs
3. Wind Energy
3.1 Wind power and its sources
3.2 Site selection, criterion, momentum theory
3.3 Momentum Theory
3.4 Wind-Electric Generating Power Plant
3.5 Types of Wind Machines
3.6 Wind characteristics
3.7 Short Answer Questions
3.8 University asked Questions
3.9 MCQs
,1. Thermo-electrical Conversions
1.1. Introduction & Principle of working
Thermoelectric energy conversion is applied in two conceptually different ways:
One is for cooling, based on the conversion of electricity into a temperature gradient
Other one is for power generation, based on the conversion of heat into electricity
Thermoelectric energy harvesting mainly depends on the operation of the thermoelectric generator (TEG). A
TEG converts heat directly into electrical energy according to the Seebeck effect. In this case, the motion of
charge carriers (electrons and holes) leads to a temperature difference across this device. Its operation is
described in Section 2.3. Furthermore, the thermoelectric energy harvesting system can generate power from
hundreds of μW to mW for different sensors and transmitters.
Peltier effect
In 1834 the French physicist and watchmaker Jean-Charles-Athanase Peltier observed that if a current is
passed through a single junction of the type described above, the amount of measured heat generated is not
consistent with what would be predicted solely from ohmic heating caused by electrical resistance. This
observation is called the Peltier effect
A thermoelectric harvester produces green energy for energy harvesting with a multitude of advantages:
maintenance-free, because of the use of highly reliable and compact solid-state device; silent and quiet; highly
efficient in environmental terms because the heat is harvested from waste heat sources and converted into
electricity; operation with high maximum temperatures (up to 250°C); useful scalable applications configured
to harvest wide amounts of energy when necessary; possibility to harvest power from both hot surface or cold
surface; green energy behaviour, being eco-friendly .A TEG device produces energy without using fossil
fuel, leading to a reduction of greenhouse gas emissions.
Fig 1. Principle of TEG
, Thermoelectric power generation process is based on the Seebeck effect which states that loop of dissimilar
metals will develop an emf if the two junctions are kept at different temperatures. This principle is already
being used in thermocouples for measurement of temperature. However, the recent advances in material
technology have made possible experimental thermo-electric generators of a few kW size. The simplest
thermo-electric power generator consists of a thermocouple, comprising a P-type and N-type thermo-element
connected electrically in series and thermally in parallel. Heat is pumped into one side of the couple and
rejected from the opposite side. An electrical current is produced, proportional to the temperature gradient
between the hot and cold junctions.
The net useful power output is given as:
Pout = I2R watts …(4.1)
Where I is the current flowing through the circuit in amperes and R is the external load resistance connected
across output terminals of the thermo-electric generator in ohms.
The current in the circuit is given by:
I = αΔT /(Rin + R) amperes… (4.2)
where α is Seebeck coefficient in V/k, ΔT is the temperature difference between hot and cold junctions in
degrees absolute, K and Rin is the internal resistance of thermoelectric generator in ohms.
The magnitude of potential difference depends on the pair of conductor materials and on the temperature
difference of the junctions.
For a loop made of copper and constantan wire, the value of Seebeck coefficient is 0.04 mV/k. For a
temperature difference of 600 K between the junctions, a voltage of 24 mV will be produced.
Thermoelectric Materials in Thermoelectric Power Generation:
The efficiency of thermoelectric generator depends upon suitable properties of the elements. It was later in
1909 and 1911 that Altenkirch showed that good thermoelectric materials should have large Seebeck
coefficients, high electrical conductivity, and low thermal conductivity. A high electrical conductivity is
necessary to minimize Joule heating, whilst a low thermal conductivity helps to retain heat at junctions and
maintain a large temperature gradient.
These three properties were later embodied in the so-called figure-of-merit, Z. Since Z varies with
temperature, a useful dimensionless figure-of-merits can be defined as ZT. The thermal conductivity of
thermoelectric materials can be reduced by introducing suitable impurities.
The other requirements of thermoelectric materials are:
1. The mobility of current carriers (electrons or holes) should be as high as possible. The electrical
conductivity can be raised by introducing suitable impurities.
One element should be purely P-type and the other N- type. The semiconductor material should have low
ionization energy and narrow forbidden band.
