the thermoelectric effect in internal combustion engines
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Mazilu Adrian-Ștefan
AE 1721
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The Seebeck effect is the conversion of
temperature differences directly, when applied on a
thermocouple, into electricity.
The Peltier effect is the conversion of electricity
directly, when applied on a thermocouple, into
temperature differences.
The Thomson effect describes the heating or
cooling of a current-carrying conductor with a
temperature gradient.
*The Peltier and Seebeck effects are essentially the
inverses of one another, while thermoelectricity is a
wider definition that includes both.
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Thermoelectricity refers to a class
of phenomena in which a
temperature difference creates an
electric potential or an electricpotential creates a temperature
difference.
The thermoelectric effect is the
direct conversion of temperature
differences to electric voltage and
vice versa.
This effect can be used to generate
electricity, to measure
temperature, to cool objects, or to
heat them.
One of the most commonly usedmaterial in such application is
Bismuth telluride (Bi2Te3), a
chemical compound of bismuth
and tellurium.
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Electricity requirements in vehicles
is increasing due to the demands
of enhanced performance
To gain fuel efficiency, it may be
possible to shift energy draw from
the engine (in certain cases) to theelectrical load in the car
Thermoelectric devices are thus
being investigated to convert
waste-heat into usable energy
using the Seebeck Effect.
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Almost 70% of the energy released
from the fuel by a car engine is
lost, mostly in the form of heat
Assembled into so-called
thermoelectric generators, or
TEGs, they can soak up heat that
would otherwise be wasted andproduce an electrical current.
Without the requirement for any
moving parts!
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TEGs depend upon a temperature
difference to "drive" the device –
so one side needs to be hot and
the other side cold.
The electrons one the "hot" side
vibrate more vigorously so theytend to move towards the colder
side where the electrons are
moving more slowly.
This movement gives rise to a
current that can be tapped off as
electricity.
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After its nineteenth Century
discoverers, Jean Charles Athanase
Peltier and Thomas Johann
Seebeck
Seekbeck showed that linking up
two different conductors that areat different temperatures results in
a voltage being produced between
them
This voltage is related to the
difference between the two
temperatures.
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The trick with thermoelectrics is
that you want the heat to stay at
the hot end for as long as possible,
keeping the temperature gradient
in place, yet still allowing the
electrons to flow freely.
But because materials that allow
electricity to flow also generallyallow heat to flow. So finding a
material that does one but not the
other is a huge challenge.
That said, materials with high
electrical conductivity but low
thermal conductivity do exist. Infact, most commercial TEGs
contain bismuth telluride
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The rather exotic-sounding
bismuth telluride (Bi2Te3), which is
about 4% efficient at 250°C
For higher temperatures we needto use silicon and germanium.
These are more common materials
but are much less efficient at
turning heat into electricity.
Thankfully, scientists are confident
that, by resorting to
"nanosculpture" to craft the
structures of the materials in just
the right way, it is possible to
create substances that
simultaneously impede the flow ofheat but are very permissive for
the flow of electrons, and this will
dramatically improve the
efficiency.
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The Apollo astronauts relied on
these devices during their Moonmissions, and the Cassini and
Voyager spacecrafts are also
powered by on-board RTGs, which
work by converting the heat
released by the decay of a
radioactive source, such as
strontium-90 or plutonium-238,
into an electric current.
In space, the required "cold side"
for the device is also easy to supply
given that the average
temperature is just three degrees
above absolute zero
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Caterpillar is working on a thermo-electricity concept to reduce fuelconsumption on Diesel engines.They provide a cold side of the
thermo-electric element withliquid that is part of a secondarycooling system.
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BMW eventually limited the usage ofthe alternator in a test vehicle bysupplying power from a TEG deviceinstead.
BMW 530i is equipped with a thermo-electric generator in the exhaust.
The program goal is 10% fuel efficiencyimprovement
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Although thermoelectrics can only
capture only a small percentage of the
world’s “waste” energy, on a global scale
this amounts to a huge potential saving...
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The Promise and Problems of
Thermoelectric Generators
www.wikipedia.org
www.heat2power.net
www.thenakedscientists.com
http://www.wikipedia.org/http://www.heat2power.net/http://www.heat2power.net/http://www.wikipedia.org/