Thermo-electric power generation using porous metal blocks having a plurality of thermocouples connected in series

Abstract: A thermo-electric power generating element has the structure that two kinds of metal sheets or foils 10, 11 being in the relation of thermocouple combination are laminated together and connected at one end and the other end alternatively, so as to form a plurality of thermocouples connected in sereis. When hot junctions 12 are held at a high temperature, a temperature gap along the thermal flux is generated in the sheets or foils 10, 11. Electromotive force at every thermocouple derived from the temperature gap is summed up to a voltage level effective for outputting electric power through takeoff leads 13, 14. This power generator is useful for converting waste heat to electric power. When the thermocouple pile is made from corrugated sheets or foils, electric power is outputted with high efficiency.

Description: The present invention relates to a fuel combustion-type thermo-electric power generating element composed of a porous block formed by laminating two kinds of metal sheets or foils being in the relation of thermocouple combination, and also relates to a thermo -electric power generator using said element. When two junctions between different metals or semiconductors are held with a temperature gap, electromotive force is generated due to Seebeck effect. The thermo-electric power generator which uses the electromotive force for directly converting thermal energy to electricity has the features that the generator is of simplified structure, small in size and driven with less noize. Although researches for material having the property suitable for the thermo-electric conversion have been continued in various fields so far, the material which meets the requirements including costs has not been proposed for practical use, yet. In this consequence, although the thermo-electric power generation is regarded as effective means for converting waste heat discharged from factories in various industrial fields to electric power, its application is limited only to specified fields such as the power source of a space craft. A conventional thermo-electric power generator has the structure as shown in Fig. 1. This power generator comprises a member 1 made of type-p thermo-electric material coupled with another member 2 made of type-n thermo-electric material through an electric insulator 3. A cold plus electrode 4 and a cold minus electrode 5 are connected to the faces of the members 1 and 2, respectively at one side, while a hot common electrode 6 is connected to the opposite faces of the members 1, 2 at the other side. When the hot site of the element is heated, or heat is collected at the hot site, while heat is diffused from the cold site by cooling or heat radiation, thermal flux 7 is generated in the thermo-electric members 1, 2. As a result, electromotive force derived from the temperature gap between the hot electrode 6 and the cold electrodes 4, 5 is generated and outputted as electric power through takeoff leads 8, 9. The thermo-electric power generator having the porous block of a thermo-electric power generating element for burning a fuel therein was proposed in Japanese Patent Application Laid-Open 6-302867. A heat generated by the combustion of the fuel in the porous block is confined in a narrow space due to the superadiabatic effect of the porous block, and outputted as electric power through electrodes connected to the both faces of the porous block. The same power generator has been proposed by Professor Echigo. In the proposed power generator, a temperature gap effective for outputting electric power can begenerated by periodically switching the flowing direction of premixed gas, in XI Intern. Conference on Thermoelectrics, Oct. 7-9, 1992. The material to be used in the conventional thermo-electirc power generation shall have a big performance factor Z. The performance factor Z is defined by the formula of Z=α 2 /ρ · λ, wherein α represents Seebeck coefficient equal to thermo-electric voltage per the temperature gap of 1°C, ρ electric resistivity and λ the coefficient of thermal conductivity. According to the formula, the material which has big Seebeck coefficient α , small electric resistivity ρ and the small coefficient λ of thermal conductivity is suitable for thermo-electric power generation. The material for the purpose shall be good of heat resistance accounting the atmosphere of use. Taking into consideration these properties, various semiconductor marterials which have big electromotive force and a big performance factor Z, especially FeSi 2 excellent in heat resistance, have been developed recently. However, such the material which satifies the requirements for thermo-electric power generation has not been offered for practical use due to expensiveness and practicability. German Utility Model DE 90 15 019 describes a conventional thermo-electric generator with a plurality of thermocouples connected in series for adding the thermoelectric