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109-465: This effect can be used to generate electricity , measure temperature or change the temperature of objects. Because the direction of heating and cooling is affected by the applied voltage, thermoelectric devices can be used as temperature controllers. The term "thermoelectric effect" encompasses three separately identified effects: the Seebeck effect (temperature differences cause electromotive forces),

218-733: A bridge circuit . The cathode-ray oscilloscope works by amplifying the voltage and using it to deflect an electron beam from a straight path, so that the deflection of the beam is proportional to the voltage. A common voltage for flashlight batteries is 1.5 volts (DC). A common voltage for automobile batteries is 12 volts (DC). Common voltages supplied by power companies to consumers are 110 to 120 volts (AC) and 220 to 240 volts (AC). The voltage in electric power transmission lines used to distribute electricity from power stations can be several hundred times greater than consumer voltages, typically 110 to 1200 kV (AC). The voltage used in overhead lines to power railway locomotives

327-430: A capacitor ), and from an electromotive force (e.g., electromagnetic induction in a generator ). On a macroscopic scale, a potential difference can be caused by electrochemical processes (e.g., cells and batteries), the pressure-induced piezoelectric effect , and the thermoelectric effect . Since it is the difference in electric potential, it is a physical scalar quantity . A voltmeter can be used to measure

436-446: A Compound Annual Growth Rate (CAGR) of 18.3% in the period from 2015 to 2020 due to the high demand of thermoelectric generators by the automotive industries to increase overall fuel efficiency, as well as the growing industrialization in the region. Small scale thermoelectric generators are also in the early stages of investigation in wearable technologies to reduce or replace charging and boost charge duration. Recent studies focused on

545-438: A bulk material or electrons of negative charge), heat can be carried in either direction with respect to voltage. Semiconductors of n-type and p-type are often combined in series as they have opposite directions for heat transport, as specified by the sign of their Seebeck coefficients . The Seebeck effect is the electromotive force (emf) that develops across two points of an electrically conducting material when there

654-423: A cold sink to replenish with heat energy. This rapid reversing heating and cooling effect is used by many modern thermal cyclers , laboratory devices used to amplify DNA by the polymerase chain reaction (PCR). PCR requires the cyclic heating and cooling of samples to specified temperatures. The inclusion of many thermocouples in a small space enables many samples to be amplified in parallel. For certain materials,

763-412: A complicated system. If the material is not in a steady state, a complete description needs to include dynamic effects such as relating to electrical capacitance , inductance and heat capacity . The thermoelectric effects lie beyond the scope of equilibrium thermodynamics. They necessarily involve continuing flows of energy. At least, they involve three bodies or thermodynamic subsystems, arranged in

872-491: A connected n-type and p-type material. The arrangement of the thermocouples is typically in three main designs: planar, vertical, and mixed. Planar design involves thermocouples put onto a substrate horizontally between the heat source and cool side, resulting in the ability to create longer and thinner thermocouples, thereby increasing the thermal resistance and temperature gradient and eventually increasing voltage output. Vertical design has thermocouples arranged vertically between

981-533: A current is driven. Some of the junctions lose heat due to the Peltier effect, while others gain heat. Thermoelectric heat pumps exploit this phenomenon, as do thermoelectric cooling devices found in refrigerators. The Peltier effect can be used to create a heat pump . Notably, the Peltier thermoelectric cooler is a refrigerator that is compact and has no circulating fluid or moving parts. Such refrigerators are useful in applications where their advantages outweigh

1090-573: A current is made to flow through a junction between two conductors, A and B, heat may be generated or removed at the junction. The Peltier heat generated at the junction per unit time is Q ˙ = ( Π A − Π B ) I , {\displaystyle {\dot {Q}}=(\Pi _{\text{A}}-\Pi _{\text{B}})I,} where Π A {\displaystyle \Pi _{\text{A}}} and Π B {\displaystyle \Pi _{\text{B}}} are

1199-420: A cylinder. Many designs for TEGs can be made for the different devices they are applied to. Using thermoelectric modules, a thermoelectric system generates power by taking in heat from a source such as a hot exhaust flue. To operate, the system needs a large temperature gradient, which is not easy in real-world applications. The cold side must be cooled by air or water. Heat exchangers are used on both sides of

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1308-402: A distinct arrangement of surroundings. But in the case of continuous variation in the media, heat transfer and thermodynamic work cannot be uniquely distinguished. This is more complicated than the often considered thermodynamic processes, in which just two respectively homogeneous subsystems are connected. In 1854, Lord Kelvin found relationships between the three coefficients, implying that

1417-482: A junction, the associated heat flow will develop a discontinuity if Π A {\displaystyle \Pi _{\text{A}}} and Π B {\displaystyle \Pi _{\text{B}}} are different. The Peltier effect can be considered as the back-action counterpart to the Seebeck effect (analogous to the back-EMF in magnetic induction): if a simple thermoelectric circuit

