Thermoelectric generating coil and thermoelectric generating module

Abstract

To provide a thermoelectric generating module using general-purpose metal used in thermocouples.SOLUTION: A thermoelectric generating coil includes a metal core wire (100) made of a metal material serving as a negative leg of a thermocouple, and a tubular metal body (200) made of a metal material serving as a positive leg of the thermocouple. A high-temperature end coaxial joint portion (300) joined such that a circumferential surface of the metal core wire is covered with an inner circumferential surface of the tubular metal body, a metal core wire connection portion (108) elongated between a low-temperature end of the metal core wire and the high-temperature end coaxial joint portion, a tubular metal body connection portion (208) elongated between a low-temperature end of the tubular metal body and the high-temperature end coaxial joint portion, a cooling fin (500) connected to the low-temperature end of the tubular metal body connection portion, and a low-temperature end of the metal core wire that is thermally joined to but electrically insulated from the low-temperature end of the tubular metal body connection portion are set as a unit. The electrical connections each including the high-temperature end joint portion and the low-temperature end in the unit are repeated in series, in parallel, or in both series and parallel.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a thermoelectric generator coil and a thermoelectric generator module that use a metal material used in thermocouples. [Background technology]

[0002] To conserve energy, the Seebeck effect is used to convert thermal energy directly into electricity, and the thermoelectromotive force generated by applying a temperature difference between both ends of a semiconductor or two dissimilar metals is utilized. Thermal power generation using semiconductors utilizes the electromotive force that is generated when carriers (electrons and holes) with increased kinetic energy in high temperature areas diffuse to areas with lower temperatures. Because the potential difference is reversed between n-type and p-type semiconductors, the electromotive force can be increased by connecting in series π-structure elements in which n-type and p-type semiconductors are alternately connected via metal electrodes. (Patent Document 1)

[0003] Since electrons are carriers of electricity and heat at the same time, thermoelectric materials are required to have two properties: low thermal conductivity and high electrical conductivity. There are few materials that have such trade-off properties, and harmful semiconductors such as bismuth tellurium alloy (Bi2Te3) are used for thermoelectric power generation. For thermoelectric generation using metals, a thermoelectric generation module has been disclosed in which n-type semiconductors and metal Ni are alternately joined at an inclination to form a tube, with the heat flow and electric current directions perpendicular to each other. With this technology, when a temperature difference is created between the inside and surface of the thermoelectric generation tube, heat is preferentially transferred through the metal Ni layer, which has better thermal conductivity than the n-type semiconductor layer, and a component in the z-axis direction is generated in the temperature gradient of each layer. As a result, an electromotive force in the z-axis direction is generated in each layer due to the Seebeck effect. (Patent Document 2)

[0004] However, since the layers of the thermoelectric tube are not insulated from each other and are electrically integrated, when the heat flow fluctuates at a microscopic level, reactive current is generated between the layers, lowering the thermoelectric conversion efficiency. There are problems such as large heat loss due to the heat being transmitted through the metal Ni layer. In the embodiment, Bi2Te3 is used as the n-type semiconductor, and in addition to the fact that Te compounds are harmful to the human body, the problem inherent to semiconductors, that is, the electromotive force decreases at high temperatures, is not resolved. In order to solve the problems that arise when metals and semiconductors are used together, a coaxial thermoelectric coil using only metals was developed.

[0005] Metals used in thermocouples for temperature measurement have been considered unsuitable as materials for thermoelectric generation because they have a small Seebeck coefficient and a large thermal conductivity. In principle, it is possible to generate thermoelectric power using metals used in thermocouples, but when thermocouples are connected in series, although the voltage increases, the output does not increase very much due to the increased internal resistance. A thermocouple manufacturer conducted experiments on thermoelectric generation using thermocouples, and confirmed that effective thermoelectric generation is not possible with thermocouples, and made the results public. (Non-Patent Document 1)

