pat5065085-aspden-thermoelectricenergytransfer

8/6/2019 pat5065085-Aspden-ThermoElectricEnergyTransfer

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United States Patent [19]Aspden et ale

[11] Patent Number:[45] Date of Patent:

5,065,085Nov. 12, 1991

[54] THERMOELECTRIC ENERGYCONVERSION[75] Inventors: Harold Aspden, Chilworth, Isle ofMan; John S. Strachan, Edinburgh,Scotland[73] Assignee: Strachan-Aspden Limited,

Edinburgh, Scotland[21] Appl. No.: 429,608[22] Filed: Oct. 31, 1989[30] Foreign Application Priority DataNov. 18, 1988 [GB] United Kingdom 8826952[51] Int. Cl.s H02N 3/00[52] U.S. Cl 322/2 R; 310/306;

322/2 A[58] Field of Search 322/2 A, 2 R; 310/306[56] References Cited

U.S. PATENT DOCUMENTS3.149,246 9/1964 Mason 322/2 R X3,199,302 8/1965 Rollinger et al. 322/2 R X

3 1

3,365,653 1/1968 Gabor et aI 322/2 R4,004.210 1/1977 Yater 322/2 R4,368,416 1/1983 James 322/2 R4,419,617 12/1983 Reitz 322/2 R

PrimaryExaminer-R. J. HickeyAttorney,Agent, orFirm-Ratner & Prestia[57] ABSTRACTA thermoelectric energy converter incorporates ther-mocouples ina circuit carrying A. C. current via capac-itors which provide electrical coupling but obstructheat transfer between hot and cold junctions. The cyc-lic current oscillations through the capacitors are di-verted by special circuits so as to be rendered asymmet-ric as current oscillations through the thermoelectricjunctions. One such circuit includes the use of a diodeconfiguration regulating current flow through differentthermoelectric junctions spaced apart in the thermalgradient. Another involves the action of a unidirec-tional magnetic field having a polarizing effect on a-three-metal thermoelectric junction.

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1THERMOELECfRIC ENERGY CONVERSION

FIELD OF INVENTIONThis invention relates to energy conversion by ther-moelectric techniques. In particular, it relates to a novelmethod by which a temperature differential can eitherbe established by supplying electrical power or utilizedto generate such electrical power.Conventional thermoelectric energy conversion de- 10

vices use the Peltier effect or the converse, the Seebeckeffect. Hot and cold junctions connect dissimilar metalsin a closed circuit and the EMF develops current in thecircuit in a measure related to the temperature differen-tial and rate of heat input or output. However, such 15devices find little application as energy sources, owingto their poor conversion efficiency. This arises becausethe design criteria for minimizing ohmic resistance loss,e.g. by having the junctions in close proximity, maxi-mize the heat loss by heat conduction. For this reason 20the use of inexpensive metallic materials as conductorsin thermopiles is not generally deemed practical.To achieve tolerable efficiencies. as in refrigerationsystems, research has tended to concentrate upon theuse of semi-conductor techniques or scarce substances 25which are expensive. Evenso, the power conversionefficiencies of known thermocouple devices cannotcompare with the efficiency of the heat to electricityconversion of conventional electrical power generationusing heat engines.This invention overcomes the above deficiency inthermoelectric circuit design. It implements a novelprinciple in a special way with the remarkable resultthat very high efficiencies of power conversion fromheat to electricity or vice versa can be achieved without 35using expensive materials. Given a high efficiency ofenergy conversion the design problem then centers onassuring a high enough rate of energy throughput towarrant commercial application.It is foreseen that apparatus implementing this inven- 40tion can ultimately replace the heat engines used as theprime movers in electric power generation. However,inasmuch as the apparatus can operate efficiently withlow temperature differentials measured in tens of de-grees rather than hundreds. an intermediate application 45will be that of generating electricity from what hashitherto been regarded as waste heat in conventionalsystems.In the reverse mode, where electricity is used to setup temperature differentials, the invention providescooling apparatus of such efficiency that wholly newkinds of technological design become feasible.In summary, this invention relates to a new kind ofthermoelectric circuit based on the Peltier and Seebeckeffects. It departs from what is conventional by apply- 55ing a novel principle which obstructs heat flow betweenhot and cold thermocouple junctions, whilst admittingthe passage of electric current through the junctions ina way which involves a net energy conversion.

BACKGROUND OF THE INVENTIONThe basic principle of the invention to be described isbelieved by the inventors to be wholly original in thesense that what has been achieved uses an A.C. excita-tion technique which interposes capacitors in.a thermo-couple circuit. The operation is in A.C. mode, eventhough the electrical power supplied to or by the sys-tem can be D.C. or A.C. The inventors have no knowl-

