Field of the Invention
The present invention relates generally to the field of converting
heat energy directly to electrical energy. More particularly, an improved thermionic
electric converter is provided.
Background of the Invention
Heretofore, there have been known thermionic converters such as those
shown in U.S. Patent Nos. 3,519,854, 3,328,611, 4,303,845, 4,323,808, and 5,459,367
(all to the inventor of the present invention and all hereby incorporated by reference),
which disclose various apparatus and methods for the direct conversion of thermal
energy to electrical energy. In U.S. Patent No. 3,519,854, there is described a
converter using Hall effect techniques as the output current collection means. The
'854 patent teaches use of a stream of electrons boiled off of an emissive cathode
surface as the source of electrons. The electrons are accelerated toward an anode
positioned beyond the Hall effect transducer. The anode of the '854 patent is a
simple metallic plate, which has a heavily static charged member circling the plate
and insulated from it.
U.S. Patent No. 3,328,611 discloses a spherically configured thermionic
converter, wherein a spherical emissive cathode is supplied with heat, thereby emitting
electrons to a concentrically positioned, spherical anode under the influence of
a control member and having a high positive potential thereon and insulated from.
As with the '854 patent, the anode of the '611 patent is simply a metallic surface.
U.S. Patent No. 4,303,845 discloses a thermionic converter wherein
the electron stream from the cathode passes through an air core induction coil located
within a transverse magnetic field, thereby generating an EMF in the induction coil
by interaction of the electron stream with the transverse magnetic field. The anode
of the '845 patent also comprises a metallic plate which has a heavily static charged
member circling the plate and insulated from it.
U.S. Patent No. 4,323,808 discloses a laser-excited thermionic converter
that is very similar to the thermionic converter disclosed in the '845 patent. The
main difference is that the '808 patent discloses using a laser which is applied
to a grid on which electrons are collected at the same time the potential to the
grid is removed, thereby creating electron boluses that are accelerated toward the
anode through an air core induction coil located within a transverse magnetic field.
The anode of the '808 patent is the same as that disclosed in the '845 patent, i.e.,
simply a metallic plate which has a heavily static charged member circling the plate
and insulated from it.
U.S. Patent 5,459,367 advantageously uses an improved collector element
with an anode having copper wool fibers and copper sulfate gel instead of a metallic
plate. Additionally; the collector element has a highly charged (i.e., static electricity)
member surrounding the anode and insulated from it.
Another prior design has an anode and cathode which are relatively
close together such as two microns apart within a vacuum chamber. Such a prior design
uses no attractive force to attract electrons emitted from the cathode to the anode
other than induction of cesium into the chamber housing the anode and cathode. The
cesium coats the anode with a positive charge to keep the electrons flowing. With
the cathode and anode so close together, it is difficult to maintain the temperatures
of the cathode and anode at substantially different temperatures. For example, one
would normally have the cathode at 1800 degrees Kelvin and the anode at 800 degrees
Kelvin. A heat source is provided to heat the cathode and a coolant circulation
system is provided at the anode in order to maintain it at the desired temperature.
Even though the chamber is maintained at a vacuum (other than the cesium source),
heat from the cathode goes to the anode and it takes a significant amount of energy
to maintain the high temperature differential between the closely spaced cathode
and anode. This in turn lowers the efficiency of the system substantially.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, an object of the present is to provide and new and improved
thermionic electric converter.
A more specific object of the present invention is provide a thermionic
electric converter with improved conversion efficiency.
Yet another object of the present invention is to provide an improved
cathode for a thermionic electric converter.
A further object of the present invention is to provide a thermionic
electric converter having the cathode and anode spaced apart significantly such
that they are relatively thermally isolated from each other.
Yet another object of the present invention is to provide a thermionic
electric converter wherein energy can be removed from electrons just before they
strike the anode.
The above and other objects of the present invention, which will be
apparent as the description proceeds, are realized by a thermionic electric converter
having a casing member, a cathode within the casing member operable when heated
to serve as a source of electrons, and an anode within the casing member operable
to receive electrons emitted from the cathode. The cathode is a wire grid having
wires going in at least two directions that are transverse to each other. A charged
first focusing ring is in the casing member, between the cathode and the anode,
and is operable to direct electrons emitted by the cathode through the first focusing
ring on their way to the anode. A charged second focusing ring is in the casing
member, between the first focusing ring and the anode, and is operable to direct
electrons emitted by the cathode through the second focusing ring on their way to
the anode. Additional focusing rings may be necessary. The cathode is preferably
separated from the anode by 4 microns to five centimeters. More preferably, the
cathode is separated from the anode by one to three centimeters. A laser operable
to hit electrons (i.e., apply a laser beam to the electrons) between the cathode
and anode. The laser hits the electrons just before they reach the anode. The laser
is operable to provide quantum interference with the electrons such that electrons
are more readily captured by the anode.