[0006] The material properties required for a thermocouple include the generation of a voltage proportional to temperature, a wide temperature measurement range, high durability, etc., and low current is not a problem. For this reason, no research has been conducted into reducing the internal resistance of thermocouples, which is the cause of low current. In recent years, the applicant has proposed a technology to reduce internal resistance by 30% by joining two dissimilar metals at the high-temperature end in a comb-tooth shape to increase the joining surface area, thereby paving the way for thermal power generation using the metals used in thermocouples. (Patent Document 3) However, the technology in Patent Document 3 is a comb-tooth shape made by joining thin plates of different metals and slitting them, so when used at high temperatures, the joint at the high-temperature end deforms and peels off from the joint end surface. To improve durability at high temperatures, it was necessary to improve the structure of the high-temperature end. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-016685 A [Patent Document 2] JP 2016-63075 A [Patent Document 3] JP 2021-40084 A [Non-patent literature]

[0008] [Non-Patent Document 1] Heat Laboratory - Let's Make a Thermocouple Battery November 2004 Hakko Electric Co., Ltd. https: / / www.hakko.co.jp / expe / new / exnew0301.htm Summary of the Invention [Problem to be solved by the invention]

[0009] As mentioned above, the Seebeck coefficient of semiconductors used for thermoelectric power generation is high, but there is an inherent problem with semiconductors that it decreases at high temperatures, and in order to solve this problem, semiconductor thermoelectric materials have been developed for many years. However, the development of semiconductor thermoelectric materials has not yet overcome the 700°C barrier. On the other hand, the metal materials used in thermocouples have a small Seebeck coefficient, and although the voltage increases when thermocouples are connected in series, the internal resistance increases at the same time, so the electromotive force hardly increases at all. For this reason, thermal power generation using thermocouple materials has not yet been put to practical use. Although the Seebeck coefficient of the metal materials used in thermocouples is low, it increases uniformly up to high temperatures of 900°C. Increasing the number of thermocouples connected in series can compensate for the low Seebeck coefficient, but in order to reduce the increased internal resistance, it is necessary to increase the number of parallel connections, so there was room for further improvement in the device structure.

[0010] The present invention has been made to solve the above-mentioned problems of the conventional technology, and has an object to provide a thermoelectric generation coil and a thermoelectric generation module that use a metal material used in thermocouples. [Means for solving the problem]

[0011] The inventors believed that even when manufacturing a thermoelectric generation coil and thermoelectric generation module using a metal material used for thermocouples, the above-mentioned problems could be solved by increasing the number of thermocouples connected in series by reducing the internal resistance, and by compensating for the weaknesses of metal materials, such as a small Seebeck coefficient and high thermal conductivity, through the device structure, making it possible to generate thermoelectric power using metals instead of semiconductors, while at the same time using a refractory structure with high high-temperature durability at the hot end, and thus arrived at the present invention.

[0012] [1] As shown in FIG. 1A, for example, a thermoelectric generating coil of the present invention comprises a metal core wire (100) made of a metal material that forms the negative leg of a thermocouple, and a tubular metal body (200) made of a metal material that forms the positive leg of the thermocouple, and a high-temperature end coaxial joint (300) that is joined so that the outer circumferential surface of the metal core wire is covered with the inner circumferential surface of the tubular metal body, a metal core wire connection part (108) that is elongated between the low-temperature end of the metal core wire and the high-temperature end coaxial joint, and a low-temperature end of the tubular metal body. and the high-temperature end coaxial joint, a tubular metal body connecting portion (208) extending long and thin between the high-temperature end coaxial joint, a cooling fin (500) connected to the low-temperature end of the tubular metal body connecting portion, and the low-temperature end of the metal core wire which is thermally joined to the low-temperature end of the tubular metal body connecting portion and electrically insulated from it are defined as a unit unit, and the electrical connection including the high-temperature end joint portion and the low-temperature end in the unit unit is repeated in series, in parallel, or in series and in parallel.

