electric power generation
Thermo ionic power generation
Magneto hydro dynamic systems
nuclear fusion power generation
The pioneer in thermoelectric was a German scientist
Thomas Johann Seebeck (1770-1831)
Thermoelectricity refers to a class of phenomena in
which a temperature difference creates an electric
potential or an electric potential creates a
Thermoelectric power generator is a device that
converts the heat energy into electrical energy based
on the principles of Seebeck effect
Later, In 1834, French scientist, Peltier and in 1851,
Thomson (later Lord Kelvin) described the thermal
effects on conductors
In the purer metallic conductors outer electrons, less
connected to others, can move freely around all the
material, as if they do not belong to any atom. These
electrons transmit energy one to another through
temperature variation, and this energy intensity varies
depending on the nature of the material.
If two distinct materials are placed in contact, free
electrons will be transferred from the more “loaded”
material to the other, so they equate themselves, such
transference creates a potential difference, called contact
potential, since the result will be a pole negatively
charged by the received electrons and another positively
charged by the loss of electrons.
When the junctions of
two different metals are maintained
temperature, the emf is produced in the
circuit. This is known as Seebeck effect.
The material A is maintained at T+∆T
The material B is maintained at
Since the junctions are maintained at
different temperature, the emf „V‟ flows
across the circuit.
The electric potential produced by a temperature
difference is known as
the Seebeck effect
and the proportionality constant is called the
If the free charges are positive (the material is ptype),
charge will build up on the
cold which will have a
Similarly, negative free charges (n-type material)
will produce a negative potential at the cold end.
Whenever current passes
through the circuit of two
depending on the current
direction, either heat is
absorbed or released at the
junction of the two conductors.
This is known as Peltier effect.
conversion of electrical energy
into heat when a current I flows through a
Thermoelectric power generation (TEG) devices
typically use special semiconductor materials, which
are optimized for the Seebeck effect.
The simplest thermoelectric power generator
consists of a thermocouple, comprising a p-type and
n-type material connected electrically in series and
thermally in parallel.
Heat is applied 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
Therefore, for any TEPG, there are four basic component required
Heat source (fuel)
P and N type semiconductor stack (TE module)
Heat sink (cold side)
Electrical load (output voltage)
As the heat moves from hot side to cold side, the
carrier moves in the semiconductor materials
the potential deference is created.
The electrons are the charge carriers in the case of Ntype semiconductor and Hole are in P-type
In a stack, number of
semiconductors is connected.
A single PN connection can produce a Seebeck
of 40 mV.
The heat source such as natural gas or propane are
used for remote power generation
I= V/R =P
= (when R=RL) = P
Figure of merit
Efficiency of the generator =
Energy provided to the load
Heat energy absorbed at the hot junction
I 2 Rl
) ITh K T 0.5I 2 R
Max. Ideal efficiency
(Th Tc )
1 ZTm 1
[(k1 / 1 )1/ 2 (k2 /
)1/ 2 ]2
where: w is the power
delivered to the
external load and qH is
the positive heat flow
from source to sink
1 ZTm Tc / Th
A high electrical conductivity is necessary to minimize
Joule heating and low thermal conductivity helps to retain
heat at the junctions and maintain a large temperature
gradient. A large Seebeck coefficient is advicable.These
three properties were later put together and it is called
The good thermoelectric materials should possess
1. Large Seebeck coefficients
2. High electrical conductivity
3. Low thermal conductivity
The example for thermoelectric materials
Lead Telluride (PbTe),
Easy maintenance: They works electrically without any moving parts so
they are virtually maintenance free.
Environment friendly: Thermoelectric generators
pollution. Therefore they are eco friendly generators.
Compact and less weight: The overall thermoelectric cooling system
is much smaller and lighter than a
comparable mechanical system.
High Reliability: Thermoelectric modules exhibit very
due to their solid-state construction
• No noise: They can be used in any orientation and in
environments. Thus they are popular in
Convenient Power Supply: They operate directly
Cryogenic IR Night Vision
The standard material we work with is BiTe. The best
efficiency that can be achieved with this material is
But once the material is constructed into a module, efficiency
drops to 3 to 4% because of thermal and electrical impedance.
No other semiconductor material can perform as well as BiTe
as far as efficiency is concerned. Other material such as PbTe
are used but are far less efficient, and must be used at
significantly higher temperatures (450°C- 600°C) hot side and
are not commercially available!