The wire grid of the cathode preferably includes at least four layers
of wires. Further, each of the wire layers has wires extending in a different direction
from each of the other of the wire layers, the wire grid of the cathode thus including
wires extending in at least four different directions. This is designed to greatly
increase the emissive surface of the cathode.
The present invention may alternately be described as a thermionic
electric converter having a casing member, a cathode within the casing member operable
when heated to serve as a source of electrons, an anode within the casing member
operable to receive electrons emitted from the cathode; and a laser operable to
hit electrons between the cathode and anode. The laser thus provides quantum interference
with the electrons such that electrons are more readily captured by the anode. The
laser is operable to hit electrons just before they reach the anode. The laser is
operable to hit electrons within 2 microns of when they reach the anode. The cathode
is a wire grid having wires going in at least two directions that are transverse
to each other. The cathode is separated from the anode by 4 microns to five centimeters.
The present invention may alternately be described as a thermionic
electric converter having a casing member, a cathode within the casing member operable
when heated to serve as a source of electrons, and an anode within the casing member
operable to receive electrons emitted from the cathode and which proceed generally
along a movement direction defining the direction from the cathode to the anode.
The cathode has a planar cross section area normal to the movement direction, the
cathode has an electron emission surface area for electron emission towards the
anode, and the electron emission surface area is at least 30 percent greater than
the planar cross section area. The cathode is a wire grid having wires going in
at least two directions that are transverse to each other. Alternately, or additionally,
the cathode is curved in at least one direction perpendicular to the movement direction.
A laser operable to hit electrons between the cathode and anode just before they
reach the anode. Preferably, the electron emission surface area is at least double
the planar cross section area. More preferably, the electron emission surface area
is at least double the planar cross section area. The smaller the diameter of the
wire the larger the emissive area. This is an exponential relationship.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in detail herein with reference to
the following figures in which like reference numerals denote like elements, and
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
- FIG. 1 is a schematic diagram of a prior art thermionic electric converter;
- FIG. 2 is a schematic diagram of a prior art laser-excited thermionic electric
- FIG. 3 is a side view with parts in cross section and schematic diagram of a
thermionic electric converter according to the present invention;
- FIG. 4 is a top view of a wire grid structure used for a cathode;
- FIG. 5 is a side view of a part of the wire grid structure;
- FIG. 6 is a side view of a part of an alternate wire grid structure;
- FIG. 7 is a side schematic diagram multiple layers in a wire grid structure;
- FIG. 8 is a simplified side view of an alternate cathode structure.
FIGS. 1 and 2 show prior art thermionic electric converters as shown
and described in U.S. Patent Nos. 4,303,845 and 4,323,808, respectively, both to
Edwin D. Davis, the inventor of the present invention, the disclosures of which
are incorporated by reference herein in their entirety. While the operation of both
thermionic converters is described in detail in the incorporated patents, a general
operational overview is presented herein with reference to FIGS. 1 and 2. This may
provide background useful in understanding the present invention.
FIG. 1 shows a basic thermionic electric converter. FIG. 2 shows a
laser-excited thermionic converter. The operation of both converters is very similar.
With reference to the FIGS., a basic thermionic electric converter
10 is shown. The converter 10 has an elongated, cylindrically shaped outer housing
12 fitted with a pair of end walls 14 and 16, thereby forming a closed chamber 18.
The housing 12 is made of any of a number of known strong, electrically non-conductive
materials, such as, for example, high-temperature plastics or ceramics, while the
end walls 14, 16 are metallic plates to which electrical connections may be made.
The elements are mechanically bonded together and hermetically sealed such that
the chamber 18 may support a vacuum, and a moderately high electrical potential
may be applied and maintained across the end walls 14 and 16.
The first end wall 14 contains a shaped cathode region 20 having an
electron emissive coating (not shown) disposed on its interior surface, while the
second end wall 16 is formed as a circular, slightly convex surface which is first
mounted in an insulating ring 21 to form an assembly, all of which is then mated
to the housing 12. In use, the end walls 14 and 16 function respectively as the
cathode terminal and the collecting plate of the converter 10. Between these two
walls, an electron stream 22 will flow substantially along the axis of symmetry
of the cylindrical chamber 18, originating at the cathode region 20 and terminating
at the collecting plate 16.