[0013] [2] In the thermoelectric generating coil [1] of the present invention, preferably, the high-temperature end coaxial joint (300) has a first region (102) of the metal core wire (100) connected to the metal core wire connection portion (108), a second region (106) connected to the tubular metal body connection portion 208, and a U-shaped or C-shaped third region (104) connecting the first region (102) and the second region (106), and the tubular metal body (200) has a fourth region (202) covering the first region (102), a fifth region (206) covering the second region (106), and a sixth region (204) covering the third region (104). [3] The thermoelectric generator coil [1] or [2] of the present invention preferably further comprises a ceramic portion (400) covering the high-temperature end coaxial joint, and a refractory brick portion (600) covering the high-temperature end coaxial joint (300) covered by the ceramic portion (400). [4] In the thermoelectric generator coil [1] of the present invention, preferably, the metal material that is the positive leg of the thermocouple is a metal material selected from the group consisting of copper, iron, aluminum, and alloys thereof, The metal material forming the negative leg of the thermocouple is preferably a constantan alloy. [5] In the thermoelectric generator coil [1] of the present invention, preferably, the metal material making up the positive leg of the thermocouple is chromel, and the metal material making up the negative leg of the thermocouple is alumel. [6] In the thermoelectric generator coil [1] of the present invention, preferably, each of the individual units further has a cooling fin (500) located in an area extending beyond the low-temperature end of the tubular metal body connection portion.

[0014] [7] The thermoelectric generation module of the present invention, as shown in FIG. 2, for example, is a unit described in [1] or [2] having a plurality of thermoelectric generation coils stacked in the stacking direction of the high-temperature end coaxial joint inside the firebrick portion described in [3]. [8] In the thermoelectric generation module [7] of the present invention, it is preferable to use a housing that houses a plurality of the thermoelectric generation coils, and an insulating filler that fills the gap between the housing and the thermoelectric generation coils, the insulating filler insulating the thermoelectric generation coils from each other and having plasticity that absorbs thermal displacement of the thermoelectric generation coils. [9] In the thermoelectric generation module [8] of the present invention, preferably, the housing is a firebrick section (600), the insulating filler is a ceramic section (400), and the thermoelectric generation coil is housed in the firebrick section together with the insulating filler to prevent high-temperature oxidation.

[10] In the thermoelectric power generation module [7] of the present invention, it is preferable that the width of the metal core wire connection part and the tubular metal body connection part described in [1] is set to a diameter φ of the high-temperature end joint part of 1 mm or more and 3 mm or less, the length of the metal core wire connection part and the tubular metal body connection part is set to 5 cm or more and 50 cm or less, and the metal core wire connection part and the tubular metal body connection part are housed in an insulating case for the connection part. Effect of the Invention

[0015] In the thermoelectric generating coil and thermoelectric generating module of the present invention, the circumferential surface of the metal core wire is bonded so as to be covered by the inner circumferential surface of the tubular metal body (coaxial bonding type), thereby increasing the bonding area between the metal core wire and the inner circumferential surface of the tubular metal body and reducing the resistance when electrons diffuse through the bonding interface, thereby increasing the electron diffusion that occurs at the bonding interface between the dissimilar metals at the high-temperature end, and increasing the electromotive force due to the electron density difference that occurs at the bonding interface between the dissimilar metals at the high-temperature end. In addition, by making the bonding part at the high-temperature end a coaxial bonding type and making the bonding surface cylindrical and not exposing the bonding end surface, it is possible to solve the problem that occurred in the structure of Patent Document 3, that when the high-temperature end is heated to a temperature of 700°C or higher, the thermal expansion difference between the dissimilar metals causes the bonding part at the high-temperature end to bend like a bimetal, and peel off from the end surface of the bonding part when the temperature changes are repeated. In addition, in the thermoelectric generation coil and thermoelectric generation module of the present invention, by providing a long and slender metal core wire connection portion and a tubular metal body connection portion, a heat transfer distance is ensured between the high-temperature end coaxial joint and the low-temperature end (the portion thermally joined to the cooling fin), and by connecting an air-cooled fin to the portion equivalent to the cold junction of the thermocouple for cooling, a structure is formed which increases the temperature difference between the portion equivalent to the cold junction and the high-temperature end of the thermocouple, thereby increasing the electromotive force due to the Seebeck effect and compensating for the problem of the high thermal conductivity of the metal for the thermocouple. [Brief description of the drawings]

