US20070175217A1

US20070175217A1 - Thermoacoustic thermomagnetic generator

Info

Publication number: US20070175217A1
Application number: US11/695,874
Authority: US
Inventors: Oscar Fellows
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-05-24
Filing date: 2007-04-03
Publication date: 2007-08-02
Also published as: US20060266041A1

Abstract

The present invention is a thermoacoustic thermomagnetic generator 100. The generator includes a stator 5 that supports and channels magnetic fields. It further includes a magnetic field generator 2 that magnetically couples to the stator. In addition, the generator includes a magnetic circuit opening and closing member 1 that changes magnetic states in response to changes in temperature where the member couples to the stator to complete a magnetic circuit. Further, the generator includes a thermal insulator 4 that couples to the stator and the magnetic circuit opening and closing member. And, the generator includes a plurality of induction windings 3 that conduct electric current where the induction windings couple to the stator. The periodic opening and closing of the magnetic circuit creates a magnetic field in the stator that induces an alternating electric current in the induction windings which allows the generator to produce electric power.

Description

CROSS REFERNECE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 10/908,711, filed May 24, 2005, which is incorporated by reference for all purposes into this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to thermoacoustic generators. More specifically, the present invention relates to thermoacoustic thermomagnetic generators.
2. Description of the Related Art
The first record known of a thermo-magnetic motor making use of the Curie point property of materials is the Nikola Tesla patent, 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, which uses the property in an inverse way from this 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 Umeå 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: TATIANA L. MAKAROVA, BERTIL SUNDQVIST, ROLAND HOHN!, PABLO ESQUINAZI, YAKOV KOPELEVICH, PETER SCHARFF, VALERII A. DAVYDOV, LUDMILA S. KASHEVAROVA, ALEKSANDRA V. RAKHMANINA, “Magnetic Carbon”, issue 413 of Nature, 2001, pps. 716-718.
Other documented research on non-metallic magnetic materials can also be found in the article FERNANDO PALACIO, “A Magnet Made From Carbon”, issue 413 of Nature, 2001, pps. 690-691, which 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 Néel temperature, TN, is the temperature at which a ferromagnetic or anti-ferromagnetic 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.
The present invention differs from Tesla and Guruprasad in that it applies the thermomagnetic Curie point property of materials, alternately called the thermomagnetic or pyromagnetic property, to create an induction generator with no moving parts. In the present 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 one example of a thermoacoustic engine is described in U.S. Pat. No. 6,385,972 (The Thermoacoustic Resonator Patent) and in U.S. Pat. No. 6,910,332 (The Thermoacoustic Engine Patent), both patents have a common inventor to the present invention. These patents describe an electromagnetic generator that is actuated dynamically by the oscillating pressure gradient in the thermoacoustic wave. In other words the armature of the generator is caused to reciprocate by the oscillating thermoacoustic wave-train, like a piston in a pneumatic motor. The present invention, however, describes a solid state, non-dynamic thermoacoustic thermomagnetic generator 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. Thus, the generator of the present invention 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. By means of the present invention, 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 present invention uses the thermal gradient in thermoacoustic waves to periodically raise the temperature of a thermomagnetic material past its Curie point so that it alternates between magnetic and non-magnetic states. In conjunction with a stator, induction windings and magnet, the metal alloy forms a magnetic circuit that is periodically interrupted and re-established by the action of the thermoacoustic waves. The expanding and collapsing magnetic field induces an alternating current in the stator windings. The resultant generator has no moving parts. This invention can be used in a thermoacoustic engine with hot and cold heat exchangers, a working fluid contained in a reservoir that is divided into hot and cold zones, and a resonant waveguide that are typical of the art of thermoacoustic engine. The basic arrangement of components of the present invention can be scaled in size from the micro-miniature to the very large. The present invention can also be arrayed in a thermoacoustic engine that contain multiple units of the present invention and includes a common waveguide, housing and hot and cold heat exchanger, such as in a panel array of multiple miniature units.

SUMMARY OF THE INVENTION

The present invention is a thermoacoustic thermomagnetic generator. The generator comprises a stator that supports and channels magnetic fields. It further comprises a magnetic field generator that magnetically couples to the stator. In addition, the generator includes a magnetic circuit opening and closing member that changes magnetic states in response to changes in temperature where the member couples to the stator to complete a magnetic circuit. Further, the generator includes a thermal insulator that couples to the stator and the magnetic circuit opening and closing member. And, the generator includes a plurality of induction windings that conduct electric current where the induction windings couple to the stator. The periodic opening and closing of the magnetic circuit creates a magnetic field in the stator that induces an alternating electric current in the induction windings which allows the generator to produce electric power.
In addition, the magnetic circuit opening and closing member further comprises a thermomagnetic or pyromagnetic material that changes state from a ferromagnetic condition to an austenitic non-magnetic condition when its temperature is periodically increased past its Curie Point temperature by the thermal energy transported by the thermoacoustic waves impinging upon it.