1526-490: A large number of thermal cycles. Thus, the junctions and materials must be selected so that they survive these tough mechanical and thermal conditions. Also, the module must be designed such that the two thermoelectric materials are thermally in parallel, but electrically in series. The efficiency of a thermoelectric module is greatly affected by the geometry of its design. Thermoelectric generators are made of several thermopiles , each consisting of many thermocouples made of

1635-633: A large voltage while in a temperature gradient. The measure of the magnitude of electrons flow in response to a temperature difference across that material is given by the Seebeck coefficient (S). The efficiency of a given material to produce a thermoelectric power is simply estimated by its “ figure of merit ” zT = S σT/κ. For many years, the main three semiconductors known to have both low thermal conductivity and high power factor were bismuth telluride (Bi 2 Te 3 ), lead telluride (PbTe), and silicon germanium (SiGe). Some of these materials have somewhat rare elements which make them expensive. Today,

1744-410: A localized hot or cold spot in a single homogeneous conducting material, since the overall emfs from the increasing and decreasing temperature gradients will perfectly cancel out. Attaching an electrode to the hotspot in an attempt to measure the locally shifted voltage will only partly succeed: it means another temperature gradient will appear inside of the electrode, and so the overall emf will depend on

1853-477: A magnetic field or is itself magnetically ordered ( ferromagnetic , antiferromagnetic , etc.), then the second Thomson relation does not take the simple form shown here. Now, using the second relation, the first Thomson relation becomes Thermoelectric generator A thermoelectric generator ( TEG ), also called a Seebeck generator , is a solid state device that converts heat (driven by temperature differences) directly into electrical energy through

1962-501: A more reliable device that does not require maintenance for long periods. The durability and environmental stability have made thermoelectrics a favorite for NASA's deep space explorers among other applications. One of the key advantages of thermoelectric generators outside of such specialized applications is that they can potentially be integrated into existing technologies to boost efficiency and reduce environmental impact by producing usable power from waste heat. A thermoelectric module

2071-455: A particular way, along with a special arrangement of the surroundings. The three bodies are the two different metals and their junction region. The junction region is an inhomogeneous body, assumed to be stable, not suffering amalgamation by diffusion of matter. The surroundings are arranged to maintain two temperature reservoirs and two electric reservoirs. For an imagined, but not actually possible, thermodynamic equilibrium, heat transfer from

2180-749: A phenomenon called the Seebeck effect (a form of thermoelectric effect ). Thermoelectric generators function like heat engines , but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient. When the same principle is used in reverse to create a heat gradient from an electric current, it is called a thermoelectric (or Peltier) cooler . Thermoelectric generators could be used in power plants and factories to convert waste heat into additional electrical power and in automobiles as automotive thermoelectric generators (ATGs) to increase fuel efficiency . Radioisotope thermoelectric generators use radioisotopes to generate

2289-785: A photovoltaic panel, despite intending to invent a thermoelectric generator with thermocouples, in 1909. He notes that heat alone didn't produce any power, only incident light, but he had no explanation for how it could be working. The operational principle is now understood to have been a very simple form of Schottky junction . The typical efficiency of TEGs is around 5–8%, although it can be higher. Older devices used bimetallic junctions and were bulky. More recent devices use highly doped semiconductors made from bismuth telluride (Bi 2 Te 3 ), lead telluride (PbTe), calcium manganese oxide (Ca 2 Mn 3 O 8 ), or combinations thereof, depending on application temperature. These are solid-state devices and unlike dynamos have no moving parts , with

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2398-464: A significant scattering effect on electrons. The breakthrough is then applying a pressure to the liquid in the sintering process, which creates a transient flow of the Te rich liquid and facilitates the formation of dislocations that greatly reduce the lattice conductivity. The ability to selectively decrease the lattice conductivity results in reported zT value of 1.86, which is a significant improvement over

2507-538: A temperature gradient. If a current density J {\displaystyle \mathbf {J} } is passed through a homogeneous conductor, the Thomson effect predicts a heat production rate per unit volume. q ˙ = − K J ⋅ ∇ T , {\displaystyle {\dot {q}}=-{\mathcal {K}}\mathbf {J} \cdot \nabla T,} where ∇ T {\displaystyle \nabla T}

2616-570: A thermocouple but involves an unknown material instead of an unknown temperature: a metallic probe of known composition is kept at a constant known temperature and held in contact with the unknown sample that is locally heated to the probe temperature, thereby providing an approximate measurement of the unknown Seebeck coefficient S {\displaystyle S} . This can help distinguish between different metals and alloys. Thermopiles are formed from many thermocouples in series, zig-zagging back and forth between hot and cold. This multiplies

2725-733: A variety of applications. Frequently, thermoelectric generators are used for low power remote applications or where bulkier but more efficient heat engines such as Stirling engines would not be possible. Unlike heat engines, the solid state electrical components typically used to perform thermal to electric energy conversion have no moving parts. The thermal to electric energy conversion can be performed using components that require no maintenance, have inherently high reliability, and can be used to construct generators with long service-free lifetimes. This makes thermoelectric generators well suited for equipment with low to modest power needs in remote uninhabited or inaccessible locations such as mountaintops,

