JP7396621B2 - Thermoelectric cells and thermoelectric modules - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thermoelectric generating cell and a thermoelectric generating module using a metal thermoelectric material.

The need of the times is to use waste heat to reduce environmental impact, and the Seebeck effect, which generates an electromotive force when a temperature difference is created between the ends of dissimilar metals or semiconductors, is an energy-saving method that directly converts thermal energy into electricity. There is a need for thermoelectric materials with a large Seebeck effect.

Thermoelectric materials have a large Seebeck coefficient, which indicates the magnitude of the Seebeck effect, and because electrons are carriers of electricity as well as carriers of heat, thermoelectric materials have low thermal conductivity and high electrical conductivity. Off-related properties are required, and a bismuth-tellurium alloy (Bi ₂ Te ₃ ) having these properties is used as a thermoelectric material even though it is harmful.

For example, in a semiconductor thermoelectric material, carriers (electrons and holes) that have increased kinetic energy in a high temperature region diffuse to a lower temperature region, generating an electromotive force. Since the potential difference between n-type and p-type semiconductors is opposite, it is common to generate thermal power by connecting multiple pn-p π-type structures in which n-type and p-type semiconductors are alternately connected via metal electrodes. (for example, Patent Document 1).

On the other hand, since the only carriers in metals are electrons, metals cannot have a π-type structure like semiconductors. When multiple metal thermocouples are connected in series, positive and negative electromotive force parts are generated alternately. Furthermore, the Seebeck coefficient of metals is much smaller than that of semiconductors. Therefore, metal thermoelectric materials are not used for thermal power generation except for special purposes, but are generally used as materials for thermocouples that measure temperature.

In principle, the kinetic energy of electrons increases in the high temperature part of the metal and diffuses to the low temperature side, causing the Seebeck effect, which is the same as in semiconductors, and it is possible to generate thermal power using the metal material of the thermocouple. . However, when multiple thermocouples are connected, the internal resistance increases and the current does not increase much. In other words, if technology can be developed to reduce internal resistance, it will become possible to generate thermal power using metal materials for thermocouples.

The characteristics required for thermocouples used for temperature measurement include stable generation of a voltage proportional to temperature, wide measurement range, and durability, and low current is not a problem. Therefore, no technology has been developed to reduce the internal resistance of thermocouples, which is the cause of low current flow.
Under the above circumstances, in order to popularize environmentally friendly thermal power generation as a countermeasure against global warming, it is necessary to use safe materials such as those used in thermocouples instead of expensive and toxic materials such as Bi ₂ Te ₃ . Thermoelectric power generation using general-purpose thermoelectric materials is necessary.

As a prior art of thermoelectric power generation using metal thermoelectric materials, for example, Patent Document 2 discloses a series thermocouple in which two different metal members are arranged alternately and connected in a zigzag shape, and a plurality of thermocouple elements are connected. We are proposing a hot-air infrared stove that generates hot air by heating the high-temperature side with an infrared stove and cooling the low-temperature side with a small fan driven by thermally generated electricity. This technical innovation uses an insulating spacer to prevent contact with neighboring thermocouples, and at the same time creates a space between the thermocouples to increase the cooling effect of the fan and suppress the temperature rise on the low-temperature side. The purpose of this is to secure a temperature difference between the fans and generate the electricity necessary to drive the fan, and no special measures have been taken to reduce internal resistance.
Patent Document 3 proposes a structure that effectively increases the number of connections by increasing the bonding area at the high temperature end and reducing internal resistance. However, the effect is limited, and if the number of connections is increased to 100 or more pairs, the internal resistance increases, causing a problem in which the increase in power reaches a ceiling.

JP2013-016685A Japanese Patent Application Publication No. 2003-124533 International publication WO2018/180131A1

When thermocouples used for temperature measurement are connected in series, the voltage increases, but at the same time the internal resistance increases and the current does not increase much, so it is generally accepted among those skilled in the art that thermocouples cannot effectively generate heat. It has been.
In order to solve the above-mentioned problems, the present invention aims to review the device structure of thermoelectric power generation by going back to its principles, and to provide a thermoelectric conversion device using a safe and general-purpose metal thermoelectric material used in thermocouples. purpose.

In order to compensate for the weak point of metal's small Seebeck coefficient, the inventors first developed a method for generating thermoelectric power using metal thermoelectric materials used in thermocouples. In contrast to the wire, we used a strip-shaped thin plate with a thickness of 0.1 to 1 mm and a width of 3 to 6 mm, and then created a comb-like structure in which three layers were bonded at the high-temperature end with a length of 9 to 12 cm to increase the bonding area. By increasing the number of thermocouples and reducing the internal resistance, it was possible to increase the voltage and current and increase the electromotive force by increasing the number of thermocouples connected.
Next, as shown in Table 1, in order to compensate for the weakness that metals have high thermal conductivity, the temperature at the low temperature end rises and the temperature difference with the high temperature end becomes small, resulting in a small electromotive force, we Focusing on the fact that the resistance is three orders of magnitude lower than that of semiconductors such as BiTe, we made the distance between the high-temperature end and the low-temperature end more than 10 times longer than in the case of semiconductors, and made the board width at the middle part the same as the board width at the high-temperature end. By narrowing the tube to 1/10 of that, the structure substantially suppresses heat conduction and cools the low-temperature end to below 60 degrees Celsius.
In addition, by taking advantage of the fact that the Seebeck coefficient of metal thermoelectric materials does not decrease at high temperatures, it was possible to obtain an electromotive force that exceeds that of semiconductor thermoelectric materials by raising the high temperature end to 500°C or higher.

