Data publikacji: 2018.01.05

Generatory termoelektryczne

Generatory termoelektryczne przetwarzają ciepło bezpośrednio w elektryczność, wytwarzając napięcie generowanego na połączeniu dwóch różnych metali.

Historia zaczyna się w 1821, gdy Thomas Johann Seebeck odkrył, że prąd elektryczny powinien przepływać w obwodzie zrobionym z dwóch odmiennych metali, z węzłów w różnych temperaturach. To tak zwane zjawisko Seebecka. Oprócz wytwarzania prądu, jest ono podstawą dla termopary, powszechnie stosowana metoda pomiaru temperatury.


Wytwarzany napięcie jest proporcjonalny do różnicy temperatur między dwoma węzłami. Stała proporcionalności nazywa się współczynnikiem Seebecka.

Połączony szeregowo ciąg termopar występuje pod nazwą "stos termoelektryczny", przez analogię do stosu galwanicznego, chemicznej baterii z ogniwami ułożonymi naprzemiennie. Duński fizyk Oersted oraz francuski fizyk Fourier wynaleźli pierwszy termoelektryczny stos w około 1823, używając par małych antymonowych i bizmutowych pasków połączonych szeregowo. Stos termoelektryczny został rozbudowany przez Leopoldo Nobiliego (1784-1835) i Macedonio Melloniego (1798-1854). Początkowo był używany do pomiarów temperatury i promieniowania podczerwonego, ale także został błyskawicznie wykorzystany jako trwałe źródło zasilania we wszelkiego rodzaju doświadczeniach fizycznych.

George Simon Ohm był prawdopodobnie najsłynniejszym użytkownikiem termopary. W 1825 pracował nad zależnością między natężeniem i napięciem na połączeniu naprzemiennie drutów o różnej oporności bliskiej zwarcia. Po początkowym szybkim przepływie prądu polaryzacja stosu powodowała regularne obniżanie się napięcia, bardzo komplikując pomiary. Ohm wziął radę kolegi i zastąpił stos galwaniczny stosem termoelektrycznym, i rezultaty okazały się dużo lepsze. Informacja ta, to tylko cztery lata po odkryciu zjawiska Seebecka, więc idea stosu termoelektrycznego była szybko rozbudowana. Niestety nie byłem w stanie zidentyfikować pierwszego zastosowania efektu do zasilania urządzeń.

Tak na marginesie, prawo Ohma spotkało z bardzo chłodnym przyjęciem w jego własnym kraju; jak ktoś trzeźwo oświadczył, że: "niestety, prawo Ohma spotkało się z opornością". Pruski minister edukacji wypowiedział się, że "profesor który głosił takie herezje jest niegodny uczyć nauk ścisłych."
To jest właśnie to, co się zdarza, wtedy gdy politycy próbują się angażować w nauki ścisłe. I w związku z tym rozwój nauki był nieco ograniczany.

 

WCZESNA HISTORIA GENERATORÓW TERMOELEKTRYCZNYCH


Przedstawiamy poniżej kilka pierwszych generatorów termoelektrycznych lub "stosów termoelektrycznych". Próbowałem ułożyć je w porządku chronologicznym ale nie wszystkie mają zdefiniowaną datę powstania. Moc maksymalna jest uzyskana z stosu termoelektrycznego, wtedy gdy jego opór obciążenia jest równy jego oporowi wewnętrznemu. Jak przy wszystkich źródłach elektrycznych. 
Podczas gdy opór wewnętrzny ciągu termopar jest bardzo mały, może to być źródło zasilania o dużym prądzie ale niskim napięciu i odwrotnie, gdy opór wewnętrzny ciągu termopar jest duży, wtedy jest to źródło zasilania o dużym napięciu i małym prądzie. Oczywiście łączenie szeregowe i równoległe łańcuchów termopar pozwala regulować natężenie i napięcie prądu wg. potrzeb.

 

Stos termoelektryczny Pouilleta: około 1840.

Myślę, że ten, jest najwcześniejszym stosem termoelektrycznym jaki do tej pory znalazłem. Niestety nie znam szczegółów na tentemat i jego obsługa jest niejasna. Nie wiadomo, gdzie jest podawanatemperatura; być może jeden mosiężny zbiornik trzymał gorącą wodę adrugi zimną? Jeżeli tak, to było to dużo mniej efektywne źródło ciepła niż płomień gazowy.

W każdym zbiorniku, każda z rur w kształcie litery L, z niezrozumiałychprzyczyn, wydaje się wchodzić do szklanego naczynia.