An annular focusing element 24 is concentrically positioned within
the chamber 18 at a location adjacent to the cathode 20. A baffle element 26 is
concentrically positioned within the chamber 18 at a location adjacent to the collecting
Disposed between these two elements is an induction assembly 28 comprised
of a helical induction coil 30 and an elongated annular magnet 32. The coil 30 and
the magnet 32 are concentrically disposed within, and occupy the central region
of, the chamber 18. Referring briefly to the schematic end view of FIG. 2, the relative
radial positioning of the various elements and assemblies may be seen. For clarity
of presentation, the mechanical retaining means for these interiorly located elements
have not been included in either figure. Focusing element 24 is electrically connected
by means of a lead 34 and a hermetically sealed feed through 36 to an external source
of static potential (not shown). The induction coil 30 is similarly connected via
a pair of leads 38 and 40 and a pair of feed-throughs 42 and 44 to an external load
element shown simply as a resistor 46.
The potentials applied to the various elements are not explicitly
shown nor discussed in detail as they constitute well known and conventional means
for implementing related electron stream devices. Briefly, considering (conventionally)
the cathode region 20 as a voltage reference level, a high, positive static charge
is applied to the collecting plate 16 and the external circuit containing this voltage
source is completed by connection of its negative side to the cathode 20. This applied
high, positive static charge causes the electron stream 22 which originated at the
cathode region 20 to be accelerated towards the collecting plate 16 with a magnitude
directly dependent upon the magnitude of the high static charge applied. The electrons
impinge upon the collecting plate 16 at a velocity sufficient to cause a certain
amount of ricochet. The baffle element 26 is configured and positioned to prevent
these ricochet electrons from reaching the main section of the converter, and electrical
connections (not shown) are applied thereto as required. A negative voltage of low
to moderate level is applied to the focusing element 24 for focusing the electron
stream 22 into a narrow beam. In operation, a heat source 48 (which could be derived
from diverse sources such as combustion of fossil fuels, solar devices, atomic devices,
atomic waste or heat exchangers from existing atomic operations) is used to heat
the electron emissive coating on the cathode 20, thereby boiling off quantities
of electrons. The released electrons are focused into a narrow beam by focusing
element 24 and are accelerated towards the collecting plate 16. While transiting
the induction assembly 28, the electrons come under the influence of the magnetic
field produced by the magnet 32 and execute an interactive motion which causes an
EMF to be induced in the turns of the induction coil 30. Actually, this induced
EMF is the sum of a large number of individual electrons executing small circular
current loops thereby developing a correspondingly large number of minute EMFs in
each winding of the coil 30. Taken as a whole, the output voltage of the converter
is proportional to the velocity of the electrons in transit, and the output current
is dependent on the size and temperature of the electron source. The mechanism for
the induced EMF may be explained in terms of the Lorentz force acting on an electron
having an initial linear velocity as it enters a substantially uniform magnetic
field orthogonally disposed to the electron velocity. In a properly configured device,
a spiral electron path (not shown) results, which produces the desired net rate
of change of flux as required by Faraday's law to produce an induced EMF.
This spiral electron path results from a combination of the linear
translational path (longitudinal) due to the acceleration action of collecting plate
16 and a circular path (transverse) due to the interaction of the initial electron
velocity and the transverse magnetic field of magnet 32. Depending on the relative
magnitude of the high voltage applied to the collecting plate 16 and the strength
and orientation of the magnetic field produced by the magnet 32, other mechanisms
for producing a voltage directly in the induction coil 30 may be possible. The mechanism
outlined above is suggested as an illustrative one only, and is not considered as
the only operating mode available. All mechanisms, however, would result from various
combinations of the applicable Lorentz and Faraday considerations.
The basic difference between the basic converter shown in U.S. Patent
No. 4,303,845 and the laser-excited converter shown in U.S. Patent No. 4,323,808,
is that the laser-excited converter collects electrons boiled off the surface of
the cathode on a grid 176 having a small negative potential applied thereon by a
negative potential source 178 through lead 180, which traps the electron flow and
mass of electrons. The electrical potential imposed on the grid is removed, while
the grid is simultaneously exposed to a laser pulse discharge from laser assembly
170, 173, 174, 20 causing a bolus of electrons 22 to be released. The electron bolus
22 is then electrically focused and directed through the interior of the air core
induction coils located within a transverse magnetic field, thereby generating an
EMF in the induction coil which is applied to an external circuit to perform work,
as set forth above with respect to the basic thermionic converter.
