DE1614281A1 - Thermoelectric generator - Google Patents

Description

TeL29512lS N 161 - Dr. Hk / P

Nuclear Materials Ana Equipment Corporation, Apollo, Pa. V.St.A.

Thermoelectric generator

The invention relates to a thermoelectric generator for Generation of electrical energy in places where there is no public power grid, e.g. in space or in remote locations Areas of the world, In particular, the invention relates to a thermoelectric generator in which as A radioactive nuclear fuel is used as the heat source. The object of the invention is to improve such a generator to the extent that that it can deliver a power on the order of 1 to 100 watts and more.

The known thermoelectric generators contain this type a radioactive fuel, e.g. strontium 90 or Plutonium 238, and a number of thermocouples, which are in heat exchange with the radioactive heat source, per required protection of the thermocouples against radioactivity is provided by a shield, which can be made of tungsten or a tungsten alloy. The efficiency of this known generators is very small and the invention is concerned

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nit measures to improve efficiency.

The thermocouples used in such generators are of the semiconductor type. For example, doped lead telluride or silicon and germanium are used. It has been shown that the blocks made from it are very sensitive to shock and break or jump easily. The thermal stresses caused by thermal expansion or contraction have the same influence. The object of the invention is also to improve the thermoelectric generator so that the thermocouples from materials mentioned type mechanical and Can withstand thermal stresses better.

The thermoelectric generator according to the invention with one or more thermopiles, their hot and cold soldering points are connected to common heat supply and discharge lines, a radioactive heat source and a radiopaque shield between the heat source and the heat supply lines is characterized in that the shield is in a thermally conductive connection with the heat source and the heat supply lines stands.

The arrangement is preferably made so that metallic Connections between the heat source and shield or the shield and the heat supply lines are made.

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In the embodiment described below, the shielding is with a saddle made of copper or a another material with good thermal conductivity is hard-soldered and the The saddle itself is connected to the hot soldering points by DiJruission.

The thermopiles preferably each contain melarier ones Elements of opposite polarity, some of which are connected in parallel. Each thermopile is as a block or cylinder executed whose base and cover plate represent the hot and cold solder joint. The cover plate, which the represents the hot solder joint is by diffusion with the saddle connected, which in turn is soldered to the shield.

So that the semiconductor elements located in the thermopiles are better able to cope with the impact and temperature stresses, they are preloaded according to the invention. It has been shown that such thermocouples can withstand considerable pressure forces against tensile forces but are very sensitive. If the thermocouples are now under strong compressive stress, mechanical impacts or temperature increases only reduced the preload, but no tensile stresses can occur in the elements. Preferably, the bias is applied to the elements of each thento column by a helical or conical spring. AaF changes a part of the characteristic curve of a conical spring

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the restoring force changes only slightly with the displacement. the Spring is set so that its working point in this Area of the spring characteristic is so that the force exerted by the spring on the thermocouples in the event of a shock or thermal expansion does not change very much. Additionally the thermoelectric generator can be mounted on shock absorbers, which also serve to dissipate heat.

An embodiment of the invention is based on the following described in the drawing. Here are:

Fig. 1 is an oblique view of the thermoelectric according to the invention Generator with parts broken away;

Fig. 2 is a plan view of the generator;

3 shows a section along the line III-III in FIG. 2;

Fig; 4 is a longitudinal section of a thermopile according to the invention;

FIG. 5 is a schematic plan view of the thermopile in FIG Direction of line V-V in Fig. 4 with removed upper heat transfer plate;

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Fig. 6 is a schematic view in the direction of arrow VI in Fig. 4 with the lower heat transfer plate removed; .-..- '■■ / .; ■

Fig. 7 is a partially broken plan view of the heat shield within the thermopile of Fig. 4 and

Fig. 8 is a section through such a heat shield,

The main parts of the thermoelectric shown in the drawing Generators are housed in a container. In the M tte of the same sits the radioactive heat source, which is enclosed by a radio-opaque shield nearby people from the radioactivity protection. Thermal insulation surrounds the shield. Below the seal are in the thermal insulation the thermopiles (Fig. 4, 5. and 6).

