Abstract: This Essay will discuss the feasibility of harnessing the 'Maxwell Demon'. What is proposed involves the technological development of composite panels having a microscopic structure that can concentrate electromagnetic wave energy. This is something for those in the Research Departments of major corporations involved in fabricating optical structures or electronic microcircuit boards to think about, but it does not involve electronics, just the design and assembly skills that go with high technology fabrications of panel structures having special micro-features.
The topic is the subject of a U.S. Patent which I abandoned because its
filing was premature and because I had no way of taking the project forward
myself. Nevertheless, the invention warrants consideration as a future energy
development. The Patent is U.S. Patent No. 5,101,632 issued April 7,
1992.
The grant of this U.S. Patent is also something that is quite
remarkable when considered alongside the saga of my efforts in trying to secure
grant of a patent on energy conversion having relevance to what has become known
as Cold
Fusion.
The reason I say this is something that will become evident
as you read Claim 13 of the patent. Note that the patent was granted without any
objection from the Examiner except for directing my attention to the need to
correct a 'blurred' line in one of the drawings! Then note, that the invention
claimed, particularly in Claim 13, is one that declares that it is possible to
connect two 'heat engines' back-to-back as it were, with ambient heat being
converted into useful heat at a higher temperature. This, ostensibly, is a clear
contradiction of the Second Law of Thermodynamics.
There is, however, no
faulty reasoning in the technical proposition presented. Indeed, apart from a
verdict that says it will not work because there is that 'Second Law of
Thermodynamics', the two technical elements that are combined are both
separately feasible. I can further say that when I first published the proposal,
what I wrote was seen by the U.K. government officials who fund research
projects in universities. Then, to the surprise of the head of the university
department to which I belonged at the time, one of those officials actually
contacted the university and intimated a willingness to provide government
funding of the project, even though no such request had been
submitted.
The publication of mine to which I refer appeared in the
journal Nature on September 6, 1990 at p. 25 of volume 347. See 1990h.
I
was a member of staff there in my capacity as a Visiting Senior Research Fellow
and you might think that I would have readily undertaken such a project, but,
whilst I would have been content to consult on such a development I was not
prepared to divert my full attention to it and relinquish my effort to further
my basic theoretical work or relinquish my related patent interests to the
university system. Besides that, the development of such a project demands the
resource which is only found in the corporations who can fabricate
microstructures, as in the computer industry, and at my age time was not on my
side. So, in the event, I published the proposal in more detail, as by the
subject patent and, soon thereafter, allowed the patents to lapse, so that those
corporations that might see its potential could pursue the technology at their
will.
However, as we know only too well, there is something called the
'NIH' factor, the 'not-invented-here' factor, and so many researchers lack the
conviction or perhaps the wisdom needed to challenge orthodoxy and urge their
directors to venture into such uncharted territory.
In this regard I
often wonder whether IBM, which does have a research facility in USA at Yorktown
Heights, where quite a few research scientists are given free rein to work on
their own pet projects, could develop interest in this direction. The world of
computing is, however, very far removed from the world of power generation. Yet,
there is that common technological feature concerned with microfabrication of
cellular units in panel form.
I also mention this because, at this time
(March/April 1998) someone reading these Web pages, namely John Allan, E-Mail:
energy@gold.globalcafe.co.uk, has drawn my attention to a recently granted U.S.
Patent No. 5,590,031 entitled: 'System for converting electromagnetic radiation
energy to electrical energy'. He gave an access Web address of
http://www.patents.ibm.com/details?patent_number=5590031 and this caused me to
wonder if this patent might be one belonging to IBM. However, that would appear
not to be the case. It would seem that the address
In any event, the patent in question is interesting in that its
inventors:
Mead, Jr.; Franklin B., Lancaster, CA 93535
have secured grant on Dec. 31, 1996 for an
invention, the abstract of which reads:
Nachamkin; Jack,
Poway, CA 92064
A system is disclosed for converting high frequency zero point
electromagnetic radiation energy to electrical energy. The system includes a
pair of dielectric structures which are positioned proximal to each other and
which receive incident zero point electromagnetic radiation. The volumetric
sizes of the structures are selected so that they resonate at a frequency of
the incident radiation. The volumetric sizes of the structures are also
slightly different so that the secondary radiation emitted therefrom at
resonance interfere with each other producing a beat frequency radiation which
is at a much lower frequency than that of the incident radiation and which is
amenable to conversion to electrical energy. An antenna receives the beat
frequency radiation. The beat frequency radiation from the antenna is
transmitted to a converter via a conductor or waveguide and converted to
electrical energy having a desired voltage and waveform.
Now, I
see this as evidence that there are those who do believe that there is future
prospect in tapping energy from the environment and generating useful electrical
power. However, it is one thing to talk about 'zeropoint energy' as well as
resonant interference aimed at developing radiation at a low beat frequency and
quite another to think in terms of tapping ambient heat as a source of radiation
in the manner I have described in my U.S. Patent No. 5,101,632. So I stress here
that, whatever you may have heard about 'zero-point' energy, notably from papers
such as that of Dr. Hal Puthoff entitled: 'Source of Vacuum Electromagnetic
Zero-Point Energy', Physical Review, v. 40, No. 9, November 1, 1989, and his
other writings on this subject, the invention I describe below in the subject
patent does not depend upon tapping that kind of aether energy. Indeed, I shall
now introduce you to three energy conversion routes, two of which do depend upon
that aether energy resource but one, the one I am concerned with here, only
involving the normal thermal background energy resource.