voltages per thermocouple. It is suggested to insert and electrically connect p- and n-doped semiconductors into the wires made of thermoelectrically positive and negative conducting metals respectively to enhance the poor power generating efficiency. Additional heat-conducting plates can be attached via heat links to the contact regions of these wires in order to increase the small surface area of the wires to allow a more efficient heat transfer. The semiconductors (5,6) and the parts of the wires are embedded in an embedding compound that isolates the hot and cold junctions thermally from another. It is an object of the invention to provide an improved thermo-electric power generating element and a thermo-electric power generator of the fuel combustion type using the same, which allows efficient heat to electrical power conversion, wherein the heat is provided by gasses in particular fuel-combustion gasses. This object is fulfilled by a thermo-electric power generating element having the features disclosed in claim 1 and a thermo-electric power generator having the features disclosed in claim 7. Preferred embodiments are defined in further dependent subclaims. A thermo-electric power generating element according to the present invention comprisies a porous block having a plurality of thermocouples connected in series. The porous block is prepared by laminating two kinds of metal sheets or foils together and connecting them at one end and the other end alternatively so as to form a zig-zag folded structure. Each sheet or foil is electrically insulated from the adjacent sheet or foil at the part except the junction, and the cavity which permits the passage of fuel gas is formed in the porous block. The metal sheet or foils are preferably corrugated to a wave or concavo-convex shape, and the small holes which permit the passage of a fuel or combustion gas are formed in the sheets or foils, in order to hold a space for the passage of gas between adjacent sheets or foils. The metal sheet or foil may be laminated on the adjacent sheet or foil with an angle between the directions of the wave or concavo-convex shapes formed in the adjacent sheets or foils. Takeoff leads are connected to take off ends of the metal sheet or foil structure folded in the zigzag state. The two kinds of metals for forming the porous blocks are preferable in the combination having an output ratio P of 1×10 -3 w·m -1 ·K -2 or more. The output ratio P is defined by the formula of: P = α 2 /ρ wherein α represents Seebeck coefficient and ρ electric resistivity. The porous block formed to a flat shape may be used as a partition wall or embedded in a partition wall to separate a high-temperature zone from a low-temperature zone. The metal sheets or foils connected together at the ends may be formed to the block having the minimum volume. This porous block is useful as the thermosensor which outputs big potential with high sensitivity. Two porous blocks may be arranged in series along the flowing direction of a combustion improving gas. In this case, a fuel is supplied to a space beteween the porous blocks. Such combustion improving gas as air, oxygen or oxygen-enriched air is alternatively supplied along one direction and a reversal direction through the porous blocks in predetermined time intervals. The temperature gap along the flowing direction of combustion gas in the porous blocks generated by the combustion of the supplied fuel is converted to electric power and outputted through takeoff leads. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view illustrating a conventional thermo -electric power generator. Fig. 2 is a view illustrating the thermocouple which principally constructs one unit of the thermo-electric power generating element not according to the present invention. Fig. 3 is a view illustrating a thermo-electric power generating element not according to the present invention. Fig. 4 is a view illustrating a thermo-electric power generator useful as a thermosensor not according to the present invention. Fig. 5 is a view illustrating a thermo-electric power generator useful as a partition wall to separate a high-temperature zone from a low-temperature zone not according to the present invention. Fig. 6 is a view illustrating a thermo-electric power generator embedded in a partition wall not according to the present invention. Fig. 7 is a view illustrating a tubular thermo-electric power generator having a center hole for the passage of hot gas not according to the present invention. Fig. 8 is the sectional view of the same tubular thermo-electric power generator not according to the present invention. Fig. 9 is a sectional view illustrating a tubular thermo-electric power gebnerator embedded in an exhaust pipe not according to the present invention. Fig. 10 is a view illustrating a corrugated sheet to be used in a thermo-electric power generator according to the present invention. Fig. 11 is a view illustrating the lamination of corrugated sheets. Fig. 12 is a sectional view illustrating