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The first record known to this inventor, of a thermo-magnetic motor making use of the Curie point property of materials, is the Nikola Tesla patent of 1886, U.S. Pat. No. 396,121. In his patent Dr. Tesla describes a kinematic thermo-magnetic motor in which a mechanism is caused to reciprocate by means of interrupting a magnetic circuit by the periodic application of heat to a metal “keeper” component that completes the magnetic circuit. The application of heat causes the keeper to transition between magnetic and non-magnetic states, and temporarily lose its ability to conduct magnetic lines of force, thereby opening the magnetic circuit. When the heat is removed the keeper cools below the Curie point transition temperature and returns to a ferromagnetic state, and the magnetic circuit is re-established.
The material property that facilitates this application is known today as the Curie point of the material. It is the temperature at which a given ferromagnetic element or composition of matter, usually a metal alloy, transitions from a ferromagnetic state to an austenitic or non-magnetic state.
By periodically heating and cooling the keeper and causing the keeper to periodically change states, by increasing and decreasing its temperature above and below the Curie point, Dr. Tesla created a fluctuating magnetic field that alternately attracted and released a mechanical armature and produced a reciprocating motor action.
The thermomagnetic, or pyromagnetic, Curie point property of materials is also described in U.S. Pat. No. 5,714,829 by Guruprasad, Feb. 3, 1998. Guruprasad uses the property in an inverse way from my invention in that magnetic fields developing and collapsing in a pyromagnetic material also generate thermal energy, and by means of this property such alloys can be made to pump heat. In Guruprasad's invention, this effect is used for refrigeration.
While ferromagnetism is generally a property of metallic materials, there are exceptions. Some organic materials such as isotopes of graphite and carbon have been known to exhibit ferromagnetic properties.
Tatiana Makarova, a Russian scientist working at Umea University in Sweden, discovered that a polymerized isotope of carbon will exhibit ferromagnetic properties above room temperature. She was experimenting with buckyballs, isotopic carbon C60, searching for superconducting properties. By heating and compressing the carbon molecules, she forced them to join together in polymeric layers.
To her surprise, she found that the new material was magnetic even above 200° C. Prior to her discovery, the highest known temperature at which a non-metallic material was magnetic was −255° C. This record was held by a different molecular form of carbon.
Dr. Makarova's work is documented in the article: “Magnetic Carbon”, Tatiana L. Makarova, Bertil Sundqvist, Roland Hohni, Pablo Esquinazi, Yakov Kopelevich, Peter Scharff, Valerii A. Davydov, Ludmila S. Kashevarova, Aleksandra V. Rakhmanina, issue 413 of Nature, 2001, pps. 716-718.
Documented research on non-metallic magnetic materials can also be found in the article “A Magnet Made From Carbon”, Fernando Palacio, issue 413 of Nature, 2001, pps. 690-691. The article states that experiments with nanostructured forms of graphite may have superconducting and ferromagnetic properties, also above room temperature.
The NASA-Ames Laboratory also reports a rapidly expanding field within nanomagnetism called “single magnetic molecules”. Their research has involved compounds synthesized as crystalline samples composed of identical molecular units. In these compounds, intramolecular magnetic interactions greatly exceed those between molecules, and macroscopic measurements reflect the magnetic properties of an individual magnetic molecule.
Organic magnets could be important because they are much lighter than metals, and can also be made flexible and transparent. The study of magnetic molecules and nanoscale magnets may lead to non-metallic magnetic materials that can be used to build lighter motors and generators.
It should be noted that the Neel temperature, TN, is the temperature at which a ferrimagnetic or antiferromagnetic material becomes paramagnetic—that is, the thermal energy becomes large enough to upset the magnetic ordering within the material. This is analogous to the Curie point in ferromagnetic materials, and may be important in constructing thermomagnetic generators and refrigerators from non-metallic materials such as carbon-based materials.
In my invention, I have differed from Tesla and Guruprasad in that I have applied the thermomagnetic Curie point property of materials, alternately called the thermomagnetic or pyromagnetic property, to create an induction generator with no moving parts. In my invention, the periodic application of heat to a thermomagnetic material, preferably a metal alloy though other thermomagnetic materials could be used, in order to periodically open and close a magnetic circuit, is accomplished by means of a thermoacoustic wave train generated by a thermoacoustic engine.