Introduction
In these Web pages I aim to guide those who
are responsible for research that will lead us to new methods of generating
energy to take stock of three possibilities. I classify these as 'TEC', 'MEC'
and 'HEC', which are, respectively, abbreviations for:
(a) Thermodynamic Energy Conversion, (TEC)
(b)
Magnetohydrodynamic Energy Conversion (MEC) and
(c) Hadrodynamic Energy
Conversion (HEC).
My case is based upon the realization that
there are some fundamental flaws in what physicists have come to believe
concerning the creative forces at work in Nature and how Nature deploys its
energy.
They tell us how the Sun is powered as a kind of hot fusion
reactor which, for some curious reason, does not explode and disintegrate. They
admit that their theories do not embrace the unifying link that relates
gravitation and electrical action and they admit that they really do not know
how the electron and the proton, the components of the hydrogen atom, are
created. They cannot, for example, gave a theoretical basis for deriving the
proton-electron mass ratio or G, the constant of gravitation, in terms of the
electron charge-mass ratio. Yet, they are so overwhelmingly confident that they
know what they are talking about when it comes to pronouncing on energy issues
on this grand scale!
I have shown in these Web pages, as in the Tutorial
Notes, that I can give answers to these questions, including that elusive
derivation of the proton-electron mass ratio and G, but I can only do this by
building my theory on energy activity latent to the medium that we otherwise see
as empty space. So, if a physicist tells you that Einstein eliminated the need
to contemplate a real medium filling space and substituted the notion of
something called 'four-space', then you have the choice of putting your energy
future in the hands of physicists of that calibre who thrive on abstract
mathematical notions or those who have their feet well rooted in the real energy
world of the engineer.
I have never lost sight of my early education as a
professional engineer, much as my interest in electrical science has made me
also a professionally-qualified physicist. I know that, so far as energy is
concerned, there are options which the physicist rejects as contrary to his
'beliefs', whether those beliefs are concerned with Einstein's teachings or
those preached as a result of misdirected knowledge of thermodynamics.
To
put my case on a firm base I will declare those options as being 'TEC', 'MEC'
and 'HEC', as listed above.
In this section of these Web pages I will
concentrate attention upon 'TEC'. Eventually, I will deal quite thoroughly with
'MEC', which concerns magnetism and electric motors. As to 'HEC' I am now
watching developments, because this is really the 'cold fusion' theme. I have
shown my interest in that in the Web pages to be found in Cold
Fusion Index. Note that that subject is all about the dynamics of 'hadrons'
which are the heavy ions involved in the energy transactions that one encounters
in the so-called 'cold fusion' research. As anyone who reads the specification
of my U.S.
Patent No. 5,734,122 can see, I have good reason for challenging the beliefs
of those who see a Big Bang energy syndrome as the only creative event followed
by our perpetual decline. However, I will bring things 'down to Earth' by
concentrating here on 'Thermodynamic Energy Conversion', beginning by reference
to my U.S. Patent No. 5,101,632.
U.S. PATENT NO. 5,101,632
Abstract
Thermal energy radiation is converted into another energy form by
setting up a temperature differential between two heat sinks forming part of a
conventional converter or heat engine, but the warmer heat sink derives its
input energy by collecting opticallyfocused thermal radiation from a primary
heat sink within the converter structure. Heat rejected by the cooler heat
sink is recycled to the primary heat sink to enhance the thermal efficiency
above the Carnot level set by the base temperature conditions. The power
rating of the converter is enhanced by combination with a reverse heat engine
which elevates the temperature of heat input to the primary heat sink and so
the temperature of the radiating surface.
Field of Invention
This invention relates to the conversion
of thermal energy into a form that has greater potential for application in
powering heat engines subject to the Carnot performance criterion.
By
using mirrors or lenses the radiant energy from a thermal source is concentrated
to heat or cool the thermal heat sinks which activate a heat engine.
Background of the Invention
By establishing a temperature
differential between two heat sinks which interface with a device categorized as
a heat engine or its equivalent, it is possible to derive mechanical or electric
output power, subject to a limit set by the efficiency of the perfect Carnot
cycle.
Boltzmann derived the Stefan-Boltzmann law, by which the rate of
heat radiation is proportional to the fourth power of absolute temperature, by
deducing the connection between temperature and the energy density of black-body
radiation. This involved the conception of an 'aether engine', a Carnot engine
without any working substance, driven by the pressure of radiation.
In
principle, radiation admitted to a cylinder expands to drive a piston and so
does mechanical work as the temperature of the radiation reduces. The
temperature reduction is argued on the basis that if work is done and removed as
useful output then radiant energy has to flow in to replenish the system at the
end of the cycle and this could only occur if the temperature had, in fact,
reduced.