the lamination of corrugated sheets. Fig. 13 is a view illustrating a thermo-electric power generating element made from corrugated sheets. Fig. 14 is a view illustrating another thermo-electric power generating element made from corrugated sheets. Fig. 15 is a sectional view for explaining one combination of metal sheets. Fig. 16 is a sectional view for explaining another combination of metal sheets. Fig. 17 is a plan view illustrating metal sheets having wave patterns extending along opposite directions. Fig. 18 is a schematic view for explaining a thermo-electric power generator having two porous blocks arranged in series. Fig. 19 is a perspective view illustrating the same thermo -electric power generator. Fig. 20 is a graph explaining temperature distribution generated in the thermo-electric power generator. Fig. 21 is a graph explaining the distribution of oxygen and waste gas concentrations in the thermo-electric power generator. Fig. 22 is a graph explaining a combustion zone in the thermo -electric power generator according to the present invention, compared with a known thermo-electric power generator. Fig. 23 is a view illustrating a thermo-electric power generating element in Example 1. Fig. 24 is a graph for explaining temperature distribution along the flowing direction of combustion gas passing through porous blocks in Example 4. DETAILED DESCRIPTION Conventionally two kinds of metal sheets or foils 10, 11 in the relation of thermocouple combination such as alumel/chromel, iron/constantan or chromel/constantan are connected at one end, as shown in Fig. 2. When the connected end, i.e. a hot junction 12, is held at a high temperature, thermal flux from the hot junction 12 to the other end is generated in the sheets or foils 10, 11. Electric power originated in the temperature gap in the metal sheets or foils 10, 11 is outputted through the takeoff leads 13, 14 connected to the cold site. However, the electric power outputted from one thermocouple is too tiny for practical use. We suppose the electromotive force of the thermocouples can be summed up to a level applicable for practical use, when a plurality of thermocouples are connected in series. The series of thermocouples is formed as follows. A plurality of metal sheets or foils 10, 11 are arranged in face-to-face contact with each other, and connected at one end and the other end alternatively to form hot junctions 12 and cold junctions 15, as shown in Fig. 3. The zigzag-folded thermocouple pile 16 in which a plurality of thermocouples are connected in series is obtained in this way. The junctions 12, 15 may be formed by proper means such as welding, pressure welding, brazing or soldering to electrically connect the metal sheets or foils 10, 11 at the both ends alternatively. After the metal sheets 10, 11 are connected together, it is necessary to form dielectric films on the surface of the metal sheets or foils 10, 11. The dielectric films may be formed by proper means such as thermal oxidation, ceramic coating or chemical treatment with an acid or the like. These means are selected in response to the property of the materials. For instance, firm dielectric films composed of alumina and chromium oxide excellent in insulating power are easily formed by thermal oxidation in the case using the combination of alumel/chromel representative as a thermocouple. The insulating film does not necessarily have high withstanding property, since voltage charged between the adjacent sheets or foils 20, 21 is only several tens mV. Since the thermocouple pile 16 has the structure that a plurality of thermocouples are connected in series, electromotive forces generated at the thermocouples are collected together and outputted as electric power through the takeoff leads 13, 14. Consequently, a potential enough to output electric power is obtained, regardless the combination of metals which generate small electromotive force per one thermocouple. The thermocouple pile may be reformed to a proper shape in response to use. For instance, when the thermocouple pile 16 is used as a thermosensor, the pile 16 is preferably formed to the minimum volume as shown in Fig. 4. The thermosensor obtained in this way is very sensitive due to big output voltage. The thermocouple pile 16 may be used as a partition wall (shown in Fig. 5) or embedded in a partition wall 19 (shown in Fig. 6) to separate a high-temperature zone from a low temperature zone. The hot junctions 12 are faced to the burners of a boiler, while the cold junctions are faced to a water tank. Thermal flux along the direction shown by the arrow is generated in the pile 16, and electric power in response to the temperature gap is outputted. When the metal sheets or foils 10, 11 are partially elongated to form fins for collecting or discharging heat, the block made from such the metal sheets or foils 10, 11 efficiently collects heat from or discharges heat to a gas or liquid at the surroundings. When a plurality of couples of the metal sheets or foils 10, 11 are arranged in the radial