In other words, rather than satisfying the conditions of "large Seebeck coefficient, low thermal conductivity, and high electrical conductivity" required for thermoelectric materials by material properties, we rely on the excellent workability and electrical conductivity of metals. By creating a structure that takes advantage of its large size, the above conditions are met through the function of the structure, and furthermore, by taking advantage of the fact that the Seebeck coefficient of metal materials does not decrease at high temperatures, high-output thermal power generation can be achieved by using it at high temperatures. This is a feature of the present invention.

[1] The thermoelectric generation cell of the present invention comprises: a comb-shaped metal thin plate made of a metal material that serves as the + leg of the thermocouple; a comb-teeth shaped intermediate metal thin plate made of a metal material that serves as the - leg of the thermocouple; A high-temperature end joint made of a three-layer laminate formed by joining three layers of a comb-shaped metal thin plate and a backing metal thin plate made of the same metal material,
The comb-shaped metal thin plate, the comb-shaped intermediate metal thin plate, and the backing metal thin plate each have a comb-shaped structure having a plurality of teeth with slits formed in a base provided therein, The tooth portions have a shape that overlaps each other, and the thickness of each tooth portion is 0.1 to 2 mm ,
Each tooth of the comb-shaped thin metal plate has a conductive portion that is electrically connected to each corresponding tooth of the backing thin metal plate,
the base portions provided on each of the comb-shaped metal thin plate, the comb-shaped intermediate metal thin plate, and the backing metal thin plate are directly electrically insulated from each other;
a connecting portion having one end provided at the base of the comb-tooth-shaped metal thin plate and the comb-tooth-shaped intermediate metal thin plate, and extending into an elongate on a side of the base opposite to the side where the plurality of teeth are provided;
a low-temperature end formed by electrically insulating and thermally bonding the comb-shaped metal thin plate and the comb-shaped intermediate metal thin plate at the tip of the connecting portion;
is a unit, and the electrical connection including the high-temperature end joint and the low-temperature end in the unit is repeated in series, in parallel, or in series and parallel.

[2] In the thermoelectric power generation cell of the present invention, preferably, the conductive portion is connected to a tip of each tooth of the comb-shaped metal thin plate and a tip of each corresponding tooth of the lining metal thin plate. are connected in a U-shape or a U-shape, or are preferably bent integrally.
[3] In the thermoelectric power generation cell of the present invention, preferably, the conductive portion is between the slit-side side surface of each tooth of the comb-shaped metal thin plate and the slit side of each corresponding tooth of the backing metal thin plate. The side surfaces may be connected in a U-shape or U-shape, or may be bent or curved integrally.
[4] In the thermoelectric generation cell of the present invention, preferably, the metal material serving as the + leg of the thermocouple is a metal material selected from copper, iron, aluminum, or an alloy thereof, and the - leg of the thermocouple The metal material used is preferably a constantan alloy.
[5] In the thermoelectric generation cell of the present invention, preferably, the metal material forming the + leg of the thermocouple is chromel, and the metal material forming the - leg of the thermocouple is preferably alumel.
[6] In the thermoelectric power generation cell of the present invention, preferably, the unit further includes cooling fins located in a region extending beyond the low temperature end of the comb-shaped thin metal plate.

[7] The thermoelectric power generation module of the present invention is characterized in that the unit unit includes a plurality of the thermoelectric power generation cells stacked in the stacking direction of the high-temperature end joint made of the three-layer laminate.
[8] The thermoelectric generation module of the present invention preferably includes a casing that accommodates a plurality of the thermoelectric cells, and an insulating filler that fills a gap between the casing and the thermoelectric cells, It is preferable that the power generation cells be integrated using the insulating filler having plasticity that insulates each other and absorbs thermal displacement of the thermoelectric power generation cells.
[9] In the thermoelectric generation module of the present invention, preferably, the casing is a heat-resistant case, and the thermoelectric generating cell is housed in the heat-resistant case together with the insulating filler to prevent high-temperature oxidation.
[10] In the thermoelectric power generation module of the present invention, preferably, the width of the connecting portion is 1/50 or more and 1/5 or less of the width of the high temperature end joint, and the length of the connecting portion is 5 cm or more and 50 cm or less. It is preferable that the connecting portion is housed in a heat insulating case for the connecting portion.
The width of the connecting portion is set to 1/50 or more and 1/5 or less of the width of the high-temperature end joint to suppress heat flow, preferably 1/20 or more and 1/8 or less, and more preferably 1/12 or more. It is preferable to set it to 1/10 or less. The length of the connecting portion is set to 5 cm or more and 50 cm or less to maintain the temperature at the low temperature end close to room temperature, and preferably 10 cm or more and 20 cm or less. By accommodating the connecting portion in the connecting portion heat insulating case, heat loss can be reduced.

According to the thermoelectric power generating module of the present invention, it is possible to obtain a high output thermoelectric power generating module that utilizes high temperature energy of 900° C., exceeding the 600° C. barrier that conventional semiconductor thermoelectric materials have not been able to overcome.

The present invention enables thermal power generation using safe and inexpensive thermoelectric materials by replacing some of the material properties necessary for thermal power generation with the functions of the device structure. Rather than competing with other material developments, the goal is to develop and popularize thermoelectric power generation through a device structure that maximizes the performance of general-purpose thermoelectric materials.