2834-423: A well-defined voltage between nodes in the circuit, since the electric force is not a conservative force in those cases. However, at lower frequencies when the electric and magnetic fields are not rapidly changing, this can be neglected (see electrostatic approximation ). The electric potential can be generalized to electrodynamics, so that differences in electric potential between points are well-defined even in

2943-458: A zT of 2–3. Most research in thermoelectric materials has focused on increasing the Seebeck coefficient (S) and reducing the thermal conductivity, especially by manipulating the nanostructure of the thermoelectric materials. Because both the thermal and electrical conductivity correlate with the charge carriers, new means must be introduced in order to conciliate the contradiction between high electrical conductivity and low thermal conductivity, as

3052-465: Is Π = T S . {\displaystyle \Pi =TS.} This relation expresses a subtle and fundamental connection between the Peltier and Seebeck effects. It was not satisfactorily proven until the advent of the Onsager relations , and it is worth noting that this second Thomson relation is only guaranteed for a time-reversal symmetric material; if the material is placed in

3161-405: Is a circuit containing thermoelectric materials which generate electricity from heat directly. A thermoelectric module consists of two dissimilar thermoelectric materials joined at their ends: an n-type (with negative charge carriers), and a p-type (with positive charge carriers) semiconductor. Direct electric current will flow in the circuit when there is a temperature difference between the ends of

3270-496: Is a growing part of the TEG market, capitalizing on the latest technologies. Main applications are sensors, low power applications and more globally Internet of things applications. A specialized market research company indicated that 100,000 units have been shipped in 2014 and expects 9 million units per year by 2020. Voltage Voltage , also known as (electrical) potential difference , electric pressure , or electric tension

3379-478: Is a temperature difference between them. The emf is called the Seebeck emf (or thermo/thermal/thermoelectric emf). The ratio between the emf and temperature difference is the Seebeck coefficient. A thermocouple measures the difference in potential across a hot and cold end for two dissimilar materials. This potential difference is proportional to the temperature difference between the hot and cold ends. First discovered in 1794 by Italian scientist Alessandro Volta , it

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3488-468: Is a well-defined voltage across the inductor's terminals. This is the reason that measurements with a voltmeter across an inductor are often reasonably independent of the placement of the test leads. The volt (symbol: V ) is the derived unit for electric potential , voltage, and electromotive force . The volt is named in honour of the Italian physicist Alessandro Volta (1745–1827), who invented

3597-548: Is affected by thermodynamics. The quantity measured by a voltmeter is the negative of the difference of the electrochemical potential of electrons ( Fermi level ) divided by the electron charge and commonly referred to as the voltage difference, while the pure unadjusted electrostatic potential (not measurable with a voltmeter) is sometimes called Galvani potential . The terms "voltage" and "electric potential" are ambiguous in that, in practice, they can refer to either of these in different contexts. The term electromotive force

3706-473: Is also relatively inexpensive and stable up to this temperature in a vacuum, and can be a good alternative in the temperature range between materials based on Bi 2 Te 3 and PbTe. Among the most exciting developments in thermoelectric materials was the development of single crystal tin selenide which produced a record zT of 2.6 in one direction. Other new materials of interest include Skutterudites, Tetrahedrites, and rattling ions crystals. Besides improving

3815-475: Is an extension of the Peltier–Seebeck model and is credited to Lord Kelvin . Joule heating , the heat that is generated whenever a current is passed through a conductive material, is not generally termed a thermoelectric effect. The Peltier–Seebeck and Thomson effects are thermodynamically reversible , whereas Joule heating is not. At the atomic scale, a temperature gradient causes charge carriers in

3924-427: Is between 12 kV and 50 kV (AC) or between 0.75 kV and 3 kV (DC). Inside a conductive material, the energy of an electron is affected not only by the average electric potential but also by the specific thermal and atomic environment that it is in. When a voltmeter is connected between two different types of metal, it measures not the electrostatic potential difference, but instead something else that

4033-454: Is closed, then the Seebeck effect will drive a current, which in turn (by the Peltier effect) will always transfer heat from the hot to the cold junction. The close relationship between Peltier and Seebeck effects can be seen in the direct connection between their coefficients: Π = T S {\displaystyle \Pi =TS} (see below ). A typical Peltier heat pump involves multiple junctions in series, through which

4142-498: Is critical, as with heat removal from an electrical device such as microprocessors. While TEG technology has been used in military and aerospace applications for decades, new TE materials and systems are being developed to generate power using low or high temperatures waste heat, and that could provide a significant opportunity in the near future. These systems can also be scalable to any size and have lower operation and maintenance cost. The global market for thermoelectric generators

4251-402: Is defined as s = 1 + z T − 1 S T {\displaystyle s={\frac {{\sqrt {1+zT}}-1}{ST}}} . When the compatibility factor from one segment to the next differs by more than a factor of about two, the device will not operate efficiently. The material parameters determining s (as well as zT) are temperature-dependent, so

