Dictionary:

thermoelectricity

  (thûr'mō-ĭ-lĕk-trĭs'ĭ-tē, -ē'lĕk-)

Electricity generated by a flow of heat, as in a thermocouple.

The direct conversion of heat into electrical energy, or the reverse, in solid or liquid conductors by means of three interrelated phenomena—the Seebeck effect, the Peltier effect, and the Thomson effect—including the influence of magnetic fields upon each. The Seebeck effect concerns the electromotive force (emf) generated in a circuit composed of two different conductors whose junctions are maintained at different temperatures. The Peltier effect refers to the reversible heat generated at the junction between two different conductors when a current passes through the junction. The Thomson effect involves the reversible generation of heat in a single current-carrying conductor along which a temperature gradient is maintained. Specifically excluded from the definition of thermoelectricity are the phenomena of Joule heating and thermionic emission. See also Electromotive force (emf); Joule's law; Peltier effect; Seebeck effect; Thermionic emission; Thomson effect.

The three thermoelectric effects are described in terms of three coefficients: the absolute thermoelectric power (or thermopower) S, the Peltier coefficient II, and the Thomson coefficient μ, each of which is defined for a homogeneous conductor at a given temperature. These coefficients are connected by the Kelvin relations, which convert complete information about one into complete information about all three. It is therefore necessary to measure only one of the three coefficients; usally the thermopower S is chosen.

The most important practical application of thermoelectric phenomena is in the accurate measurement of temperature. The phenomenon involved is the Seebeck effect. Of less importance are the direct generation of electrical power by application of heat (also involving the Seebeck effect) and thermoelectric cooling and heating (involving the Peltier effect).

A basic system suitable for all four applications is shown schematically in the illustration. Several thermocouples are connected in series to form a thermopile, a device with increased output (for power generation or cooling and heating) or sensitivity (for temperature measurement) relative to a single thermocouple. The junctions forming one end of the thermopile are all at the same low temperature T_L, and the junctions forming the other end are at the high temperature T_H. The thermopile is connected to a device D which is different for each application. For temperature measurement, the temperature T_L is fixed, for example, by means of a bath; the temperature T_H becomes the running temperature T, which is to be measured; and the device is a potentiometer for measuring the thermoelectric emf generated by the thermopile. For power generation, the temperature T_L is fixed by connection to a heat sink; the temperature T_H is fixed at a value determined by the output of the heat source and the thermal conductance of the thermopile; and the device is whatever is to be run by the electricity that is generated. For heating or cooling, the device is a current generator that passes current through the thermopile. If the current flows in the proper direction, the junctions at T_H will heat up, and those at T_L will cool down. If T_H is fixed by connection to a heat sink, thermoelectric cooling will be provided by T_L. Alternatively, if T_L is fixed, thermoelectric heating will be provided at T_H. Such a system has the advantage that at any given location it can be converted from a cooler to a heater merely by reversing the direction of the current.

Thermopile, a battery of thermocouples connected in series. D is a device appropriate to the particular application; A and B are the two different conductors.

Thermoelectric power generators, heaters, or coolers made from even the best presently available materials have the disadvantages of relatively low efficiencies and concomitant high cost per unit of output. Their use has therefore been largely restricted to situations in which these disadvantages are outweighed by such advantages as small size, low maintenance due to lack of moving parts, quiet and vibration-free performance, light weight, and long life. See also Thermoelectric power generator.

The noun has one meaning:

Meaning #1: electricity produced by heat (as in a thermocouple)

It has been suggested that Thermoelectric effect be merged into this article or section. (Discuss)

Thermoelectricity (thermo-electricity) refers to a class of phenomena in which a temperature difference creates an electric potential or an electric potential creates a temperature difference. In modern technical usage, the term almost always refers collectively to the Seebeck effect, Peltier effect, and the Thomson effect. Analyzing the word thermoelectricity by its etymological components, it might be taken to refer generically to all heat engines that are used to generate electricity and all electrically powered heating devices, for which there is an almost arbitrary number of conceivable techniques, but in practice such a broad use of the term is seldom encountered.

See also

• Thermoelectric effect
• Thermopower
• Batteryless radio
• Joule's law
• Heat transfer
• Thermoelectric cooling/ Peltier device
• Pyroelectric effect - the creation of an electric field in a crystal after uniform heating
• Thermogenerator
• Thermionic emission

External links

• Thermoelectricity diagrams
• How kerosene refrigerator works
• Image:Kerosene_radio.jpg
• History of thermoelectric devices
• International Thermoelectric Society
• Thermoelectric News
• Tellurex thermoelectric module
• Amerigon

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