state as shown in Figs. 7 and 8, electric power is outputted from a small heat source. In this case, the heat of waste gas passing through an exhaust pipe 18 located at the center is used as a heat source. Since the cold junctions 15 are radially directed outwards, thermal diffusion is effectively promoted so to enlarge the thermal flux, i.e. the temperature gap in the metal sheets or foils 10, 11. Consequently, big electric power can be outputted. The metal sheets or foils 10, 11 may be embedded in the partition wall 19 to separate a high-temperature zone from a low-temperature zone, as shown in Fig. 9. In this case, the hot junctions 12 and the cold junctions 15 are preferably projected to the high-temperature atmosphere and the low-temperature atmosphere, respectively, so as to generate thermal flux in the metal sheets or foils 10, 11. Due to this arrangement, the collection or discharging of heat at the high-temperature site is efficiently performed. This type element can be attached to an exhaust tube in an engine for an automobile or the like, to effectively recover heat as electric power from exhaust gas. Next, preferred embodiments of the invention will be described with reference to Figures 10-24. In order to promote heat exchange between the thermocouple pile and combustion gas, the thermocouple pile is preferably formed to a porous block having big surface area. The surface area is made bigger by corrugating the metal sheets or foils and forming gas-permeable holes in the metal sheets or foils. A metal sheet or foil 30 for forming the porous block is corrugated to the shape having a wave or concavo-convex patttern 31, as shown in Fig. 10. When a plurality of currugated sheets or foils 30 are laminated together, spaces 32 are formed between the adjacent sheets or foils 30, as shown in Fig. 11. The spaces 32 serve as the passages of combustion gas. When the wave or concavo-convex pattern 31 is formed with waviness 33 along the longitudinal direction, the space 32 is partially bigger or smaller. Since the combustion gas passing through the spaces 32 is periodically expanded or compressed, the combustion gas flows in turbulent state through the spaces 32, so as to promote the heat exchange with the metal sheets or foils 30. Gas-permeable small holes 34 with projections 35 may be formed in the sheet or foil 30. The projections 35 may be burrs formed by the formation of the holes 34. When the metal sheets or foils 30 are laminated together, the projections 35 are engaged with the adjacent sheets or foils 30, as shown in Fig. 12, so as to maintain the predetermined shape of the spaces 32. The holes 34 and the projections 35 are effective for enlarging the surface area of the metal sheet or foil 30, too. The effective surface area of the metal sheet or foil 30 may be made larger by the sand or beand blasting treatment to roughen the surface of the metal sheet or foil 30, too. A plurality of corrugated sheets or foils 10, 11 are laminated together and connected at one end and the other end alternatively by welding, pressure welding, brazing or soldering, as shown in Fig. 13. After the metal sheets 10, 11 are formed to the zigzag-folded state, electrically insulating films are formed on the metal sheets or foils 10, 11. The corrugated sheets or foils 10, 11 may be combined in various ways. For instance, one sheet or foil 10 is connected to two sheets or foils 11, as shown in Fig. 14. The corrugated sheets 10 are combined with flat sheets 11, as shown in Fig. 15. The corrugated sheets or foils 10 are connected to the corrugated sheets or foils 11 having different wave or concavo-convex patterns, as shown in Fig. 16. The different patterns effectively assures the presence of the spaces 32 (shown in Fig. 11) between the adjacent sheets or foils 10 and 11. The wave or concavo-convex pattern formed in the sheets or foils 10 preferably has a direction opposite to that of the pattern formed in the other sheets or foils 11, as shown in Fig. 17. When the sheets or foils 10, 11 are laminated together in the state that the wave pattern of the sheets or foils 10 cross the wave pattern of the other sheets or foils 11, the vacancy of the lamination can be made higher and uniform over the whole body. The conversion efficiency of heat to electric power can be improved by the system shown in Figs. 18 and 19. This system 40 has a couple of porous blocks 41, 42 received in a combustion chamber 43 and arranged in series along the flowing direction of combustion improving gas or combustion gas. A fuel supply pipe 44 extends to a space 45 between the porous blocks 41 and 42. A combustion improving gas, e.g. air, oxygen or oxygen-enriched gas, flows along the direction I through a supply-discharge pipe 46, the porous block 41, the space 45 and the other porous block 42 and then discharged through another supply-discharge pipe 47, or along the reversed direction II. The flowing direction is alternatively switched between I and II in predetermined time intervals. A fuel is supplied through the pipe 