4360-417: Is defined so that negatively charged objects are pulled towards higher voltages, while positively charged objects are pulled towards lower voltages. Therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Historically, voltage has been referred to using terms like "tension" and "pressure". Even today, the term "tension" is still used, for example within

4469-460: Is estimated to be US$ 320 million in 2015 and US$ 472 million in 2021; up to US$ 1.44 billion by 2030 with a CAGR of 11.8%. Today, North America captures 66% of the market share and it will continue to be the biggest market in the near future. However, Asia-Pacific and European countries are projected to grow at relatively higher rates. A study found that the Asia-Pacific market would grow at

Thermoelectric effect - Misplaced Pages Continue

4578-460: Is named after the Russian born, Baltic German physicist Thomas Johann Seebeck who rediscovered it in 1821. Seebeck observed what he called "thermomagnetic effect" wherein a magnetic compass needle would be deflected by a closed loop formed by two different metals joined in two places, with an applied temperature difference between the joints. Danish physicist Hans Christian Ørsted noted that

4687-402: Is needed. When selecting materials for thermoelectric generation, a number of other factors need to be considered. During operation, ideally, the thermoelectric generator has a large temperature gradient across it. Thermal expansion will then introduce stress in the device which may cause fracture of the thermoelectric legs or separation from the coupling material. The mechanical properties of

4796-573: Is the Seebeck coefficient (also known as thermopower), a property of the local material, and ∇ T {\displaystyle \nabla T} is the temperature gradient. The Seebeck coefficients generally vary as function of temperature and depend strongly on the composition of the conductor. For ordinary materials at room temperature, the Seebeck coefficient may range in value from −100 μV/K to +1,000 μV/K (see Seebeck coefficient article for more information). In practice, thermoelectric effects are essentially unobservable for

4905-552: Is the joule per coulomb , where 1 volt = 1 joule (of work) per 1 coulomb of charge. The old SI definition for volt used power and current ; starting in 1990, the quantum Hall and Josephson effect were used, and in 2019 physical constants were given defined values for the definition of all SI units. Voltage is denoted symbolically by Δ V {\displaystyle \Delta V} , simplified V , especially in English -speaking countries. Internationally,

5014-714: Is the thermal conductivity . The first term is the Fourier's heat conduction law , and the second term shows the energy carried by currents. The third term, q ˙ ext {\displaystyle {\dot {q}}_{\text{ext}}} , is the heat added from an external source (if applicable). If the material has reached a steady state, the charge and temperature distributions are stable, so e ˙ = 0 {\displaystyle {\dot {e}}=0} and ∇ ⋅ J = 0 {\displaystyle \nabla \cdot \mathbf {J} =0} . Using these facts and

5123-486: Is the Joule heating, and the last term includes both Peltier ( ∇ S {\displaystyle \nabla S} at junction) and Thomson ( ∇ S {\displaystyle \nabla S} in thermal gradient) effects. Combined with the Seebeck equation for J {\displaystyle \mathbf {J} } , this can be used to solve for the steady-state voltage and temperature profiles in

5232-427: Is the absolute temperature, K {\displaystyle {\mathcal {K}}} is the Thomson coefficient, Π {\displaystyle \Pi } is the Peltier coefficient, and S {\displaystyle S} is the Seebeck coefficient. This relationship is easily shown given that the Thomson effect is a continuous version of the Peltier effect. The second Thomson relation

5341-484: Is the difference in electric potential between two points. In a static electric field , it corresponds to the work needed per unit of charge to move a positive test charge from the first point to the second point. In the International System of Units (SI), the derived unit for voltage is the volt (V) . The voltage between points can be caused by the build-up of electric charge (e.g.,

5450-530: Is the intensity of the electric field. In this case, the voltage increase from point A to point B is equal to the work done per unit charge, against the electric field, to move the charge from A to B without causing any acceleration. Mathematically, this is expressed as the line integral of the electric field along that path. In electrostatics, this line integral is independent of the path taken. Under this definition, any circuit where there are time-varying magnetic fields, such as AC circuits , will not have

5559-405: Is the local voltage , and σ {\displaystyle \sigma } is the local conductivity . In general, the Seebeck effect is described locally by the creation of an electromotive field E emf = − S ∇ T , {\displaystyle \mathbf {E} _{\text{emf}}=-S\nabla T,} where S {\displaystyle S}

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5668-450: Is the sum of the voltage between A and B and the voltage between B and C . The various voltages in a circuit can be computed using Kirchhoff's circuit laws . When talking about alternating current (AC) there is a difference between instantaneous voltage and average voltage. Instantaneous voltages can be added for direct current (DC) and AC, but average voltages can be meaningfully added only when they apply to signals that all have

5777-410: Is the temperature gradient, and K {\displaystyle {\mathcal {K}}} is the Thomson coefficient. The Thomson effect is a manifestation of the direction of flow of electrical carriers with respect to a temperature gradient within a conductor. These absorb energy (heat) flowing in a direction opposite to a thermal gradient, increasing their potential energy, and, when flowing in