Claude Pouillet (1790-1868) był pionierem w detekcji promieniowania podczerwonego. Używał "pyroheliometru" - zasadniczo kalorymetruwodnego - do pomiaru intensywności promieniowania słonecznego. Aparatura przedstawiona powyżej nie jest pyroheliometrem; może to być raczej pewnego rodzaju przyrząd pomiarowy niżjako takie źródło prądu. 

Przykład w CNAM, Conservatoire National des Arts et Metiers, w Paryżu. Fotografia autora.

 

Z lewej: Stos termoelektryczny Ruhmkorffa: około 1860.

Palniki gazowe są wewnątrz czarnego korpusu urządzenia; kurek na rurze doprowadzającej gaz jest na dole po lewej stronie. Mosiężne zbiorniki trzymają schłodzoną wodę dla zimnych węzłów.

Interesującą cechą jest styk ślizgowy na górze, który pozwala zmieniać napięcie wyjściowe przez połączenie z różną liczbą węzłów do obwodu.Terminale wyjściowe są u góry po prawej stronie.

Heinrich Daniel Ruhmkorff, elektryczny wynalazca  i twórca przyrządów, jest najbardziej znany z niezwykłych usprawnień jakie zrobił w zwojnicy indukcyjnej. Niemniej jednak wydaje się, że był także zaangażowany w biznes dotyczący stosu termoelektrycznego. Ruhmkorff urodził się 15 stycznia 1803, w Hanover, Niemcy, a zmarł 20 grudnia 1877, w Paryżu.

Przykład w CNAM, Conservatoire National des Arts et Metiers, w Paryżu. Fotografia autora.

 

Z lewej: Stos termoelektryczny Markusa: 1864.

SEM pojedynczej pary była nazywana "jedną dwudziestą bateriiDaniela" która wytwarzała około 55 mili woltów. Ujemny metal byłw proporcjach 10:6:6 stopem miedzi, cynku i niklu, podobny do niemieckiegosrebra, a dodatni metal w proporcjach 12:5:1 był stopem antymonu, cynku i bizmutu.Sztaba żelazna a-b była podgrzewana a dolne końce chłodzone przez zanurzeniew wodzie. Błędem tego projektu był szybki wzrost oporu wewnętrznego,jako że dwa stopy utleniały się na ich punkcie styku.

Stos termoelektryczny Markusa wygrał nagrodę w 1864/5 WiedeńskiegoStowarzyszenia Studenckiego dla Rozwoju Nauki. 

Od opublikowania w czasopiśmie "Elektryczność w Służbie Człowiekowi" w artykule jego trzeciego wydania w 1896; stos termoelektryczny wydaje się pojawiać dużo wcześniej,  i na pewno przed 1888. Początkowo był opublikowany w Niemczech i opisany przez Dr A R Von Urbanitsky-ego.

 

Z lewej: stos termoelektryczny Becquerela.

This was invented by M. EdmondBecquerel (1820-1891), at a date unknown. The junctions were composedof copper sulphide for one metal, and German silver for the other.
It appears that D is a trough of cooling water for the cold junctions,supplied at B and exiting at C. There appears to be another trough onthe other side of the central burner E. Gas for the burner is suppliedvia pipe A.

Edmond Becquerel was the father of physicist Henri Becquerel, who discovered radioactivity

 

From "Electricity and Magnetism", 1891.

 

 

Z lewej: Stos termoelektryczny Clamonda.

This pile, developed inassociation with Mure, used a zinc-antimony alloy for one metal andiron as the other. It was gas-fired, and could liberate 0.7 oz ofcopper per hour by electrolysis while consuming 6 cubic feet of gas inthe same period. The output current was quoted in this outlandishfashion because electroplating was the main application of these devices; possibly practical ammeters did not yetexist.
The diagonal connections that join each ring of couples in series can be seen between the two verticalstrips.

The gas pipe can be seen comingin from bottom right. The little coffee-pot thing in the line isactually a gas pressure regulator.

 

From "Electricity in The Service of Man"

 

 

Z lewej: Stos termoelektryczny Clamonda. Schemat.

The solid sectors A were madeof the alloy, while the cooling fins F were made of sheet iron to actas cooling fins for the cold junctions.

 

From "Electricity in The Service of Man", a much longer book than "Electricity in The Service of Chameleons"

 

 

Z lewej: Stos termoelektryczny Clamonda w rzeczywistości.

Note gas feed with tap running into the centre of the pile.

 

To eksponat z Muzeum Uniwersytetu w Pawii, Lombardia, Włochy.

 

 

Left: The Clamond Thermopile: section.

Showing the multiple annular burners in the centre of the pile. Gas enters through tube T.