Such argument derives from the second law of thermodynamics, but
one wonders about that reference to the temperature of radiant energy. We have
come to accept that radiation comprises photons having a spectrum of frequencies
and do not regard photons as having a temperature. Only radiating matter can be
said to have a temperature, usually related to the thermal energy of its
molecules via the Boltzmann constant.
Thus radiation has an intensity
characteristic of its energy concentration and it has a quality representing its
source by virtue of its frequency spectrum. Blackbody radiation from sources of
lower temperature contains photons having frequencies which are the same as
those from higher temperature sources. It is the distribution of energy as
between these different frequencies or the number of photons at a particular
frequency which characterizes the temperature of the source. Therefore, if that
radiation from the cooler source can be concentrated in some way it can heat an
absorbing surface to a higher temperature.
The formal statement of the
second law of thermodynamics is very carefully worded to make it clear that heat
cannot travel from a cooler body to a warmer body of its own accord, but the
intervention of a means for focusing photon energy, as by use of a lens or
mirror, or as by the fanciful textbook notion of the intervention of the Maxwell
demon can affect that self-accord.
The use of mirrors or lenses to
reflect or refract thermal radiation, whether sourced in a heated or cooled
surface, was a curiosity in early scientific experiments. Indeed, one such
notable experiment was performed by Count Romford in Edinburgh, Scotland, in the
year 1800. He repeated the experiment of Pictet, by which the radiation and
reflection of cold was demonstrated, to show that objects seated at one focus of
a concave mirror could be cooled by a cool object seated at the other focus. See
article entitled: 'Pictet's experiment: The apparent radiation and reflection of
cold' by J. Evans and B. Popp, American Journal of Physics, vol. 53, p. 737
(1985).
The point about this experiment was that there is heat transfer
until there is equilibrium between the radiation exchanged by the two surfaces
as governed by the areas of the two surfaces put in juxtaposition by the mirror
focusing. The temperatures adjust to keep the radiation in balance, unless some
is absorbed and conducted away in the apparatus.
From a technological
viewpoint these phenomena are traditionally deemed to be of little consequence,
though they do find application in the design of bolometers.
So far as
this inventor has been able to ascertain, it has not been foreseen in the prior
art that, by combining optics and heat engines and focusing radiation in the
manner suggested, the concentration of heat radiation driven at the speed of
light can develop temperatures at an absorbing surface which exceed those of the
radiating source and can be used to convert heat into engine power. Nor, so far
as the inventor is aware, has it been suggested that useful power could be
generated by combining a heat engine and an optical system to concentrate heat
radiation sourced in a radiating surface which is within the fabricated
structure of the converter.
It has been suggested to combine a heat
engine and a parabolic mirror, with the flow of heated fluid used to power the
engine passing through a tubular heat exchange element at the linear focus of
the mirror. Such an arrangement for caputuring solar radiation is disclosed in
'Solar Electric Systems', Hemisphere Publishing Corporation, USA (1984), Editor
George Warfield. See paper by Jean-Pierre Causse entitled 'Solar Thermal Power
Plants' at pp. 101-113. Also, the paper by Jerald D. Parker entitled 'Components
of Solar Thermal Electric Systems' at pp. 89-100 is relevant because it suggests
the use of a Stirling engine. However, these specific proposals relate to solar
power, that is heat energy sourced in the sun at a temperature of 6,000 K. There
is no teaching in these prior art disclosures suggesting that the heat engine
can be driven by radiation sourced at a temperature that is less than that of
the input to the engine.
Indeed, it would not be feasible to power a heat
engine from the solar source if the proposals of the subject invention were
applied to that purpose, simply because no practical heat engine can be built to
operate at that 6,000 K temperature.
The subject invention was the basis
of a priority filing dated 16 November 1989 and the inventor notes that John
Maddox, the Editor of the journal Nature, has had occasion since that date to
raise the subject of possible breach of the second law of thermodynamics in his
editorial 'Maxwell's Demon Flourishes' (Nature, vol. 345, p. 109; 1990). Also,
in this same journal (Nature, vol. 346, p. 802; 1990), there is a report sourced
in the Enrico Fermi Institute in Chicago announcing that terrestrial sunlight
has been concentrated by a two-stage system including a mirror to an intensity
which exceeds that at the surface of the sun.
It is clear, therefore,
that by the astute use of mirrors or lenses, two thermally radiating surfaces at
different temperatures and of different area can be caused to maintain a state
of equilibrium at those temperatures, simply because the same rate of heat is
radiated by each surface. The proviso is that the radiation is guided both ways
through the optical system so as to be confined to exchanges restricted to those
surface areas.
On this basis, since some heat energy can be drawn off by
conduction from the hotter surface, one can contemplate radiant transfer of heat
from the cooler body to the warmer body, notwithstanding the validity of the
second law of thermodynamics as correctly worded. Here the proviso is that heat
is continuously extracted from the hotter body via a separate channel and
replenishment heat is continuously supplied to the cooler body also via a
separate channel. Energy has, of course, to be conserved, a requirement of the
first law of thermodynamics.