44 to the space 45 between the porous blocks 41 and 42, and burnt with the combustion improving gas fed out of the porous block 41 or 42. Combustion gas is discharged through the other porous block 42 or 41 and then the pipe 47 or 46. Since the fuel supply line is separated from the combustion improving gas supply line, the combustion zone is limited to the narrow region defined by the space 45 and the inner parts of the porous blcoks 41, 42 near the space 45. When the combustion improving gas flows along the direction I, the combustion improving gas heated at a high temperature during passing through the porous block 41 comes in contact with the fuel in the space 45, so that the fuel is instantaneously burnt with the high-temperature combustion improving gas in sufficient amount. As a result, the temperature gradiation in the blockes 41, 42 becomes sharp as shown in Fig. 20, so as to output big electric power through takeoff leads 48, 49. The distribution of oxygen concentration along the flowing direction sharply dropped around the space 45, while the concentration of combustion gasses such as CO, CO 2 and H 2 O sharply increases around the space 45, as shown in Fig. 21. These sharp changes mean that almost all the supplied fuel is burnt in the space 45, while the remaining fuel is burnt in the interior of the porous block 42 adjacent to the space 45. Consequently, the discharge of the supplied fuel in unburnt state is is inhibited. Just after the flow of the combustion improving gas is switched from the direction I to II, the combustion improving gas returns from the porous block 42 to the porous block 41. Since oxygen remains in excessive amount under the stable condition, the amount of oxygen necessary and sufficient for the combustion is kept so as not to intercept the continuation of the combustion due to the switching of the flowing direction. In addition, since the fuel is supplied in small amount with dilute concentration, the combustion zone is held in stable state and limited to a narrow space as shwon in Fig. 22 without lowering its temperature even by supplying an unpreheated fuel to the space 45. On the contrary, in a conventional system as disclosed in Japanese Patent Application Laid-Open 6-302867, there is the period during which the fuel is not supplied between the discharge of the combustion gas through the porous block and the arrival of a fuel gas supplied through the pipe at the combustion zone, as shown in Fig. 22. Therefore, the combustion is inevitably unstabilized, and unburnt fuel is discharged. In the thermo-electric power generator having the syustem as afore-mentioned, the fuel is efficiently burnt without such the discharge of unburnt gas just after switching the flowing direction as in the conventional system. The supply of the fuel is not interrupted, and the combustion of the fuel is held in stable state. Consequently, electric power can be outputted with high efficiency through the takeoff leads 48, 49. When the aggregate of metal meshes or wires are disposed in the space, the efficiency of combustion is further improved. The aggregate of the metal meshes or wires may be disposed as a unit body in the space or inserted in each of the porous blocks 41, 42 facing to the space 45. In this case, the fuel fed out of the pipe 46 comes in contact with the metal meshes or wires before entering into the porous block 41 or 42, so as to improve the efficiency of combustion. In this thermo-electric power generator, the time intervals for swtiching the flowing direction can be made shorter to the time period t for discharging the whole amount of air having oxygen concentration reduced by combustion. The time period t is determined by the formula of t=V/F, wherein V represents the capacity of the combustion chamber 43, and F the flow amount of gas. The switching intervals can be determined to the optimum value with the high degree of freedom. On the ocntrary, the consumption efficiency of fuel gas is dropped to approximately 50 % in the conventional system, when the time intervals for switching the flowing direction is made short to the time period t (=V/F). EXAMPLE Example 1: The combination of alumel (Ni-2Al alloy)/chromel (Ni-10Cr alloy) having an output ratio P of 2-3 × 10 -3 W · m -1 · K -2 was used as metal sheets 10, 11 in this example. After the metal sheets of 50 µm in thickness were corrugated to wave shape (shown in Fig. 10), the metal sheets were sheared to the dimensions of 50mm × 40mm. The sheared alumel and chromel sheets, 32 pieces each, were laminated together as shown in Fig. 11, and connected at the upper end and the lower end alternatively by spot welding, as shown in Fig. 13. By this way, the metal sheets 10, 11 were connected together in zigzag-folded state, and 32 alumel/chromel thermocouples were connected in series. The obtained porous block was reformed to the shape having the sectional dimensions of 38mm × 38mm with respect to the flowing direction of fuel gas. The reformed block was devided to two blocks 50, 51 as shown in Fig. 