5886-652: The Peltier effect (thermocouples create temperature differences), and the Thomson effect (the Seebeck coefficient varies with temperature). The Seebeck and Peltier effects are different manifestations of the same physical process; textbooks may refer to this process as the Peltier–Seebeck effect (the separation derives from the independent discoveries by French physicist Jean Charles Athanase Peltier and Baltic German physicist Thomas Johann Seebeck ). The Thomson effect

5995-430: The voltaic pile , possibly the first chemical battery . A simple analogy for an electric circuit is water flowing in a closed circuit of pipework , driven by a mechanical pump . This can be called a "water circuit". The potential difference between two points corresponds to the pressure difference between two points. If the pump creates a pressure difference between two points, then water flowing from one point to

6104-699: The Peltier and Thomson effects, we must consider the flow of energy. If temperature and charge change with time, the full thermoelectric equation for the energy accumulation, e ˙ {\displaystyle {\dot {e}}} , is e ˙ = ∇ ⋅ ( κ ∇ T ) − ∇ ⋅ ( V + Π ) J + q ˙ ext , {\displaystyle {\dot {e}}=\nabla \cdot (\kappa \nabla T)-\nabla \cdot (V+\Pi )\mathbf {J} +{\dot {q}}_{\text{ext}},} where κ {\displaystyle \kappa }

6213-422: The Peltier coefficients of conductors A and B, and I {\displaystyle I} is the electric current (from A to B). The total heat generated is not determined by the Peltier effect alone, as it may also be influenced by Joule heating and thermal-gradient effects (see below). The Peltier coefficients represent how much heat is carried per unit charge. Since charge current must be continuous across

6322-428: The Seebeck coefficient is not constant in temperature, and so a spatial gradient in temperature can result in a gradient in the Seebeck coefficient. If a current is driven through this gradient, then a continuous version of the Peltier effect will occur. This Thomson effect was predicted and later observed in 1851 by Lord Kelvin (William Thomson). It describes the heating or cooling of a current-carrying conductor with

6431-393: The Thomson, Peltier, and Seebeck effects are different manifestations of one effect (uniquely characterized by the Seebeck coefficient). The first Thomson relation is K ≡ d Π d T − S , {\displaystyle {\mathcal {K}}\equiv {\frac {d\Pi }{dT}}-S,} where T {\displaystyle T}

6540-618: The above effects is involved in the operation of a real thermoelectric device. The Seebeck effect, Peltier effect, and Thomson effect can be gathered together in a consistent and rigorous way, described here; this also includes the effects of Joule heating and ordinary heat conduction. As stated above, the Seebeck effect generates an electromotive force, leading to the current equation J = σ ( − ∇ V − S ∇ T ) . {\displaystyle \mathbf {J} =\sigma (-{\boldsymbol {\nabla }}V-S\nabla T).} To describe

6649-429: The advantage of not having any moving parts. When an electric current is passed through a circuit of a thermocouple , heat is generated at one junction and absorbed at the other junction. This is known as the Peltier effect : the presence of heating or cooling at an electrified junction of two different conductors. The effect is named after French physicist Jean Charles Athanase Peltier , who discovered it in 1834. When

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6758-509: The armchair axis); n-type doped InP 3 {\displaystyle {\ce {InP3}}} (ZT = 3.23); p-type doped SnP 3 {\displaystyle {\ce {SnP3}}} (ZT = 3.46); p-type doped SbP 3 {\displaystyle {\ce {SbP3}}} (ZT = 3.5). Thermoelectric power generators consist of three major components: thermoelectric materials, thermoelectric modules and thermoelectric systems that interface with

6867-413: The circuit are not negligible, then their effects can be modelled by adding mutual inductance elements. In the case of a physical inductor though, the ideal lumped representation is often accurate. This is because the external fields of inductors are generally negligible, especially if the inductor has a closed magnetic path . If external fields are negligible, we find that is path-independent, and there

6976-459: The compatibility factor may change from the hot side to the cold side of the device, even in one segment. This behavior is referred to as self-compatibility and may become important in devices designed for wide-temperature application. In general, thermoelectric materials can be categorized into conventional and new materials: Many TEG materials are employed in commercial applications today. These materials can be divided into three groups based on

7085-406: The conversion efficiency, by reducing the lattice thermal conductivity. Researchers are trying to develop new thermoelectric materials for power generation by improving the figure-of-merit zT. One example of these materials is the semiconductor compound ß-Zn 4 Sb 3 , which possesses an exceptionally low thermal conductivity and exhibits a maximum zT of 1.3 at a temperature of 670K. This material

7194-415: The cost and complexity of the system. Only a few known materials to date are identified as thermoelectric materials. Most thermoelectric materials today have a zT, the figure of merit, value of around 1, such as in bismuth telluride (Bi 2 Te 3 ) at room temperature and lead telluride (PbTe) at 500–700 K. However, in order to be competitive with other power generation systems, TEG materials should have