1 is an exploded view of essential parts of a comb-tooth type thermoelectric power generation unit showing an embodiment of the present invention, including a comb-teeth type metal thin plate 1, a comb-teeth type intermediate metal thin plate 2, and a backing metal thin plate 3. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a thermoelectric power generating cell according to an embodiment of the present invention, showing a thermoelectric generating cell in which comb-shaped thermoelectric generating units are stacked. FIG. 1 is a sectional view of a thermoelectric power generation module showing an embodiment of the present invention. This figure compares the electromotive force between the thermoelectric power generation module of the present invention and a conventional semiconductor thermoelectric material, where the horizontal axis shows temperature and the vertical axis shows thermoelectromotive force. FIG. 3 is a diagram showing an example of measurement of electromotive force and back electromotive force within a thermoelectric generation cell showing an embodiment of the present invention. FIG. 3B is an explanatory diagram of measurement terminal numbers shown in FIG. 3A. FIG. 3 is a diagram showing the influence of the joining length of the high temperature end on the internal resistance of the thermoelectric power generation unit. This is an explanatory diagram of the structure and thermoelectric power generation characteristics of a copper/constantan thermoelectric power generation unit in the case of four pairs of 0.3 mmΦ thermocouples (comparative example 1), where black diamonds ◆ indicate thermovoltage and load current, and white circles indicate thermogenic Shows power. FIG. 7 is an explanatory diagram of thermoelectric power generation characteristics in a case where there are four pairs of thermoelectric power generating units (comparative example 2) with high temperature end joints of 3×120 mm. FIG. 7 is an explanatory diagram of thermoelectric power generation characteristics in a case where there are 144 pairs of thermoelectric power generating units each having a high temperature end joint portion of 3×120 mm (Comparative Example 3). FIG. 3 is an explanatory diagram of thermoelectric power generation characteristics when 48 pairs x 3 sets of thermoelectric power generating units with high temperature end joints of 3 x 120 mm are arranged in parallel (Comparative Example 4).

Definition of technical terms used in this specification Regarding thermocouples, the standard is defined by JIS C1602.
・Seebeck coefficient When a temperature difference is applied across a metal or semiconductor, a voltage proportional to the temperature difference is generated, and the proportional coefficient between the temperature difference and the voltage is called the Seebeck coefficient. The Seebeck coefficient has the property of changing depending on temperature, and the sign is negative when the main carriers that carry electricity are electrons, and positive when the main carriers are holes. The unit is V/K, but since the Seebeck coefficient for metals is about 10 ⁻⁶ V/K and for semiconductors about 10 ⁻⁴ V/K, μV/K is usually used as the unit.
・Absolute Seebeck coefficient refers to the Seebeck coefficient of a single material to be measured. By making one of the thermocouple wires superconducting, the absolute Seebeck coefficient of the other wire can be directly measured.
・The relative Seebeck coefficient includes contributions from the Seebeck coefficients of the material to be measured and the material of the measurement electrode. This is because in order to measure thermoelectric voltage, it is necessary to place the electrode attached to the voltmeter on the material, and the temperature gradient also induces thermoelectric voltage at one terminal of the measuring electrode of the voltmeter.

Hereinafter, the structure of the thermoelectric power generation cell according to the present invention will be explained using FIG. 1.
FIG. 1A is an exploded view of the main parts of a comb-tooth type thermoelectric power generation unit showing an embodiment of the present invention, including a comb-tooth type metal thin plate 1, a comb-teeth type intermediate metal thin plate 2, and a backing metal thin plate 3. ing.
In FIG. 1A, the thermoelectric power generation unit according to the present invention includes a comb-shaped metal thin plate 1, a comb-shaped intermediate metal thin plate 2, and a backing metal thin plate 3.

The comb-shaped metal thin plate 1 is a thin plate made of copper, for example, and has a length L of 100 to 500 mm and a thickness t of 0.1 to 2 mm. The reason why the thickness is limited to a numerical value is that if the thickness is 0.1 mm or less, bonding becomes difficult, and if the thickness is 2 mm or more, the number of laminated layers decreases, so that an effective thermoelectric current cannot be obtained. The comb-shaped metal thin plate 1 has a tooth portion (high temperature side joint portion) 1a, a base portion 1b, a connecting portion 1c, a low temperature side joint portion 1d, and a fan-shaped enlarged portion 1e.
The tooth portion 1a has a length obtained by subtracting the width of the base portion 1b from the length _LH of the thin metal backing plate 3. For example, if the width of the base portion 1b is 5 mm, the length of the tooth portion 1a is 45 to 95 mm. It has become. The thickness of the tooth portion 1a is approximately the same as the thickness t of the comb-shaped thin metal plate 1. By providing slits between adjacent teeth 1a, generation of eddy currents is prevented.
The base 1b has the rigidity to hold the teeth 1a, and the number of teeth 1a is preferably about 5 to 25, for example. The spacing between adjacent teeth 1a is, for example, a comb structure with 1 mm wide slits. The connecting portion 1c prevents excessive heat flow between the temperature of the tooth portion (high temperature side joint) 1a (for example, 700°C to 900°C) and the temperature of the low temperature side joint 1d (for example, room temperature). In order to prevent this, it is preferable to have a cross-sectional shape that is approximately the same as the tooth portion (high-temperature side joint portion) 1a, for example, but the present invention is not limited to this. The low temperature side junction portion 1d corresponds to a low temperature side contact of a thermocouple. The fan-shaped enlarged portion 1e is located on the tip side of the low temperature side joint portion 1d, and forms an air cooling fin 6.
The comb-shaped thin metal plate 1 is not limited to a thin plate made of copper, but may be a thin plate made of a metal used for a thermocouple, such as iron or chromel. Here, chromel is an alloy consisting of 89% nickel (Ni), 9.8% chromium (Cr), 1% iron (Fe), and 0.2% manganese (Mn). The comb-shaped metal thin plate 1 may be made of copper alloy, iron alloy, or aluminum alloy.