Brief Description of the Invention
Stated in simple terms,
the invention involves the use of optics to concentrate radiant heat and so feed
it to a heat sink at a higher temperature. Then a heat engine uses the
temperature differential to generate power in a useful non-thermal form. In
practical terms the preferred implementation depends upon the ability to build
into a system a very large radiating surface area, which in turn demands a
miniature form of compact heat engine preferably built into each cell of the
system structure. The engine, furthermore, must have a high efficiency as
measured relative to the Carnot condition. To enhance the power output in terms
of the size of the system, the invention further provides for some sacrifice of
overall efficiency, by using a reverse heat engine in an auxiliary capacity to
input heat at higher temperature to the radiating surfaces.
According to
the invention, a thermally powered energy converter comprises a first heat sink
having a surface from which heat is radiated, a second heat sink having a
surface at which heat is absorbed, optical focusing means arranged to capture
radiation from the radiating surface of the first heat sink and to focus it upon
the smaller absorbing surface of the second heat sink, a third heat sink,
thermodynamic energy conversion means activated by a temperature differential
between the second and third heat sinks and operative to supply a non-thermal
power output, means for supplying an inflow of heat energy to the first heat
sink and means for extracting heat energy from the third heat sink.
The
word 'focus' as used in this specification is intended to mean the general
action of a mirror or lens by which it causes radiation reflected by the mirror
or refracted by the lens to be concentrated in intensity in being directed onto
a receiving surface. A significant degree of concentration requires positioning
of the surfaces in relation to the optical system so that the focusing power of
the system is utilized, but perfect image focusing is not the essential
requisite. Maximum rate of energy transfer from a larger radiating surface area
to a smaller radiating surface, as determined by the design criteria, is the
objective of the focusing action. The optical focusing means may be a mirror
and, in embodiments of the invention designed to operate by reflecting heat
radiation from radiating surfaces at temperatures of 500 or 600 K, a metal
reflector of parabolic section is the preferred implementation. However,
depending upon the design temperature and the materials used, the invention can
use a lens system for focusing the radiation.
According to a feature of
the invention, the means for extracting heat energy from the third heat sink
comprises a thermally-conductive connection between the third heat sink and the
first heat sink, whereby heat energy exhausted at the lower heat sink
temperature of the thermodynamic energy conversion means augments the inflow of
heat energy supplied to the first heat sink.
This requires that the third
heat sink will be at a slightly higher temperature than the first heat sink,
but, since all the action stems from the amplification of temperature
differential between the first and second heat sinks owing to the action of the
optical system, there is still a temperature differential between the second and
third heat sinks.
According to a further feature of the invention, the
converter comprises an auxiliary thermodynamic energy conversion means operative
as a reverse heat engine and connected to be powered by a portion of said
non-thermal power output, this auxiliary thermodynamic energy conversion means
operating to preheat fluid conveying the inflow heat to the first heat
sink.
The object of this is to sacrifice some efficiency in the
generation of useful net power output as measured in terms of the amount of heat
circulating in the system, in order to elevate the temperature of the radiating
surface. This is a very significant technological factor, where the temperature
of the primary source of heat input is low and, for example, close to normal
ambient temperature. By doubling the temperature in degrees absolute and
sacrificing just over half of the non-thermal power generated to drive the
reverse heat engine, the radiation capacity of the surface of the first heat
sink can, on the basis of the Stefan-Boltzmann law, be enhanced by a factor of
16. There is then a significant gain in power output capacity for a given area
of radiation surface of that first heat sink, notwithstanding the sacrifice of
the power drawn by the reverse heat engine.
According to another feature
of the invention, the optical focusing means comprises a lens system formed by a
curved transparent bounding structure with the space intervening the structure
and the heat radiating surface of the first heat sink defining a duct for fluid
conveying the inflow heat to the first heat sink.
The lens system may
incorporate in the space intervening the bounding structure and the heat
radiating surface a transparent liquid, which may be water, arranged to flow via
an external heat exchange circuit to carry the inflow heat to the first heat
sink.
According to another aspect of the invention, a thermally powered
energy converter has a multicell structure having a cross-section which
comprises a lattice-like array of converter units, each of which comprises a
first heat sink having a surface from which heat is radiated, a second heat sink
having a surface at which heat is absorbed, optical focusing means arranged to
capture radiation from the radiating surface of the first heat sink and to focus
it upon the smaller absorbing surface of the second heat sink, a third heat
sink, thermodynamic energy conversion means activated by a temperature
differential between the second and third heat sinks and operative to supply a
nonthermal power output, means for supplying an inflow of heat energy to the
first heat sink and means for extracting heat energy from the third heat sink.
Alternatively, instead of each cell of the array comprising a converter unit
including its own thermodynamic energy conversion means, such a means may be
shared by a plurality of converter units. This applies especially where these
conversion means are engines having a working fluid which is subjected to a
temperature cycle, rather than solid state 'engines' using the thermoelectric
Seebeck effect.
According to a further feature of the invention, the
thermodynamic energy conversion means comprise a Stirlingtype heat engine shared
by a plurality of converter units and operating on heat energy drawn from a gas
heated by a second heat sink and rejecting exhaust heat to a third heat
sink.