5,065,085 2edge of any prior disclosure which is based on the con-ception that a thermocouple device can operate bycurrent passage through the junctions in a sustainedA.C. mode. Indeed. the normal expectation of such aproposal would be that the cyclic heating and coolingof each thermocouple junction at the operating fre-quency should have no advantage for energy transferand should merely generate ohmic lossand lose heat bythermal conduction.Concerning the effects of a magnetic field on thermo-couple operation, a subject which arises in describingcertain aspects of the invention, the inventors are awareof experiments where the effects of magnetic fields areused to measure the Nernst effect, for example. In theseexperiments thermocouples are used to measure tem-perature differentials in the presence of strong magneticfields. However, none of the scientific papers seen bythe inventors discusses any anomalous effects of themagnetic field upon thermocouple operation. Bearing inmind that instrumentation techniques based on galva-nometer measurement using direct current often rely ona minimal current flow by using balancing potentials, itis conceivable that certain effects occurring when alter-nating or significantly high current densities flowthrough thermocouple junctions subjected to magneticfields have not hitherto been researched. In these cir-cumstances, though the primary invention in its broad-est concept is not concerned with the interaction with30 magnetic fields, the scope of certain aspects of the in-vention to be disclosed extends in this direction.BRIEF DESCRIPTION OF THE INVENTIONThe invention centers around providing a means forrestricting the conduction of heat between junctions ina thermocouple circuit. while allowing the relativelyfree flow of electrical energy.The invention is based on the principle of a thermo-electric circuit in which electric current flows betweenthe hotand cold junctions by the capacitative inductionprocesses acting across a dielectric between the platesof a capacitor. Heat flow is obstructed by the heat insu-

lation properties of the dielectric insulation.In implementing this invention it is essential that thecircuit design is such that the thermoelectric junctionsfunction asymmetrically in the heat transfer relationshipwith respect to the direction of current flow.The preferred implementation of the basic principleunderlying the invention involves several inventive50, features, which have found their endorsement by exper-iment rather than being based on the logic of establishedtheoretical expectations. These features, in combina-tion, can be demonstrably shown to provide highlyefficient operation as a practical thermoelectric powerconverter, based on an oscillatory current in the ther-mocouple junctions.In accordance with one aspect, a thermoelectric en-ergy converter comprises:a thermoelectric circuit assembly having two partsa thermally non-conductive barrier mounted betweensaid parts being respectively connected to terminalsadapted to be coupled to an external electric powersystem,a structure for housing the thermoelectric assembly.65 said housing being bounded by heat transfer elementsproviding two external thermal interface surfaces andtwo internal thermal interface surfaces, there beinglayers of heat-conducting electrically non-conducting

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3insulation separating the heat transfer elements from thethermoelectric circuit assembly,a first pair of thermocouple junctions included in said

assembly, said junctions being formed by contact be-tween metals having different thermoelectric properties 5and connected by these metals as part of a closed loopcircuit, the thermocouple junctions being respectivelyin said parts of the assembly,a second pair of thermocouple junctions included in

said assembly, formed by contact between metals hav- 10ing different thermoelectric properties and connectedby these metals as part of a closed loop circuit, thethermocouple junctions being respectively in said partsof the assembly,a pair of capacitors having dielectric insulation, both 15

capacitors being included in each of the closed loopcircuits and both capacitors having their electrodesrespectively connected in said two parts of the circuitassembly, whereby the capacitor dielectric insulationprovides the thermally non-conductive barrier and 20whereby connection of the capacitors in both closedloop circuits provides alternative flow paths for capaci-tor current through different pairs of thermocouplejunctions,circuit polarization means selectively responsive to 25

the capacitor current flow direction positioned so as todivert at least some of the current through one pair ofthermocouple junctions for current flow in one direc-tion and through the other pair of thermocouple junc-tions for current flow in the opposite direction, andcircuit interrupter means connected between the cir-

cuit assembly and the terminals for varying the loadimpedance effective in the loop circuits at a rapid rate toset up current oscillations through the capacitors whenthermoelectrically powered currents flow around the 35thermocouple loop circuits that are commensuratelyrelated to a temperature differential set up between thetwo heat transfer elements.For an integral capacitor-thermocouple fabrication,

the incorporation of capacitor impedance in the ther- 40mocouple circuit implies that the utility of the converterin power applications may depend upon there being ahigh operating frequency, which in certain embodi-ments of the invention will be several hundred kilo-hertz. Optimum performance criteria include the use of 45resonant circuits based on the provision of inductors inthe general circuitry of the system. Also the circuitrycan include electronic components which operate ac-cording to conventional circuit principles to cause thecircuit to self-activate the oscillatory condition. Alter- 50natively, the means for activating an oscillatory circuitcurrent flow comprises an external source of A.C.power, characterized in that the frequency of thissource is the same as the resonant frequency of thethermoelectric circuit.A thermoelectric energy converter based on this

invention can be used in air conditioning, heating orrefrigeration apparatus, besides constituting elementsfor primary generation of electric power using lowgrade heat sources or heat sources of moderate temper- 60ature differential.Other features of the invention will be evident from

the following description by reference to the drawings.Also, as will be seen from this description, the optimumperformance of devices incorporating this invention is 65very much dependent upon the tuning of the resonantcircuitry involved. A high Q factor is necessary to se-cure high efficiency but its actual value in relation to the

5,065,085 4damping factor of the source circuit is important so as toavoid instability, particularly for devices operating inthe Peltier mode.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 shows schematically a general circuit which

operates according to the principles of the invention butaccording to an aspect of the invention which does notinvolve magnetizing means for assuring asymmetricoperation.FIG. 2 is a temperature gradient diagram relating to

the operation of the circuit shown in FIG. 1.FIG. 3 shows a sectional view of a thermoelectric

apparatus incorporating the invention by using an elec-tric A.C. input at conventional power frequency to setup a cooling action on one face of the panel and a heat-ing action on the other face.FIG. 4 shows diagrammatically a typical circuit ar-

rangement suited to the excitation of the electrical reso-nance in the operation of thermoelectric convertersincorporating the invention.