DESCRIPTION OF THE DRAWINGS

To further aid in understanding the invention, the attached drawings help illustrate specific features of the invention and the following is a brief description of the attached drawings:
FIG. 1 is a cross-sectional view of the present invention showing the component parts.
FIG. 2 is a cross-sectional view of the present invention housed within an exemplary thermoacoustic engine.
FIG. 3 is a cross-sectional view of a panel array of multiple units of the present invention housed in a second exemplary thermoacoustic engine that features a common waveguide, housing, cold-side heat exchanger and insulators.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method and apparatus for a thermoacoustic thermomagnetic generator. This disclosure describes numerous specific details in order to provide a thorough understanding of the present invention. One skilled in the art will appreciate that one may practice the present invention without these specific details. Additionally, this disclosure does not describe some well known items in detail in order not to obscure the present invention.
The present invention is a major operational component of a thermoacoustic engine such as describe in the Thermoacoustic Resonator Patent and the Thermoacoustic Engine Patent. To fully appreciate the novelty of the present invention, I make reference to the operation of the present invention as used in an exemplary thermoacoustic engine as previously described and illustrated in those patents. A thermoacoustic engine generates an acoustic wave that transports thermal energy. There is a thermal gradient between the nodes and antinodes of the acoustic wave. As these nodes and antinodes alternately impinge upon the magnetic field opening and closing member, they impart pulses of thermal energy to it. Through this operation, the present invention is able to use the thermoacoustic waves to periodically raise the temperature of the magnetic field opening and closing member past its Curie point so that it alternates between magnetic and non-magnetic states.
In conjunction with a stator and magnetic field generator, the magnetic field opening and closing member 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 member. The expanding and collapsing magnetic field created thereby induces an alternating current in the inductive windings that are coupled to the stator. As a result of the synergy between its component members, the present invention has no moving electromechanical parts. In addition, it is also appropriate to describe the present invention as a solid state, that is to say a non-kinetic, electromagnetic induction generator.
The stator of the present invention is preferably comprised of ferromagnetic steel laminates such as is common to electric motors and generators, though future materials may also be applicable. In addition, the magnetic field generator may be comprised of either permanent magnets, which are the preferred embodiment, or electric current carrying coils which create a magnetic field when energized. Further, the 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 by the magnetic field generator and the magnetic circuit opening and closing member. Further, the magnetic circuit opening and closing member is preferably comprised of a thermomagnetic metal alloy, though non-metal materials that 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 generator is so disposed that the magnetic field generated by it permeates the stator and the magnetic circuit opening and closing member, 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 member is in a ferromagnetic state the magnetic circuit is complete and a static magnetic field exists within the stator. When the temperature amplitude of the magnetic circuit opening and closing member changes sufficiently so that the Curie Point is exceeded and the magnetic circuit opening and closing member changes state and becomes non-magnetic, the magnetic circuit is opened, or interrupted, and the magnetic field within the stator collapses, and in so doing generates an electric current in the induction windings. When the temperature amplitude of the magnetic circuit opening and closing member changes again in the opposite direction, falling below the Curie point temperature of the material, the magnetic circuit opening and closing member reverts to its former state and becomes ferromagnetic, thereby re-closing the magnetic circuit and re-establishing the magnetic field in the stator. 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 member so that the magnetic circuit opening and closing member repeatedly transitions from magnetic to non-magnetic and back again, an alternating electric current can be generated in the induction windings.
The magnetic circuit opening and closing member is so disposed that a portion extends through a thermal insulator, such as a ceramic baffle, which separates the stator and other components comprising the present invention from the waveguide in a thermoacoustic engine and the thermoacoustic wave, so that the magnetic field generator, the stator, and the induction coils are maintained at a cooler temperature than that of the waveguide. The portion of the magnetic circuit opening and closing member that extends through the thermal insulator 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 member.
With reference to FIG. 1, the thermoacoustic thermomagnetic generator 100 comprises the magnetic circuit opening and closing member 1 that in fixed contact with the stator 5 and completes the magnetic circuit path with the poles of the magnetic field generator 2. The thermal insulator 4 is formed around the ends of the stator 5 and the magnetic circuit opening and closing member 1 near where they are joined. The induction windings 3 are wound around the stator pole piece. The thermoacoustic waves 6 impinge upon the magnetic circuit opening and closing member 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 member 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 electric current is induced into the induction windings 3.
FIG. 2 is a cross-sectional view of an exemplary thermoacoustic engine that uses the thermoacoustic thermomagnetic generator of the present invention. 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 member 1 and periodically increase its temperature above its Curie point, thereby interrupting the magnetic circuit in the stator 5, causing the magnetic field to collapse and inducing an electric current in the induction winding 3. The thermal insulator 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 generator 2, the induction windings 3 and the stator 5 reside. 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 thermal insulator 4 where the magnetic field generator 2 resides. The pressure differential is periodically equalized by the working fluid flowing from the waveguide 7 (which is also the hot side heat exchanger) hot zone side of the generator housing 8, through a check valve not shown, into a cold side heat exchanger 10, where the working fluid is cooled and returned back to the cold zone of the engine housing 8 where the magnetic field generator 2 resides. The cooler working fluid is periodically scavenged from the cold zone of the generator housing 8 by a thermoacoustic wave generator 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 a cross-sectional view of another exemplary thermoacoustic engine that has an engine housing 80 configured into a panel array of multiple generator units, of the present invention. Each thermoacoustic thermomagnetic generator is so disposed that the magnetic circuit opening and closing member 1 penetrates through a common thermal insulator 4 which divides the housing 80 into a hot zone and a cold zone, and separates the magnetic field generator 2 and other generator components in the cold zone from the common waveguide cavity 70 hot zone. The waveguide 70 (also the hot side heat exchanger) 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 70 from an external source 9. The acoustic waves 6 convey heat to the magnetic circuit opening and closing member 1, periodically increasing their temperature above the Curie point and thereby causing a magnetic flux to produce alternating electric current in the induction windings 3. The thermoacoustic wave 6 periodically produces a pressure differential between the waveguide 70 hot zone of the engine housing 80 and the cold zone of the engine housing 80, with the hot zone and the cold zone being disposed on opposing sides of the thermal insulator 4. The pressure differential is periodically equalized by the working fluid flowing from the waveguide 70 hot zone side of the engine housing 80, through a check valve not shown, into the cold side heat exchanger 10, where the working fluid is cooled and returned back to the cold zone of the engine housing 8. The cooler working fluid is periodically scavenged from the cold zone of the generator housing 8 by a thermoacoustic wave generator 11 and injected back into the waveguide 70 hot zone where thermal expansion of the injected working fluid produces periodic thermoacoustic waves 6.
To summarize, the present invention is a thermoacoustic thermomagnetic generator. The generator comprises a stator that supports and channels magnetic fields. It further comprises a magnetic field generator that magnetically couples to the stator. In addition, the generator includes a magnetic circuit opening and closing member that changes magnetic states in response to changes in temperature where the member couples to the stator to complete a magnetic circuit. Further, the generator includes a thermal insulator that couples to the stator and the magnetic circuit opening and closing member. And, the generator includes a plurality of induction windings that conduct electric current where the induction windings couple to the stator. The periodic opening and closing of the magnetic circuit creates a magnetic flux in the stator that induces an alternating electric current in the induction windings which allows the generator to produce electric power.
In addition, the magnetic circuit opening and closing member further comprises a thermomagnetic or pyromagnetic material that changes state from a ferromagnetic condition to an austenitic non-magnetic condition when its temperature is periodically increased past its Curie Point temperature by the thermal energy transported by the thermoacoustic waves impinging upon it.
Other embodiments of the present invention will be apparent to those skilled in the art after considering this disclosure or practicing the disclosed invention. The specification and examples above are exemplary only, with the true scope of the present invention being determined by the following claims.