Thermoelectric Seebeck effect modules are designed for very
high power densities, on the order of 50 times greater than
Bismuth telluride is the best bulk TE material with ZT=1
Trends in TE devices:
• Superlattices and nanowires: Increase in S, reduction in k
• Nonequilibrium effects: decoupling of electron and phonon
• Bulk nanomaterial synthesis
Trends in TE systems
• Microrefrigeration based on thin film technologies
• Automobile refrigeration
• TE combined with fluidics for better heat exchangers
To match a refrigerator, an effective ZT= 4 is needed
To efficiently recover waste heat from car, ZT = 2 is
emission is the basis for the working
of this system.
In 1873, the Britain professor Frederic Guthrie
invented the Thermionic phenomenon.
In 1883, Thomas A. Edison observed that the
electrons are emitted from a metal surface when
it was heated. This effect is called Edison effect.
Later in 1904, a British physicist John Ambrose
Fleming developed two-element vacuum tube
known as diode.
power generator (TPG) is a static
device that converts heat energy into electrical
energy by boiling electrons from a hot emitter
surface (= 1800K) across a small inter electrode
gap (< 0.5 mm) to a cooler collector surface (=
A thermionic energy converter (or) thermionic power
generator is a device consisting of two electrodes placed
near one another in a vacuum.
One electrode is normally called the cathode, or emitter,
and the other is called the anode, or plate.
Ordinarily, electrons in the cathode are prevented from
escaping from the surface by a potential-energy barrier.
When an electron starts to move away from the surface,
induces a corresponding positive charge in the
which tends to pull it back into the surface.
To escape, the electron must somehow acquire enough
energy to overcome this energy barrier.
At ordinary temperatures, almost none
can acquire enough energy to escape.
However, when the cathode is very hot, the electron
energies are greatly increased by thermal motion.
At sufficiently high temperatures, a considerable number
electrons are able to escape.
The liberation of electrons
called thermionic emission
For the electrons to travel, the unit is at vacuum. This
limit the size of the generator.
Electron emission is inhibited by space charge, small
quantity of Cesium metal is introduced into the evacuated
Molybdenum, tantalum, tungsten impregnated barium
oxide.Uranium carbide, zirconium carbide.
Prototype combustion-heated thermionic systems for
domestic heat and electric power cogeneration
Higher efficiency and high power density
Compact to use
There is a possibility of vaporization of
Thermal breaking is possible during
The sealing is often gets failure
MHD generator is a device for
converting heat energy of a fuel directly
into electrical energy without conventional
In advanced countries MHD generators are widely used but in
developing countries like INDIA, it is still under construction, this
construction work in in progress at TRICHI in TAMIL NADU, under
the joint efforts of BARC (Bhabha atomic research center),
Associated cement corporation (ACC) and Russian technologists.
(magneto fluid dynamics or hydro
discipline which studies the dynamics of
electrically conducting fluids.
Examples of such fluids include plasmas,
liquid metals, and salt water. The
word magneto hydro dynamics (MHD) is
magnetomeaning magnetic field, and hydromeaning liquid, and -dynamics meaning
movement. The field of MHD was
initiated by Hannes Alfvén , for which he
received the Nobel Prize in Physics in
This effect is a result of FARADAYS LAWS OF ELECTRO
MAGNETIC INDUCTION. (i.e. when the conductor moves through a
magnetic field, it generates an electric field perpendicular to the
magnetic field & direction of conductor).
The induced EMF is given by
Eind = u x B
where u = velocity of the conductor.
B = magnetic field intensity.
The induced current is given by,
Iind = C x Eind
where C = electric conductivity
The retarding force on the conductor is the Lorentz force given by
Find = Iind X B
The conducting fluid flow is forced between the plates
with a kinetic energy and pressure differential sufficient
to over come the magnetic induction force Find.
An ionized gas is employed as the conducting fluid.
Ionization is produced either by thermal means I.e. by
an elevated temperature or by seeding with substance
like cesium or potassium vapors which ionizes at
relatively low temperatures.
The atoms of seed element split off electrons. The
presence of the negatively charged electrons makes
the gas an electrical conductor.
90% conductivity can be
achieved with a fairly low degree
of ionization of only about 1%.
Seeded Inert gas system.
Liquid metal system
Temperature of CC MHD plants is very
less compared to OC MHD plants. It’s
The fuel used maybe oil through an oil tank or gasified
coal through a coal gasification plant
The fuel (coal, oil or natural gas) is burnt in the
combustor or combustion chamber.
The hot gases from combustor is then seeded with a
small amount of ionized alkali metal (cesium or
potassium) to increase the electrical conductivity of the
The seed material, generally potassium carbonate is
injected into the combustion chamber, the potassium is
then ionized by the hot combustion gases at
temperature of roughly 2300‟ c to 2700‟c.
To attain such high temperatures, the compressed air is used
to burn the coal in the combustion chamber, must be adequate
to at least 11000c.
