Thermoelectricity refers to a class of phenomena in which a temperature difference creates an electric potential or an electric potential creates a temperature difference - as in a thermocouple.
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa.
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.
Thermoelectricity (thermo-electricity, abbreviated as TE) 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.
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. Simply put, a thermoelectric device creates a voltage when there is a different temperature on each side, and when a voltage is applied to it, it creates a temperature difference. This effect can be used to generate electricity, to measure temperature, to cool objects, or to heat them. Because the direction of heating and cooling is determined by the sign of the applied voltage, thermoelectric devices make very convenient temperature controllers.
Traditionally, the term thermoelectric effect or thermoelectricity encompasses three separately identified effects, the Seebeck effect, the Peltier effect, and the Thomson effect. The Peltier and Seebeck effects are the most basic of the three and are essentially the inverses of one another, for which reason the thermoelectric effect may also be called the Peltier–Seebeck effect. This separation derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and Estonian-German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated whenever a voltage is applied to a resistive material, is somewhat related, though it is not generally termed a thermoelectric effect (and it is usually regarded as being a loss mechanism or non-ideality in thermoelectric devices) . The Peltier–Seebeck and Thomson effects are reversible; Joule heating has not been reversed, but is theoretically possible under the laws of thermodynamics.
In recent years, thermoelectricity sees rapidly increasing usages in applications like portable refrigerators, beverage coolers, electronic component coolers, metal alloy sorting devices etc. One of the most commonly used material in such application is Bismuth telluride (Bi2Te3), a chemical compound of bismuth and tellurium.
Currently there are two primary arenas in which thermoelectric devices can lend themselves to increase energy efficiency and/or decrease pollutants: conversion of waste heat into usable energy and refrigeration.
In the transportation sector, although very common as a means of powering vehicles, internal combustion engines are highly inefficient in energy use (using only 20-25% of the energy generated during fuel combustion). Furthermore, the electricity requirement in vehicles is increasing due to the demands of enhanced performance, on-board controls and creature comforts (stability controls, telematics, navigation systems, electronic braking, etc.). In order to gain fuel efficiency, it may be possible to shift energy draw from the engine (in certain cases) to the electrical load in the car, e.g. electrical power steering or electrical coolant pump operation. Thermoelectric devices are thus being investigated to convert waste-heat into usable energy using the Seebeck Effect.
Currently, some power plants use a method known as cogeneration in which in addition to the electrical energy generated, the heat produced during the process is used for alternative purposes. Thermoelectrics may find applications in such systems or in solar thermal energy generation.
Thermoelectric devices applied to refrigeration using the Peltier effect could reduce the emission of ozone-depleting refrigerants into the atmosphere. Hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) are known ozone depleting substances (ODSs); however, these chemicals have long been at the heart of refrigeration technology. Recently, there has been legislation regulating the use of such chemicals for refrigeration; current international legislation mandates caps on HCFC production and will prohibit their production after 2020 in developed countries and 2030 in developing countries. These mandates as well as the environmental mindedness of consumers is leading to an increased effort in developing effective thermoelectric refrigeration units. Such units could reduce the use of such harmful chemicals and would operate more quietly (since they are solid state and do not require noisy compressors.) Vapor compression refrigerators are still more efficient than peltier refrigerators, but they are larger, and require more maintenance.
Materials of interest
There are a number of materials being researched for thermoelectric device applications and temperature ranges. Some such materials include: Bismuth chalcogenides, Skutterudite thermoelectrics, Oxide thermoelectrics, Nanomaterials.
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