Later, in 1834, Jean Peltier found that the opposite of the Seebeck
effect is also true: that a potential difference (and thus a current)
can cause a temperature difference, regardless of what the ambient
Since the hot junction can be placed
outside of an
insulated area, and the cold junction can be placed inside the region,
effect can be used to cool a region (or an object)
Peltier Elements (Thermo-electric
The method of thermoelectric
(using the Peltier effect) is useful because it can cool an object
without any moving pieces or other complex machinery that isolates the
cooler from its ambient surroundings. The devices that are
constructed to take advantage of this phenomenon are known as Peltier
, or thermo-electric
. The basic ideas from the simple
Peltier elements can be connected in series to construct far more
known as practical TECs),
which have greater cooling capabilities. However, the
temperature difference between the heat sink and the cool region for a
Peltier device is on the order of 50°C.
Common uses for Pelier elements include
cooling computer components, especially the CPU.
The most common combination of materials
in the thermocouples of
Peltier elements (TECs) are the two semiconductors Bismuth and
Telluride. Generally, a TEC has an array of cubes or pellets
of the semiconductors, each of which is in contact with the radiators
on the hot and cold side of the Peltier element. These cubes
"doped" -- that is to say that extra impurities are added so that there
are extra or fewer free electrons in each cube. The
cubes with extra free electrons (and thus carry mainly negative charge)
are known as N-type semiconductors, while those with few free electrons
(and carry mainly postive charge) are P-type semiconductors.
pairs of P and N semiconductor cubes are set up and connected in an
array so that the pairs have an electrical series connection, but a
thermal parallel connection. When a current is applied to
system (the TEC), the way the current flows through the semiconductors
induces a temperature difference, and causes the heat-sink side of the
Peltier element to heat up, and the cold side to cool (or cooling
whatever is in thermal contact with that side).
inside view of a TEC (Peltier element).
A Peltier element, with
ceramic plates to partially insulate
inside from the outer environment.
The heat-sink side of the TEC gets very
hot, so it is necessary to have
a fan and/or some sort of radiator to dissipate this
heat. Otherwise, the entire TEC would begin to heat up, and
would fuse together.
"Normal" Peltier elements are roughly a
few centimeters thick and a
few millimeters or centimeters on a side. To obtain greater
abilities, the individual elements are connected in stacks, or they can
be connected in some combination of series and parallel electrical
A Peltier module with a
fan and radiator to
dissipate heat from the heat sink.
Price 26 March
2007 Physics 212 Web Project