The operation of the thermoacoustic engine is described in U.S. Pat. No. 6,385,972, Fellows, Thermoacoustic Resonator, and in U.S. Pat. No. 6,910,332, Fellows, Thermoacoustic Engine-Generator. The subject Invention differs from the previous Fellows patents and other prior art as follows: The referenced U.S. Pat. Nos. 6,385,972 and 6,910,332 describe electromagnetic generator means that are actuated dynamically by the oscillating pressure gradient in the thermoacoustic wave. In other words the armature of the generator mean is caused to reciprocate by the oscillating thermoacoustic wave-train, like a piston in a pneumatic motor.
In the subject application (Ser. No. 10/908,711), I am describing a solid state, non-dynamic generator means in which the electromagnetic field flux is caused to fluctuate, to be interrupted and re-established periodically, by the oscillating thermal gradient in the thermoacoustic wave-train. In this subject invention, the generator means has no armature, and no moving dynamic parts.
The ability of acoustic waves propagating in an elastic working fluid to transport thermal energy is well established in the physical sciences, and thermoacoustic engines and various methodologies for making them are well documented. In this instance the term “thermoacoustic” is used to describe an acoustic wave transporting thermal energy. Typically, all thermoacoustic engines have some components in common, such as an elastic working fluid, hot and cold heat exchangers, etc., though these components may differ in design and operating characteristics. Such commonalities may be found in the patents of Fellows, Ceperley, Swift et al, Symko, Hoffler, Garrett and US 2005/0016171. Most thermoacoustic engines are designed for refrigeration purposes. Fellows thermoacoustic engines, including this application, are designed to convert heat energy into electrical energy.
In my invention, the primary magnetic field is generated by a magnetic field generating means, a magnet, which is coupled magnetically to a ferromagnetic stator means, a stator, and a magnetic circuit opening and closing means, a thermomagnetic material. The magnetic field generating means, stator means and magnetic circuit opening and closing means together form a magnetic circuit that supports a magnetic field, or loop of magnetic force. The magnetic circuit is periodically opened and closed by alternately heating and cooling the magnetic circuit opening and closing means so as to cause it to transition back and forth between magnetic and non-magnetic states, by means of a periodic thermoacoustic wave which is caused to impinge upon the magnetic circuit opening and closing means. A fluctuating magnetic field is created by the thermoacoustic wave periodically opening and closing the magnetic circuit, which induces an electric current in a conductor, an inductive winding, wound around the stator means.
By means of this Thermoacoustic Thermomagnetic Generator, the more practical form of electrical energy, derived from the less practical thermal energy, can then be used to power a wide variety of useful equipment.
The thermoacoustic engine generates an acoustic wave which transports thermal energy. There is a thermal gradient between the nodes and antinodes of the acoustic wave. As these nodes and antinodes alternately impinge on the magnetic field opening and closing means, they impart pulses of thermal energy to it. By this means, this Thermoacoustic Thermomagnetic Generator uses thermoacoustic waves to periodically raise the temperature of the magnetic field opening and closing means past its Curie point so that it alternates between magnetic and non-magnetic states.
In conjunction with a stator means and magnetic field generating means, the magnetic field opening and closing means forms a magnetic circuit in which the magnetic lines of force are periodically interrupted and re-established by the action of the nodes and antinodes of the thermoacoustic waves passing over the magnetic circuit opening and closing means. The expanding and collapsing magnetic field created thereby induces an alternating current in the inductive windings of the stator means. The resultant generator has no moving parts.
The invention is comprised of a housing means and combination waveguide and hot-side heat exchanger means containing an elastic working fluid, and disposed therein a stator means, a magnetic field generating means, a multiplicity of induction windings, a thermally-activated magnetic circuit opening and closing means, a thermal insulator means, and a thermoacoustic wave generating means. There also is an external cold-side heat exchanger means for cooling the working fluid.
Said stator means is preferably comprised of ferromagnetic steel laminates such as is common to electric motors and generators, though future materials may differ. Said stator means, in conjunction with said magnetic field generating means, said multiplicity of induction windings and said thermally-activated magnetic circuit opening and closing means comprise a solid state, that is to say a non-kinetic, electromagnetic induction generator.