23. The blocks 50, 51 were connected in series through a U-shaped trunk electrode 52. As a result, 64 thermocouples were connected in series. Thereafter, the blocks 50, 51 were heated 45 minutes at 1000°C in the open atmosphere so as to form electric insulating films composed of alumina and chromium oxide on the surface of the alumel and chromel sheets, respectively. Takeoff leads 13, 14 were connected to the blockes 40, 41 at the side opposit to the trunk electrode 42 by spot welding. When electric resistance between the takeoff leads 13 and 14 was measured under the condition that pressure was applied onto the blocks 50, 51 along the folding direction, the deviation of electric resistance was not detected regardless the magnitude of pressure. The constant electric resistance means that each sheet was sufficiently insulated from the other sheets. The porous blocks obtained in this way were inserted in a quartz tube having the inner dimensions of 40 mm × 40 mm. LP gas in a flow amount of 0.2 l/minutes and air in a flow amount of 10 l/minutes were introduced into the quartz tube for combustion-power generating test. As a result, release voltage between terminals was E=2.0 V, and internal resistance during operation was R i = 5Ω. It was understood from this result that the electric power of approximately 200 mW was outputted according to the formula of P out =E 2 /4R i , when a load of 5 Ω was connected. It was supposed that the temperature gap of 750K was generated in the porous blocks, since release voltage between terminals was approximately 31 mV per one thermocouple. These results mean that the porous blocks according to the present invention had high performance similar to that of a thermo-electric power generator made of high-quality semiconductor material such as FeSi 2 . Example 2: Alumel and chromel sheets were corrugated to form waves inclined with an angle of 5 dgrees to oppsite direction from each other. Small holes 34 were formed in the corrugated metal sheets 30. The ridges of the small holes 34 and projections 35 (shown in Fig. 10) at the surroundings were polished and rounded, so that burrs formed at the periphery of the hole 34 would not make a short-cut circuit between the adjacent sheets. The metal sheets 10 were laminated alternatively together with the other metal sheets 11 in the manner such that the waves alternatively extended to the opposite directions. Thereafter, the laminated metal sheets 10, 11 were formed to a porous block by the same way as that in Example 1. The porous block obtained in this way had 19 alumel/chromel thermocouples. The porous block was used for making up a thermo-electric power generator by the same way as that in Example 1. LP gas in a flow amount of 0.1 l/minutes and air in a flow amount of 10 l/minutes were supplied into the quartz tube for combustion-power generating test. In this case, combustion was continued for a long period under uniform and stable condition over the whole body of the porous block. Release voltage between terminals was E=0.7 V, and internal resistance during operation was R i =0.8Ω. From these results, it is supposed that the electric power of approximately 150 mW was outputted, while the temperature gap of 890 K was generated in the porous block. Example 3: The combination of alumel/chromel having the output ratio P of 2-3 × 10 -3 W/mK 2 were used as the metal sheets 10, 11. The alumel and chromel sheets 10, 11 of 50 µm in thickness were sheared to the dimensions of 50mm × 40mm. The sheared alumel and chromel sheets, 41 pieces, were alternatively laminated as shown in Fig. 3, and connected at the upper end and the lower end alternatively by spot welding. As a result, the metal sheets 10, 11 were connected together in zigzag-folded state, and 41 alumel/chromel thermocouples were connected in series. The folded bundle obtained in this way was reformed to a block of 10 mm in width, 5 mm in thickness and 40 mm in length. When this block was oxidatively heated 45 minutes at 1000 °C in the open atmosphere, dielectric alumina and chromium oxide films were formed on the surface of the alumel and chromel sheets, respectively. Thereafter, takeoff leads 13, 14 were connected to the both sides of the block. When electric resistance between the takeoff leads 13 and 14 was measured while applying pressure to the block along the folding direction, the deviation of the resistance with the magnitude of the applied pressure was not detected. This result means that each layer was sufficiently insulated from the other layers. The obtained block was examined for power generating test, while folding its hot site at 650 °C and its cold site at 50°C so as to make a temperature gap of 600K. As a result, release voltage between terminals was E=1.0 V, and internal resistance during operation was R i =5Ω. It was understood from these values that the electric power of 50 mW was outputted according to the relation of P out =E 2 /4R i , when a load of 5 Ω was connected to the power generator. Example 4: The same porous block as that in