The container is a vacuum-tight hollow cylinder. It has a cylindrical wall 23 which preferably consists of multilayer metal, namely a stainless steel jacket 25 with an aluminum lining 26. Ribs 27 made of stainless steel or the like are welded to the jacket 25. An output line ^: -'28 is passed through the wall 23 and connected to the inner conductor of a coaxial cable 30. To carry out the line

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serves an insulating sleeve 32 made of aluminum oxide, which in turn . Vacuum-tight with a stainless steel socket 50 is connected, which is welded into the end face of a stainless steel pot 34. The pot 34 sits in the wall 23 and is connected to the jacket 25 tightly welded. The pot 34 has a cover 36 which, with the interposition of a sealing ring on the flange 38 of the The pot is screwed on. The cable 30 is through the lid 36 and is held by a clamp 52 which is tightly connected to the cover 36. Another implementation 40 in the end face of the pot 34 is for measuring lines 42 provided. The output conductor 28, the bushing 32 and the measuring lines are made of a synthetic resin (Epoxy resin, or silicone rubber) potted. The container has furthermore a lid 31, e.g. made of stainless steel. In the middle of Cover is a vertical rod 33, from which ribs 35 extend radially. A drawbar eye 37 (Fig. 3) can be attached to the cover. The cover 31 is vacuum-tight with the wall 23 tied together.

A pump nozzle 39 for evacuating the container is attached to the cover 31. After evacuation, the pump port 31 clamped and by means of a resin 43 in a sleeve 41 embedded.

The bottom 51 of the container, like the side wall, is made of multilayer metal and is pressure-tight with the side wall 23

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wears out. A plurality of shock absorbers 53 are provided on the floor 51 attached to the holder of the heat source ^ - the shield and the thermoelectric converter. They are so many Shock absorbers 53 present, as thermopiles 21 are provided. Each shock absorber serves simultaneously to transfer heat from the heat dissipation plate 54 of the associated I&M column 21 to the bottom of the container.

Each shock absorber 53 has a plate 55 attached to the aluminum lining 57 of the floor and a freely floating L-shaped plate 59 and are also connected to the L-shaped slat 59. The L-shaped plate 59 is supported by springs 65, which sit in recesses 67 of the lining 57 and surround the heads by screws 69, which are generally attached to the diverter plate 54 and loosely pass through the plate 59 (Pig ₀ 3).

At Bodnm 51 is. an ABsehlusssttick 71 Cfig <, 2 | attached. It is aur ¥ erbinduag des therOToelelctriscÄQä.üJiföS'fflQ ^ S rait of the output line 28 «The connection stliclc 71 consists of two insulating plates 73 and the like. 75 »". A »B." from boron nitride: / - | Fig _ö iS} - :, These, plates are _: attached to the bottom 51 The upper i

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75 is provided with holes that are countersunk. the Terminals 77 and 79 »with which the output conductors 81 (Fig. 2) from the last thermopile 21 and the supply lines 83 connected to the output line 28 are held by screws 85 which pass through these holes. The screws 85 are isolated from the conductive floor 51 by the plate 73. There is also a grounding clamp 87 is provided in good electrical contact with the floor 51 and the earth lines are from the first thermopile fixed in this grounding clamp.

The heat source is a fuel capsule 91 (Fig. I) in which a fuel cylinder 93 is located. This consists e.g. from the oxide of radioactive strontium 90. The cylinder 93 is enclosed in a sleeve 95 made of a material that is resistant to corrosion and high temperatures and does not react with SrO. The sleeve 95 is in turn made into a jacket 97 Material resistant to oxidation and high temperatures included. As materials for the sleeve 95 and the Sheath 97 is preferably made of nickel alloys as described in F-30 1037D of October 1964 and F-30, 1007C dated June 1963 of Union Carbide Stellite in Lokomo, Indiana are described. A pin 99 on the jacket 97 makes this easier Handling the capsule 91.

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The shield consists of one of the following: cylinder ^; he 10.1 ^ _of:;! one em material which gamma rays aft ^

of 97.6% tungsten and 2.4% ttickel and Eupf erü-j & fceiSfi », -,; d» in the company publication L-502 of the company KenßBnreMl; lnc. is described in Lätrobe _r Pennsylvania; ?