The comb-shaped intermediate metal thin plate 2 is a thin plate of constantan or alumel, for example, and has a length L of 100 to 500 mm and a thickness t of 0.1 to 2 mm. The reason why the thickness of the comb-shaped intermediate metal thin plate 2 is limited to a numerical value is the same as the tooth portion (high temperature side joint portion) 1a of the comb-shaped metal thin plate 1.
The comb-shaped intermediate metal thin plate 2 has a tooth portion (high temperature side joint portion) 2a, a base portion 2b, a connecting portion 2c, and a low temperature side joint portion 2d. The tooth portion 2a and the base portion 2b are shaped so that the tooth portion 1a and the base portion 1b overlap each other. Constantan is an alloy consisting of 55% copper and 45% nickel. Constantan has an elemental composition determined for thermocouples, but constantan-based alloys containing constantan may be used for thermoelectric power generation. For constantan-based alloys, Cu _x Ni _1-x (0.5≦x≦0.6: mass ratio) is sufficient as a copper-nickel-based binary alloy, and Cu as a copper-nickel-manganese-based ternary alloy. It may be _x Ni _1-xy Mn _y (0.5≦x≦0.6, 0.005≦y≦0.03: mass ratio). Alumel is an alloy having a composition of 94% nickel (Ni), 2.5% manganese (Mn), 2% aluminum (Al), 1% Si (silicon), and 0.5% iron (Fe).

The backing thin metal plate 3 is a thin plate made of copper, for example, and has a length _LH of 50 to 100 mm and a thickness of 0.1 to 2 mm. The reason for limiting the numerical value to the thickness t of the thin metal backing plate 3 is the same as that for the tooth portion (high temperature side joint portion) 1a of the thin metal backing plate 3. The thin metal backing plate 3 has a tooth portion (high temperature side joint portion) 3a and a base portion 3b. The length _LH of the thin metal backing plate 3 corresponds to the length of the three-layer laminate 4, and the entire length _LH constitutes the high-temperature side joint.
Note that the backing metal thin plate 3 is preferably made of the same material as the comb-shaped metal thin plate 1. In terms of mechanical design, the two-layer structure of the comb-shaped metal thin plate 1 and the comb-shaped intermediate metal thin plate 2 made of copper and constantan thermally deforms like a bimetal when exposed to high temperatures. Therefore, we created a three-layer structure in which copper thin plates are bonded to the front and back sides of the constantan thin plate, and we designed the lining metal thin plate 3 to compensate for the thermal deformation caused by the comb-shaped metal thin plate 1 and the comb-shaped intermediate metal thin plate 2. Determine the thickness to suppress bimetal-like thermal deformation. Further, in the thin metal backing plate 3, slits are provided between the teeth 3a to prevent generation of eddy currents.

The three-layer laminate 4 of comb-shaped metal thin plates is one in which tooth portions 1a, tooth portions 2a, and tooth portions 3a are integrally laminated. By integrally joining the teeth 1a, 2a, and 3a, the thermoelectric power generation area generated at the bonding surface of the two-layer structure made of copper and constantan is the same as that of the bonding surface of the teeth 1a and 2a. There are two joining surfaces of the toothed portion 2a and the toothed portion 3a. Therefore, when both of these joint surfaces are electrically connected, the electric power generated by thermoelectric generation increases, for example, twice as much as when compared to a one-sided contact between the tooth portions 1a and 2a.
As the conductive portion that conducts these two joint surfaces, for example, for the tooth portion 1a and the tooth portion 3a, the tips of the corresponding tooth portions may be connected in a U-shape or a U-shape. . Alternatively, the tooth portions 1a and 3a may be bent integrally so that one metal thin plate sandwiches the tip of the tooth portion 2a of the comb-shaped intermediate metal thin plate 2.
Further, the conductive portions that conduct the two joint surfaces are, for example, the slit-side side surface of each tooth portion 1a of the comb-shaped thin metal plate 1 and the slit side of each corresponding tooth portion 3a of the backing thin metal plate 3. The side surfaces may be connected in a U-shape or a U-shape. Alternatively, the tooth portions 1a and 3a may be bent or curved integrally so that one metal thin plate sandwiches the slit-side side surface of the tooth portion 2a of the comb-shaped intermediate metal thin plate 2. The slit-side side surfaces of the toothed intermediate thin metal plate 2 between which the toothed portions 2a are sandwiched may be either both sides or one side.

Various joining techniques can be employed to join the tooth portions 1a, 2a, and 3a, such as solid phase diffusion, brazing, adhesive, welding, and pressure bonding. However, since copper and copper alloy form a perfect solid solution, it is desirable that no third element is present at the bonding interface because they form the high-temperature side bond of the thermoelectric power generation cell. good. Brazing has a problem in that the heat resistance is usually as low as 600°C. With adhesives, the effects of impurities such as organic compounds are unknown, with welding, there are large variations in the shape of the interface, and with ordinary pressure bonding, there is a risk of delamination due to insufficient strength at high temperatures.
Note that the three-layer laminate 4 of the comb-shaped metal thin plates has a structure in which the base portion 1b, the base portion 2b, and the base portion 3b are directly electrically insulated from each other, so that they are not directly joined to each other. . Since the base portions 1b, 2b, and 3b are electrically insulated from each other, generation of eddy currents can be prevented. The three-layer laminate 4 of comb-shaped metal thin plates has a structure in which the base 1b, the base 2b, and the base 3b are not directly joined to each other, but through the joining of the teeth 1a, the teeth 2a, and the teeth 3a. It has a mechanically integrated structure.