A lower preheat temperature would be adequate if the air is
enriched in oxygen. An alternative is used to compress oxygen
alone for combustion of fuel, little or no preheating is then
required. The additional cost of oxygen might be balanced by
saving on the preheater.
The hot pressurized working fluid leaving the combustor flows
through a convergent divergent nozzle. In passing through the
nozzle, the random motion energy of the molecules in the hot
gas is largely converted into directed, mass of energy. Thus ,
the gas emerges from the nozzle and enters the MHD
generator unit at a high velocity.
In a closed cycle system the carrier gas operates in the form
of Brayton cycle. In a closed cycle system the gas is
compressed and heat is supplied by the source, at essentially
constant pressure, the compressed gas then expands in the
MHD generator, and its pressure and temperature fall. After
leaving this generator heat is removed from the gas by a
cooler, this is the heat rejection stage of the cycle. Finally the
gas is recompressed and returned for reheating.
The complete system has three distinct but interlocking loops.
On the left is the external heating loop. Coal is gasified and
the gas is burnt in the combustor to provide heat. In the
primary heat exchanger, this heat is transferred to a carrier
gas argon or helium of the MHD cycle. The combustion
products after passing through the air preheater and purifier
are discharged to atmosphere.
Because the combustion system is separate from the
working fluid, so also are the ash and flue gases.
Hence the problem of extracting the seed material from
fly ash does not arise. The flue gases are used to
preheat the incoming combustion air and then treated
for fly ash and sulfur dioxide removal, if necessary
prior to discharge through a stack to the atmosphere.
The loop in the center is the MHD loop. The hot argon
gas is seeded with cesium and resulting working fluid
is passed through the MHD generator at high speed.
The dc power out of MHD generator is converted in ac
by the inverter and is then fed to the grid.
When a liquid metal provides the electrical conductivity, it is
called a liquid metal MHD system.
An inert gas is a convenient carrier
The carrier gas is pressurized and heated by passage through
a heat exchanger within combustion chamber. The hot gas is
then incorporated into the liquid metal usually hot sodium to
form the working fluid. The latter then consists of gas bubbles
uniformly dispersed in an approximately equal volume of liquid
The working fluid is introduced into the MHD generator
through a nozzle in the usual ways. The carrier gas then
provides the required high direct velocity of the electrical
After passage through the generator, the liquid metal is
separated from the carrier gas. Part of the heat exchanger to
produce steam for operating a turbine generator. Finally the
carrier gas is cooled, compressed and returned to the
combustion chamber for reheating and mixing with the
recovered liquid metal. The working fluid temperature is
usually around 800‟c as the boiling point of sodium even under
moderate pressure is below 900‟c.
At lower operating temp, the other MHD conversion systems
may be advantageous from the material standpoint, but the
maximum thermal efficiency is lower. A possible compromise
might be to use liquid lithium, with a boiling point near 1300‟c
as the electrical conductor lithium is much more expensive
than sodium, but losses in a closed system are less.
It has no moving parts & the actual conductors are replaced
by ionized gas (plasma). The magnets used can be
electromagnets or superconducting magnets.
The plasma temperature is typically over 2000 °C, the duct
containing the plasma must be constructed from nonconducting materials capable of withstanding this high
temperature. The electrodes must of course be conducting as
well as heat resistant.
Superconducting magnets of 4~6Tesla are used. Here
exhaust gases are again recycled & the capacities of
these plants are more than 200MW.
Non-conducting walls of the channel must be constructed
from an exceedingly heat-resistant substance such as
yttrium oxide or zirconium dioxide to retard oxidation
Ionization of GAS:
Various methods for ionizing the gas are available, all of
which depend on imparting sufficient energy to the gas. The
ionization can be produced by thermal or nuclear means.
Materials such as Potassium carbonate or Cesium are often
added in small amounts, typically about 1% of the total mass
flow to increase the ionization and improve the conductivity,
particularly combustion of gas plasma
In MHD the thermal pollution of water is eliminated. (Clean Energy
Use of MHD plant operating in conjunction with a gas turbine power
plant might not require to reject any heat to cooling water.
These are less complicated than the conventional generators,
having simple technology.
There are no moving parts in generator which reduces the energy
These plants have the potential to raise the conversion efficiency up
to 55-60%. Since conductivity of plasma is very high (can be treated
It is applicable with all kind of heat source like nuclear, thermal,
thermonuclear plants etc. Extensive use of MHD can help in better
The construction of superconducting magnets for small MHD
plants of more than 1kW electrical capacity is only on the
Difficulties may arise from the exposure of metal surface to
the intense heat of the generator and form the corrosion of
metals and electrodes.