According to a further feature of the invention, the thermodynamic
energy conversion means comprise a Stirlingtype heat engine shared by a
plurality of converter units and operating on heat energy drawn from a gas
heated by the second heat sink and rejecting exhaust heat to the third heat
sink, which heat is conveyed to the first heat sink by gas flow activated by the
cyclic operation of the engine.
According to another alternative feature
of the invention, the thermodynamic energy conversion means comprise a
thermoelectric element utilizing the Seebeck Effect, there being one such
element in each converter unit, the heated surface of the element being the
second heat sink and the cooled surface being the third heat sink, heat from
which is conveyed by thermal conduction through metal to the first heat
sink.
Brief Description of the Drawings
Fig. 1 shows a part-section
of a multicell structure in which convex lenses are used to focus heat radiation
in an thermoelectric energy converter incorporating the invention.
Fig. 2
shows a part-section of a multicell structure in which concave mirrors are used
to focus heat radiation in a thermoelectric energy converter intended to operate
at higher temperatures than are applicable in Fig. 1.
Fig. 3 shows a
part-section of a multicell structure in which concave mirrors are used to focus
heat radiation in an energy converter using an external heat engine for power
generation.
Fig. 4 shows a schematic system in which the energy converter
operates in conjunction with a reverse heat engine.
Detailed Description of the Invention
It is well known in
thermodynamics that, if a temperature differential is maintained between two
heat sinks, an engine operating on the Carnot cycle can operate to convert that
heat into another form, whether mechanical or electrical, with an efficiency
limited to that set by the Carnot efficiency. This is a factor which is the
temperature difference divided by the absolute value of the higher temperature
involved. In practice, it is possible to achieve as much as 80% of the Carnot
efficiency.
Heat engines usually involve fluids which are subject to
expansion and compression, but solid-state devices working on the Carnot
principle also exist. The latter tend to have lower performance, but it is
foreseen that much improved efficiencies will soon be available from
thermoelectric devices using the Peltier and Seebeck effects.
On this
basis it can be expected that compact, maintenance-free, solid-state
thermodynamic energy converters operating at near-to-Carnot efficiencies will
soon be commercially available. Indeed, the prototype technology for such
thermoelectric devices is already of public record in the published
specification of UK Patent Application No. 2,227,881 A. (Corresponding U.S.
Patent Application Serial No. 07/439,829).
The Carnot efficiency
limitation is set by the temperature of the heat sinks of the thermodynamic
energy converter and not by the temperature of the primary heat source. If,
therefore, the heat has the form of radiation from a surface replenished by the
primary heat source and such radiation can be concentrated by optical focusing,
then the higher temperature of the thermodynamic energy converter can be
increased. This will give an overall increase in thermal efficiency of the
system, meaning that a greater proportion of the heat energy available can be
converted into useful energy, whether of mechanical or electrical
form.
In the following description the specific form of the thermodynamic
energy converters will not be described, but they can be deemed to be planar
thermoelectric units operating by the Seebeck or Peltier actions to convert heat
into electricity or vice versa if working in reverse heat engine mode.
Alternatively, they can be fluid driven heat engines, such as a Stirling engine
in which a piston and cylinder system causes air under pressure to be oscillated
between a warm heat sink and a cool heat sink, with thermodynamic action
allowing mechanical power to be drawn from the piston movement at the expense of
heat transfer between the two sinks. The thermoelectric version can have the
form described in the above referenced patent application, whereas the Stirling
engine can have the form described in the above-referenced paper by Jerald D.
Parker.
Referring to FIG. 1, a cross-section of what appears to be a kind
of honeycomb structure of a thermally powered system of energy converter units
is shown. It comprises numerous planar thermoelectric elements 10 mounted with
their lower temperature heat exchange surfaces in contact with heat-conducting
metal plates 11, which are assembled mutually parallel in the structure to
divide the cross-section into an alternate sequence of two different spatial
forms. One such space form constitutes a passage way or duct 12 for fluid at the
lower temperature. The other such space form constitutes a heat radiation cavity
13.
The thermoelectric elements 10 have external electric output
leads (not shown) but which are mounted on the plates 11 and connect the various
elements 10 in a suitable parallel-series network to suit the voltage/current
design requirements of the system.
In operation, input heat is fed to the
surfaces of plates 11 by air flow through the ducts 12. Heat radiation from the
first heat sink, the surfaces of plates 11 within the cavities 13, is refracted
by the lenses 14 and converges at an increasing intensity onto the smaller
heat-absorbing surfaces of the elements 10. This heat then passes through the
thermoelectric junctions to generate electrical power, some of which is fed as
electrical output into the external output power leads, but much of which is
rejected as heat at a lower temperature and conducted into the metal of the
plates 11.
The convex form of the lenses 14 focuses the radiation to
increase its intensity and so elevate the temperature of the absorbing surface.
Assuming little heat dissipation by convection, the heat energy absorbed by
elements 10 will only be very slightly less than that radiated by the plates 11.
The result of this is that the third heat sink, which is defined by the parts of
the plate 11 in contact with the elements 10, will be very nearly at the same
temperature as the absorbing surface, the second heat sink. This means that so
long as heat is supplied via the fluid in the ducts 12, there will be an
electrical output from the thermoelectric elements.
