Base metal thermopile
United States Patent 2490196

This invention relates to thermoelectric generators and more particularly to thermopiles for the generation of electrical energy through the utilization of heat. An object of my invention is the provision of a simple, efficient and thoroughly practical thermoelectric generator which is particularly...

Beach, Ralph H.
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Beach, Ralph H.
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Other Classes:
136/222, 136/236.1, 136/239, 420/8, 420/117, 428/595, 428/603, 428/614, 428/676, 428/682
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US Patent References:
2325759Ferrous alloy thermocouple element1943-08-03
2290902Thermoelectric element1942-07-28
2126656Thermoelectric converter1938-08-09
1584882Thermoelectric pyrometer1926-05-18


This invention relates to thermoelectric generators and more particularly to thermopiles for the generation of electrical energy through the utilization of heat.

An object of my invention is the provision of a simple, efficient and thoroughly practical thermoelectric generator which is particularly adapted for utilizing waste heat from heat engines, although not limited to that use.

A further object of my invention is the provision of a compact and inexpensive generator characterized by relatively high thermoelectric power and by efficiency of electrical output.

A further object of my invention is the provision of a thermopile from cheap and readily available materials, which is thoroughly satisfactory and highly efficient in transforming heat energy to electrical energy.

A still further object of my invention is the provision of thermoelectrical apparatus which is characterized by low electrical resistance and by high electrical output efficiency.

Other objects of my invention will in part be obvious and in part pointed out hereinafter.

The invention accordingly consists in the composition of materials, features of construction, combination of elements, in the features of operation, and in the relation of each of the same to one or more of the others as described herein, the scope of the application of which is indicated in the following claims.

In the accompanying drawing, illustrating certain embodiments of my invention, Figure 1 represents a thermoelectric generator assembly; Figure 2 is a cross-sectional view taken along the line A-A of the apparatus represented in Figure 1; Figure 3 is a fragmentary view of a thermopile having metal strip or ribbon type electropositive and electronegative members and metal cooling fins; Figure 4 represents a thermocouple having wire or rod type electropositive and electronegative members; and Figure 5 schematically represents a thermoelectric generator and internal combustion engine assembly.

As a conducive to a clearer understanding of certain features of my invention it may be noted at this point that thermopiles, including a plurality of thermocouples which are electrically connected in aiding relationship, have been employed in the prior art for generating electrical energy through the utilization of heat, such as waste heat from prime movers in the heat engine category.

For the generation of electrical energy by means of the thermopile, the thermocouples thereof are heated at points of hot junction as with a direct flame, hot fluids, or the like, while other junction points are at relatively low temperature such as through the influence of some positive cooling appurtenance. A resulting temperature differential across hot and cold junction points of the thermolo couples causes an electromotive force to be set up across output terminals of the thermopile.

There are certain thermopiles in the prior art which have objectionably low thermoelectric power which as a cindition is attributable to the materials employed in the thermocouple components or to the character of junction points of these same components. Then, too, another problem confronted in the thermopile art has to do with electrical resistance properties of the ineluded thermocouples. Often, due to the composition of metals or alloys employed, the thermocouple components introduce electrical resistance effects which seriously reduce current output, cause excessive heating which extends to the cold junctions, and otherwise impair efficient operation of the thermopile.

There is also an outstanding problem of maintaining the necessary cold junctions in thermopiles so as to achieve maximum temperature differential in a practical manner with respect to hot junctions in the same assembly. In this connection, certain cooling appurtenances in the prior art are found to be excessively expensive either to construct or to maintain or often too cumbersome or heavy for use in installations which should be compact or light in weight.

The character of included materials for obtaining the thermoelectrical effect, and the construction and arrangement of parts in the thermopile proper also frequently eliminate the possibility of achieving a lightweight or compact installation.

A practical limit necessarily imposed on cost of materials likewise is found to an extent to have influenced the ultimate quality, weight, compactness and performance of thermopiles in the prior art.

An outstanding object of my invention accordingly is the provision of a relatively lightweight thermoelectric generator in which cold junctions of included thermocouples are kept effectively cool with simple compact cooling apparatus, and which generator is capable of developing a maximum of electrical energy per degree of temperature differential gained through cooling of the Cold junctions and heating of hot Junctions of the included thermocouples.

Referring now more particularly to a preferred embodiment of thermoelectric generator apparatus of my invention (indicated generally ai 10 in Figure 1 of the accompanying drawing) there is provided a thermopile II which includes a plurality of thermocouples 12 (Figure 4) electrically connected in series-aiding relationship.

Each of the thermocouples connected in the pile includes an electropositive member 12a prefer-' ably of substantially pure iron, such as of Armco Magnetic ingot iron containing in approximate percentages 0.015% carbon, 0.028% manganese, 0.005% phosphorus, 0.025% sulphur, 0.003% silicon and the remainder principally all iron.

An electronegative member 12b also is included in each thermocouple 12; this preferably being an iron-silicon alloy steel member in which the silicon ranges from about 3% to approximately 4% with iron being a principal part of the remainder. The Iron-silicon steel members illustratively are made of Armco grade 72 transformer steel containing in addition to iron the following in approximate percentages: 0.01% S carbon, 0.1% manganese, 0.01% phosphorus, 0.03% sulphur and 3.1% silicon. The voltage had is on the order of 550 microvolts per degree C. difference between the hot and cold junctions.

Instead of the iron-silicon steel members, which I are preferred, there are other satisfactory types of electronegative members 12b which I employ with the electropositive and preferably iron members 12a in my thermoelectric generators.