FIG. 1B is a perspective view showing a thermoelectric power generation cell according to an embodiment of the present invention, and shows a thermoelectric power generation cell in which comb-shaped thermoelectric power generation units are stacked.
In FIG. 1B, a thermoelectric power generation cell 7 according to the present invention includes a three-layer laminate 4 (high-temperature end joint 4) of comb-shaped thin metal plates to be heated of a thermoelectric power generation unit, a low-temperature end contact 5, and a heat dissipation section. The air cooling fins 6 are provided in the air cooling fins 6.
The three-layer laminate 4 of comb-shaped metal thin plates includes a comb-shaped metal thin plate 1, a comb-shaped intermediate metal thin plate 2, and a tooth portion (high-temperature side joint) 1a of a comb-shaped metal thin plate 2, and a tooth portion (high-temperature side joint) part) 2a and tooth part (high temperature side joint part) 3a are integrally laminated, and constitute the high temperature end/joint part of the thermoelectric power generation unit. Further, the low-temperature side joint portion 2d of the comb-shaped intermediate metal thin plate 2 is joined to the low-temperature side joint portion 1d of the comb-shaped metal thin plate 1 of the adjacent thermoelectric generation unit to form a low-temperature end contact 5. The fan-shaped enlarged portion 1e of the comb-shaped thin metal plate 1 forms air cooling fins 6 to naturally cool the low temperature end to, for example, 60° C. or lower, preferably to about room temperature.

In the three-layer laminate 4 of comb-shaped metal thin plates, the single cellular three-layer laminate 4 has teeth (high temperature side joint) 1a, teeth (high temperature side joint) 2a, teeth (high temperature side The joint portion 3a is integrally laminated and has a thickness t and a width w. The distance between a single cellular three-layer laminate 4 and the adjacent cellular three-layer laminate 4 is Δt in the thickness direction and Δw in the width direction. It is preferable that an insulating filler 8 be filled in the space between a single cellular three-layer laminate 4 and an adjacent cellular three-layer laminate 4.
In addition, in the three-layer laminate 4 of comb-shaped metal thin plates, the single cell-shaped three-layer laminate 4 has a structure in which the base 1b, the base 2b, and the base 3b are not directly mechanically joined to each other. , has a mechanically integrated structure through the joining of the tooth portions 1a, 2a, and 3a. As another joining mode, in the single cellular three-layer laminate 4, the base 1b, the base 2b, and the base 3b are directly mechanically joined to each other, but an electrically insulated state is ensured. Therefore, an insulating film may be formed between each layer of the base 1b, the base 2b, and the base 3b.

In the device configured as described above, each feature specific to the invention of the thermoelectric generating cell has the following effects.
A plurality of high-temperature end joints 4 (10 in FIG. 1A) are formed in a part where three layers of the comb-shaped metal thin plate 1/comb-shaped intermediate metal thin plate 2/backing metal thin plate 3 are stacked and bonded in the order shown in FIG. 1A. ) By creating a comb structure with 1 mm wide slits, the bonding area between copper and constantan is increased and the internal resistance is reduced. Furthermore, by forming a slit in the long and narrow area of the bonding surface between copper and constantan, it is possible to prevent the generation of eddy currents.

FIG. 1C is a cross-sectional view of a thermoelectric power generation module showing one embodiment of the present invention.
In the thermoelectric power generation module shown in FIG. 1C, a thermoelectric power generation cell 7 in which a plurality of thermoelectric power generation units (eight units in FIG. 1B) are connected is placed in a heat-resistant case 9, filled with an insulating filler 8, and fixed. There is.

The insulating filler 8 is preferably one that has plasticity and does not degenerate even at the temperature of the high-temperature end joint 4 (eg, 700° C. to 900° C.). The insulating filler 8 is preferably an inorganic material such as magnesia, zirconia, alumina, etc., which has an insulating property of about 1 kV/mm, as well as plasticity and heat resistance to absorb thermal deformation between laminated layers.

The operation of the device configured in this manner will be described next.
The heat received at the high-temperature end joint 4 shown in FIG. is emitted into the atmosphere. The generated thermoelectrons flow to the high-temperature end joint 4 via the comb-shaped thin metal plate 1 of the next thermoelectric power generation unit, and repeat the generation of thermoelectromotive force. In the thermoelectric power generation cell, the above mechanism is repeated as many times as the number of stacked units, and an increased thermal current flows from the positive electrode to the external load circuit.
Therefore, in the thermoelectric generation cell of the present invention, the electrical connection including the high temperature end joint and the low temperature end in the unit constituting the thermoelectric generation cell may be repeated in series, in parallel, or in series and parallel. It becomes possible. Therefore, by selecting the electrical connections of the units that make up the thermoelectric power generation cell so that the output voltage and output current in thermoelectric power generation are optimal values, the optimal thermoelectric power generation characteristics can be achieved for the required amount of power generation. It is possible to construct a thermoelectric power generation cell having the following.