According to the French journal La Nature for 1874, one of these piles was in use at the printing works of the Banque de France, presumably forelectroplating.

 

Picture from La Nature 1874.

 

 

Left: The Improved Clamond Thermopile: 1879.

The EMF of this pile was noless than 109 Volts, with an internal resistance of 15.5 Ohms. Themaximum power output was therefore 192 Watts, at 54 Volts and 3.5 Amps.

This pile was fired by coke.The hot junctions were at C, while the cold junctions D were cooled bysheet iron as in the original design above. What purpose was served bythe tortuous path T-O-P taken by the hot gases is unclear, becausethere seem to have been no hot junctions in the inner sections.
This beast was 98 inches high and 39 inches in diameter.

It was a serious piece of machinery, quite capable of delivering a lethalvoltage.

 

From "Electricity in The Service of Man"

 

 

Left: The Noe Thermopile.

The hot junctions are thepointed things directed inwards to the central burner. The coldjunctions are cooled by radiation and convection from the verticalstrips on the outside.

The inventor, Fr. Noe, camefrom Vienna. The output EMF of this pile was about 2 Volts, with aninternal resistance of 0.2 Ohm. This was for a pile with 128 couples.

 

From "Electricity in The Service of Man".

 

 

Left: One thermocouple from the Noe Thermopile.

The hot junction is a copper pin in a brass case, surrounded by"an alloy" which is presumably the other half of the junction.

The connecting wires visiblehere on each side were of "German silver". German silver (better knownnowadays as nickel silver) is the generic name for a range of brightsilver-grey metal alloys, composed of copper, nickel and zinc; itcontains no real silver.
These wires were essential to join the thermocouples together, butreduced its efficiency as they conducted heat away from the hotjunctions to the cold ones. The problem is elegantly solved in modernsemiconductor versions by using alternate P and N type materials thatdo not require these connections.

 

From "Electricity in The Service of Man".

 

 

Left: The Noe Thermopile in reality.

This high-performance versionis surrounded by little cylindrical fins for cooling the cold junctions, permitting a greateroutput.

 

This example is in the History Museum of the University of Pavia in Lombardy, Italy.

 

 

Left: Hauck's thermopile.

The EMF of a single couple wasquoted as "0.1 of a Daniel cell" which makes it about 110 milliVolts;this seems rather high to me. The current capacity using 30 couples was "capable of making a platinum wire 1.2 inches longred-hot" which isnot a very useful sort of spec, since we have no idea how thick thewire was.
The Hauck pile was fired by gas, using something looking very much likea Bunsen burner. The cold junctions were water-cooled by a series oflittle cylindrical tanks, and there was an obscure little glass devicein the middle; possibly to show the rate of gas flow?

These devices appear to havebeen produced commercially in different sizes, with two or three placedon a common frame. They were used for science education and electroplating. To put a time marker onthis, it was 1843 when MosesPoole took out a patent for the use of thermoelectricity instead ofbatteries for electro-deposition purposes. This was long beforepractical dynamos and alternators.

In the days when chemical cellsneeded a lot of attention, something that provided power at the strikeof a match must have had its attractions.

 

From "Electricity in The Service of Man".

 

 

Left: Article in Nature: Nov 18,1875.

Doctor Stone reads an article on thermopiles.

This gives some interestingpractical details on the problems of brittle thermocouple materials andthe difficulty of avoiding oxidation when iron was used as one half ofthe couple, as it was in the Clamond pile. There is also theinteresting suggestion that petroleum should be vaporised at the cool junctions, reducing theirtemperature, and the resulting vapour burntat the hot junctions.

Attempts to find out more about Dr Stone have so far failed.

 

This article comes from the English journal Nature, not to be confused with the French journal of the same name.

 

 

Left: Gülcher's thermopile: c 1898.

It looks as if it wasgas-fired, with the gas going in through the spigot on the right, butunfortunately that is all I know about it at present.

 

This example is in the History Museum of the University of Pavia in Lombardy, Italy.

 

 

Left: Commercial thermopile: 1898.

A handy thermopile withwall-mounting bracket. It is gas-fired, with the gas going in throughthe central spigot. The output terminals are bottom left. Manufacturerunknown, but if it really could be supplied by "any respectableelectrician" it must have seen some commercial success.

Cooling looks like it might beany issue; presumably it relied on convection and radiation from thecylindrical outer surface, as there are no signs of water coolingarrangements. I would have thought that would have reduced itseffciency markedly. There are no visible fins to improve cooling.

If the biggest model gave 2.5A at 8.5V, that's a healthy output of 21 Watts.