[0016] [Figure 1A] 1 is a longitudinal cross-sectional view illustrating the overall structure of a pair of coaxial junction type thermoelectric coils that constitute a thermoelectric module. [Figure 1B] 1B is a cross-sectional view of the hot end coaxial joint of the thermoelectric generating coil shown in FIG. 1A. [Diagram 2] FIG. 1 is a schematic diagram of a thermoelectric module showing one embodiment of the present invention, in which (A) is a front cross section, (B) is a plan cross section in the direction of the arrow bb, and (C) is an elevation cross section in the direction of the arrow cc. [Figure 3A] FIG. 1 is a diagram showing the configuration of a main part of a thermoelectric generation module in which two pairs of coaxial junction type thermoelectric generation coils are connected, showing one embodiment of the present invention. [Figure 3B] FIG. 3B is a diagram showing cumulative changes in voltage and current generated between the negative electrode of the thermoelectric module shown in FIG. 3A and nine measurement points. [Figure 4] This shows the characteristics of a thermoelectric generation module according to one embodiment of the present invention, where (A) shows the maximum voltage of a coaxially junction type thermoelectric generation coil that increases with an increase in the high-temperature end temperature and the number of thermoelectric generation coils connected in series, and (B) shows the maximum power. [Figure 5A] FIG. 1 is a diagram showing the configuration of a main part of a thermoelectric generation module in which two pairs of coaxial junction type thermoelectric generation coils are connected in series, showing one embodiment of the present invention. [Figure 5B] 5B is a diagram illustrating the relationship between the output current, output voltage, and output power of the thermoelectric power generation module shown in FIG. 5A. FIG. [Figure 5C] FIG. 13 is a diagram showing the configuration of a main part of a comparative thermoelectric generation module in which two pairs of JIS-T type thermocouples are connected in series. [Figure 5D] 5D is a diagram illustrating the relationship between the output current, output voltage, and output power of the thermoelectric power generation module shown in FIG. 5C. FIG. [Figure 6] This is an explanatory diagram of the number of thermocouples connected in series in a coaxial junction thermoelectric coil and the temperature change in the Seebeck coefficient, where the horizontal axis is temperature and the vertical axis is the Seebeck coefficient Sv (μV / K). Unlike semiconductor thermoelectric materials such as CuGa5Te8, the Seebeck coefficient of the coaxial junction thermoelectric coil increases uniformly up to high temperatures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will now be described with reference to the drawings. Fig. 1A is a longitudinal cross-sectional view illustrating the overall structure of a pair of coaxially joined thermoelectric generating coils that constitute a thermoelectric generating module, and Fig. 1B is a cross-sectional view of the high-temperature end coaxial joint of the thermoelectric generating coils shown in Fig. 1A. The thermoelectric generating coil has as its units the metal core wire 100, the metal core wire connection portion 108, the tubular metal body 200, the tubular metal body connection portion 208, the high-temperature end coaxial joint portion 300, and the cooling fin 500. In the thermoelectric generating module of the present invention, the electrical connections including the high-temperature end coaxial joint portion 300 and the low-temperature end in the units are repeated in series, in parallel, or in series and in parallel.

[0018] The metal core wire 100 is made of a metal material that will be the negative leg of the thermocouple, and is preferably a constantan alloy, for example, a constantan wire made of the same material as the JIS-T type thermocouple, and is preferably 1.2 mm in diameter, but is not limited to this. The metal core wire 100 has a first region 102 connected to the metal core wire connecting part 108, a second region 106 connected to the tubular metal body connecting part 208, and a U-shaped or C-shaped third region 104 that connects the first region 102 and the second region 106. The first region 102 and the second region 106 are parallel to each other inside the high temperature end coaxial joint 300, and the third region 104 corresponds to a region where the metal core wire 100 is bent into a U-shape or a C-shape. The tubular metal body 200 is made of a metal material that will be the positive leg of the thermocouple, and may be a metal material selected from copper, iron, aluminum, or an alloy thereof. For example, it may be a copper tube made of the same material as the JIS-T type thermocouple, and may have an inner diameter of 1.3 mm, but is not limited to this. The tubular metal body 200 has a fourth region 202 that covers the first region 102, a fifth region 206 that covers the second region 106, and a sixth region 204 that covers the third region 104. The fourth region 202 and the fifth region 206 are parallel to each other inside the high temperature end coaxial junction 300, and the sixth region 204 corresponds to a region where the tubular metal body 200 is bent into a U-shape or a C-shape.

