Electrical generator or motor structure – Non-dynamoelectric – Thermal or pyromagnetic
Reexamination Certificate
1998-08-31
2004-04-13
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Thermal or pyromagnetic
C136S205000, C136S200000, C313S310000, C438S380000, C438S141000, C062S003200, C062S003300
Reexamination Certificate
active
06720704
ABSTRACT:
BACKGROUND
1. Field of Invention
The present invention is related to diode devices, in particular, to diode devices in which the separation of the electrodes is set and controlled using piezo-electric, electrostrictive or magnetostrictive positioning elements. These include thermionic converters and generators, photoelectric converters and generators, and vacuum diode heat pumps. It is also related to thermotunnel converters.
2. Thermionic Generators
One form of thermionic vacuum diode is the thermionic converter. A problem associated with the design of these is the space-charge effect, which is caused by the electrons themselves as they leave the cathode. The emitted electrons have a negative charge that deters the movement of other electrons towards the anode. Theoretically, the formation of the space-charge potential barrier may be prevented in at least two ways: positive ions may be introduced into the cloud of electrons in front of the cathode, or the spacing between the electrodes may be reduced to the order of microns.
The use of positive ions to reduce space charge is not without problems. Although cesium and auxiliary discharge thermionic converters have been described, they do not have high efficiency, are costly to fabricate, and, particularly in the high-pressure ignited mode, do not have a long life. The technique of introducing a cesium plasma into the electrode space brings with it further disadvantages. These include heat exchange reactions within the plasma during the operation of the device, and the reactivity of the plasma, which can damage the electrodes.
Although Fitzpatrick (U.S. Pat. No. 4,667,126) teaches that “maintenance of such small spacing with high temperatures and heat fluxes is a difficult if not impossible technical challenge”, in an article entitled “Demonstration of close-spaced thermionic converters”, 28
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Intersociety Energy Conversion Engineering Conference, Vol. 1, pages 1573-1580, he goes on to disclose a close spaced thermionic energy converter which operates at temperatures of 1100 to 1500 degrees Kelvin at a variety of cesium pressures. Electrodes are maintained at a separation of the order of 10 &mgr;m by 3 ceramic spacers mounted on the collector. With electrodes at 1300 and 800 degrees Kelvin, conversion efficiencies of 11.6% were obtained. It utilizes advanced monocrystal materials to achieve reliable operation and long life, and produces a reasonable output power with good efficiency at lower temperatures where typical ignited mode devices would produce no useful power at all. It is, therefore, useful at the bottom end of cascaded thermionic systems, with a very high temperature barium-cesium thermionic converter at the top end.
To operate a converter with a gap spacing of less than 10 &mgr;m, the electrode surface must be very flat and smooth, with no deformation larger than about 0.2 &mgr;m. This places a limitation on the practical size of electrodes for the emitter and collector, because heat flux through the surfaces causes a differential thermal expansion from one side relative to the other, leading to thermal expansion-caused deformation into a “dome-like” shape. This issue is even more important in high power operation. Although this deformation can be tolerated if the diameter of the electrodes is very small, the devices described by Fitzpatrick have diameters of several centimeters. Another issue is degradation of the in-gap spacers at high emitter temperatures.
Fitzpatrick addresses both these in a later paper, entitled “Close-spaced thermionic converter with active control and heat-pipe isothermal emitters”, 31
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Intersociety Energy Conversion Engineering Conference, Vol. 2, pages 920-927. He proposes a device having a large isothermal emitter, utilizing a heat pipe built into its structure with a single crystal emitting surface. The proposed device avoids degradation of the in-gap spacers at high emitter temperatures by using active spacing control, utilizing piezo-electric actuators in conjunction with feedback control for continuously adjusting the gap size.
The proposed device, however, is relatively large, expensive and not amenable to mass-production. There remains a need, therefore, for a thermionic generator which is easy to fabricate, inexpensive, reliable, of high efficiency, modular, compact and having an extended life.
For example, the alternator of the automobile could be replaced by a thermionic generator using the heat contained in the exhaust gases as a source of energy, which would lead to an increase in the efficiency of the engine. Svensson and Holmlid, in their paper entitled: “TEC as Electric Generator in an Automobile Catalytic Converter” 31
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Intersociety Energy Conversion Engineering Conference, Vol. 2, pages 941-944, propose the possible use of carbon covered electrodes which become coated with Rydberg matter, resulting in the reduction of the interelectrode distance. They report that such a device might be expected to have an efficiency of 25-30% at temperatures of 1500-1600 degrees Kelvin. To obtain the high temperatures required, a fuel mixture would be injected into the device. Different configurations are discussed, but it is not clear how such a device would be economically constructed.
Another application is in domestic and industrial heating systems. These need a pump to circulate heated water around the system, which requires a source of power. The control circuitry regulating the temperature of the building being heated also requires power. These could both be supplied by means of a thermionic generator powered by the hot flue gases.
A further application utilizes heat generated by solar radiation. This could either be in space or earth-based solar power stations, or on the roof of buildings to supply or augment the power requirements of the building.
In U.S. Pat. No. 5,994,638 to Edelson, assigned to the same assignee as the present invention, and incorporated herein in its entirety by reference, a thermionic converter having close spaced electrodes is disclosed which is fabricated using micromachining techniques. This device addresses many of the problems described above, particularly those relating to economic fabrication and how to achieve close spaced electrode design. However, in operation, temperature differences between the hot emitter and cooler collector may cause high thermal stresses leading to the shape of the region between the electrodes being altered.
The present invention extends the robustness of Edelson's previous device without detracting from its ease and economy of fabrication by allowing it actively to respond to these high thermal stresses by means of active piezo-electric, electrostrictive or magnetostrictive elements incorporated to produce a micro-electromechanical thermionic converter.
Thermotunnel Converter
The thermotunnel converter is a means of converting heat into electricity which uses no moving parts. It has characteristics in common with both thermionic and thermoelectric converters. Electron transport occurs via quantum mechanical tunneling between electrodes at different temperatures. This is a quantum mechanical concept whereby an electron is found on the opposite side of a potential energy barrier. This is because a wave determines the probability of where a particle will be, and when that probability wave encounters an energy barrier most of the wave will be reflected back, but a small portion of it will leak into the barrier. If the barrier is small enough, the wave that leaked through will continue on the other side of it. Even though the particle does not have enough energy to get over the barrier, there is still a small probability that it can tunnel through it. The thermotunneling converter concept was disclosed in U.S. Pat. No. 3,169,200 to Huffman. In a later paper entitled “Preliminary Investigations of a Thermotunnel Converter”, [23rd Intersociety Energy Conversion Engineering Conference vol. 1, pp. 573-579 (1988)] Huffman and Haq disclose chemically spaced graphite layers in which cesium is intercalated in highl
Edelson Jonathan S.
Tavkhelidze Avto
Boreaiis Technical Limited
Tamai Karl
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