Note that this
process of heat conversion into electricity is one which recycles the heat not
converted into electricity. This means that the overall thermal conversion
efficiency can be close to 100%. The power rating, meaning the amount of power
that can be produced from a system of a certain size with a given heat input
temperature, is affected by the percentage efficiency in relation to the Carnot
criterion. The closer the performance of the thermoelectric elements to the
Carnot value, the smaller the cyclic iteration sequence and the faster input
heat is converted into electricity. Similarly, the stronger the optical
concentration and so the temperature enhancement, the smaller the cyclic
iteration sequence. The greater the temperature of the heat input, the greater
the heat transfer by radiation, by a factor scaled up by the fourth power of
absolute temperature. Therefore, the greater the power rating.
Bearing in
mind that the thermoelectric converters based on the suggested prototype design
can operate at ambient (atmospheric temperatures) with some 70% of Carnot
efficiency and with an absorbing heat surface of millimeter width and no more
than 3 millimeters in length, one can contemplate multicell structures of
lattice dimension of a few centimeters. This means that as many as 1000 cells
can be present in a 1 meter square crosssection and a radiating surface acting
as what has been termed 'the first heat sink' can be as great as 60 square
meters in a cubic meter structure.
Blackbody radiation from 60 square
meters at 300 K occurs at a rate of 25 kW. If the intensity of this radiant
energy is concentrated to 500 K at the second heat sink, then, allowing for a
70% of Carnot efficiency of conversion, one has the potential for generating 7
kW output as electricity per cubic meter of converter structure, based on heat
input at ambient temperature.
Essential to such performance, however, is
that high conversion efficiency in relation to the Carnot criterion plus the
availability of technology for building miniature solid-state thermoelectric
converters on the scale suggested. This technology is, however, already
demonstrably proven and is the subject of the patent applications already
referenced.
The structure shown in FIG. 1 can be modified by using plates
11 common to adjacent cavities and eliminating the ducts 12. This saves on space
and allows even more compact design and so enhanced power rating. However, to
input the heat energy in this case, the lenses 14 can be formed as an acrylic
Fresnel lens defining a fluid duct between the lens and the radiating surface of
the plate 11. Air could then flow through the lens structure to sustain the
temperature of plates 11. Alternatively, the lens could rely mainly on the
refractive index of a liquid, such as water, and a flow of this liquid through
such a duct could be the means for heat input.
A preferred implementation
of the invention is one which uses concave parabolic mirrors with the
thermoelectric elements at the linear focus. Two complete cell units and two
halves of cell units of such a structure are shown in FIG 2. Here the space
between the back of concave mirrors 16 and metal plates 11 defines the ducts or
passage ways through which a fluid flows to supply heat to the plates. The
radiation flows as shown by the arrowed lines and heats the surface of the
thermoelectric elements 10 to generate electricity as already described by
reference to FIG. 1.
The invention does extend to the use of conventional heat
engine technology as the means for generating power output from the radiant heat
collected from the optical focusing. In this case, as shown in FIG. 3, the
thermoelements 10, which are elongated structures extending the full length of
the main converter structure at right angles to the cross-sections shown in
Figs. 1 and 2, can be replaced by small bore copper pipes mounted on plates 11
but heatinsulated from those plates by their supports and by appropriate
shielding. Similarly, the heat input, instead of being supplied via the ducts
formed between the mirrors and plates 11 could be provided by fluid flow through
small bore copper pipes mounted in good heat conducting contact on the opposite
face of plates 11, but otherwise heat-insulated to minimize convection if not
part of an evacuated structure.
To enhance the power generating capacity of a system using the
invention, it is desirable to operate at higher temperatures, because heat
radiation is proportional to the fourth power of absolute temperature. If the
heat source is low grade but abundant and freely available, such as a geothermal
water source, then efficiency of energy conversion is primarily related to the
more effective use of an installation and its capital expense. As already
stated, it then becomes feasible to operate a heat engine in reverse mode with
the object of elevating the operating temperature of the system. Then some of
the power produced has to be deployed into powering the reverse heat
engine.
If such higher temperatures are used the structure of FIG. 2 or 3
has advantages because of the possibility of its fabrication by use of metal and
ceramics to the exclusion of liquids or plastic materials, which can feature in
the structure of FIG. 1.
The reverse heat engine
23 may be of any conventional form, provided it has a high near-to-Carnot
efficiency. Its role is to take heat input from a low grade heat source (denoted
as heat input H) and bring this up to a much higher temperature. This heat at an
elevated temperature is fed as output by a suitable fluid flow means to provide
input heat to the first heat sink in the converter system 20. Thus such heat is
supplied to the metal plates 11 in Figs. 1, 2 or 3, which are part of the
structure of system 20.