As set forth the present inventor's prior U.S. Patent 5,459,367, there
are numerous attendant disadvantages usually associated with having a collecting
element simply made up of a conductive metal plate. Therefore, the collecting element
of that design includes a conductive layer of copper sulfate gel impregnated with
copper wool fibers. The present invention may use such an anode. However, the present
invention also may use a conductive metal plate anode as other aspects of the present
invention will minimize or avoid some of the disadvantages that such a plate anode
might otherwise cause. Basically then, the specifics of the anode are not central
to the preferred design of the present invention.
With reference now to FIG. 3, a thermionic electric converter 200
according to the present invention includes a casing member 202 in which a vacuum
would be maintained by vacuum apparatus (not shown) in known fashion. The casing
member 202 is preferably cylindrical about a central axis 202A which serves as an
axis of symmetry of the member 202 and the components therein except where otherwise
The collector 204 may include a flat anode circular plate 206 (made
of copper for example) surrounded by a statically charged ring 208 (charged to 1000
Coulombs for example) having insulating rings 210 concentric therewith. The ring
208 and rings 210 may be constructed and operable as discussed in the 5,459,367
Patent. A cooling member 212 is thermally coupled to the plate 206 such that coolant
from coolant source 214 is recirculated therethrough by coolant circuit 216. The
cooling member 212 maintains the anode plate at a desired temperature. The cooling
member 212 may alternately be the same as the anode plate 206 (in other words coolant
would circulate through plate 206). A feedback arrangement (not shown) using one
or more sensors (not shown) could be used to stabilize the temperature of anode
The cathode assembly 218 of the present invention includes a cathode
220 heated by a heat source such that it emits electrons which generally move along
movement direction 202A towards the anode 206. (As in the 5,459,367 Patent, the
charged ring 208 helps attract the electrons towards the anode.) Although the heat
source is shown as a source 222 of heating fluid (liquid or gas) flowing to heating
member 224 (which is thermally coupled to the cathode 220) via heating circuit 226,
alternate energy sources such as a laser applied to the cathode 224 might be used.
The energy input into source 222 could be solar, laser, microwave, or radioactive
materials. Further, used nuclear fuel that would otherwise simply be stored at great
expense and without benefit might be used to provide the heat to source 222.
Electrons energized to the Fermi level in cathode 220 escape from
the surface thereof and, attracted by static charge ring 208, travel along movement
direction 202A through first and second focussing rings or cylinders 228 and 230,
which may be constructed and operable in similar fashion focussing element 24 of
the prior art arrangement discussed above. In order to help the electrons move in
the proper direction a shield 232 may surround the cathode 224. The shield 232 may
be cylindrical or conical or, as shown, include a cylindrical portion closest the
cathode 224 and a conical portion further from the cathode 224. In any case, the
shield tends to keep electron movement in direction 202A. The electrons will tend
to be repelled from the shield 232 since the shield will be at a relatively high
temperature (from its proximity to the relatively high temperature cathode 220).
Alternately, or additionally, to being repelled by the high temperature of the shield,
the shield 232 could have a negative charge applied to it. In the later case, insulation
(not shown) could be used between the shield 232 and cathode 220.
The electrical energy produced corresponding to electron flow from
cathode 220 to anode 206 is supplied via cathode wire 234 and anode wire 236 to
an external circuit 238.
Turning from the overall operation of the converter 200 to specific
advantageous aspects thereof, electrons such as electron 240 tend to have a high
energy level as they approach the anode 206. Therefore, the normal tendency would
be for some to bounce off the surface and not be captured therein. This normally
results in electron scatter and diminishes the conversion efficiency of a converter.
In order to avoid or greatly reduce this tendency, the present invention uses a
laser 242 which hits the electrons (e.g., hits them with a laser beam 244) just
before they hit the anode 206. The quantum interference between the photons of the
laser beam 244 and the electrons 240 drops the energy state of the electrons such
that they are more readily captured by the surface of anode 206.
As will be understood from the dual wave-particle theory of physics,
the electrons hit by the laser beam may be exhibiting properties of waves and/or
particles. (Of course, the scope of the claims on the present invention are not
limited to any particular theory of operation unless and except where a claim expressly
references such a theory of operation, such as quantum interference.)
As used herein, saying that the laser 242 hits the electrons with
beam 244 "just before" the electrons reach the anode 206 means that the electrons
which have been hit do not pass through any other components (such as a focussing
member) as they continue to the anode 206. More specifically, the electrons are
preferably hit within 2 microns of when they reach the anode 206. Even more preferably,
the electrons are hit by the laser with 1 microns of reaching the anode 206. Indeed,
the distance from the second focussing element 230 to the anode 206 may be 1 micron
and the laser may hit electrons closer to the anode 206. In that fashion (i.e.,
hitting the electrons just before they reach the anode), the energy of the electrons
is reduced at a point where reduced energy is most appropriate and useful.