Example 1 was used as a thermo -electric power generating element in this example. The porous block prepared by shearing alumel and chromel sheets of 50 µm in thickness to the dimensions of 35mm × 40 mm, alternatively laminating 31 pieces each of the sheared alumel and chromel sheets, and spot welding the alumel and chromel sheets at one end and the other end alternatively so as to form the zigzag-folded structure wherein 31 thermocouples were connected in series. The porous block was of 40 mm in width, 40 mm in thickness and 35 mm in length. When the block was oxidatively heated 45 minutes at 1000 °C in the open atmosphere, dielectric alumia and chromium oxide films were formed on the surface of the alumel and chromel sheets, respectively. Two thermo-electric power generating elements obtained in this way were received as porous blocks 41, 42 in a combustion chamber 43, as shown in Figs. 18 and 19. A space 45 with the gap of 0.5 cm was disposed between the porous blocks 41 and 42. The porous blocks 41, 42 were positioned in the combustion chamber 43 in the manner such that takeoff leads 48, 49 were held at a cold site. Air in a flow amount of 10 l/minute was supplied through the supply-dishcharge pipe 46 at one side, while a fuel gas in a flow amount equal to 3% of the air flow amount was supplied through the fuel supply pipe 44 into the space 45 and ignited. The porous blocks 41, 42 near the space 45 were heated by the combustion of the fuel. When the porous blocks 41, 42 were heated at a sufficiently high temperature, the flow amount of the fuel was reduced to approximately 1% of the air flow amount, and then the flowing direction of the air was reversed. Thereafter, the flowing direction of the air was periodically switched in the time intervals of approximately 5-10 seconds until stable combustion state. Under the stable combustion condition, temperature distribution was generated with the temperature gap of approximately 900 K along the flowing direction, as shown in Fig. 24. Release voltage between terminals was of E=2V, and internal resistance during operation was of R=1.6Ω, when the takeoff leads 48, 49 at the blocks 41, 42 were connected in series. From these results, output power P was calculated to 625 mW according to the formula of P=E 2 /4R . The porous blocks 41, 42 used in this Example had the cross section of 4cm × 4cm and the length of 3.5 cm along the flowing direction of combustion gas. Since the porous blocks 41, 42 small in cross section were used, it was enough to locate the fuel supply pipe 23 facing to the space 45. In the case where porous blocks large in cross section are used to enhance power generating efficiency, a metal pipe having a plurality of nozzles is prefarably disposed in the space 45 in order to supply the fuel with uniform flow distribution into the space 45. A gas-permeable porous member made by aggregating metal meshes or wires is preferably disposed in the space 45, to make the burning reaction uniform and to keep the combustion under stable condition. Some of metal meshes or wires catalytically accelerate the burning reaction, so that the whole surface of the porous blocks 41, 42 as well as the space 45 are effectively used for the combustion of the fuel to make the temperature distribution uniform. The thermo-electric power generating element according to the present invention as above-mentioned has the structure that a plurality of thermocouples are connected in series along temperature gradiation. Due to this structure, electromotive forces at every thermocouple is summed up to a voltage level sufficient for outputting electric power, regardless using materials having small electromotive force per one thermocouple. In the case where corrugated metal sheets or foils are laminated to form the main body of the thermo-electric power generator, spaces serving as the passage of a fuel or combustion gas are formed between the adjacent sheets or foils. Since the spaces are properly controlled in size, direction and/or configuration by changing the wave or concavo-convex pattern of the corrugated sheets or foils, the specific surface area of the porous body are determined with the high degree of freedom so as to obtain the optimum combustion conditions with sharp temperature gradiation. Consequently, big electric power is gained in response to the sharp temperature gradiation. The power generator is useful for outputting electric power from the heat source, which has been wastefully discharged so far, such as waste heat from a blast furnace, a gas combustion oven, the engine of an automobile, an incinerator or solar heat. The bundle of zigzag -folded metal sheets or foils formed to a compact block is useful as a high-sensitive thermosensor, since elctricity is gained with high voltage. The thermo-electric power generating element according to the present invention uses the metallic materials which have been industrially produced at low costs. Therefore, the thermo-electric power generator with high performance can be offered at a low cost.