DETAILED DESCRIPTION OF THEINVENTION

The principles of the invention will now be describedby reference to two different thermocouple devices,both of which exhibit efficient energy conversion undertest.

30 One device involves a single junction pair coupled toseparate capacitor components which do not form anintegral part of the thermocouple structure. This isdesigned to function at a relatively low activationpower frequency commensurate with the larger capaci-tances involved.The second device, which will be discussed first, will

be described by reference to FIG. 1 as if it utilizes sepa-rate capacitor components of unspecified design, but apractical implementation requires the capacitors to ob-struct heat transfer across the plates of the capacitor. Tooperate in this way the capacitors must be positionedwith their respective plates heat coupled to the heatexchange surfaces serving as the heat output/input in-terfaces of the system. Thus a normal practical embodi-ment will be one in which the capacitor is fabricated aspart of an electric circuit integral with the thermocou-ples and other electrical components. Such an embodi-ment can be fabricated using the techniques and materi-als which are familiar to those skilled in the art of semi-conductor integrated circuit design.FIG. 1 shows one closed thermoelectric circuit com-

prising two capacitors 1, 2 which isolate the 'hot' and'cold' sides of the device, separating them in a thermalsense, whereas the capacitors couple them together

55 electrically. Here 'hot' and 'cold' are used in a purelyrelative sense to relate to what can be a quite smalltemperature difference a T between the two heat out-put/input interfaces. It may be supposed that the hotside is to the left of the capacitors and the cold side tothe right in FIG. 1. The circuit includes four thermo-couple junctions and four diodes. Their physical posi-tion in relation to the heat output/input interfaces orprimary heat exchange surfaces, denoted by the brokenlines 2-2, is generally as shown in the figure. Thustwo diodes 3, 4, one on the hot side and one on the coldside of the capacitors, conduct the capacitor currentduring one polarity half cycle of oscillation and twodiodes 5, 6, one on the hot side and one on the cold side


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5 5,065,085 6of the capacitors, conduct the current during the other couple junctions the ohmic losses can be very small.polarity half cycle. Although this means a high rate of heat transfer be-Each diode is connected in series with a closely adja- tween thermocouple junctions on the same side of thecent thermocouple junction. The latter are depicted by heat barrier 0-0his does not waste heat energy. Its

circles with arrows corresponding to the direction of 5 effect is to limit the build up of the temperature differen-the current flow allowed by their respective diodes. In tial denoted T in FIG. 2. However, in spite of this thereFIG. 1, each diode is positioned behind the correspond- can be a very substantial overall efficiency in the ther-ing thermocouple, meaning that current flows first moelectric energy conversion as between electricalthrough the diode in each case. Equally, all the diodes power and the thermal power associated with oT.could be positioned in advance of the corresponding 10 If the device operates to use heat input to generate andiodes to achieve the same functional effect. It can be electric power output, the temperature profile is asseen that the arrangement is such that during one half shown by the full curve in FIG. 2. However, in thecycle of circuital capacitor current the flow is through converse mode the broken curve represents the temper-the outermost diode/thermocouple junctions, that is ature profile where electric power input develops thethose closest to the surfaces 2-2, and during the oppo- 15emperature differential. The hot and cold sides of thesite half cycle the flow is through the innermost diode/-converter are then interchanged.thermocouple junctions. In the operation of this device, whether working inThe bimetallic junctions and conductors electrically Seebeck or Peltier modes, it is found that a D.C. voltagecoupling these junctions to the capacitors and diodes develops across the capacitors. The general profile ofmay comprise, for example, copper and lead. The con- 20 this voltage across the section of the device resembles infiguration must be such that the current flow in either some respects the temperature profile presented in FIG.circuit is from copper to lead in the junction on one side 2. This condition presumably arises from the Thomsonof the capacitor thermal barrier 0-0nd from lead to effect by which a temperature gradient can set up acopper on the other side. corresponding potential gradient in a conductor.Thus, in operation, assuming that there is an oscilla- 25 Experiments with operation in the Seebeck modetory current in the circuit through the capacitors, we have shown that a thermal travelling wave is set up

can suppose that the thermocouple junction paired with which flows from the hot to cold sides of the assembly.diode 3 will cool in carrying its unidirectional current The energy carried by this wave has the effect of aug-half cycles, whereas the thermocouple junction paired menting the current in the electrical circuit, which iswith diode 4 will heat. Conversely, the current half 30 tuned for resonance by an inductor in the external cir-cycle in the opposite direction will cause a heating of cuit. By placing a non-inductive load resistor acrossthe thermocouple junction paired with diode 5 and a such an inductor, tests reveal that its damping factor iscooling of the junction paired with diode 6. inversely proportional to the temperature gradient. ThisIt follows that the presence of the current oscillations current augmenting effect is analogous to the behaviourwill act to transfer heat energy thermoelectrically to set 35 of a 'current dumping amplifier', the essential difference