Said magnetic field generating means may be comprised of either permanent magnets, or electric current carrying coils which create a magnetic field when energized, though permanent magnets are the preferred magnetic field generating means in this instance.
Said multiplicity of induction windings are comprised of electric current carrying wires in which electric current flows when induced to do so by a changing magnetic field, and are so disposed as to be affected by the fluctuating magnetic fields generated in the stator means by the magnetic field generating means and the magnetic circuit opening and closing means.
The magnetic circuit opening and closing means is preferably comprised of a thermomagnetic metal alloy, though non-metal materials which exhibit the ability to transition between magnetic and non-magnetic states as a condition of temperature may also be used. The Curie point is the temperature at which this transition, or change of state, takes place.
The magnetic field generating means is so disposed that the magnetic field generated thereby permeates the stator means and the magnetic circuit opening and closing means, and these three components together complete a magnetic circuit that can be visualized as a closed loop of magnetic lines of force. When the magnetic circuit opening and closing means is in a ferromagnetic state the magnetic circuit is complete and a static magnetic field exists within the stator means. When the temperature amplitude of the magnetic circuit opening and closing means changes sufficiently so that the Curie Point is exceeded and the magnetic circuit opening and closing means changes state and becomes non-magnetic, the magnetic circuit is opened, or interrupted, and the magnetic field within the stator means collapses, and in so doing generates an electric current in the induction windings. When the temperature amplitude of the magnetic circuit opening and closing means changes again in the opposite direction, falling below the Curie point temperature of the material, the magnetic circuit opening and closing means reverts to its former state and becomes ferromagnetic, thereby re-closing the magnetic circuit and re-establishing the magnetic field in the stator means. The magnetic field, in the course of being regenerated, expands across the turns of the induction windings and induces a current of opposite polarity to the first current. By periodically changing the temperature amplitude of the magnetic circuit opening and closing means so that the magnetic circuit opening and closing means repeatedly transitions from magnetic to non-magnetic and back again, an alternating electric current can be generated in the induction windings.
This effect is described in U.S. Pat. No. 396,121, Application #197,115 filed Mar. 30, 1886 by Nikola Tesla.
I have improved upon the efforts of Dr. Tesla by means of rare earth magnet materials not available in 1886, and by means of combining them and the Curie point magnetic circuit opening and closing means with my thermoacoustic engine. The Fellows thermoacoustic engine generates a thermoacoustic wave which periodically changes the temperature amplitude of the magnetic circuit opening and closing means so that an alternating current is generated in the induction windings as described above.
The magnetic circuit opening and closing means is so disposed that a portion extends through an insulating means, such as a ceramic baffle, which separates the stator means and other components comprising the thermomagnetic generator, from the thermoacoustic engine waveguide and the thermoacoustic wave, so that the magnetic field generating means, the stator means and the induction coils are maintained at a cooler temperature than that of the waveguide.
The portion of the magnetic circuit opening and closing means that extends through the insulating means and is exposed to the thermoacoustic wave, is disposed inside the waveguide hot-side heat exchanger section of the thermoacoustic engine containing an elastic working fluid. The working fluid is maintained at a temperature amplitude below the transitional state, or Curie Point, of the magnetic circuit opening and closing means.
Thermoacoustic waves generated inside the waveguide periodically impinge upon the exposed portion of the magnetic circuit opening and closing means and produce a fluctuating temperature amplitude in the magnetic circuit opening and closing means so that the magnetic circuit comprised of the magnetic field generating means, the magnetic circuit opening and closing means and the stator means is periodically opened and closed, thereby generating a fluctuating magnetic field in the stator means and an alternating electric current in the induction windings.
An external cold-side heat exchanger loop cools the working fluid from the waveguide and circulates it back to the cool section of the housing.
The thermoacoustic engine uses a multitude of fuels, waste heat sources, geothermal heat and solar energy to generate the thermoacoustic waves that are used by the thermomagnetic generator to produce electricity. This Thermoacoustic Thermomagnetic Generator is an improvement over other means used to harvest such energy resources and is therefore a new and useful invention.
FIG. 1 is a cross-sectional view of the thermomagnetic generator showing the component parts.
FIG. 2 is a cross-sectional view of the generator housed within the thermoacoustic engine.
FIG. 3 is a cross-sectional view of a panel array of multiple generator units having a common waveguide, housing, cold-side heat exchanger and insulating means.