Claims: A thermo-electric power generating element comprising a thermocouple pile (16) formed by laminating two kinds of metal sheets or foils (10, 11, 30), the metal sheets or foils (10, 11, 30) being connected at one end and another end alternately as to form a plurality of thermocouples connected in series in zigzag-folded state, the metal sheets or foils (10,11, 30) being electrically insulated from each other except at the junctions, the spaces between adjacent metal sheets or foils (10,11,30) being connected by holes (34), so that a gas permeable structure is formed, and takeoff leads (13,14;48,49) connected to takeoff ends of the thermocouple pile. The thermo-electric power generating element according to claim 1, wherein the two kinds of metal sheets or foils (10, 11, 30) are selected from combinations of alumel/chromel, iron/constantan, and chromel/constantan. The thermo-electric power generating element according to claim 1, wherein the metal sheets or foils (10, 11, 30) are corrugated to a wave or concavo-convex shape. The thermo-electric power generating element according to claim 3, wherein the wave or concavo-convex shapes of the two kinds of metal sheets or foils are inclined along directions opposite to each other. The thermo-electric power generator element according to claim 3 or 4, wherein the metal sheets or foils (10, 11, 30) are formed with a waviness (33) along a gas flow direction to induce turbulent gas flow. The thermo-electric power generator element according to one or more of the preceding claims, wherein an effective surface area of the metal sheets or foils (10, 11, 30) is enlarged by a sand blasting treatment. A thermo-electric power generator (40) comprising two blocks (41, 42) made of thermo-electric power generating elements according to claim 1-6, wherein the takeoff leads (48, 49) are connected to the cold sides of said two blocks (41, 42), a combustion chamber (43) for arranging the two blocks (41, 42) in series along a flowing direction (I,II) of a combustion gas, a fuel supply pipe (44) opened to a space between the two blocks (41, 42), and means of supplying combustion improving gas (46, 47) through the two blocks (41, 42) and alternately switching the flowing direction (I, II) of the combustion improving gas in predetermined time intervals, wherein fuel supplied through the fuel supply pipe (44) is burnt with the combustion improving gas fed out of one of the blocks (41, 42) and a resultant combustion gas is discharged through the other block (42, 41). The thermo-electric power generator according to claim 7, wherein the fuel supply pipe (44) has a plurality of nozzle openings at its top part extending into the space between the two blocks (41, 42). The thermo-electric power generator according to claim 7, wherein the space between the two blocks (41, 42) is filled with metal meshes or wires.

Inventors: OHARA SHINSUKE, OZUTSUMI MICHIO, TAKEMOTO TOSHIHIKO, OHARA, SHINSUKE, OZUTSUMI, MICHIO, TAKEMOTO, TOSHIHIKO, Ohara, Shinsuke, Ohara Metal Industries Co., Ltd., Ozutsumi, Michio, Nisshin Steel Co., Ltd., Takemoto, Toshihiko, Steel &amp; Technology Dev.Lab.
Applicants: NISSHIN STEEL CO LTD, OHARA METAL IND CO LTD, NISSHIN STEEL CO., LTD., OHARA METAL INDUSTRIES CO., LTD.
Application year: 1996
Main classification: H01L35
IPC codes: H01L35