The cylinder 10T has a cylindrical recess for the fuel cap 91 . J> ± ^ cape let 91 mxd through ^ a iach des

Cylinder used LOEL, 4 ^a ^ s ^ ^{ann rG} ^^^ "^^ 103

The recess is so dimensioned that it allows for a shape expansion: the fuel capsule allows * flat, for example, the fuel capsule 91 has a diameter of 94 mm (2.193 inches), so a margin of 1 mm ( Q.04 inches ) remain free for thermal expansion. ;

Two wire rings are screwed onto the outer surface of the cylinder 101. The wire rings should be made of a material that has high strength, low weight and low thermal conductivity. For example, they consist of a titanium alloy with 6% aluminum and 4% vanadium (see Materials in Design Engineering, mid-October 1963t p. 163). each ring 105 has a plurality of countersunk bores Ί07 through which support rods 109 for the cylinder 101 pass. The bearing rods 109 are made of a material of high tensile strength and low thermal conductivity, e.g. made of a chromium-nickel alloy with the trade name Inconel-X, which is

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International Nickel Company font with the title Handbook of Huntington Alloys, Third Edition, Jan. 1965 is described. The rods 109 are in the bores -107 slidable, but widened at the ends 111, so that they cannot slip out.

On its underside, the cylinder 101 is hard-soldered to a saddle 115 made of copper. A copper-silver solder; "(27Cu, 28Ag) serve, but - if the soldering can be carried out in a vacuum, a better connection results if a thin foil (0.005 mm) made of titanium is inserted between the cylinder 101 and the saddle 115 and heated ^{to 95O 0 C.} will.

The thermopiles 21 are pressed against the underside of the saddle 115 by the springs 65. The Wärmezuleitplatten 117 of the thermopile lie under pressure against the saddle 115. The plates 1T7 consist of the above-mentioned nickel alloy) and copper-plated. Under pressure there is a diffusion

connection between the Terfcuptf «rang and the saddle Tt5.

Bie / heat isotuersing is in. a coat X21 ieinpescfclCEs-sen. In the jacket t21 there is a pure package of cylindrical shapes. The planes of the battalion are made so that conical ends are jergieteenv. 3 inner 7ULien 1:23 'b «Äfeelten jmxs aeinem groove

Material such as titanium and the outer foils 125, e.g. made of aluminium. For example, about 7.5 titanium foils and about 25 aluminum »- £ oils available. Furthermore, the thermal insulation has a Dachshund 126, under which there is a tapered package of about 75 titanium discs 127 and 25 aluminum discs 129 are located. Also fits into the lower miter of the package 123, 125 Package of titanium and aluminum discs 131, 133. In this one Discs are, however, holes for the thermopiles 21, so that they can be moved in the package. The disks 131, 133 lie on a base 135 of the aluminum lining of the bottom 51. The titanium foils 123, 1.27 and 131 are not used only for thermal insulation, but also as a getter for that Vacuum in the container and to attenuate the gamma rays. Of the The jacket 121 and the cover 126 are made of the alloy Ti-90 Al-6 Va-4. The packages 127, 129 and 131, 133 have holes through which the rods 109 pass.

A number of U-shaped brackets 141 with outwardly curved edges serve as a carrier for the heat source with its shielding. These ends are on the periphery of the jacket 12T of the thermal insulation welded on. The bracket 141 are on the wall 23 of the Container screwed on. At their lower ends the Bracket 141 against the base 135. When the cover 31 is on the wall 23 is attached, the upper edges of the bracket 141 are through held the lid.

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Anchors 143 for the tension rods 109 are welded into the bracket 141 near their ends. Each anchor 143 has a removable one Abutment 145 through which the associated rod 109 passes. Screw heads sit on the rods 109 147. The ends 149 of the rods 109 are folded wide so that they are held in the screw heads 147. the Abutments 145 are screwed on and then nuts 151 are opened with Belleville disc springs 153 in between the screw heads screwed on. So becomes the radioactive Heat source with its shield firmly but resiliently held.

The thermoelectric converter (Fig. 4 to 8) consists of a plurality of thermopiles 21. each thermopile 21 is enclosed in a cylindrical housing, which consists of a jacket 171, a heat supply plate 117 and a Heat dissipation plate 54 is made. These parts are made of the above-mentioned heat-resistant nickel alloy.