7303-419: The current commercial thermoelectric generators with zT ~ 0.3–0.6. These improvements highlight the fact that in addition to the development of novel materials for thermoelectric applications, using different processing techniques to design microstructure is a viable and worthwhile effort. In fact, it often makes sense to work to optimize both composition and microstructure. Thermoelectric generators (TEG) have

7412-431: The device with respect to a common reference point (or ground ). The voltage drop is the difference between the two readings. Two points in an electric circuit that are connected by an ideal conductor without resistance and not within a changing magnetic field have a voltage of zero. Any two points with the same potential may be connected by a conductor and no current will flow between them. The voltage between A and C

7521-526: The difference in Seebeck coefficients between the electrode and the conductor it is attached to. Thermocouples involve two wires, each of a different material, that are electrically joined in a region of unknown temperature. The loose ends are measured in an open-circuit state (without any current, J = 0 {\displaystyle \mathbf {J} =0} ). Although the materials' Seebeck coefficients S {\displaystyle S} are nonlinearly temperature dependent and different for

7630-419: The diffusion of charge carriers. The flow of charge carriers between the hot and cold regions in turn creates a voltage difference. In 1834, Jean Charles Athanase Peltier discovered the reverse effect, that running an electric current through the junction of two dissimilar conductors could, depending on the direction of the current, cause it to act as a heater or cooler. George Cove had accidentally invented

7739-455: The disadvantage of their very low efficiency. Other heat pump applications such as dehumidifiers may also use Peltier heat pumps. Thermoelectric coolers are trivially reversible, in that they can be used as heaters by simply reversing the current. Unlike ordinary resistive electrical heating ( Joule heating ) that varies with the square of current, the thermoelectric heating effect is linear in current (at least for small currents) but requires

7848-446: The electric field in the region exterior to each component is conservative, and voltages between nodes in the circuit are well-defined, where as long as the path of integration does not pass through the inside of any component. The above is the same formula used in electrostatics. This integral, with the path of integration being along the test leads, is what a voltmeter will actually measure. If uncontained magnetic fields throughout

7957-428: The electric field, rather than to differences in electric potential. In this case, the voltage rise along some path P {\displaystyle {\mathcal {P}}} from r A {\displaystyle \mathbf {r} _{A}} to r B {\displaystyle \mathbf {r} _{B}} is given by: However, in this case the "voltage" between two points depends on

8066-431: The exact geometry of the wires. This direct relationship allows the thermocouple arrangement to be used as a straightforward uncalibrated thermometer, provided knowledge of the difference in S {\displaystyle S} -vs- T {\displaystyle T} curves of the two materials, and of the reference temperature at the measured loose wire ends. Thermoelectric sorting functions similarly to

8175-489: The figure-of-merit, there is increasing focus to develop new materials by increasing the electrical power output, decreasing cost and developing environmentally friendly materials. For example, when the fuel cost is low or almost free, such as in waste heat recovery , then the cost per watt is only determined by the power per unit area and the operating period. As a result, it has initiated a search for materials with high power output rather than conversion efficiency. For example,

8284-444: The gradient and efficiency of the device. For microelectromechanical systems , TEGs can be designed on the scale of handheld devices to use body heat in the form of thin films. Flexible TEGs for wearable electronics are able to be made with novel polymers through additive manufacturing or thermal spraying processes. Cylindrical TEGs for using heat from vehicle exhaust pipes can also be made using circular thermocouples arranged in

8393-404: The heat source. Thermoelectric materials generate power directly from the heat by converting temperature differences into electric voltage. These materials must have both high electrical conductivity (σ) and low thermal conductivity (κ) to be good thermoelectric materials. Having low thermal conductivity ensures that when one side is made hot, the other side stays cold, which helps to generate

8502-436: The hot and cool plates, leading to high integration of thermocouples as well as a high output voltage, making this design the most widely-used design commercially. The mixed design has the thermocouples arranged laterally on the substrate while the heat flow is vertical between plates. Microcavities under the hot contacts of the device allow for a temperature gradient, which allows for the substrate’s thermal conductivity to affect

8611-425: The hot reservoir to the cold reservoir would need to be prevented by a specifically matching voltage difference maintained by the electric reservoirs, and the electric current would need to be zero. For a steady state, there must be at least some heat transfer or some non-zero electric current. The two modes of energy transfer, as heat and by electric current, can be distinguished when there are three distinct bodies and

8720-437: The local material, and ∇ T {\displaystyle \nabla T} is the temperature gradient. In application, thermoelectric modules in power generation work in very tough mechanical and thermal conditions. Because they operate in a very high-temperature gradient, the modules are subject to large thermally induced stresses and strains for long periods. They also are subject to mechanical fatigue caused by

8829-400: The material to diffuse from the hot side to the cold side. This is due to charge carrier particles having higher mean velocities (and thus kinetic energy ) at higher temperatures, leading them to migrate on average towards the colder side, in the process carrying heat across the material. Depending on the material properties and nature of the charge carriers (whether they are positive holes in