If the Fig. 3 construction is used, the heat inflow
is via fluid, eg. hot air, supplied through pipes 17. In Fig. 4 these pipes are
common to three circulating loops, one passing through a heat exchange system in
the Stirling engine 19, one passing through the heat store 21 and one passing
through a heat exchange system in the reverse heat engine 23. The temperature of
the fluid flowing in these circuits is that of the first heat sink of converter
20. A single loop circuital flow connects the converter 20 and the Stirling
engine 19. This flow through pipes 19 involves the fluid, eg. hot air, which is
at the high working temperature produced by focusing the radiation inside
converter 20, that is, the temperature of the second heat sink. The lower
temperature heat exchange in the Stirling engine 19 occurs at what is termed in
the claims as the 'third heat sink' and such rejected heat is conveyed by the
circulating fluid to the first heat sink in converter 20 by the pipes
17.
The output of the system 20, which incorporates the features of the
invention already described, is either heat at an even higher temperature
carried by a fluid flow or electricity supplied by the thermoelectric elements.
Heat output could be supplied for use as heat, as for support of some chemical
process, for example, or, in the system under discussion, fed as input to the
heat engine 19. Any heat rejected from the engine 19 at the lower temperature
matching that of the elevated heat output from reverse heat engine 23 is
combined with that reverse heat engine to be fed back as input to the converter
system 20.
Such a system would not be technologically practical were it
not for the ability to construct a multicell structure incorporating miniature
cells of centimeter dimensions, each associated with its own warm and cool heat
sinks, the temperature differential of which powers the system. For this reason
the preferred implementation of the invention is one which builds on the
technology of the thermoelectric invention, which is the subject of the
above-referenced patent applications.
To understand the benefits of the
mode of implementing the invention using the reverse heat engine combination,
consider one practical implementation which input heat at 300 K and uses the
reverse heat engine to enhance this to 500 K.
Note first, however, that
what is at issue is not the overall thermal efficiency, which has to be
virtually 100% with the recycling feature, but rather the scale or power rating
of a particular system.
500 K is the temperature of the first heat sink
or radiating surface. The optical focusing system concentrates the intensity of
this radiation by a factor of 20, corresponding to the ratio of the radiating
surface to that of the absorbing surface. In consequence the temperature of that
second heat sink, or absorbing surface, is, say, 800 K. The loss of energy by
reradiation is then, in theory, 33% of the incident radiation, owing to the
fourth power effect of temperature on a surface 5% of that of the primary
radiation source. Therefore, assuming perfect blackbody radiation, 67% of the
source energy can be deployed in a single throughput cycle to power the heat
engine or the thermoelectric converter.
The latter rejects energy at the
500 K temperature and so it has an ideal Carnot efficiency of 37.5%, but, in
practice, its efficiency is 27%. This is energy converted into useful work, such
as electricity or mechanical power and some of this is needed to power the
reverse heat engine. For each unit of heat energy supplied at 500 K, the input
power to that reverse heat engine is 0.5 units, assuming an 80% of Carnot
efficiency of performance. All of the input unit of heat eventually finds its
way to the 800 K level via the concentration of the optical system, because
reradiated energy cannot degrade below the 500 K level inside the
structure.
Therefore, since 67% of 27% of the energy radiated from the
500 K surface converts into useful work, with the rest being recycled, half or
9% of the radiated energy is available as net power output after supplying the
reverse heat engine. Whatever the radiation capacity of that 500 K surface, only
9% of that radiated power can contribute to the power rating of the
system.
Given the 60 square meter radiating surface in a cubic meter
structure, as already specified, and noting that blackbody radiation at 300 K is
25 kW from such an area, there is potentially a radiation rate of 164 kW at 500
K. With a 9% overall conversion rate into electricity or other form of useful
net power output, this is approximately a 15 kW rating for a cubic meter of
structure. This may seem a large structure to generate a mere 15 kW but it is
generated from low grade heat deemed to be at the ambient temperature level of
300 K and the advantages of the invention have to be measured in terms of the
saving of reliance on fossil fuel.
The above are not optimum design data,
because higher efficiency can be achieved by operating with a higher temperature
differential in the reverse heat engine stage and the economics of the
conversion into electricity depend upon the cheapness of mass fabrication of the
miniature thermoelectric elements. Also, there are advantages not found in
conventional power generating systems, in that when output non-thermal power
surplus to demand is being generated it can be converted into heat in the
reverse heat engine stage and stored as heat in the heat store 21 for later use
at times of peak load. This relieves the electrical power feedback to the
reverse heat engine at such times and so makes the counter-productive
combination of heat engine and reverse heat engine, not just a means for
enhancing radiation temperatures and so power rating, but also a means for
matching that rating to variable load conditions.
Claims
1. A thermally powered energy converter comprising a
first heat sink having a surface from which heat is radiated, a second heat sink
having a surface at which heat is absorbed, optical focusing means arranged to
capture radiation from the radiating surface of the first heat sink and to focus
it upon the smaller absorbing surface of the second heat sink, a third heat
sink, thermodynamic energy conversion means activated by a temperature
differential between the second and third heat sinks and operative to supply a
non-thermal power output, means for supplying an inflow of heat energy to the
first heat sink and means for extracting heat energy from the third heat
sink.
2. A thermally powered energy converter according to claim 1,
wherein the means for extracting heat energy from the third heat sink comprises
a thermallyconductive connection between the third heat sink and the first heat
sink, whereby heat energy exhausted at the lower heat sink temperature of the
thermodynamic energy conversion means augments the inflow of heat energy
supplied to the first heat sink.