[0019] The high temperature end coaxial joint 300 is formed by bonding the circumferential surface of the metal core wire 100 with the inner circumferential surface of the tubular metal body 200 so as to cover the circumferential surface of the metal core wire 100. The high temperature end coaxial joint 300 may be bonded, for example, by hot isostatic pressing (HIP) to form a defect-free, three-dimensional, large-area bonded interface, and may be symmetrical so that the bonded end surface is not exposed. The high temperature end coaxial joint 300 may have a total length of, for example, 100 mm, and the gap between the metal core wire 100 and the tubular metal body 200 may be, for example, 5 mm. The metal core wire connection portion 108 is an elongated portion between the low temperature end of the metal core wire 100 (the portion thermally joined to the cooling fin 500) and the high temperature end coaxial joint portion 300. The length of the metal core wire connection portion 108 is, for example, 110 mm. The tubular metal body connecting portion 208 is an elongated portion between the low temperature end of the tubular metal body 200 and the high temperature end coaxial joint portion 300. The cooling fin 500 is connected to the low temperature end of the tubular metal body connecting portion 208. The length of the tubular metal body connecting portion 208 may be the same as the length of the metal core wire connecting portion 108, for example, 110 mm. The low-temperature end of the metal core wire 100 is thermally joined to and electrically insulated from the low-temperature end of the tubular metal body connection portion 208, thereby realizing a structure in which electrical connections including the high-temperature end coaxial joint portion 300 and the low-temperature end (the portion thermally joined to the cooling fin 500) in the individual units of the thermoelectric generating coil are repeated in series, parallel, or both series and parallel.

[0020] In a device configured in this manner, the high temperature end coaxial junction 300 is a coaxial junction type having a cylindrical, elongated junction surface rather than a contact, which reduces the internal resistance and increases the number of connections, thereby making it possible to increase the electromotive force. The metal core wire connection portion 108 and the tubular metal body connection portion 208 ensure a heat transfer distance of 100 mm or more between the high temperature end coaxial joint portion 300 and the low temperature end (the portion thermally joined with the cooling fin 500), and by connecting the air-cooling fin 500 to the portion equivalent to the cold junction of the thermocouple for cooling, the temperature difference between the portion equivalent to the cold junction and the high temperature end of the thermocouple is increased. It is preferable to reduce heat loss by keeping the metal core wire connection part 108 and the tubular metal body connection part 208 warm with a heat insulating material. Also, in order to prevent an increase in heat loss from the metal core wire connection part 108 and the tubular metal body connection part 208, which correspond to the intermediate part between the high temperature end and the low temperature end of the thermocouple, the side of the metal core wire connection part 108 and the tubular metal body connection part 208 close to the high temperature end coaxial junction part 300 is covered with a heat insulating brick part 600 to reduce heat dissipation, and the part from which heat is dissipated is limited to the low temperature end 700 and the air-cooled fins 500.

[0021] FIG. 2 is a configuration diagram of a thermoelectric module showing one embodiment of the present invention, where (A) is a front cross section, (B) is a plan cross section in the direction of the arrow bb, and (C) is an elevation cross section in the direction of the arrow cc. In addition to the thermoelectric generation coil shown in FIG. 1A , the thermoelectric generation module has a ceramic section 400 that covers the high-temperature end coaxial joint 300, and a refractory brick section 600 that covers the high-temperature end coaxial joint 300 that is covered by the ceramic section 400. According to the thermoelectric generation module of the present invention, the high-temperature end coaxial joints 300 of multiple thermoelectric generation coils are covered with a ceramic section 400 to form a durable unit, and the thermoelectric generation module is constructed by incorporating the bottoms of the multiple units into a firebrick section 600. By devising the device structure in this way, it is possible to generate thermoelectric power using general-purpose metals that are used in thermocouples.

[0022] The device shown in Fig. 2 is manufactured as follows: First, multiple thermoelectric generating coils shown in Fig. 1 are connected (six in this embodiment) and hardened with ceramic 400, and air-cooled fins 500 are connected to each low-temperature end 700 of the thermoelectric generating coil units shown in Fig. 2(B). The bottoms of multiple units (three sets in this embodiment) are assembled and fixed into firebricks 600, and the units are connected in series with lead wires to form the thermoelectric generating module shown in Fig. 2(A) and Fig. 2(C).