FIG. 2 compares the electromotive force between the thermoelectric power generation module of the present invention shown in FIG. 1C and a pair of BiTe-based semiconductors, which are conventional semiconductor thermoelectric materials. Shows electromotive force.
Whereas the thermoelectromotive force of the BiTe system decreases at 400°C, the thermoelectromotive force of the thermoelectric generation module of the present invention increases up to 900°C. Although the number of connected logs is different, the thermoelectromotive force of the BiTe system is larger in the (A) low temperature range of 400°C or lower, but in the (B) high temperature range of 500°C or higher, the thermoelectric power generation module of the present invention consisting of 30 pairs The thermoelectromotive force will be larger, and it will become possible to generate high-output thermal power generation using high-temperature energy at 900°C, exceeding the 600°C barrier that conventional semiconductor thermoelectric materials have been unable to overcome.

FIG. 3A is a diagram illustrating an example of measurement of electromotive force and back electromotive force within a thermoelectric generation cell according to an embodiment of the present invention. In FIG. 3A, the generation status of electromotive force within the thermoelectric generation cell is shown for each measurement terminal of each unit.

FIG. 3B is an explanatory diagram of measurement terminal numbers shown in FIG. 3A. Reference numeral #1 denotes a measurement terminal provided near the negative electrode of the connecting portion 1c of the comb-shaped thin metal plate 1 in the first pair of thermoelectric power generating units connected to the negative electrode of the thermoelectric generating cell. Reference numeral #2 is a measurement terminal provided at the high-temperature end joint 4 of the comb-shaped metal thin plate 1 in the first pair of thermoelectric generation units. Reference numeral #3 is a measurement terminal provided near the high-temperature end joint 4 of the connecting portion 2c of the comb-shaped intermediate metal thin plate 2 in the first pair of thermoelectric power generation units. Reference numeral #4 is a measurement terminal provided in the vicinity of the low-temperature end contact 5 of the connecting portion 2c of the comb-shaped intermediate metal thin plate 2 in the first pair of thermoelectric generation units.

Reference numeral #5 denotes a measurement terminal provided near the low-temperature end contact 5 of the connecting portion 1c of the comb-shaped thin metal plate 1 in the second pair of thermoelectric generator units connected to the negative electrode of the thermoelectric generator cell. Reference numeral #6 is a measurement terminal provided at the high-temperature end joint 4 of the comb-shaped thin metal plate 1 in the second pair of thermoelectric generation units. Reference numeral #7 is a measurement terminal provided in the vicinity of the high-temperature end joint portion 4 of the connecting portion 2c of the comb-shaped intermediate metal thin plate 2 in the second pair of thermoelectric generation units. Reference numeral #8 is a measurement terminal provided near the low-temperature end contact 5 of the connecting portion 2c of the comb-shaped intermediate metal thin plate 2 in the second pair of thermoelectric generation units.
Reference numeral #9 denotes a measurement terminal provided near the low-temperature end contact 5 of the connecting portion 1c of the comb-shaped thin metal plate 1 in the third pair of thermoelectric generator units connected to the negative electrode of the thermoelectric generator cell. Note that the measurement terminals after the third pair of thermoelectric power generation units are omitted from illustration.

In the device configured in this way, the voltage and current between the positive electrode of the thermoelectric power generation cell and the measurement terminal of each unit are determined stepwise by the terminal numbers #2-#4 and #6-#8 shown in FIG. 3A. It increases as follows. That is, terminal numbers #2-#4 and #6-#8 shown in FIG. 3A correspond to the copper/constantan bonding surface and the constantan thin plate part, and thermoelectromotive force is generated (22.4 mV + 2.16 mV). . On the other hand, terminal numbers #1-#2, #4-#6, and #8-#9 shown in Figure 3A correspond to the constantan/copper joint surface and the thin copper plate, and a slight back electromotive force is generated. (-0.06mV-0.34mV). The ratio of thermoelectromotive force to reverse thermoelectromotive force is 1:0.016.

Semiconductor thermoelectric materials have electrons and holes as carriers, but metals have only electrons as carriers. Therefore, when a plurality of thermoelectric power generation units are connected, in principle, positive and negative electromotive force parts are generated alternately, and the positive and negative electromotive forces cancel each other out. However, in the device structure of the present invention, as shown in Table 1, the relative Seebeck coefficient (43 μV) between copper and constantan is small, and in the measurement example shown in FIG. 3A, the back electromotive force (- 0.06 mV) is very small compared to the electromotive force (24.4 mV) generated at the high temperature end and can be ignored. Similarly, the fact that the absolute Seebeck coefficient of copper (4 μV) is 1/10 smaller than that of constantan (47 μV) is effective, and the back electromotive force (-0.34 mV) generated in the copper part is smaller than that of constantan. This is sufficiently small compared to the electromotive force (2.16 mV) generated in the area. As a result, as in the measurement example shown in FIG. 3 in which two pairs of thermoelectric power generation units are connected, the voltage and current increase stepwise, and the back electromotive force that is generated in principle no longer poses a problem in practice.

As explained above, if the low-temperature end is cooled to below 60°C, more preferably to room temperature, the voltage and current increase in proportion to the number of connections at the high-temperature end, and the electromotive force of the thermoelectric power generation module increases with the number of stacked units. It becomes a design guideline that can be scaled up in proportion to.