Bottone was a regular contributor to discussions in the English Mechanic at thetime.

 

From English Mechanic 9 Sept 1898, p98

 

AN ASIDE ON EARLY GAS SUPPLY.
Coke-firingis clearly not an attractive option unless you had a big thermopilelike the Improved Clamond above. Coal gas was far superior fortable-top models. But when did gas supply to buildings start? Here area few historical nuggets that show that gas could be laid on ratherearlier than you might think. But for a year or two, the Duke ofWellington could have written his despatch reporting his victory overNapoleon at Waterloo by gaslight.

By 1819, 288 miles of gas pipes had been laid in London to supply 51,000 burners.

Thefirst commercial town gas supply in the USA began at Baltimore,Maryland in 1816, lighting residences, streets, and businesses.

By 1850, all public lighting in France was by gas.

I haveso far no been able to discover when gas was introduced in the Germanstates; can anyone help? Anyway, I think I have shown that a gas supplywas in fact ready and waiting for the thermopile.

 

THERMO-ELECTRIC GENERATORS IN THE TWENTIETH CENTURY

 

 

Left: Yamamoto patent: 1905.

This thermopile was patented inJapan in 1905 by one Kinzo Yamamoto. Few other details are known; muchinformation was destroyed in the Tokyo Earthquake of 1923.

The P-type material is made ofbismuth, antimony and zinc in the proportions: Bi:Sb:Zn=12.0:48.0:36.8.In the figure, D is a P-type "Bullet" and E is a Nickel electricalconnection. (Probably that should be nickel-silver: see above)F is thepin to collect heat flow from the flame. A is an electrical and thermalmetal connection. B is a cooling fin.

 

Thisdesign has an unmistakable resemblance to the Noe thermopile above; infact it appears to be a very faithful copy. It was presumably intendedfor powering radios, but this is pure guesswork on my part.

Itappears that Great Britain was rather slow in electrification comparedwith other European countries. Light could be provided by gas, andheating by coal, but electricity was needed to run radios and agas-fired thermopile was one way to get it. Alternatively, you tookyour lead-acid filament accumulator into town to get it charged foryou, which was somewhat less than convenient.

THE THERMATTAIX: circa 1925

 

Left: The Thermattaix: circa 1925.

Not a name that exactly tripsoff the tongue. The voltmeter on the front registers from 0 to 10Volts; a suitable voltage range for charging accumulators running 6.3Volt valve heaters. The black knob below the meter obviously controlledsomething- presumably the gas supply.
It appears this device was designed to charge lead-acid accumulatorsrather than power the radio directly. This may have been because outputvoltage fluctuations would have had little effect on accumulators, butwould have been very bad for the filaments of valve heaters.

This example is in the Science Museum in London.

 

Themagazine Amateur Wireless, in April 1929 carried an advert for theThermattaix, apparently claiming that it could work your wireless setby gas, petrol, electricity or steam. Electricity? It goes on to claimthat amongst their customers were gas companies, the Italian airforce,architects of note and big game expeditions in Africa and India.

THE CARDIFF GAS LIGHT & COKE CO: 1930s

Thegas-fired machine below, which seems to have no name, but was sold bythe The Cardiff Gas Light & Coke Company, was brought to myattention by John Howell, who says that his father sold a number ofthese when working in South Wales during the 1930's; that's whattriggered this page. I must admit that I had never heard of such athing in Britain before- they must have been fairly rare. I would havethought that by 1930 the provision of mains electricity would have beenwell advanced. However, apparently not.

Whether The Cardiff Gas Light & Coke Co made this machine themselves, or bought it in, is currently unknown.

 

Left: The gas-fired thermo-electric generator: 1930s.

Well, it was certainly theinvention of a generation, but not of the generation that advertisedthis machine, as you will have seen from the thermopiles above.

It is believed it containedthermopiles (ie series arrays of thermocouples) that produced 2 Volts @0.5 amps for valve filaments/heaters and 120 Volts @ 10mA for the HT.

Thermocouples do not generatemuch voltage, but since they are simply junctions between two kinds ofwire, connecting many in series is feasible. One of the most usefulcombinations is Ni/NiCr, ie nickel/nickel-chromium. This has athermovoltage of about 4 mV/100K and a usable temperature range up tosome 1000 K. This is very likely the type of couple used in thisgenerator; it implies that 40 mV is about the most you can get fromeach thermocouple, so 50 in series would have been needed for the 2 Vfilament supply and 3000 in series for the 120 V HT. This soundspossible, though probably rather protracted to assemble and maybe heavyon labour costs. It would be interesting to know what the retail pricewas.