[0023] In a device configured in this manner, as shown in Fig. 1, a constantan wire 100 is inserted into and joined to a copper tube 200 to form a coaxially bonded thermoelectric generator coil. The other end of the constantan wire 100 is soldered to a second copper tube 200 and connected to a second coaxially bonded thermoelectric generator coil, and air-cooled fins 500 are further connected to form a cold junction 700. The coil, which has been connected in this manner multiple times (six times in this embodiment), is solidified with ceramic 400 to form a unit. Several sets of these units (three sets in this embodiment) are incorporated into a firebrick 600 and connected in series to the positive electrode with a lead wire 800 to form a thermoelectric generator module.

[0024] The operation of the thermoelectric power generation module thus formed will now be described with reference to FIG. 2(B). The heat received by the coaxial junction 300 shown in FIG. 2(B) generates a thermoelectromotive force due to the electron density difference at the cylindrical junction surface between the copper tube 200 and the constantan wire 100, and is transmitted to the constantan wire 100. During transmission to the cold junction 700, an electromotive force is generated due to the temperature difference of the constantan wire 100. At the junction surface of the cold junction 700, the electron density difference is opposite to the current direction, so a reverse electromotive force is generated, but since the junction surface is low in temperature, the back electromotive force is negligible. In the second copper tube 200 connected to the cold junction 700, the temperature difference is opposite to the current direction, so a reverse electromotive force is generated. However, since the Seebeck coefficient of copper is 1 / 10 that of constantan, the back electromotive force generated in the copper tube 200 is small and is canceled out by the electromotive force generated in the constantan wire 100. In this way, large electromotive force and small back electromotive force are generated alternately by the heat flow, and the heat flow is dissipated into the air from the air-cooling fin 500. The above mechanism is repeated the same number of times as the number of coil connections, and the accumulated thermal current flows out from the positive electrode to the external load circuit.

[0025] In order to specifically illustrate the features of the present invention, FIG. 3B shows the electromotive forces generated at each part of the thermoelectric coil when the high-temperature end is heated to 700°C, the low-temperature end is air-cooled and held at 40°C, and a resistance of 10 Ω is connected to the measurement circuit. The voltage and current measured between the negative electrode of the thermoelectric coil and the measurement terminals #1 to #9 shown in FIG. 3A increase at the measurement terminals #3 to #4 and #7 to #8, and slightly decrease at the measurement terminals #1, #2, #5, #6, and #9. Under the measurement conditions of 700°C in FIG. 3, an electromotive force of 24.4 mV is generated at the junction 300 of the high-temperature end, an electromotive force of 2.2 mV is generated at the constantan wire 100, a counter electromotive force of 0.1 mV is generated at the cold junction 700, and a counter electromotive force of 0.3 mV is generated at the copper tube 200. The electromotive force of the two pairs as a whole is 52.5 mV, which is the electromotive force of each part minus the counter electromotive force.

[0026] As described above, in principle, when two types of metal are joined and multiple junctions are connected in series, the order of the two types of metal is reversed at every other junction, and a reverse electromotive force is generated at the junctions with the reversed order, lowering the overall electromotive force. However, since the temperature of the cold junctions, where the joining order is reversed, is significantly lower than that of the hot end, the reverse electromotive force is not actually a problem. In other words, if the cold junctions are air-cooled, the voltage and current increase uniformly in proportion to the hot junction surface and the number of cold junctions connected, and the electromotive force increases with the number of thermoelectric generator coil connections and the temperature at the hot end.

[0027] Figure 4 shows the measurement results that verified the above design guidelines. As shown in Figure 4, when the number of connections of the thermoelectric coil is increased from 4 pairs to 18 pairs, which is 4.5 times, the maximum power increases by 5.7 times. In this way, the voltage and current of a thermoelectric module in which multiple thermoelectric coils of the present invention are connected increase stepwise as shown in Figure 3B, and the voltage and power increase in response to an increase in the number of connections and the high-temperature end temperature as shown in Figure 4.