up a temperature profile depicted schematically by the being that the energy is supplied thermally instead offull curve in FIG. 2. Note that since heat energy cannot electrically.easily traverse the heat barrier 0-0provided by the The device has also been shown to be capable ofcapacitor dielectric insulation, the operation of the ther- functioning in the Peltier mode, but the operation in thismoelectric junctions is to set up a substantial tempera- 40 case was critically dependent upon the frequency tun-ture differential as between the innermost thermocou- ing. The frequency has to be tuned to the overshoot andpies regulating one polarity of current flow. In contrast. hysteresis of the diodes and the thermocouple junctions.owing to the limiting effect of the temperatures of the For this reason the tuning of the overall system must beheat exchange surfaces 2-2, the thermoelectric june- very carefully set up at a Q factor just greater than thetions nearest to those surfaces and regulating the other 45 damping factor of the source impedance. The sourcepolarity of current flow have a very much smaller tem- impedance is here determined by the overshoot 'on'perature differential. time of the silicon controlled rectifier in circuit or theThe oscillations will not normally be of truly sinusoi- equivalent programmable unijunction, as a function of

dal waveform, nor will the successive polarity reversals the quarter-cycle of the resonant frequency. The gen-be strictly half-cycle in time measure. The basic condi- 50 eral form of the external tuning circuit will be describedtion is that as much electric charge must flow one way below by reference to FIG. 4.as flows the opposite way in the next polarity reversal The efficiency of the system just described by refer-period. However, because there is a significant difference to FIGS. 1 and 2 tends to the Carnot limit, sinceence in the temperature differentials determining the the speed and frequency of the wave are automaticallythermoelectric power of the respective current direc- 55 determined by the work/heat exchange of the junctionstions, the electrical oscillations are powered in EMF on either side of the capacitors at resonance with theterms in such a way that they can feed energy or absorb circuit. Like all Carnot systems, the rate at which en-energy from a suitably connected load. Assuming that ergy is exchanged is determined by the speed of thevery little heat energy is dissipated by conduction energy exchange at any part of the system. Accord-through the capacitor dielectric, and that ohmic losses 60 ingly, the system is limited in rate by the overshoot ofon the cold side of the system are small. the electrical the diodes and by the thermal conductivity of the com-input/output energy can only translate into heat output- bined junctions metals. If the frequency of the system is/input energy via the temperature differential oT across too high, the greater Thomson effect in the lead con-the heat exchange surfaces 2-2. ductor with respect to copper will cause the dampingItwill be seen that the circuit configuration described 65 factor to rise over a period of time and stall the system

does, therefore, provide the asymmetry feature already after a few thousand cycles. The maximum perfor-mentioned. By fabricating a very compact circuit which mance rate occurs when the damping factor determinedmaximizes the conductor sectional area of the thermo- by the Thomson effect and the load are as close as possi-


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7 5,065,085ble and together are less than the Q factor of the totalcircuit. Owing to the several factors involved in settingup these conditions, adjustments in the related designparameters of this particular embodiment of the inven-tion have so far been established by trial and error meth-ods.For the reasons outlined above. the system shown inFIG. 1 is best suited to applications where efficiency ofenergy conversion is more important than the energythroughput rate, so that the Q factor need not be sohigh 10as to render the system liable to instability under operat-ing conditions.It is stressed that this invention does provide systemswhich operate to convert heat and electrical energy ina highly efficient way. In choosing between the differ- 15ent methods and embodiments which implement differ-ent aspects of the invention, the primary criterion, de-pending upon the application, would normally be theenergy throughput rate. Much depends upon the ongo-ing research to find the best design and the best combi- 20nation of materials. Furthermore, though there aresome indications that the new techniques provided bythis invention do yield signal performance enhancementbeyond that of conventional thermocouple technology,the entire conversion efficiency gain, which isvery high 25and is its primary advantage, may nevertheless be dueexclusively to the way inwhich the capacitors minimizeheat dissipation.Concerning the capacitor fabrication, the relativepermittivity of most dielectrics is inversely proportional 30to the thermal conductivity, with the odd exception, sothat in general high dielectric strength materials arebetter suited to this application since they improve theratio of electric power to rate of thermal loss.There is an aspect of the system shown in FIG. 1 that 35warrants special comment. Usually, with thermoelec-tric circuits, the only potential barriers are those occur-ring at the junctions of two metals. In FIG. 1 the diodesthemselves introduce other junctions. There is purpose,therefore, in supposing that, for the purpose of setting 40up thermoelectric potentials, there are two basic metalsinvolved which have charge carrier densities denoted pand n. The diodes have an internal property that in-volves conductive substances comprising charge carrierpopulation densities p' and n', The diode operation de- 45pends upon the fact that current flow bringing p' and n'charges together is permitted current flow and actiontending to separate p' and n' is restrained by an EMFwhich blocks current flow. However, the p and n car-rier densities in the basic metals are conducive to cur- 50rent flow in either direction.Itmay then be seen that there is another asymmetryin the circuit shown in FIG. 1 because, when currentflows clockwise, supposing p applies to the base metalon the lower part, the carrier sequence is p-p'-n'-p-n on 55the left hand side and n-p'on'-n-p on the right hand side.In terms of the thermoelectric contact potentials, the