 

Picture kindly provided by John Howell.

 

 

Left: Advertising blurb for the thermo-electric generator. Probably printed on the other side of the page above.

The automatic control featureis intriguing. Given that any radio of the time would have had aClass-A output stage, whose current drain does not depend on volume,there seems no need to compensate for load changes. What might havebeen more useful (and possibly what the copywriter meant) would havebeen control to stabilise the 2V filament supply against changes in gaspressure. Excess filament voltage would have seriously reduced the lifeof the valves.

You may have heard of "steam radio" but this advertisment offers "gas radio".

 

Picture kindly provided by John Howell.

 

 

Left: The gas-fired thermo-electric generator: 1930s.

With no sign of a connection for an outside flue, I can't help wondering how much carbon monoxide these thingsproduced.

Apologies for poor picture quality.

 




RADZIECKA LAMPA: 1959r.
 

Left: A Russian thermo-electric generator based on a kerosene lamp.

This lamp was introduced in1959, once again to power radios. Presumably there were parts of Russiathat Stalin's electrification program had not reached. The outputvoltage(s) are unknown, but since a picture is known to exist of itpowering a valve radio, HT must have been generated somehow, possiblyby a vibrator power supply.
(In this context a vibrator is an electromechanical device, similiar toan electric bell, that chops low-voltage DC into crude AC that can beapplied to a step-up transformer. They were widely used in car radiosbefore semiconductors arrived)

I have just been informed byPine Pienaar that he has seen one of these things, and it yielded both1.5 and 90 Volts, so it could replace a composite dry battery with thesame output voltages. Such batteries were once widely used to operatesmall radios.
Such radios typically used four 7-pin valves and needed a 90V HT supplyat around 12mA and a 1.5V filament supply at 125mA or 250mA dependingon the valves used.

This example seems to be missing its metal chimney. (see pictures below)

 

  Z lewej: Wycinek na temat radzieckiego generatora termoelektrycznego.

This confirms that the 90V HT was generated directly.Presumably "invested" should read"invented".

Cutting kindly provided by Ed Maurus, original source unknown.

 

 

Left: Russian thermo-electric lamp partly dismantled.

Pablo Reyes tells me that thereare thirty cooling fins. The terminal plate has 5 terminals, dulynumbered 1 to 5. That's presumably two isolated thermo-electricgenerator banks and an earth terminal.

 

Photo kindly provided by Pablo Reyes.

 


WSPÓŁCZESNE GENERATORY TERMOELEKTRYCZNE
Thesemachines are alive and well, being used in remote places where smallamounts of electricity are required and the complications of aninternal-combustion engine and alternator are not welcome. Modernversions use a thermopile made up of a series array oflead-tin-telluride semiconductor elements, rather than simple thermocouples. These thermojunctions are much more efficient thansimple thermocouples, and have been available since the mid-1960s. Theyare commonly used (working in reverse, of course) to cool the littlesofa-side beer refrigerators which are now quite common.

This gives a very good account of semiconductor thermojunctions and how they work: Thermoelectrics by Tellurex(external link)

For one example of modern gas-fired thermoelectric generation, see: Global Thermoelectric. (external link)

Thermoelectricgenerators can also be heated by radioactive decay, and such devicesare used to power interplanetary space probes and the like, wheredistance from the sun means that solar power is not an option. See: Free Dictionary: RTGs

Even so, I wasthinking that thermoelectric generators must be very rare- and then Ifound one working away in my garden shed. They are everywhere around us!
They are used in central heating boilers to control the pilot-lightvalve. When the pilot is burning, the thermopile generates about 750mV- enough to actuate a small solenoid that keeps the pilot valve open.This sadly doesn't mean you can run a central-heating system with noelectric power, as the main gas valve is operated by mains powerswitched by the room thermostat; in any case, the pump wouldn't run.

 

 

Left: A modern thermo-electric generator or thermopile made by Honeywell for boiler control.

The voltageoutput is 750 mV with the "Cold" Junction at 416 degC (780 F) and theHot Junction at 760 degC. (1400 F) I know that 416 degC is not exactlycold, but this thing is mounted inside the boiler combustion chamber.
Assuming Ni/NiCr thermocouples are used, we can deduce from this that the device contains about 55 thermocouples in series.

So why is a thermopile used forthis job? Presumably because it is very simple and reliable; it is hardto see how a thermopile could fail to the danger state- it can hardlygenerate electricity when it isn't hot.

 

Źródło oryginału: http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm

Źródło strony, tłumaczenie i uzupełnienia: www.aztekium.pl

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