[0028] Fig. 5A is a diagram showing the configuration of the main parts of a thermoelectric generation module in which two pairs of coaxial junction type thermoelectric generation coils are connected in series, showing one embodiment of the present invention. Fig. 5B is a diagram explaining the relationship between the output current, output voltage, and output power of the thermoelectric generation module shown in Fig. 5A, where the horizontal axis shows the output current, the left vertical axis shows the output voltage, and the right vertical axis shows the output power. Fig. 5C is a diagram showing the main components of a comparative thermoelectric module in which two pairs of JIS-T type thermocouples are connected in series. Fig. 5D is a diagram explaining the relationship between the output current, output voltage, and output power of the thermoelectric module shown in Fig. 5C, where the horizontal axis indicates the output current, the left vertical axis indicates the output voltage, and the right vertical axis indicates the output power. As shown in Figure 5, the internal resistance of the two pairs of thermoelectric coils was 0.2 Ω, which was reduced to 15% of the internal resistance of the two pairs of thermocouples (1.3 Ω). In other words, it was demonstrated that by reducing the internal resistance, it is possible to increase the number of connections and thus the electromotive force.

[0029] As shown in Figure 6, the Seebeck coefficient of semiconductor thermoelectric materials such as CuGa5Te8 decreases at high temperatures. In contrast, the Seebeck coefficient of a coaxial junction type thermoelectric generator coil using the thermocouple material (Cu / Constantan) increases steadily up to high temperatures. Therefore, by increasing the number of thermoelectric coil connections and using it at high temperatures, it becomes a thermoelectric conversion device with performance that exceeds that of semiconductors.

[0030] That is, in conventional thermoelectric power generation elements, materials with low thermal conductivity are used to increase the temperature difference (ΔT) between the high-temperature end and the low-temperature end, but in this invention, to cover the drawback of metals having high thermal conductivity, the theoretical formula of heat flow Q=k·ΔT·S / L is used to increase L and decrease S to compensate for the high thermal conductivity (k), increasing ΔT and decreasing the heat flow Q. Specifically, the distance between the high-temperature end and the low-temperature end is set to about 100 mm, more than 100 times longer than in the case of semiconductors, and the cross section is set to 3 mmφ or less to suppress the heat flow Q. Furthermore, an air-cooled fin is connected to the tip of the low-temperature end to lower the temperature of the low-temperature end and increase the temperature difference (ΔT).

[0031] In the above embodiment, the thermocouple is a copper-constantan wire, but the present invention is not limited to this. Thermocouples standardized in JIS C 1602 in Japan, IEC 60584 as an international standard, and ASTM E 230 as an American standard may be used. These thermocouples include precious metal thermocouples using metals with high melting points such as platinum and rhodium, and base metal thermocouples not using platinum or rhodium. There are three types of precious metal thermocouples: B thermocouple, R thermocouple, and S thermocouple, but they are not suitable for thermoelectric power generation because their thermoelectromotive force is small. There are six types of base metal thermocouples: N thermocouple, K thermocouple, E thermocouple, J thermocouple, T thermocouple, and C thermocouple. Here, the T thermocouple is a thermocouple with a + leg made of pure copper and a - leg made of an alloy (constantan) mainly composed of nickel and copper, which has a small electrical resistance and is most suitable for thermoelectric power generation. A K thermocouple has a positive leg made of a nickel-chromium alloy (chromel) and a negative leg made of a nickel-aluminum alloy (alumel). A J thermocouple has a positive leg made of iron and a negative leg made of a nickel-copper alloy (constantan). A C thermocouple has a positive leg made of a tungsten-rhenium alloy with 5% rhenium and a negative leg made of a tungsten-rhenium alloy with 26% rhenium. There are two other base metal thermocouples that are not suitable for thermoelectric power generation because of their high electrical resistance: Type E thermocouples have a positive leg made of an alloy mainly of nickel and chromium (chromel) and a negative leg made of an alloy mainly of nickel and copper (constantan). Type N thermocouples have a positive leg made of an alloy mainly of nickel, chromium and silicon (nicrosil) and a negative leg made of an alloy mainly of nickel and silicon (nisil). [Industrial Applicability]

[0032] The thermoelectric coil and thermoelectric module of the present invention enable thermoelectric generation using safe, inexpensive, general-purpose metal thermoelectric materials without using harmful semiconductors such as bismuth telluride (Bi2Te3), and make it possible to utilize high-temperature waste heat of over 700°C, which was not possible with conventional semiconductor thermoelectric materials. Furthermore, the thermoelectric coil and thermoelectric module of the present invention do not compete with the development of conventional thermoelectric materials such as semiconductors, but are a technology that maximizes the performance of thermoelectric materials by optimizing the device structure and dimensions, and will contribute to the development and spread of thermoelectric power generation. [Explanation of symbols]