8938-405: The materials must be considered and the coefficient of thermal expansion of the n and p-type material must be matched reasonably well. In segmented thermoelectric generators, the material's compatibility must also be considered to avoid incompatibility of relative current, defined as the ratio of electrical current to diffusion heat current, between segment layers. A material's compatibility factor

9047-409: The materials. Generally, the current magnitude is directly proportional to the temperature difference: J = − σ S ∇ T {\displaystyle \mathbf {J} =-\sigma S\nabla T} where σ {\displaystyle \sigma } is the local conductivity , S is the Seebeck coefficient (also known as thermopower), a property of

9156-404: The modules to supply this heating and cooling. There are many challenges in designing a reliable TEG system that operates at high temperatures. Achieving high efficiency in the system requires extensive engineering design to balance between the heat flow through the modules and maximizing the temperature gradient across them. To do this, designing heat exchanger technologies in the system is one of

9265-574: The most important aspects of TEG engineering. In addition, the system requires to minimize the thermal losses due to the interfaces between materials at several places. Another challenging constraint is avoiding large pressure drops between the heating and cooling sources. If AC power is required (such as for powering equipment designed to run from AC mains power), the DC power from the TE modules must be passed through an inverter, which lowers efficiency and adds to

9374-546: The novel development of a flexible inorganic thermoelectric, silver selenide, on a nylon substrate. Thermoelectrics represent particular synergy with wearables by harvesting energy directly from the human body creating a self-powered device. One project used n-type silver selenide on a nylon membrane. Silver selenide is a narrow bandgap semiconductor with high electrical conductivity and low thermal conductivity, making it perfect for thermoelectric applications. Low power TEG or "sub-watt" (i.e. generating up to 1 watt peak) market

9483-535: The occasional exception of a fan or pump to improve heat transfer. If the hot region is around 1273K and the ZT values of 3 - 4 are implemented, the efficiency is approximately 33-37%; allowing TEG's to compete with certain heat engine efficiencies. As of 2021, there are materials (some containing widely available and inexpensive arsenic and tin) reaching a ZT value > 3; monolayer AsP 3 {\displaystyle {\ce {AsP3}}} (ZT = 3.36 on

9592-407: The other will be able to do work, such as driving a turbine . Similarly, work can be done by an electric current driven by the potential difference provided by a battery . For example, the voltage provided by a sufficiently-charged automobile battery can "push" a large current through the windings of an automobile's starter motor . If the pump is not working, it produces no pressure difference, and

9701-424: The path taken. In circuit analysis and electrical engineering , lumped element models are used to represent and analyze circuits. These elements are idealized and self-contained circuit elements used to model physical components. When using a lumped element model, it is assumed that the effects of changing magnetic fields produced by the circuit are suitably contained to each element. Under these assumptions,

9810-697: The phrase " high tension " (HT) which is commonly used in thermionic valve ( vacuum tube ) based and automotive electronics. In electrostatics , the voltage increase from point r A {\displaystyle \mathbf {r} _{A}} to some point r B {\displaystyle \mathbf {r} _{B}} is given by the change in electrostatic potential V {\textstyle V} from r A {\displaystyle \mathbf {r} _{A}} to r B {\displaystyle \mathbf {r} _{B}} . By definition, this is: where E {\displaystyle \mathbf {E} }

9919-430: The points across which the voltage is measured. When using a voltmeter to measure voltage, one electrical lead of the voltmeter must be connected to the first point, one to the second point. A common use of the term "voltage" is in describing the voltage dropped across an electrical device (such as a resistor). The voltage drop across the device can be understood as the difference between measurements at each terminal of

10028-414: The presence of time-varying fields. However, unlike in electrostatics, the electric field can no longer be expressed only in terms of the electric potential. Furthermore, the potential is no longer uniquely determined up to a constant, and can take significantly different forms depending on the choice of gauge . In this general case, some authors use the word "voltage" to refer to the line integral of

10137-438: The rare earth compounds YbAl 3 has a low figure-of-merit, but it has a power output of at least double that of any other material, and can operate over the temperature range of a waste heat source. To increase the figure of merit (zT), a material’s thermal conductivity should be minimized while its electrical conductivity and Seebeck coefficient is maximized. In most cases, methods to increase or decrease one property result in

10246-406: The required temperature difference to power space probes. Thermoelectric generators can also be used alongside solar panels . In 1821, Thomas Johann Seebeck discovered that a thermal gradient formed between two different conductors can produce electricity. At the heart of the thermoelectric effect is that a temperature gradient in a conducting material results in heat flow; this results in

10355-447: The same direction as a thermal gradient, they liberate heat, decreasing their potential energy. The Thomson coefficient is related to the Seebeck coefficient as K = T d S d T {\displaystyle {\mathcal {K}}=T{\tfrac {dS}{dT}}} (see below ). This equation, however, neglects Joule heating and ordinary thermal conductivity (see full equations below). Often, more than one of

10464-474: The same effect on other properties due to their interdependence. A novel processing technique exploits the scattering of different phonon frequencies to selectively reduce lattice thermal conductivity without the typical negative effects on electrical conductivity from the simultaneous increased scattering of electrons. In a bismuth antimony tellurium ternary system, liquid-phase sintering is used to produce low-energy semicoherent grain boundaries, which do not have