Although casing member 202 may be opaque, such as a metal member,
a laser window 246 is made of transparent material such that the laser beam 244
can travel from laser 242 into the chamber within member 202. Alternately, the laser
242 could be disposed in the chamber.
In addition to improving conversion efficiency by using the laser
242 to reduce the energy level of electrons just before they reach the anode 206,
the cathode 220 of the present invention is specifically designed to improve efficiency
by increasing the electron emission area of the cathode 220.
With reference to FIG. 4, the cathode 220 is shown as a circular grid
of wires 248. Wires 250 of a top or first layer of parallel wires extend in direction
252, whereas wires 254 of a second layer of parallel wires extend in direction 256,
transverse to direction 252 and preferably perpendicular to direction 252. A third
layer of parallel wires (only one wire 258 shown for ease of illustration) extend
in direction 260 (45 degrees from directions 252 and 256. A fourth layer of parallel
wires (only one wire 262 shown for ease of illustration) extend in direction 264
(90 degrees from direction 260).
It should also be noted that FIG. 4 shows the wires with relatively
large separation distances between them but this is also for ease of illustration.
Preferably, the wires are finely extruded wires and the separation distances between
parallel wires in the same layer would be similar to the diameter of the wires.
Preferably, the wires have diameters of 2 mm or less to fine filament size. The
wires may be tungsten or other metals used in cathodes.
With reference to FIG. 5, the wires 250 and 254 may be offset from
each other with all wires 250 (only one shown in FIG. 5) disposed in a common plane
offset from a different common plane in which all wires 254 are disposed. An alternate
arrangement shown in FIG. 6 has wires 250' (only one visible) and 254' which are
interwoven in the manner of fabric.
With reference to FIG. 7, an alternate cathode 220' may have three
portions 266, 268, and 270. Each of portions 266, 268, and 270 may have two perpendicular
layers of wires (not shown in FIG. 7) such as 250 and 254 (or 250' and 254'). Portion
266 would have wires going into the plane of view of FIG. 7 and wires parallel to
the plane of FIG. 7. Portion 268 has two layers of wires, each having wires extending
in a direction 30 degrees from one of the directions of the wires for portion 266.
Portion 270 has two layers of wires, each layer having wires extending in a direction
60 degrees from one of the directions of the wires for portion 266.
It will be appreciated that FIG. 7 is illustrative of the point that
multiple layers of wires extending in different directions could be used.
The various wire grid structures for the cathode increase the effective
electron emission surface area by way of the shape of the wires and their multiple
layers. An alternative way of increasing the surface area is illustrated in FIG.
8. FIG. 8 shows a side cross section view of a parabolic cathode 280 operable to
emit electrons for movement generally along movement direction 220A'. The cathode
280 has a planar cross section area A normal to the movement direction 202A. Significantly,
the cathode 280 has an electron emission surface area EA (from the curvature of
the cathode) for electron emission towards the anode which is at least 30 percent
greater than the planar cross section area A. Thus, a greater density of electrons
are generated for a given size cathode. Although the cathode 280 is shown as a parabola,
other curved surfaces may be used. The cathode 280 may be made of a solid member
or may also incorporate multiple layer wire grid structures like described for FIGS.
4-7 except that each layer would be curved and not planar.
Although the curved cathode arrangement of FIG. 8 provides an electron
emission surface area EA that is at least 30 percent greater than the side cross
section area A, the various wire grid arrangements such as FIG. 4 provide an electron
emission surface area that is at least double the side cross section area (i.e.,
defined as shown for FIG. 8). Indeed, the electron emission surface area in the
grid arrangements should be at least ten times the side cross section area.
Advantageously, the present invention allows the cathode 220 and anode
206 to be offset from each other by from 4 microns to 5 cm. More specifically, that
offset or separation distance will be from 1 to 3 cm. Thus, the cathode and anode
are sufficiently far apart that heat from the cathode is less likely to be conveyed
to the anode than in the arrangements where the cathode and anode must be in close
proximity. Therefore, the coolant source 214 can be a relatively low coolant demand
arrangement since less cooling is required than in many prior designs.
While the invention has been described in conjunction with specific
embodiments thereof, it is evident that many alternatives, modifications and variations
will be apparent to those skilled in the art. Accordingly, the preferred embodiments
of the invention, as set forth herein, are intended to be illustrative, not limiting.
Various changes may be made without departing from the spirit and scope of the invention
as defined herein and in the following claims.