Each housing contains a plurality of negatively and positively doped cylindrical thermocouples 173 and 175, labeled N and P in FIG. These thermocouples consist of a material with solid state conduction, preferably lead telluride. The lead telluride would change in a vacuum, which is why the housing is filled with an inert gas, e.g. high-purity argon (0.0001 %). When the housing is cold, the pressure is des. A ^ gonsL etya 1 / 3O atmosphere, but

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at the operating temperature of the thermopile, the pressure rises on about an atmosphere. The feed plate 117 is provided with a hole 177 in order to carry out the argon filling. The pick-up electrodes 179 and 180, for those in the Ihermos column Electric voltage developed 21 are carried through the A ^ line plate 54.

The heat transfer from the feed plate 117 to the

hot ends of cylinders 173 and 175 happens via "

an iron disc T81, copper sheets 183 and 184, one

Copper washer 185, an insulating washer 187 (for example ■

wise made of aluminum oxide) and a copper washer 189 »Die Disk 189 is soldered to the lead plate 117, the Disk 187 to 189, disk 185 to 187, the sheets 183 and 184 to disk 185 and disk 181 to 183.

A copper titanium solder at around 878 ° C is used for soldering.

The disk 181 rests mechanically on the cylinders 173 and

at. (

At the cold end of the cylinder, the heat and the electrical power are dissipated via copper bars 191, which are connected to a Lead 40, tin 60 solder on cylinders 173 and 175 and on Connecting plates 193 to 198 are soldered. The latter are made of copper and are provided with slots 199. In order to the lead from the solder does not diffuse into cylinders 173 and 175 can, the faces of the cylinders 173 ^ and 175 with

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coated with a thin diffusion barrier. The heat is from the connecting plates 193 to 198 via copper washers 2oo and 201 and an intermediate insulating washer 203 (e.g. of aluminum oxide) transferred to the heat dissipation plate 54. The heat flows from the individual heat dissipation plates 54 Via the associated 'shock absorber 53 to the wall 23 and the Ribs 27 of the container. The connecting plates 193 to 198 are soldered to the disc 200 with a copper-silver solder, the washers 200 and 201 to the insulating washer 203 with a copper-titanium alloy and the washer 201 to the Conductor plate 54 with a copper-silver solder. The copper-titanium solder has a eutectic temperature of 878 ° C, the copper-silver solder a temperature of 779 ° C.

In each slot 199 there is a conical spring 211, the is compressed between the bottom of the recess and the underside of a freely movable bolt 213 and one exerts substantially constant pressure on cylinders 173 and 175 to keep them under constant tension. During assembly, the bolt 213 is held in place by a wire which passes through a slot 215 in the connecting plates 193 to 198 and a not shown hole in the bolt 213 goes through.

Each cylinder 173 or 175 is surrounded by ring insulators 221

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which preferably consist of boron nitride. A heat shield, which consists of a package 223 of titanium foils, surrounds the cylinders 173 and 175. The foils have crosswise grooves 225 and 227 (Figs. 7 and 8) so that the heat transfer between the foils on the contact points 229 between the uils is limited. A short circuit between the connecting plates

183 and the balls 191 over the foils 223 is through the Isolation rings 230 and 228 prevented, for example, from boron nitride exist. .

The cylinders 173 and 175 are connected by the connecting plates 183,

184 and 193 to 198 connected in parallel in pairs. The current path runs through a thermopile as follows; from the terminal 179 via the connecting plate 198 to two positive thermocouples 175, through this and then the connecting plate 184 to two negative cylinders 173, further via one Connection sad he 231 to the connecting plate 195 »then through

the two positive cylinders 175 to the connecting plate (

183 and finally via the two negative cylinders 173 and the connecting plate 193 to the output terminal 180. The Terminals 179 and 180 are connected via cable lugs 251 and connecting conductors 253 so that the thermopiles 21 are in series lie.

When assembling the device, the housing of each thermopile becomes.

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21 by electron beam welding of the plates 117 and formed with the jacket 171. The assembly is then assembled in the container and the container is through the Port 39 evacuated and then filled with high-purity argon under the appropriate pressure (e.g. 1/30 atmosphere). That Argon flows through holes 177 into the housings of the thermopiles 21. The holes 177 are then welded by tungsten arc fusion locked. Finally, the container is evacuated and the pump nozzle 39 is melted.