10573-415: The same frequency and phase. Instruments for measuring voltages include the voltmeter , the potentiometer , and the oscilloscope . Analog voltmeters , such as moving-coil instruments, work by measuring the current through a fixed resistor, which, according to Ohm's law , is proportional to the voltage across the resistor. The potentiometer works by balancing the unknown voltage against a known voltage in

10682-565: The second Thomson relation (see below), the heat equation can be simplified to − q ˙ ext = ∇ ⋅ ( κ ∇ T ) + J ⋅ ( σ − 1 J ) − T J ⋅ ∇ S . {\displaystyle -{\dot {q}}_{\text{ext}}=\nabla \cdot (\kappa \nabla T)+\mathbf {J} \cdot \left(\sigma ^{-1}\mathbf {J} \right)-T\mathbf {J} \cdot \nabla S.} The middle term

10791-465: The symbol U is standardized. It is used, for instance, in the context of Ohm's or Kirchhoff's circuit laws . The electrochemical potential is the voltage that can be directly measured with a voltmeter. The Galvani potential that exists in structures with junctions of dissimilar materials is also work per charge but cannot be measured with a voltmeter in the external circuit (see § Galvani potential vs. electrochemical potential ). Voltage

10900-639: The temperature difference was in fact driving an electric current, with the generation of magnetic field being an indirect consequence, and so coined the more accurate term "thermoelectricity". The Seebeck effect is a classic example of an electromotive force (EMF) and leads to measurable currents or voltages in the same way as any other EMF. The local current density is given by J = σ ( − ∇ V + E emf ) , {\displaystyle \mathbf {J} =\sigma (-\nabla V+\mathbf {E} _{\text{emf}}),} where V {\displaystyle V}

11009-402: The temperature range of operation: Although these materials still remain the cornerstone for commercial and practical applications in thermoelectric power generation, significant advances have been made in synthesizing new materials and fabricating material structures with improved thermoelectric performance. Recent research has focused on improving the material’s figure-of-merit (zT), and hence

11118-672: The thermal conductivity of semiconductors can be lowered without affecting their high electrical properties using nanotechnology . This can be achieved by creating nanoscale features such as particles, wires or interfaces in bulk semiconductor materials. However, the manufacturing processes of nano-materials are still challenging. Thermoelectric generators are all-solid-state devices that do not require any fluids for fuel or cooling, making them non-orientation dependent allowing for use in zero-gravity or deep-sea applications. The solid-state design allows for operation in severe environments. Thermoelectric generators have no moving parts which produce

11227-401: The turbine will not rotate. Likewise, if the automobile's battery is very weak or "dead" (or "flat"), then it will not turn the starter motor. The hydraulic analogy is a useful way of understanding many electrical concepts. In such a system, the work done to move water is equal to the " pressure drop" (compare p.d.) multiplied by the volume of water moved. Similarly, in an electrical circuit,

11336-401: The two materials, the open-circuit condition means that ∇ V = − S ∇ T {\displaystyle \nabla V=-S\nabla T} everywhere. Therefore (see the thermocouple article for more details) the voltage measured at the loose ends of the wires is directly dependent on the unknown temperature, and yet totally independent of other details such as

11445-430: The vacuum of space, or the deep ocean. The main uses of thermoelectric generators are: Besides low efficiency and relatively high cost, practical problems exist in using thermoelectric devices in certain types of applications resulting from a relatively high electrical output resistance, which increases self-heating, and a relatively low thermal conductivity, which makes them unsuitable for applications where heat removal

11554-400: The voltage between two points in a system. Often a common reference potential such as the ground of the system is used as one of the points. In this case, voltage is often mentioned at a point without completely mentioning the other measurement point. A voltage can be associated with either a source of energy or the loss, dissipation, or storage of energy. The SI unit of work per unit charge

11663-408: The voltage output. Thermoelectric generators are like a thermocouple/thermopile but instead draw some current from the generated voltage in order to extract power from heat differentials. They are optimized differently from thermocouples, using high quality thermoelectric materials in a thermopile arrangement, to maximize the extracted power. Though not particularly efficient, these generators have

11772-465: The work done to move electrons or other charge carriers is equal to "electrical pressure difference" multiplied by the quantity of electrical charges moved. In relation to "flow", the larger the "pressure difference" between two points (potential difference or water pressure difference), the greater the flow between them (electric current or water flow). (See " electric power ".) Specifying a voltage measurement requires explicit or implicit specification of

11881-617: Was first used by Volta in a letter to Giovanni Aldini in 1798, and first appeared in a published paper in 1801 in Annales de chimie et de physique . Volta meant by this a force that was not an electrostatic force, specifically, an electrochemical force. The term was taken up by Michael Faraday in connection with electromagnetic induction in the 1820s. However, a clear definition of voltage and method of measuring it had not been developed at this time. Volta distinguished electromotive force (emf) from tension (potential difference):

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