n-type interface with a p-type tends to give the samepotential difference as a function of temperature, re-gardless of carrier density. However, there is no such 60equality for the p'-p and n'-n junctions, where the po-tential isa function of temperature and the logarithm ofthe charge carrier density ratio.What this means is that the effective Peltier coeffici-ents of the two parts of the circuit on the different sides 65of the capacitors need not be identical, even at the sametemperature. This results in an asymmetry which isexploited to cause continuous energy transfer via the

8electrical route without significant heat transfer acrossthe capacitors. Note, therefore, the importance of posi-tioning the diodes on either side of the capacitors so thatthey are all in advance of the the thermoelectric junc-tions in the sense of current flow, as shown in FIG. 1,or, alternatively, are all in the retarded position, as theywould be if all the diodes were reversed in FIG. 1.The action described by reference to FIG. 2 must beseen as a transient condition if based exclusively onconventional thermodynamic theory, which condition,however, is sustained by extending the theory in theway just described, owing to the special asymmetryprovided by the diode characteristics.Thus, inunderstanding the basic mode of operation ofthe system in terms of Carnot effects it is best to regardthe thermocouples as all at the same initial temperature.Then, if working in Seebeck mode, application of heaton one side of the capacitors sets up the transients lead-ing to electrical power output in the manner discussed.However, the sustained operation within the limits setby the Carnot thresholds depends upon the asymmetryfeatures incorporated in the system and such asymmetryis essential.The next embodiment of the invention aims to avoidthe dual thermocouple-diode configuration and theneed for semi-conductors in the internal system of thethermoelectric assembly. Instead, the asymmetry ofconventional operation is introduced in a basic thermo-electric circuit by using a magnetic field action.However, there is an asymmetry associated with thenon-conventional thermodynamic aspect as well. Thisarises because three metals are used and, by the argu-ment just presented, if one involves p-type carriers andthe other two involve n-type carriers, the closed circuitseries loop formed by the three metals must have twoopposing-potential p-n junctions and one junction thathas a thermoelectric contact potential determined bythe logarithm of the ratio of the two n-type densities. Ofnecessity this will set up a circulating bias currentwhere the three metals are united and then any passageof other current through the junctions will tend to besubject to a bias effect regulated by the direction ofcurrent flow. Note that n-type and p-type, as applied tobase metals, does not refer to doping in the sense under-stood from semiconductor theory. Rather it refers tothe polarity, negative or positive, of the charge carriers,as evidenced by the sign of the Hall effect or, in somecases, the Thomson effect applicable to the metal.The essential principle on which the invention isbased is that if the dielectric of a capacitance separatesthe relatively hot and cold parts of the thermocouplesystem, there can be no significant heat energy trans-ported by the electric current. The electric charge isarrested at the capacitor plates. There can, with appro-priate design, be a nearly uniform temperature in theparts of the circuit on the hot and cold sides of thecapacitor, which then precludes appreciable actionbased on the Thomson Effect and leaves the thermo-electric power of the couple as the primary EMF.This requires operation in an A.c. mode and this canallow another principle to operate. This is that, if theenergy exchange between heat and electric power at ajunction depends preferentially upon the direction ofcurrent flow as a function of frequency and currentdensity, then the optimization of these parameters canyield a greater rate of energy exchange. Given thatthere is a contact potential difference across a metallicinterface, flow of current in the same direction as the


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9 5,065,085 10potential drop will cause cooling and flow in the oppo- thermocouple circuit. It is essentially a low voltagesite direction will cause heating. If the physical action device producing high current throughput and usinginvolved can be caused to be biased to ensure this opera- much larger metal junctions. It operates at power or .tion is asymmetrical then there will be a residual heating low kilocycle frequencies.or cooling related to overall passage of A.C. current. 5 To secure the same advantage of heat insulation in theEspecially as the capacitances involved can be very electric circuit. capacitors are used. However, these cansmall, a high frequency operation. perhaps measured in be self-standing capacitors with much larger capaci-hundreds of kilocycles, can allow substantial current tance than might be fabricated using a single dielectricflow. The latter assures the higher energy throughput layer integrated circuit technique. Though techniquesrate. 10 for generating electrical oscillations are possible. as byThe action described is reversible, in the sense that if using variable magnetic reluctance systems, this de-electric current flow produces a heating effect at a scription will relate to a device operating in the Peltier