Among these other types are those fashioned | from constantan or copper-nickel alloy metals containing, in approximate percentages, 60% to 45% copper, 40% to 55% nickel, with or without manganese ranging up to 1.5%, and any remainder principally all iron. 4 The electropositive and electronegative members of each thermocouple 12a and 12b are joined together at their one ends by welding, preferably by fusion or autogenous welding, so as to form a hot junction 12c. The two metals fuse to- 4 gether and form the junction. The end of one couple also is Joined to the beginning of the next to form a cold Junction 12d also preferably by fusion or autogenous welding. All thermocouples of the pile thus are Joined in electrical 5Q series wherein the electropositive and electronegative members are disposed in alternate throughout the series; this being a thermoelectrical series. Opposite ends of the series, such as terminals TI and T2, are used for the output 51 of power from the thermopile. * An electrically conductive coating on the wire 12e, formed as by electrodeposition and preferably of copper, advantageously is employed as a cladding on the surface of one or both of the 6( electropositive and electronegative members of each thermocouple to minimize electrical resistance effects along the couples in the thermopile.

As an alternative, either or both of the elements may employ a parallel circuit of low resistance, 61 as for example, a copper wire, in place of the low resistance cladding. The cladding metal, or parallel conductor of low resistance, is omitted from the welded zones of hot junctions 12a and cold junctions 12b to avoid any impairment of 7( the thermoelectric effect. I find that coppernickel alloy members such as of constantan when clad as described are especially useful as electronegative members in my thermoelectric generator or thermopile apparatus. 7i The thermopile illustratively is mounted in a fireproof block I of heat insulating, electrically non-conductive material such as in a block of transite or bonded asbestos which, for example, s is formed around the same by molding and pressing. On one side of the block the various thermocouple hot Junctions in the pile protrude and are exposed for heating as within a housing on duct 14; which illustratively is sealed gas-tight to the block as by means of gaskets along lips 14a, 14b and constitute part of exhaust manifold 15a (see Figure 5) of internal combustion engine 15 so as to transfer hot exhaust gases from the engine to the hot Junctions.

1i I find advantage in employing heat-radiating fins 16, preferably of copper, as means for cooling the thermopile cold junctions, particularly when an increased temperature differential is needed across hot and cold junctions of the ther0g mopile to provide a corresponding increase in electrical output. These fins, in preferred manner of attachment, are affixed one each to the thermopile cold junctions by brazing or by welding without separating or disrupting the preI viously welded electropositive and electronegative thermocouple members. In the fireproof block mounting arrangement mentioned hereinbefore, the thermopile cold junctions protrude, with fins attached, from the block 13 on an opO posite side remote from the hot junctions. When desired the fins may be exposed to a forced draft of cooling air, for example by housing the fins in a suitable conduit connected with an air fan (not shown).

6 A thermoelectric generator provided in accordance with my invention is highly useful in installations which desirably are compact or relatively light in weight such as in installations which depend for heating of the thermopile hot 0 junctions upon heat engines or heat-transfer means of the same such as an aircraft or other Internal combustion engine exhaust manifold or a steam intake or exhaust manifold of a steam engine. The metallic components such as the 5 electropositive or electronegative members and the manner of joining the same, suggested herein, also contribute to lightness of weight of my thermoelectrical apparatus and are instrumental in the obtainment of outstanding efficiency of 0 generator operation.

Thus it will be seen that in my invention means are provided whereby the various objects hereinbefore noted together with many thoroughly practical advantages are successfully achieved.

S It will also be seen that my apparatus is suitable for use in meeting a wide variety of demands for electrical power and in many of which uses serves an important function of conserving residual energy which otherwise would be wasted in the 0 form of heat.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments noted, it will be understood that all matter described and/or illustrated Sherein is to be interpreted as illustrative and not as a limitation.

I claim: 1. In a thermoelectric generator, the combination which includes a plurality of iron members Seach of carbon content not exceeding about 0.02%, and a corresponding plurality of ironsilicon members each consisting of about 3% to 4% silicon with carbon content not exceeding about 0.01% and the remainder all iron welded to I said iron members in a sequence of hot junctions and cold junctions so as to form a thermoelectrical series.

2. In a thermoelectric generator, the combination which includes a plurality of iron and ironsilicon members each of carbon content not exceeding about 0.02%, with the silicon content of the latter amounting to about 3% to 4%, welded together in a sequence of hot junctions and cold junctions so as to form a thermoelectrical series; and electrically conductive copper coatings on at least said iron-silicon members for alleviating electrical resistance effects along the series.

3. In a thermoelectric generator, the combination which includes a plurality of iron and ironsilicon members each of carbon content not exceeding about 0.02%, with the silicon of the ironsilicon members amounting to about 3% to 4%, joined together in thermoelectrical series in a sequence of hot junctions and cold junctions; and heat conductive metal fins mounted on at least some of said cold junctions for radiating heat from the same.


REFERENCES CITED The following references are of record in the file of this patent: a UNITED STATES PATENTS Number 241,859 808,086 842,391 1,118,269 1,242,499 1,584,882 2,126,656 2,224,573 2,290,902 2,325,759 Name Date Higgs ----------- May 24, 1881 Hell -----------. Dec. 26, 1905 Diecks ---------- Jan. 29, 1907 Creveling ....---- Nov. 24, 1914 Webb -----.---.--. Oct. 9, 1917 Marsh et al. .----. . May 18, 1926 Pack ------------- Aug. 9, 1938 Hunter -----------Dec. 10, 1940 Wiegand --------- July 28, 1942 Pinch ------------ Aug. 3, 1943 OTHER REFERENCES Kowalke, O. L., Trans. Electrochemical Socy., 20 vol. 26 (1914), pages 200, 201. (Copy in Division 56.) Caswell, A. E., Int. Critical Tables, vol. 6 (1929), pp. 214 and 224. (Copy in Scientific Library.)