Claims

1. A thermoacoustic thermomagnetic generator, comprising:

a stator that supports and channels magnetic fields;

a magnetic field generator that magnetically couples to said stator;

a magnetic circuit opening and closing member that changes magnetic states in response to changes in temperature, said member couples to said stator to complete a magnetic circuit;

a thermal insulator that couples to said stator and said magnetic circuit opening and closing member;

a plurality of induction windings that conduct electric current, said induction windings couple to said stator; and

wherein the periodic opening and closing of said magnetic circuit creates a magnetic field in said stator that induces an alternating electric current in said induction windings.

2. The claim of claim 1 wherein said magnetic circuit opening and closing member further comprises a thermomagnetic or pyromagnetic material that changes state from a ferromagnetic condition to an austenitic non-magnetic condition when its temperature is periodically increased past its Curie Point temperature by the thermal energy transported by the thermoacoustic waves impinging upon it.

3. A method to manufacture a thermoacoustic thermomagnetic generator, comprising:

providing a stator that supports and channels magnetic fields;

magnetically coupling a magnetic field generator to said stator;

coupling a magnetic circuit opening and closing member to said stator to complete a magnetic circuit, said member changes magnetic states in response to changes in temperature;

coupling a thermal insulator to said stator and said magnetic circuit opening and closing member;

coupling a plurality of induction windings to said stator, said induction windings conduct electric current; and

4. The claim of claim 3 wherein said magnetic circuit opening and closing member further comprises a thermomagnetic or pyromagnetic material that changes state from a ferromagnetic condition to an austenitic non-magnetic condition when its temperature is periodically increased past its Curie Point temperature by the thermal energy transported by the thermoacoustic waves impinging upon it.

5. A method to use a thermoacoustic thermomagnetic generator, comprising:

providing a stator that supports and channels magnetic fields, said stator magnetically couples to a magnetic field generator, said stator couples to a magnetic circuit opening and closing member that changes magnetic states in response to changes in temperature which completes a magnetic circuit, said stator and said member further couple to a thermal insulator, said stator further couples to a plurality of induction windings that conduct electric current;

periodically opening and closing said magnetic circuit creates a magnetic field in said stator that induces an alternating electric current in said induction windings.

6. The claim of claim 5 wherein said magnetic circuit opening and closing member further comprises a thermomagnetic or pyromagnetic material that changes state from a ferromagnetic condition to an austenitic non-magnetic condition when its temperature is periodically increased past its Curie Point temperature by the thermal energy transported by the thermoacoustic waves impinging upon it.