junction, a cold regulating heat sink associated with the mode. An A.C . electrical current is supplied and used tojunction will encourage current to flow and so develop regulate heat exchange.an EMF at that junction. Thus the principles apply for 15 Referring to FIG. 3, a thermoelectric energy conver-systems converting electricity into heat energy transfer sion system comprises two heat exchange surfaces 30between cold and hot interfaces or systems operating to and 31 which are electrically insulated from the thermo-generate such electricity from heat transfer between couple elements by layers 32 of heat sink compound.those surfaces. The enormous advantages provided by The circuit configuration includes two capacitors 33,the invention arise essentially from the saving of heat 20 which serve as A.C. electrical couplings in the circuitenergy otherwise lost by conduction through metal but block heat conduction by electron flow. The ther-conductors connecting the thermocouple junctions. mocouple junctions are composite configurations 34 ofHowever, it is necessary to assure the asymmetrical metal assemblies of copper, nickel and zinc. denoted A,response of the thermocouple junction. One methodused in the embodiment of the invention now to be 25 Band C, respectively. The arrangement is such thatelectric current around the circuit can flow eitherdescribed involves the use of a composite junction inwhich there are two metals A, B and an intermediate through the copper-nickel A-B junction or betweenmetal C, configured according to their different ther- copper or nickel via their interface A-C, B-C junctionsmoelectric properties and conductivities and subject to with zinc. Note, however, that a strong magnetic fielda magnetic field. 30 denoted by the circular arrows and symbol H acts onThe effect of a magnetic field is that it may have a the circuits thus formed. The circuits lie in a common

migratory effect on electron flow at interface bound- plane and the field H is perpendicular to that plane. Thisaries, the direction of migration being independent of field H is unidirectional and is produced by a permanentthe direction of the main current flow, but it may also magnet field whose source is not shown.have an effect on collision probabilities by modifying 35 As already explained, the current flow in circuits A-Cthe electron mean free path. and B-C is asymmetrical with regard to polarity rever-However, a particular implementation of the inven- sals of A.C. flowing through the capacitors. The balanc-

tion operates more by what can be termed 'polarized ing current flow needed to keep the current oscillationsinductive response'. The principle is to cause a current via the capacitors in polarity balance is that in the A-Bto flow along a section of conductor C which is com- 40 circuit. Thus the current flow through the junctionmon to two separate closed circuit paths through con- interfaces has an asymmetrical feature.ductors A and B. The current in C will divide at a The A.C. excitation of the circuit can be via the ter-junction between the parallel routes through A and B, minals at 35, which may be supplied by an external A.C.which are also in interface contact in the junction as- source, which may itself include a capacitor for furthersembly. The circuits lie in a common plane, so that, in 45 heat insulation purposes.flowing around the A-C circuit, the current flows In operation a supply of A.C. power is found to de-around, say, a clockwise circuit when the current in the velop a temperature differential between surfaces 30B-C circuit circulates anti-clockwise, and vice versa and 31. The conversion of electrical power into anduring the alternate half-cycles of the alternating cur- action transferring heat between the two surfaces isrent. 50 very efficient. Experimental work verifying the opera-Given now that there is a unidirectional ferromag- tion of this technique shows that the A.C. operation is

netic field linking both the A-C and B-C circuits in the effective at normal power frequencies. The maximumsame direction transverse to the plane of the circuits, frequency that has been achieved to data with this sys-the mutual inductive coupling between that field source tern is only a few kilohertz, which means that the capac-and the circuits can have an asymmetric inductive effect 55 itors must have a large capacitance.in the two circuits. In effect, magnetic energy stored in In one arrangement in which the nickel conductorcircuit A-C during one half cycle of A.C. will involve a was replaced by lead the need to balance the circuitgreater back EMF than energy stored in circuit B-C resistance in the two parallel paths through A and Bduring the same half cycle. This will favor current flow presented problems owing to the dimensions and fragil-in circuit B-C. Then, during the next half cycle current 60 ity of the lead part of the circuit. By using a ferromag-flow is favoured in circuit A-C. netic material for a conductor such as A. specificallyThe effect of this is to cause an asymmetrical response nickel. it was found possible to have an operative sys-

to the opposite polarity current cycles, even though the tern by confining the region of action of the magneticcircuit paths through metal A and B are designed to field H to the interface regions of the junctions. It seemshave the same resistance. 65 that Lenz's law then operates to take care of the differ-In FIG. 3 a thermoelectric energy conversion device ential impedance as between the two paths through A-C

based on these principles is shown which does not nee- and B-C and a moderately acceptable A.c. performanceessarily require fabrication of capacitors as part of the is obtained.


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5,065,08511A possible effect of the magnetic field H, which ac-counts for the phenomenon effective in this latter em-bodiment of the invention, is to produce a helical mo-tion of conduction electrons as they react to the field inconforming with the Lorentz force law. This motion isabout axes parallel to the field H and so, at the contactsurfaces forming the thermocouple junctions, the fieldhas negligible effect on electron motion across the junc-tions interfacing with zinc. On the other hand it affectsconduction electron migration across the copper-nickel 10A-B interface.In a sense, the Lorentz force also gives rise to a Halleffect and this plus the thermoelectric features of thethree metal combination can be factors militating infavour of any asymmetry. T.he effect of all this is that 1 5flow of current in one direction favours a circuitthrough the zinc, whereas that in the other direction itfavours the direct circuit across the copper-nickel inter-face. This applies when the field H is present, and, forbalanced operation, a similar magnetic field should be 20provided in the other composite thermocouple junctionconfiguration 34.A practical circuit incorporating the system de-scribed by reference to FIGS. 1 or 3 would normallyinclude an inductor tuned to resonate with the capacitor 25at the operating frequency.The circuit design could incorporate inductive ele-ments in series with the capacitors or in parallel, but inthe interests of minimizing ohmic losses there are ad-vantages in providing the inductance external to the 30thermally active components of the converter. Thus inFIG. 4 a configuration isshown inwhich an inductor 40is connected to two capacitative units 41, 42 and twodiodes 43, 44 in a bridge configuration. The arrange-ment is such that, with the capacitances of units 41 and 35