The features of the present invention will be specifically explained below.
(A) By making the high-temperature end a comb-toothed structure of three-layer bonding of copper/constantan/copper, the bonding area becomes more than three orders of magnitude larger than the point contact of a normal 0.3 mmΦ thermocouple.
(b) The internal resistance decreases as the bonding area increases, but the internal resistance decreases when the bonding length (L _H ) is in the range of 80 to 110 mm, as shown in FIG. This is believed to be because when the bonding width is 50 mm or more, the internal resistance does not decrease and eddy currents occur.
(c) In order to reduce the heat flow from the high temperature end to the low temperature end, reduce heat loss, and increase the thermoelectric conversion rate, the width of the strip-shaped thin plate in the middle part is made smaller to about 1/10 of the width of the high temperature end. By making the length about 18 cm within a range that does not increase the resistance and making it difficult for heat to be transferred to the low temperature end, the low temperature end is lowered to 60° C. or less by natural air cooling.

<Comparative example 1>
As shown in Figure 5A, the power generation characteristics (temperature 450°C) of a conventional example in which four pairs of thermocouples made of 0.3 mmΦ copper and constantan wires of 10 cm length are connected are as follows: internal resistance: 2.0 Ω; Load voltage: 44 mV, maximum output is only 250 μW.

<Comparative example 2>
Instead of the 0.3mmΦ wire, a 3mm wide strip of copper and constantan with a thickness of 0.3mm was used, and a 12cm long part was joined by laser welding to form a high temperature end, and a point 18cm away from the high temperature end was used. As Comparative Example 2, a thermoelectric power generation cell consisting of four pairs of thermoelectric power generation units each having a low-temperature end soldered was fabricated.

As shown in Figure 5B, the power generation characteristics of Comparative Example 2 (temperature 700°C) are as follows: internal resistance: 0.4Ω, maximum output: 3500μW, no-load voltage: 79mV, compared to Comparative Example 1, the internal resistance is 1 /5, the maximum output increased by 14 times, and the no-load voltage increased by 1.8 times. However, since the number of laminated units is as small as 4 pairs, the electromotive force of the thermoelectric power generation module is as small as 3500 μW, and remains a comparative example.

<Comparative example 3>
The power generation characteristics (at a temperature of 900°C) when 144 pairs of the same thermoelectric power generation units as in Comparative Example 2 were connected were as shown in Figure 5C: internal resistance: 5.8Ω, maximum output: 450mW, and no-load voltage: 3197mV. Compared to Comparative Example 2, the maximum output increased 128 times and the no-load voltage increased 40 times, but the problem of internal resistance increasing to 5Ω or more recurred.

<Comparative example 4>
In order to reduce the internal resistance of Comparative Example 3, the same 144 pairs of thermoelectric power generating units as in Comparative Example 2 were divided into three sets and connected in parallel to form a thermoelectric generating module. Its power generation characteristics (temperature 900°C) are as shown in Figure 5D: internal resistance: 1.0Ω, maximum output: 372mW, no-load voltage: 1217mV, and compared to Comparative Example 2, the maximum output is 106 times, The load voltage increased 15 times and the internal resistance decreased to 1Ω, confirming the effect of paralleling the thermoelectric power generation units. In other words, by forming a thermoelectric generation module in which a plurality of thermoelectric power generating units are combined in series and parallel, the present invention has versatility that can be scaled up to generate power according to needs.

<Example 1>
Comparative Example 4 demonstrated that the internal resistance was reduced by paralleling the thermoelectric power generation units, but the device became less compact. To solve this problem, creating a 10-comb tooth structure by making slits in the high-temperature end/junction shown in Figure 1 produces the same effect as arranging 10 sets of thermoelectric power generation units in parallel. In Example 1, a thermoelectric power generation module configuration was adopted in which 60 sets of thermoelectric power generation units having a 10 comb structure were stacked. Its power generation characteristics (at a temperature of 900°C) have internal resistance reduced to 0.4Ω, a maximum output of 0.6W, and a no-load voltage of 1.5V, which is a practical level. It has been demonstrated that it is effective in reducing Furthermore, since the high-temperature ends/junctions of Comparative Examples 2, 3, and 4 were two-layer junctions of Cu and constantan, there was a problem that they bent and deformed into a bimetallic shape when heated to high temperatures. Therefore, in Example 1, the problem of thermal deformation and high-temperature oxidation was solved by using three-layer bonding of Cu/constantan/Cu to prevent thermal deformation, and by putting the high-temperature end/joint part in a heat-resistant case and fixing it with an insulating filler. solved.

<Example 2>
In Example 1, Cu and constantan were used as the thermoelectric materials, but in Example 2, in which Al was used instead of Cu, as shown in Table 1, the absolute Seebeck coefficient (2 μV/K) of Al was the same as that of Cu. Since it is as small as 1/2 of the Seebeck coefficient (4 μV/K), it has the effect of halving the back electromotive force generated in the Al portion. On the other hand, since the relative Seebeck coefficient of Al/constantan (45 μV/K) is larger than the relative Seebeck coefficient of Cu/constantan (43 μV/K), the electromotive force at the high temperature end increases by 5%, but the back electromotive force at the low temperature end also increases. The difference is almost the same, and the difference is almost the same. The maximum output at 550°C of a thermoelectric power generation module in which 60 sets of thermoelectric power generation units having the same structure as in Example 1 using Al and constantan were stacked was 0.27 W, which is 45% of that in Example 1. In other words, the weight can be reduced by using Al, but because of its low melting point, the heat source is limited to 550°C, resulting in a significant drop in output. Therefore, Example 2 is effective only when the heat source is about 550°C, and the effects of the present invention are exhibited by Example 1, which is used at a high temperature of about 900°C, where semiconductor thermoelectric materials cannot be used. .