Construction of generator is uneconomical due to its high
Construction of Heat resistant and non conducting ducts of
generator & large superconducting magnets is difficult.
MHD without superconducting magnets is less efficient when
compared with combined gas cycle turbine.
There are great challenges that are associated
with fusion, but there are also very large possible
A coal power plant uses 9000 tons of coal a day to
produce 1000 MW and emits many pollutants
including 30,000 tons of carbon dioxide
A fusion power plant would use 5.35Kg of
deuterium and tritium for the same amount of
power and would emit only 4.28Kg of helium
The amount of lithium contained in a single
computer battery along with about half of a bathtub
full of water can produce as much energy as 40
tons of coal
Deuterium -----------In ocean water---- 1 D atom for every 6500 ordinary H
atom in sea water.
Tritium is produced in nuclear reactors by neutron
activation of lithium-6.
Tritium is also produced in heavy water-moderated
reactors whenever a deuterium nucleus captures a
Tritium is an uncommon product of the nuclear
fission of uranium-235, plutonium-239, and uranium-233,
with a production of about one per each 10,000 fissions
electrostatic force between the
positively charged nuclei is repulsive, but
when the separation is small enough, the
attractive nuclear force is stronger.
the prerequisite for fusion is that
the nuclei have enough kinetic energy that
they can approach each other despite the
Lawson criterion, first derived on fusion reactors
(initially classified) by John D. Lawson in 1955 and
published in 1957.
Is an important general measure of a system that
defines the conditions needed for a fusion reactor to
reach ignition, that is, the heating of the plasma by the
products of the fusion reactions is sufficient to maintain
the temperature of the plasma against all losses without
external power input.
Breakeven is the point in which the energy supplied
equals or exceeds the energy output
Ignition is the point in which the energy from fusion
supplies the heat necessary to sustain the reaction
without external sources
As originally formulated the Lawson criterion gives
a minimum required value for the product of the
plasma (electron) density ne and the "energy
confinement time" .
Later analysis suggested that a more useful figure
of merit is the "triple product" of density,
confinement time, and plasma temperature T. The
triple product also has a minimum required value,
and the name "Lawson criterion" often refers to
Minimum value of (electron density *
energy confinement time) required for
self-heating, for three fusion reactions.
For DT, neτE minimizes near the
temperature 25 keV (300 million
The fusion triple product
condition for three fusion
In terms of reaction rate. (m3/s), break even condition.
For a D-T plasma at 100million oC the break even condition is
around 6 X1013 sec/cm3
temperatures needed to initiate nuclear fusion reactions, there is no
material container which can withstand such temperatures.
One solution to this dilemma is to keep the hot plasma out of contact
with the walls of its container by keeping it moving in circular or
helical paths by means of the magnetic force on charged particles.
Magnetic confinement.(1015 particle density, time 0.1sec)
Inertial confinement.(1026 nuclei/cm3, 10-12 sec)
The motion of electrically charged particles is constrained by
a magnetic field.
In the absence of the magnetic field heated particles will move in
straight lines in random directions, quickly striking the walls of the
container. When a uniform magnetic field is applied the charged
particles will follow spiral paths encircling the magnetic lines of force.
The motion of the particles across the magnetic field lines is
restricted and so is the access to the walls of the container.
• Toroidal field
• Poloidal field
1. Laser beams or laser-produced X-rays rapidly heat the surface of the
fusion target, forming a surrounding plasma envelope.(ablation)
2. Fuel is compressed by the rocket-like blowoff of the hot surface
3. During the final part of the capsule implosion, the fuel core reaches 20
times the density of lead and ignites at 100,000,000 ˚C.
4. Thermonuclear burn spreads rapidly through the compressed fuel,
yielding many times the input energy.
In the inertial confinement fusion method a very large
plasma density (more than twenty times the density of
lead) is attained at the expense of the energy
In the magnetic confinement method an energy
confinement time longer than one second is attained in
very low density plasmas.
A density of solid D-T (0.2 g/cm³) would require an
implausibly large laser pulse energy. Assuming the
energy required scales with the mass of the fusion
plasma (Elaser ~ ρR3 ~ ρ−2), compressing the fuel to
103 or 104 times solid density would reduce the energy
required by a factor of 106 or 108, bringing it into a
With a compression by 103, the compressed density
will be 200 g/cm³, and the compressed radius can be
as small as 0.05 mm. The radius of the fuel before
compression would be 0.5 mm. The initial pellet will
be perhaps twice as large since most of the mass
will be ablated during the compression.
The optimum temperature for inertial confinement
fusion is that which maximizes <σv>/T 3/2, which is
slightly higher than the optimum temperature for