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Claims (1)

ünoha # Munich, 20 / Sep. 1987 yteß, ₄₆ T * i295i _2ö N 161 - Dr. Hk / P Nuclear Materials And Equipment Corporation, Apollo, Pa. V _v St-A. P a t ent a η s ρ r ti c h e Λ Thermoelectric generator with one or more thermopiles, the hot and cold soldering points of which are connected to common heat supply and discharge lines, a radioactive heat source and a radiopaque shield between the heat source and the heat supply line, characterized in that the shielding ( DEAD). is in thermally conductive connection with the heat source (9T) and the heat supply lines (117). · Ν 2. Generator according to claim 1, characterized in that the Heat supply lines (117) connected to the hot soldering points (181) in a thermally conductive manner, but electrically from them are isolated. 3. Generator according to claim 1 or 2, characterized in that that the radioactive shielding (TOi) with the heat supply lines (117) is in metallic connection. 4. Generator according to one of the preceding claims thus » 009822/0595 characterized in that the thermopiles (21), the heat source (9t) and the radioactive shield (101) inside an evacuated container (23) in a heat-insulating one Screen (121), which consists entirely or partially of a getter material (123, 127, 131), are included. 5. Generator according to claim 4, characterized in that the heat source and the radioactive shield to the Walls of the container with the help of tension wires (109) are suspended, which are anchored to the container walls and connected to the shielding. 6. Generator according to one of the preceding claims, in particular to generate electrical power in the order of magnitude from 1 to 100 watts and more, in which the thermocouples in the thermopiles are made of materials that are adversely affected by a vacuum ^ - eg (lead telluride) characterized in that the thermocouples (173 »175) a thermopile (71) in a vacuum-tight housing (171 1 54 »117) are included in the. an inert Gas is under significant pressure that will prevent thermocouple degradation. 7. Generator according to claim 1, characterized in that the radioactive shield (101) to a thermally conductive 009822 / 059S Intermediate conductor (115) is soldered and that the intermediate conductor metallic with the heat supply lines due to diffusion bonding (117) is connected. . " 8. Generator according to one of the preceding claims, characterized characterized in that the radioactive shield is made of an alloy based on tungsten, the intermediate conductor predominantly 1 - """■■■■" - made of copper and the heat supply from a copper-plated Warming & standing. 9. Generator according to one of the preceding claims, characterized characterized in that the heat source, the radioactive shield and the / thermal acids mounted on shock absorbers (53) which simultaneously serve to dissipate heat from the heat dissipators (54) of the thermopiles 10. Generator according to one of the preceding claims, characterized by a heat-insulating screen; the one "Has a getter effect, shows strong thermal insulation ability and at the same time absorbs gamma rays. .Thermal column, in particular for a thermoelectric generator according to one of the preceding claims, consisting of a plurality of thermocouples of opposite polarity, which are connected to common heat supply and discharge plates 009822/0595 ~ are bound, characterized in that the thermocouples (173, 175) at their cold ends by conical springs (211) are supported, which the thermocouples under almost constant pressure in contact with the heat supply plate • Hold (117), this pressure being greater than normal occurring tensile and thermal loads. 12. Thermopile, especially for a thermoelectric Generator according to one of Claims 1 to 11, with a plurality of thermocouples of opposite polarity, which are connected to common heat supply and discharge lines, characterized in that each thermocouple heat conductive and electrically conductive connecting piece (193, 195, 197 »198) is assigned and that a flexible Connection (191) for the thermally conductive and electrically conductive connection of the connector to the thermocouple serves. 13. Thermopile, in particular for a thermoelectric generator according to one of claims 1 to 10, with a plurality of thermocouples of opposite polarity, which are connected to common heat supply and discharge lines, characterized in that the thermocouples are surrounded by a package of heat radiating foils (123) and that between the foils and the thermocouples (173 _f ITS) there is thermal and electrical insulation (221, 228, 00 9 822/059 5 230) are located. 14. Thermopile according to claim 13, characterized in that successive foils (223, 227) with crossed
Tilting (225, 227) are provided so that the individualisn ■ foils of the package are only at the intersection points of the
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