3. A thermally powered energy converter
according to claim 1, comprising an auxiliary thermodynamic energy conversion
means operative as a reverse heat engine and connected to be powered by a
portion of said nonthermal power output, this auxiliary thermodynamic energy
conversion means operating to preheat fluid conveying the inflow heat to the
first heat sink.
4. A thermally powered energy converter according to
claim 1, wherein the optical focusing means comprises a lens system formed by a
curved transparent bounding structure with the space intervening the structure
and the heat radiating surface of the first heat sink defining a duct for fluid
conveying the inflow heat to the first heat sink.
5. A thermally powered
energy converter according to claim 4, wherein the lens system incorporates in
the space intervening the bounding structure and the heat radiating surface a
transparent liquid arranged to flow via an external heat exchange circuit to
carry the inflow heat to the first heat sink.
6. A thermally powered
energy converter according to claim 1, wherein the optical focusing means
comprises a mirror system formed by a curved reflecting structure with the space
intervening the nonreflecting surface of the structure and the heat radiating
surface of the first heat sink defining a duct for fluid conveying the inflow
heat to the first heat sink.
7. A thermally powered energy converter
according to claim 1, wherein the optical focusing means comprises a mirror
system formed by a curved metal reflecting structure with the space bounded by
surfaces including the non-reflecting surface of the structure defining a duct
for fluid conveying the inflow heat to the first heat sink, the metal reflecting
structure being in heat conducting relationship with the heat radiating surface
of the first heat sink.
8. A thermally powered energy converter
incorporating a multicell structure having a cross-section which comprises a
lattice-like array of converter units, each of which comprises a first heat sink
having a surface from which heat is radiated, a second heat sink having a
surface at which heat is absorbed, optical focusing means arranged to capture
radiation from the radiating surface of the first heat sink and to focus it upon
the smaller absorbing surface of the second heat sink, a third heat sink,
thermodynamic energy conversion means activated by a temperature differential
between the second and third heat sinks and operative to supply a non-thermal
power output, means for supplying an inflow of heat energy to the first heat
sink and means for extracting heat energy from the third heat sink.
9. A
thermally powered energy converter incorporating a multicell structure having a
cross-section which comprises a lattice-like array of converter units, each of
which comprises a first heat sink having a surface from which heat is radiated,
a second heat sink having a surface at which heat is absorbed, optical focusing
means arranged to capture radiation from the radiating surface of the first heat
sink and to focus it upon the smaller absorbing surface of the second heat sink
and a third heat sink, the converter further comprising thermodynamic energy
conversion means, shared by a plurality of converter units, which energy
conversion means are activated by a temperature differential between the second
and third heat sinks and are operative to supply a nonthermal power output,
there being means for supplying an inflow of heat energy to each of the first
heat sinks and means for extracting heat energy from each of the third heat
sinks.
10. A thermally powered energy converter according to claim 9,
comprising a Stirling-type heat engine shared by a plurality of converter units
and operating on heat energy drawn from a gas heated by a second heat sink and
rejecting exhaust heat to a third heat sink.
11. A thermally powered
energy converter according to claim 9, comprising a Stirling-type heat engine
shared by a plurality of converter units and operating on heat energy drawn from
a gas heated by a second heat sink and rejecting exhaust heat to a third heat
sink, which heat is conveyed to the first heat sink by gas flow activated by the
cyclic operation of the engine.
12. A thermally powered energy converter
according to claim 8, wherein the thermodynamic energy conversion means include
thermoelectric elements utilizing the Seebeck effect, there being one such
element in each converter unit, the heated surface of the element being the
second heat sink and the cooled surface being the third heat sink, heat from
which is conveyed by thermal conduction through metal to the first heat
sink.
13. A thermally powered energy converter comprising, in
combination, a converter system supplying non-thermal power output, a heat store
and an auxiliary thermodynamic energy conversion means powered by at least some
of said non-thermal power output to generate heat, the converter system
comprising a first heat sink having a surface from which heat is radiated, a
second heat sink having a surface at which heat is absorbed, optical focusing
means arranged to capture radiation from the radiating surface of the first heat
sink and to focus it upon the smaller absorbing surface of the second heat sink,
a third heat sink, primary thermodynamic energy conversion means activated by a
temperature differential between the second and third heat sinks and operative
to supply said non-thermal power output, including a residual output for use
external to the converter, said auxiliary thermodynamic energy conversion means
being operative as a reverse heat engine operating to preheat fluid conveying
the inflow heat to the first heat sink and there being means for extracting heat
energy from the third heat sink and feeding this into the heat store, which
provides a reserve source of heat used to supplement the inflow of heat to the
first heat sink.
In the above Web page presentation I have introduced the first
chapter of my story about 'TEC' (Thermodynamic Energy Conversion). I will
progressively add more chapters. These 'chapters' may be Lectures or Essays,
depending upon their style and detail of presentation. In my onward discourse
I will refer to the above 'chapter' as 'TEC I'. To progress to the next
Chapter press TEC
II.