42 matched, there will be resonant oscillations at a fre-quency governed by the inductor-capacitor combina-tion.Presuming that one or both of the capacitative units41, 42 comprise a multiplicity of component circuits 40formed by a series connection of thermoelectric circuitsof the form shown in FIG. 1, it is seen that the inductor40 can operate to sustain current oscillations throughthe capacitor system.Assuming that the thermoelectric energy conversion 45involved in this system is using input heat energy todevelop an electrical output it isdesirable to provide anSCR (silicon controlled rectifier) 45 which operates as atrigger in limiting and controlling the oscillations. If aD.C. output is required this can be drawn from the 50terminals 46 between a centre tap on inductor 40 andthe bridge linking the diodes 43, 44 to the capacitorunits 41, 42. Conversely, if the system operates in thereverse mode, D.C. energy supplied to these terminals46 can develop a temperature differential across the 55heat exchange interfaces of the thermoelectric con-verter in this system.Research has shown that devices incorporating thegeneral principles so far described can be used in onemode at room temperature and powered by a piece of 60ice melting and generating enough power to drive anelectric motor and, in the reverse mode also at roomtemperature, to cause a input of electric power from asmall battery to freeze water at a rapid rate. Such adevice is self-activated to sustain its internal oscillations 65at several hundred kilocycles without any external addi-tional energy or signal input. The efficiency of conver-sion of heat energy to or from electrical energy is ex-

12tremely high, being in the region of 80 to 90 per cent.This is clearly demonstrated in such a simple demon-stration by the fact that, with the motor load discon-nected, the ice melts at between one seventh and onetenth of the rate applicable with the load connected.We claim:1. A thermoelectric energy converter comprises:a thermoelectric circuit assembly having two partsrespectively connected to terminals adapted to becoupled to an external power system;a thermally non-conductive barrier mounted betweensaid parts;a structure for housing the thermoelectric assembly,said housing being bounded by heat transfer ele-ments providing two external thermal interfacesurfaces and two internal thermal interface sur-faces, there being layers of heat-conducting electri-cally non-conducting insulation separating the heattransfer elements from the thermoelectric circuitassembly,a first pair of thermocouple junctions included in saidassembly, said junctions being formed by contactbetween metals having different thermoelectricproperties and connected by these metals as part ofa closed loop circuit, the thermocouple junctionsbeing respectively in said parts of the assembly,a second pair of thermocouple junctions included insaid assembly, formed by contact between metalshaving different thermoelectric properties and con-nected by these metals as part of a closed loopcircuit, the thermocouple junctions being respec-tively in said parts of the assembly,a pair of capacitors having dielectric insulation, bothcapacitors being included in each of the closedloop circuits and both capacitors having their elec-trodes respectively connected in said two parts ofthe circuit assembly, whereby the capacitor dielec-tric insulation provides the thermally non-conduc-tive barrier and whereby connection of the capaci-tors in both closed loop circuits provides alterna-tive flow paths for capacitor current through dif-ferent pairs of thermocouple junctions,circuit polarization means selectively responsive tothe capacitor current flow direction positioned soasto divert at least some ofthe current through onepair of thermocouple junctions for current flow inone direction and through the other pair of thermo-couple junctions for current flow in the oppositedirection, andcircuit interrupter means connected between the cir-cuit assembly and the terminals for varying theload impedance effective in the loop circuits at arapid rate to set up current oscillations through thecapacitors when thermoelectrically powered cur-rents flow around the thermocouple loop circuitsthat are commensurately related to a temperaturedifferential set up between the two heat transferelements.2. A thermoelectric energy converter according toclaim I, wherein the circuit polarization means com-prise four diodes, each diode having a current inputelectrode and a circuit output electrode and each diodebeing connected in series with a corresponding thermo-couple junction to form a diode-junction combination,first and second diode-junction combinations beingconnected in parallel in each part of the assembly, thetwo parallel-connected combinations being connectedby the two capacitors, the two diodes in each such part