The Thermoacoustic Thermomagnetic Generator will be described with reference to drawings that are not to scale.
With reference to FIG. 1, the magnetic circuit opening and closing means 1 is in fixed contact with the stator means 5 and completes the magnetic circuit path with the poles of the magnetic field generating means 2. The thermal insulating means 4 is formed around the ends of the stator means 5 and the magnetic circuit opening and closing means 1 near where they are joined. The induction windings 3 are wound around the stator means pole piece. The thermoacoustic waves 6 impinge upon the magnetic circuit opening and closing means 1, periodically heating it past its Curie point and opening the magnetic circuit so that the magnetic field collapses and induces an electric current in the induction windings 3. The magnetic circuit opening and closing means 1 cools during the period between the thermoacoustic waves 6 and re-establishes the magnetic field. The expanding field again induces an electric current in the induction windings 3, in the opposite direction of the first electric current. This action continues for as long as the thermoacoustic engine is generating thermoacoustic waves of the proper thermal amplitude and frequency. Thus, alternating current is induced into the induction windings 3.
FIG. 2 is a cross-sectional view of the thermoacoustic engine with the thermomagnetic generator disposed within it. Thermal energy 9 enters the waveguide 7 via conduction from an external source and heats the working fluid contained within the waveguide 7. Thermoacoustic waves 6 periodically traverse the working fluid within the heated waveguide 7 and are amplified in both pressure and thermal gradient. The periodic thermoacoustic waves 6 impinge upon the magnetic circuit opening and closing means 1 and periodically increase its temperature above its Curie point, thereby interrupting the magnetic circuit in the stator means 5, causing the magnetic field to collapse and inducing an electric current in the induction winding 3. The insulating means 4 separates the waveguide 7 and the generator housing 8 into respective hot and cool zones and reduces the quantity of heat from the waveguide 7 entering into the cooler portion of the housing 8 where the magnetic field generating means 2, the induction windings 3 and the stator means 5 are disposed. The thermoacoustic wave 6 periodically produces a pressure differential between the hot zone of the generator housing 8 adjacent to the waveguide 7, and the cold zone of the generator housing 8 on the opposite side of the insulating means 4 where the magnetic field generating means 2 resides. The pressure differential is periodically equalized by the working fluid flowing from the waveguide 7 hot zone side of the generator housing 8, through a check valve not shown, into a cooler means 10, where the working fluid is cooled and returned back to the cold zone of the generator housing 8 where the magnetic field generating means 2 resides. The cooler working fluid is periodically scavanged from the cold zone of the generator housing 8 by a pumping means 11 and injected back into the waveguide 7 hot zone where thermal expansion of the injected working fluid produces periodic thermoacoustic waves 6.
FIG. 3 shows cross-sectional view of a thermoacoustic engine housing means 8 configured into a panel array of multiple generator units, each unit comprised of a magnetic circuit opening and closing means 1, a magnetic field generating means 2, induction windings 3 and a stator means 5. Each unit is so disposed that the magnetic circuit opening and closing means 1 penetrates through a common insulating means 4 which divides the housing means 8 into a hot zone and a cold zone, and separates the magnetic field generating means 2 and other generator components in the cold zone from the common waveguide cavity 7 hot zone. The waveguide 7 contains an elastic working fluid in which acoustic waves 6 are caused to propagate. The acoustic waves 6 are heated via conduction through the wall of the waveguide 7 from an external source 9. The acoustic waves 6 convey heat to the magnetic circuit opening and closing means 1, periodically increasing their temperature above the Curie point and thereby causing a magnetic flux to produce alternating current in the induction windings 3. The thermoacoustic wave 6 periodically produces a pressure differential between the waveguide 7 hot zone of the generator housing 8 and the cold zone of the generator housing 8, said hot zone and said cold zone being disposed on opposing sides of the insulating means 4. The pressure differential is periodically equalized by the working fluid flowing from the waveguide 7 hot zone side of the generator housing 8, through a check valve not shown, into a cooler means 10, where the working fluid is cooled and returned back to the cold zone of the generator housing 8. The cooler working fluid is periodically scavanged from the cold zone of the generator housing 8 by a pumping means 11 and injected back into the waveguide 7 hot zone where thermal expansion of the injected working fluid produces periodic thermoacoustic waves 6.