Peltier-Seebeck effect
The Peltier-Seebeck effect, or thermoelectric effect, is the direct conversion of heat differentials to electric voltage and vice versa.
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2 Peltier effect 3 Thomson effect 4 See also 5 External links |
This effect was first discovered, accidentally, by the German physicist Thomas Seebeck in 1821.
He discovered that a voltage existed between two ends of a metal bar, when one end was at a different temperature than the other. This is simply due to a diffusion of electrons (which are relatively free to move in a metal) from the hot end to the cold end, since the electrons in the hot end have more thermal energy. This is called a heat current. As electrons are moving, it is also an electrical current. After reaching equilibrium, this creates a negative charge at the cooler end and a positive charge at the hotter end. The distance between the positive and negative charges produces a potential difference; an electrostatic voltage.
He also discovered that a compass needle would be deflected when a closed loop was formed of two metals, with a temperature difference between the junctions. This is because the metals respond differently to the heat difference, which creates a current loop, which produces a magnetic field.
A voltage, the thermoelectric EMF, is created in the presence of a temperature difference between two different metals or semiconductors. This usually causes a continuous current to flow in the conductors. The voltage created is on the order of several μV per degree Celsius of difference.
In the circuit:
the voltage developed can be derived from:
QA and QB are the Seebeck coefficients (also called thermoelectric power) of the metals A and B, and T1 and T2 are the temperatures of the two junctions. The Seebeck coefficients are non-linear, and depend on the conductors' absolute temperature, material, and molecular structure.
Thus, a thermocouple works by measuring the difference in potential caused by the dissimilar wires. It can be used to measure a temperature difference directly, or to measure an absolute temperature, by setting one end to a known temperature. Several thermocouples in series are called a thermopile.
This is also the principle at work behind thermal diodes, thermoelectric generators which are used for creating power from heat differentials.
The Peltier effect is the reverse of the Seebeck effect; a creation of a heat difference from an electric voltage.
It occurs when a current is passed through two dissimilar metals or semiconductors (n-type and p-type) that are connected to each other at two junctions (Peltier junctions). The current drives a transfer of heat from one junction to the other: one junction cools off while the other heats up. This effect was observed 13 years after Seebeck's initial discovery in 1834 by Jean Peltier.
The conductors are attempting to return to the electron equilibrium that existed before the current was applied by absorbing energy at one connector and releasing it at the other. The individual couples can be connected in series to enhance the effect.
The direction of heat transfer is controlled by the polarity of the current, reversing the polarity will change the direction of transfer.
A Peltier cooler/heater or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other.
Peltier coolers are also called TECs (Thermo Electric Converter).
The Thomson effect, named for William Thomson (commonly known as Lord Kelvin), describes the heating or cooling of a current-carrying conductor with a temperature gradient.
Any current-carrying conductor, with a temperature difference between two points,
will either absorb or emit heat, depending on the material.
The Seebeck effect is actually a combination of the Peltier and Thomson effects.
Seebeck effect
The Seebeck effect is the conversion of heat differences directly into electricity. 
Peltier effect
Thomson effect
See also
External links