[0033] 100, 102, 104, 106 Constantan wire 108 Metal core wire connection part (Constantan wire) 200, 202, 204, 206 copper tube 208 Tubular metal body connection part (copper tube or copper wire) 300 coaxial joint 400 Ceramic 500 Air Cooling Fin 600 Firebricks 700 cold junction 800 Leads 900 Measuring terminals (#1~#9)

Claims

1. a high-temperature end coaxial joint (300) including a metal core wire (100) made of a metal material that becomes the negative leg of a thermocouple and a tubular metal body (200) made of a metal material that becomes the positive leg of the thermocouple, the high-temperature end coaxial joint (300) being joined so that the circumferential surface of the metal core wire is covered by the inner circumferential surface of the tubular metal body; a metal core wire connection portion (108) extending elongatedly between the low temperature end of the metal core wire and the high temperature end coaxial joint portion; a tubular metal body connection portion (208) extending elongately between the cold end of the tubular metal body and the hot end coaxial joint; A cooling fin (500) connected to the low-temperature end of the tubular metal body connecting portion; a low-temperature end of the metal core wire that is thermally joined to and electrically insulated from the low-temperature end of the tubular metal body connecting portion; a thermoelectric generating coil having a plurality of unitary units each including a high-temperature end joint and a low-temperature end, the unitary units each having an electrical connection repeated in series, in parallel, or in series and in parallel.

2. The hot end coaxial joint (300) comprises: The metal core wire (100) has a first region (102) connected to the metal core wire connecting portion 108, a second region (106) connected to the tubular metal body connecting portion (208), and a U-shaped or C-shaped third region (104) connecting the first region (102) and the second region (106), The tubular metal body (200) has a fourth region (202) covering the first region (102), a fifth region (206) covering the second region (106), and a sixth region (204) covering the third region (104).

2. The thermoelectric generating coil according to claim 1 .

3. moreover, a ceramic portion (400) covering the hot end coaxial joint; 3. The thermoelectric generating coil according to claim 1, further comprising a refractory brick portion (600) covering the high-temperature end coaxial joint portion (300) covered with the ceramic portion (400).

4. The metal material that is the positive leg of the thermocouple is a metal material selected from copper, iron, aluminum, or an alloy thereof, 4. The thermoelectric generating coil according to claim 1, wherein the metal material forming the negative leg of the thermocouple is a constantan alloy.

5. The metal material that is the positive leg of the thermocouple is chromel, 4. The thermoelectric generating coil according to claim 1, wherein the metal material that forms the negative leg of the thermocouple is alumel.

6. The thermoelectric generating coil according to any one of claims 1 to 5, characterized in that the unit further has a cooling fin (500) located in an area extending beyond the low-temperature end of the tubular metal body connection portion.

7. 4. A thermoelectric module, comprising: a unit unit according to claim 1 or 2, the unit unit having a plurality of thermoelectric coils stacked in the stacking direction of the high-temperature end coaxial joint inside the refractory brick portion according to claim 3.

8. a housing that houses a plurality of the thermoelectric generating coils; The thermoelectric module according to claim 7, characterized in that the housing and the thermoelectric coils are integrated using an insulating filler that fills the gap between the housing and the thermoelectric coils, insulating the thermoelectric coils from each other and having plasticity that absorbs thermal displacement of the thermoelectric coils.

9. The housing is a refractory brick section (600), The insulating filler is a ceramic portion (400); 9. The thermoelectric module according to claim 8, wherein the thermoelectric coil is housed in the refractory brick section together with the insulating filler to prevent high-temperature oxidation.

10. The metal core wire connection part and the tubular metal body connection part according to claim 1 have a diameter of 1 mm or more and 3 mm or less, The length of the metal core wire connecting portion and the tubular metal body connecting portion is set to 5 cm or more and 50 cm or less, 10. The thermoelectric generation module according to claim 7, wherein the metal core wire connection portion and the tubular metal body connection portion are housed in a connection portion insulating case.

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