Seebeck electromotive force

When the circuit is open, there appears an electric potential difference called the Seebeck electromotive force, denoted emfoT and expressed in V. This voltage is a complex function of both the temperature difference and the type of conductors [i.e., = F(AT,A, B)]. 

In practice, the Seebeck electromotive force is related to the temperature difference by a polynomial equation, where the polynomial coefficients (i.e., c , c, Cj, C3, etc.) are empirical constants determined by experiment and that characterize the thermocouple selected. 

However for a small temperature difference, the Seebeck electromotive force can be assumed to be directly proportional to the temperature difference ... 

Thermocouples are primarily based on the Seebeck effect In an open circuit, consisting of two wires of different materials joined together at one end, an electromotive force (voltage) is generated between the free wire ends when subject to a temperature gradient. Because the voltage is dependent on the temperature difference between the wires (measurement) junction and the free (reference) ends, the system can be used for temperature measurement. Before modern electronic developments, a real reference temperature, for example, a water-ice bath, was used for the reference end of the thermocouple circuit. This is not necessary today, as the reference can be obtained electronically. Thermocouple material pairs, their temperature-electromotive forces, and tolerances are standardized. The standards are close to each other but not identical. The most common base-metal pairs are iron-constantan (type J), chomel-alumel (type K), and copper-constantan (type T). Noble-metal thermocouples (types S, R, and B) are made of platinum and rhodium in different mixing ratios. 

The Seebeck Effect The production of an electromotive force in a thermocouple under conditions of zero electric current. Thermoelectric power is the change in voltage at a thermocouple as a function of temperature. 

The working principle of the thermocouple was discovered (1823) by Seebeck who observed that if wires of two different metals were joined to form a continuous circuit, a current flowed in the circuit when the two junctions were at different temperatures. In order to make a measurement, one junction (the reference junction) is maintained at a constant temperature (typically at 0°C) and the electromotive force produced when the other junction is at the test temperature is measured, or recorded, by a suitable instrument (or used as the input of a controller ). In order to choose the right kind of thermocouple among the many types available, the temperature range to be studied must be considered, as well as several requirements regarding sensitivity, calibration stability, chemical, thermal, mechanical inertia, etc. 

In 1821 Seebeck discovered that, in an electric circuit consisting of two different materials X and Y in the form of wires, when the two junctions are at different temperatures 0, and a potential exists at the terminals on open circuit and, if the circuit is closed, a current flows 271. At each junction there exists a contact potential E r and E x respectively which depends on the type of metal employed and the temperature of the junction. When the system is on closed circuit the electromotive force (emf) is given by ... 

The most often used temperature detectors in renewable energy and most other processes are the thermocouples (TCs). Their operation is based on the principle known as the Seebeck effect. T. J. Seebeck discovered that heating the junction of dissimilar metals generates a small, continuous electromotive force (EMF). The name is a combination of thermo and couple denoting heat and two junctions, respectively. The dissimilar TC wires are joined at the hot (or measurement) end and also at the cold junction (reference end),... 

In a thermocouple, heating one junction of a bimetallic couple and cooling the other produces electromotive force in the circuit. This observation was originally was made by Seebeck in 1821. Besides the use of thermocouples, transistor electronics and semiconductors are important areas of interest for thermoelectric phenomena. Thermocouples made of semiconductors can develop relatively large electromotive potentials and are used to convert heat into electricity. 

Consider the Seebeck effect resulting from two junctions maintained at two different temperatures as shown in Figure 7.5. Assume that points 1 and 4 are at the same temperature T0. These points are connected to a potentiometer so that the electromotive force E can be measured with zero current Je = 0. Under these conditions and using the reciprocal rules, Eq. (7.287) yields... 

Seebeck experimented with a number of metals including antimony, iron, zinc, silver, gold, lead, mercury, copper, platinum, and bismuth. Later, the observation was made that the electromotive force (EMF) generated is proportional to the temperature difference between the junctions. Today, TE couples are often made from semiconductor alloys of bismuth antimony telluride, Bi Sb2- cTe3 (x 0.5), that have been suitably doped to possess distinct n- or p-type characteristics. A practical TE cooler consists of one or more couples that are connected electrically in series and thermally in parallel. 

The Seebeck coefficient were calculated from measurement of electromotive force with temperature difference of lOK. The electrical resistivity and Hall measurement were performed by van der Pauw method. The thermal conductivity were calculated from the thermal diffusivity, the specific heat and the density. The thermal diffusivity and the specific heat were measured by laser flash method and differential scanning calorimeter (DSC), respectively. 

To measure the Seebeck coefficient a, heat was applied to the sample which was placed between the two Cu discs. The thermoelectric electromotive force (E) was measured upon applying small temperature difference (JT <2 E) between the both ends of the sample. The Seebeck coefficient a of the compound was determined from the E/JT. The electrical resistivity p of the compound was measured by the four-probe technique. The repeat measurement was made rapidly with a duration smaller than one second to prevent errors due to the Peltier effect [3]. The thermal conductivity k was measured by the static comparative method [3] using a transparent Si02 ( k =1.36 W/Km at room temperature) as a standard sample in 5x10 torr. 

It should be noted in the method that the U- or II-shaped specimen is never p-n device but a single p- or n- type material. This was aimed to remove possible errors due to Seebeck and Peltier effects in the resistivity measurement where a large temperature gradient is given to a specimen. An apparent Seebeck coefficients were calculated as the temperature derivatives from the measured electromotive forces. 

The operation principle of a thermocouple is described by the Seebeck effect When two dissimilar materials are joined together at two junctions and these junctions are maintained at different temperatures, an electromotive force (EMF) exists across the two junctions. 

Temperature measurement using thermocouples is based on the thermoelectric effect. Two dissimilar metals are joined together at a junction where an electromotive force (emf) is generated according to the Seebeck effect. The emf level depends on the junction temperature. The Peltier effect causes an emf to be generated when the dissimilar metals are connected to an electrical circuit. 

In the case of a Tian-Calvet calorimeter, we note that the presence of a temperature difference between the internal and external enclosure will lead to the creation of an electromotive force that is proportional to this difference (Seebeck effect). 

Each thermocouple consists of two different metal alloy conductors joined at two junctions, called the hot jtmction and cold junction, respectively, as shown in Eig. 2. When the two junctions are maintained at different temperature, the difference will produce an electromotive force (EMF), known as the Seebeck EME. As a result, an electrical voltage proportional to the temperature will be generated by the thermocouple. The relationship between the voltage and temperature depends on the type of materials. Eor practical applications, such a relationship is uti-hzed to produce different types of thermocouples for different temperature ranges. 

To monitor a patient s body temperature, thermocouples and thermistors are typically used. Thermocouples are based on Seebeck s electromotive force (emf) across a junction of two dissimilar metals. Typical empirical calibration data can be fit by a curvilinear regression equation E = a T + + where E is Seebeck emf in... 

Seebeck Effect Generation of an electromotive force between two junctions of wires made of certain types of metals, when the junctions are at different temperatures. 

Trapezoid Module. Fig. 2 shows the distribution of temperature, potential, current density and voltage after the iterations. As expected, the temperature monotonically decreases from the hot copper electrode (0.8 mm wide, 1.0 mm thick and 0.2 mm high) at 700 K to the cold copper electrode with the same dimension at 300 K. The temperature profile is flat at the high temperature region, while the isotherm bends roundly at the lower temperature region. Because both the potential (electromotive force, EMF) generated due to Seebeck effect and the electrical conductivity relates with the local temperature at the TE element, the potential and current density in the TE element (Fig. 2(b) and (c))... 

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