Contents as per syllabus:
1. Thermo-electrical Conversions
1.1. Introduction & Principle of working
1.2. Thermoelectric Power Generator
1.3. Applications of Thermoelectric Power Generation
1.4. Performance and limitations
1.5. Short Answer Questions
1.6. University asked Questions
1.7. MCQs
2. Thermionic Conversions
2.1 Introduction
2.2 Work function ()
2.3 Thermionic generators
2.4 Thermionic converter materials
2.5 University asked Questions
2.6 MCQs
3. Wind Energy
3.1 Wind power and its sources
3.2 Site selection, criterion, momentum theory
3.3 Momentum Theory
3.4 Wind-Electric Generating Power Plant
3.5 Types of Wind Machines
3.6 Wind characteristics
3.7 Short Answer Questions
3.8 University asked Questions
3.9 MCQs
,1. Thermo-electrical Conversions
1.1. Introduction & Principle of working
Thermoelectric energy conversion is applied in two conceptually different ways:
One is for cooling, based on the conversion of electricity into a temperature gradient
Other one is for power generation, based on the conversion of heat into electricity
Thermoelectric energy harvesting mainly depends on the operation of the thermoelectric generator (TEG). A
TEG converts heat directly into electrical energy according to the Seebeck effect. In this case, the motion of
charge carriers (electrons and holes) leads to a temperature difference across this device. Its operation is
described in Section 2.3. Furthermore, the thermoelectric energy harvesting system can generate power from
hundreds of μW to mW for different sensors and transmitters.
Peltier effect
In 1834 the French physicist and watchmaker Jean-Charles-Athanase Peltier observed that if a current is
passed through a single junction of the type described above, the amount of measured heat generated is not
consistent with what would be predicted solely from ohmic heating caused by electrical resistance. This
observation is called the Peltier effect
A thermoelectric harvester produces green energy for energy harvesting with a multitude of advantages:
maintenance-free, because of the use of highly reliable and compact solid-state device; silent and quiet; highly
efficient in environmental terms because the heat is harvested from waste heat sources and converted into
electricity; operation with high maximum temperatures (up to 250°C); useful scalable applications configured
to harvest wide amounts of energy when necessary; possibility to harvest power from both hot surface or cold
surface; green energy behaviour, being eco-friendly .A TEG device produces energy without using fossil
fuel, leading to a reduction of greenhouse gas emissions.
Fig 1. Principle of TEG
, Thermoelectric power generation process is based on the Seebeck effect which states that loop of dissimilar
metals will develop an emf if the two junctions are kept at different temperatures. This principle is already
being used in thermocouples for measurement of temperature. However, the recent advances in material
technology have made possible experimental thermo-electric generators of a few kW size. The simplest
thermo-electric power generator consists of a thermocouple, comprising a P-type and N-type thermo-element
connected electrically in series and thermally in parallel. Heat is pumped into one side of the couple and
rejected from the opposite side. An electrical current is produced, proportional to the temperature gradient
between the hot and cold junctions.
The net useful power output is given as:
Pout = I2R watts …(4.1)
Where I is the current flowing through the circuit in amperes and R is the external load resistance connected
across output terminals of the thermo-electric generator in ohms.
The current in the circuit is given by:
I = αΔT /(Rin + R) amperes… (4.2)
where α is Seebeck coefficient in V/k, ΔT is the temperature difference between hot and cold junctions in
degrees absolute, K and Rin is the internal resistance of thermoelectric generator in ohms.
The magnitude of potential difference depends on the pair of conductor materials and on the temperature
difference of the junctions.
For a loop made of copper and constantan wire, the value of Seebeck coefficient is 0.04 mV/k. For a
temperature difference of 600 K between the junctions, a voltage of 24 mV will be produced.
Thermoelectric Materials in Thermoelectric Power Generation:
The efficiency of thermoelectric generator depends upon suitable properties of the elements. It was later in
1909 and 1911 that Altenkirch showed that good thermoelectric materials should have large Seebeck
coefficients, high electrical conductivity, and low thermal conductivity. A high electrical conductivity is
necessary to minimize Joule heating, whilst a low thermal conductivity helps to retain heat at junctions and
maintain a large temperature gradient.
These three properties were later embodied in the so-called figure-of-merit, Z. Since Z varies with
temperature, a useful dimensionless figure-of-merits can be defined as ZT. The thermal conductivity of
thermoelectric materials can be reduced by introducing suitable impurities.
The other requirements of thermoelectric materials are:
1. The mobility of current carriers (electrons or holes) should be as high as possible. The electrical
conductivity can be raised by introducing suitable impurities.
One element should be purely P-type and the other N- type. The semiconductor material should have low
ionization energy and narrow forbidden band.
