Batteries: thermoelectric and photoelectric – Thermoelectric – Processes
Reexamination Certificate
1999-11-30
2001-05-08
Gorgos, Kathryn (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Processes
C310S306000, C322S00200R
Reexamination Certificate
active
06229083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to thermionic generators, and in particular to thermionic generators fabricated using micromachining methods.
2. Description of The Related Art
Most electricity is generated at a power station by a process in which heat is used to convert water to steam. The steam expands through a turbine device causing it to rotate. This powers a generator unit, which produces electricity. The heat is provided by burning a fuel such as coal, oil, gas, or wood, or from nuclear, solar or geothermal energy.
On a smaller scale, the generator unit may be powered by an internal combustion engine, such as a diesel or petrol driven motor. Similarly, the alternator used with the internal combustion engine in every type of automobile for providing electricity to the vehicle is powered by the rotating drive shaft of the engine.
All these devices use moving parts which are subject to friction and wear, and only a percentage of the heat generated is converted into electricity.
The thermionic generator, a device for converting heat energy to electrical energy, was first proposed by Schlieter in 1915. This device depends on emission of electrons from a heated cathode. In a thermionic generator, the electrons received at the anode flow back to the cathode through an external load, effectively converting the heat energy from the cathode into electrical energy at the anode. Voltages produced are low, but Hatsopoulos (U.S. Pat. No. 2,915,652), herein incorporated by reference, has described a means of amplifying this output.
One of the problems associated with the design of thermionic converters is the space-charge effect, which is caused by the electrons as they leave the cathode. The emitted electrons have a negative charge which deters the movement of other electrons towards the anode. Theoretically, the formation of the spacecharge potential barrier may be prevented in at least two ways: the spacing between the electrodes may be reduced to the order of microns, or positive ions may be introduced into the cloud of electrons in front of the cathode. Additionally, in practice, more difficulties remain, such as having low efficiency, costly to fabricate, and, particularly in the high-pressure ignited mode, do not have a long life.
SUMMARY OF THE INVENTION
From the foregoing, it may be appreciated that a need has arisen for a thermionic generator which is easy to fabricate, inexpensive, reliable, of high efficiency and having an extended life. In accordance with one embodiment of the present invention, a method for building a thermionic converter comprises: providing an electrode; creating a central depression of substantially uniform depth on a face of said electrode; and coating a surface of said central depression with a layer comprising a thermionic material.
In accordance with another embodiment of the present invention, a method for building a thermionic converter using a micromachinging technique comprising the steps of: providing an electrode; creating a central depression of substantially uniform depth on a face of said electrode using a micromaching technique; coating a surface of said central depression with a layer comprising a thermionic material; and providing a second electrode comprising a face, wherein said face of said second electrode comprises a central depression of substantially uniform depth, wherein said central depression of said second electrode is coated with a layer comprising a thermionic material.
In accordance with another embodiment of the present invention, a method for converting heat to electricity comprises: providing a thermionic converter comprising: a first electrode, wherein a face of said first electrode comprises a central depression of substantially uniform depth, wherein said first electrode further comprises a coating of thermionic material on said central depression; an edge region on said first electrode comprising a channel cut along two opposing sides of said central depression; a second electrode, wherein a face of said second electrode comprises a central depression of substantially uniform depth, wherein said second electrode further comprises a coating of thermionic material; and an edge region on said second electrode comprising a channel cut along two opposing sides of said central depression, wherein said first electrode is joined with said second electrode, wherein said edge region in said first electrode is in contact with said edge region in said second electrode; providing a gap between said thermionic material on said first electrode and said thermionic material on said second electrode; connecting an electrical load to said thermionic converter; and allowing electrons to flow from said thermionic material of said first electrode to said thermionic material of said second electrode.
The present invention discloses a thermionic generator having close spaced electrodes and constructed using microengineering techniques. The present invention utilizes, in one embodiment, the technique known as MicroElectroMechanical Systems, or MEMS, to construct a thermionic generator. The present invention further utilizes, in another embodiment, microengineering techniques to construct a thermionic generator by wafer bonding. The present invention further utilizes, in another embodiment, the technique known as MicroElectroMechanical Systems, or MEMS, to construct a thermionic generator by wafer bonding.
A technical advantage of the present invention is to provide a thermionic generator constructed using micromachining techniques. Another technical advantage of the present invention is that the thermionic generator may be constructed easily in an automated, reliable and consistent fashion.
A still another technical advantage of the present invention is that the thermionic generator may be manufactured inexpensively. A yet another technical advantage of the present invention is that the thermionic generator may be manufactured in large quantities.
Another technical advantage of the present invention is that electricity may be generated without any moving parts.
Still another technical advantage of the present invention is to provide a thermionic generator in which the electrodes are close-spaced. A further technical advantage of the present invention is that the thermionic generator has reduced spacecharge effects.
A yet further technical advantage of the present invention is that the thermionic generator may operate at high current densities. Another technical advantage of the present invention is to provide a thermionic generator using new electrodes having a low work function.
An additional technical advantage of the present invention is that electricity may be generated from heat sources of 1000K or less. A still additional technical advantage of the present invention is that waste heat may be recovered.
Yet another technical advantage of the present invention is to provide a thermionic generator which produces electricity at lower temperatures than those known to the art.
A still additional technical advantage of the present invention is that a variety of heat sources may be used. Another technical advantage of the present invention is that electricity may be generated where needed rather than at a large power station.
A technical advantage of the present invention is that electricity may be generated using nuclear power, geothermal energy, solar energy, energy from burning fossil fuels, wood, waste or any other combustible material. Still another technical advantage of the present invention is to provide a thermionic generator which can replace the alternator used in vehicles powered by internal combustion engines.
A further technical advantage of the present invention is that the efficiency of the engine is increased. Another technical advantage of the present invention is to provide a thermionic generator which has no moving parts. A yet another technical advantage of the present invention is that maintenance costs are reduced.
Other technical advantages of the present inventi
Borealis Technical Limited
Gorgos Kathryn
Parsons Thomas H
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