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13 5,065,085having their polarities reversed, thereby providing al-ternative flow paths according to the flow direction ofthe capacitor current.3. A thermoelectric energy converter according toclaim 2, wherein first thermocouple junctions of each 5part of the assembly are closer to the thermal interfacesurfaces of the nearest heat transfer element than are thesecond thermocouple junctions in each part of the as-sembly.4. A thermoelectric energy converter according to 10claim 2, in which each parallel-connected combinationof diode and junction comprises a thermocouple junc-tion between different metals A and B in one part of thecircuit assembly, the metal sequence in relation to diodepolarity being such as to permit forward polarity cur- 15rent flow across the junction from metal A to metal B,whereas the metal sequence in each diode junction com-bination in the other part of the circuit assembly is frommetal B to metal A when there is forward current polar-ity flow through the corresponding diodes. 205. A thermoelectric energy converter according toclaim 4, in which the thermocouple junctions in thediode-junction combinations in at least one part of thecircuit assembly are each connected to the current out-put electrode of the corresponding diode, whereby 25forward polarity current through each diode flowsdirectly through the junction before passing into thecapacitor.6. A thermoelectric energy converter according to

claim 4, in which the thermocouple junctions in the 30diode-junction combinations in at least one part of thecircuit assembly are each connected to the current inputelectrode of the corresponding diode, whereby forwardpolarity current through each diode flows directly fromthe junction before passing into the capacitor. 357. A thermoelectric energy converter according to

claim 1, in which the circuit polarization means com-prise magnetizing means for applying a unidirectionalmagnetic field, said means being positioned to direct afield to at least one of the thermocouple junctions with 40its field orientated to act transversely with respect tocurrent flow through that junction.8. A thermoelectric energy converter according toclaim 2, in which each part of the circuit assembly in-cludes a composite thermocouple assembly of three 45metals, A, B, and C, with interfaces A-B, B-C, A-C,constituting A-B and B-A thermocouple junctions,means for connecting said junctions in a primary closedloop circuit including the two capacitors, said capaci-tors being respectively connected between the metals A 50'of two thermocouple assemblies and the metals B oftwo thermocouple assemblies, two secondary closedloop circuits, each including one of the capacitors and aconnection between the metals C of the two thermo-couple assemblies, an external closure path through the 55terminals, one secondary circuit including the A-C andC-A junctions and the other secondary circuit includingthe CoB and B-C junctions, and the junctions of each ofthe thermocouple assemblies lying in the polarizingmagnetic field produced by the magnetization means. 609. A thermoelectric energy converter according toclaim 8, in which the junction assemblies and the capac-

itors are interconnected by conductors which confinethe current oscillations to flow paths at right angles tothe field direction of the magnetizing means. 6510. A thermoelectric energy converter according to

claim 7, in which at least one of the thermocouple junc-tion assemblies comprises a composite assembly of three

14metals A, Band C, with planar junction interfaces A-B,B-C, A-C, the magnetizing means produce a field direc-tion at at least one junction interface lying in the planeof the junction interface but directed at another inter-face, so as to have a component at right angles to theplane of the junction interface.11. A thermoelectric energy converter according to

claim 7, in which at least one of the metals forming ajunction is ferromagnetic.12. A thermoelectric energy converter according toclaim 7, in which at least one thermocouple junction ina pair is subjected to a magnetic field provided by mag-netizing means adjacent that junction.13. A thermoelectric energy converter comprising:a thermoelectric circuit assembly divided into twothermally-isolated parts separated by a thermallynon-conductive barrier and connected to a pair ofterminals adapted to be coupled to an externalelectric power system,

a structure housing the thermoelectric circuit assem-bly and bounded by heat transfer elements provid-ing two external thermal interface surface and twointernal thermal interface surfaces, there beinglayers of heat-conducting electrically non-conduct-ing insulation separating the heat transfer elementsfrom the thermoelectric circuit assembly,

a first pair of thermocouple junctions incl uded in saidassembly, formed by contact between metals hav-ing different thermoelectric properties and con-nected by these metals as part of a closed loopcircuit, the thermocouple junctions being in circuitin different thermally, isolated parts of the assem-bly,

a second pair of thermocouple junctions included insaid assembly, formed by contact between metalshaving different thermoelectric properties and con-nected by these metals as part of a closed loopcircuit, the thermocouple junctions being in circuitin different thermally-isolated parts of the assem-bly,

a pair of capacitors, both capacitors being included ineach of the closed loop circuits and both capacitorshaving their electrodes connected in different ther-mally-isolated parts of the circuit assembly.whereby the capacitor dielectric insulation pro-vides the thermally non-conductive barrier and thecommon capacitor connection in both closed loopcircuits provides alternative flow paths for thecapacitor current through different pairs of ther-mocouple junctions,

circuit polarization means selectively responsive tothe capacitor current flow direction positioned todivert at least some of the current through one pairof thermocouple junctions for current flow in onedirection and through the other pair of thermo-couple junctions for current flow in the oppositedirection,

and a source of A.C. power connected across saidterminals and having a frequency which is the sameas the resonant frequency of the circuit assemblyand is operative to set up current oscillationsthrough the capacitors when thermoelectricallypowered currents flow around the thermocoupleloop circuits commensurately related to a tempera-ture differential set up between the two heat trans-fer elements.

14. A thermoelectric power converter according toclaim 1 in which an inductive circuit component is


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5,065,08515electrically connected to the capacitor circuit to deter-mine a resonant frequency for the oscillatory currentflow.15. A thermoelectric power converter according toclaim 13 in which an inductive circuit component is 5

16electrically connected to the capacitor circuit to deter-mine a resonant frequency for the oscillatory currentflow.

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