Laser bonding was used in the example as a method for bonding thin metal plates, but diffusion bonding and plating with surface treatment can be used as long as the method is durable against thermal deformation and the alloy layer formed at the bonding interface is 300 nm or less. method, rolled clad method can be used. For example, industrial production becomes possible by diffusion bonding large-area thin metal plates and cutting them into a comb-tooth structure using laser processing or the like that does not damage the bonded interface.

According to the present invention, it is possible to create a thermoelectric conversion device using inexpensive and safe copper, nickel, and aluminum without using the harmful bismuth-tellurium (Bi ₂ Te ₃ ) alloy, and this technology enables thermal power generation to become widely popular. It becomes the foundation.

1 Comb-shaped metal thin plate (thin copper plate, L: length of the thin plate)
1a Teeth (high temperature side joint)
1b Base portion 1c Connecting portion 1d Low-temperature side joint portion 1e Fan-shaped enlarged portion 2 Comb-shaped intermediate metal thin plate (constantan thin plate, L: length of thin plate)
2a Teeth (high temperature side joint)
2b Base portion 2c Connecting portion 2d Low temperature side joint portion 3 Backing thin metal plate (thin copper plate, L _H : length of thin plate)
3a Teeth (high temperature side joint)
3b Base 3c Connecting portion 4 High-temperature end joint (three-layer laminate of comb-shaped metal thin plates (L _H : joining length))
5 Low temperature end contact 6 Air cooling fin (thin copper plate)
7 Thermoelectric power generation cell 8 Insulating filler 9 Heat-resistant case 10 Insulating case for connection part

Claims (10)

A comb-shaped intermediate metal thin plate made of a metal material that serves as the + leg of the thermocouple, a comb-teeth intermediate metal thin plate made of a metal material that serves as the - leg of the thermocouple, and a comb-teeth shaped intermediate thin metal plate made of the same metal material as the comb-teeth shaped thin metal plate. A high-temperature end joint made of a three-layer laminate in which three layers of backing metal sheets are joined,
The comb-shaped metal thin plate, the comb-shaped intermediate metal thin plate, and the backing metal thin plate each have a comb-shaped structure having a plurality of teeth with slits formed in a base provided therein, The tooth portions have a shape that overlaps each other, and the thickness of each tooth portion is 0.1 to 2 mm ,
Each tooth of the comb-shaped thin metal plate has a conductive portion that is electrically connected to each corresponding tooth of the backing thin metal plate,
the base portions provided on each of the comb-shaped metal thin plate, the comb-shaped intermediate metal thin plate, and the backing metal thin plate are directly electrically insulated from each other;
a connecting portion having one end provided at the base of the comb-tooth-shaped metal thin plate and the comb-tooth-shaped intermediate metal thin plate, and extending into an elongate on a side of the base opposite to the side where the plurality of teeth are provided;
a low-temperature end formed by electrically insulating and thermally bonding the comb-shaped metal thin plate and the comb-shaped intermediate metal thin plate at the tip of the connecting portion;
A thermoelectric power generation cell characterized in that the electrical connection including the high temperature end junction and the low temperature end in the unit unit is repeated in series, in parallel, or in series and parallel. In the conductive portion, a tip of each tooth of the comb-shaped metal thin plate and a tip of each corresponding tooth of the backing metal thin plate are connected in a U-shape or a U-shape, The thermoelectric generating cell according to claim 1, characterized in that the thermoelectric generating cell is bent or integrally bent. The conductive portion is such that the slit-side side surface of each tooth of the comb-shaped thin metal plate and the slit-side side surface of each corresponding tooth of the backing thin metal plate are connected in a U-shape or a U-shape. 3. The thermoelectric power generation cell according to claim 1, wherein the thermoelectric power generation cell is curved or bent. The metal material serving as the + leg of the thermocouple is a metal material selected from copper, iron, aluminum, or an alloy thereof,
4. The thermoelectric power generation cell according to claim 1, wherein the metal material forming the negative leg of the thermocouple is a constantan alloy. The metal material serving as the + leg of the thermocouple is chromel,
4. The thermoelectric power generation cell according to claim 1, wherein the metal material forming the negative leg of the thermocouple is alumel. The thermoelectric power generation cell according to any one of claims 1 to 5, wherein the unit further includes a cooling fin located in a region extending beyond the low temperature end of the comb-shaped thin metal plate. . The thermal power generation according to any one of claims 1 to 4, wherein the unit units according to any one of claims 1 to 4 are stacked in the stacking direction of the high temperature end joint made of the three-layer laminate. A thermoelectric power generation module characterized by having a plurality of cells. a casing that accommodates a plurality of the thermoelectric generation cells;
An insulating filler that fills a gap between the casing and the thermoelectric cells, the insulating filler having plasticity that insulates the thermoelectric cells from each other and absorbs thermal displacement of the thermoelectric cells. 8. The thermoelectric power generation module according to claim 7, characterized in that the thermoelectric power generation module is integrated using a thermoelectric generator. The housing is a heat-resistant case,
9. The thermoelectric generating module according to claim 8, wherein the thermoelectric generating cell is housed in the heat-resistant case together with the insulating filler to prevent high-temperature oxidation. The width of the connecting portion is 1/50 or more and 1/5 or less of the width of the high temperature end joint,
The length of the connecting part is 5 cm or more and 50 cm or less,
The thermoelectric power generation module according to any one of claims 7 to 9, wherein the connecting portion is housed in a heat insulating case for the connecting portion.