Lonnie JOHNSON
JTEC Thermo-Electric Generator
Until now, thermodynamic engines that use compressible working fluids have generally been mechanical devices. These devices have inherent difficulties in achieving high compression ratios and in achieving the near constant temperature compression and expansion processes needed to approximate Carnot equivalent cycles. Solid-state thermoelectric converters that utilize semiconductor materials have only been able to achieve single digit conversion efficiency. Extensive resources have been applied toward Alkali Metal Thermoelectric Converters (AMTEC), which operate on a modified Rankine cycle and on the Stirling engine. However, because of inherent limitations, these systems have not achieved envisioned performance levels.
The JTEC is an all solid-state engine that operates on the Ericsson cycle. Equivalent to Carnot, the Ericsson cycle offers the maximum theoretical efficiency available from an engine operating between two temperatures. The JTEC system utilizes the electro-chemical potential of hydrogen pressure applied across a proton conductive membrane (PCM). The membrane and a pair of electrodes form a Membrane Electrode Assembly (MEA) similar to those used in fuel cells. On the high-pressure side of the MEA, hydrogen gas is oxidized resulting in the creation of protons and electrons. The pressure differential forces protons through the membrane causing the electrodes to conduct electrons through an external load. On the low-pressure side, the protons are reduced with the electrons to reform hydrogen gas. This process can also operate in reverse. If current is passed through the MEA a low-pressure gas can be "pumped" to a higher pressure.
The JTEC uses two membrane electrode assembly (MEA) stacks. One stack is coupled to a high temperature heat source and the other to a low temperature heat sink. Hydrogen circulates within the engine between the two MEA stacks via a counter flow regenerative heat exchanger. The engine does not require oxygen or a continuous fuel supply, only heat. Like a gas turbine engine, the low temperature MEA stack is the compressor stage and the high temperature MEA is the power stage. The MEA stacks will be designed for sufficient heat transfer with the heat source and sink to allow near constant temperature expansion and compression processes. This feature coupled with the use of a regenerative counter flow heat exchanger will allow the engine to approximate the Ericsson cycle.
The engine is scaleable and has applications ranging from supplying power for Micro Electro Mechanical Systems (MEMS) to power for large-scale applications such as fixed power plants. The technology is applicable to skid mounted, field generators, land vehicles, air vehicles and spacecraft. The JTEC could utilize heat from fuel combustion, solar, low grade industrial waste heat or waste heat from other power generation systems including fuel cells, internal combustion engines and combustion turbines. As a heat pump, the JTEC system could be used as a drop in replacement for existing HVAC equipment in residential, commercial, or industrial settings.
http://www.physorg.com/news119107136.html
Nuclear Engineer Lonnie Johnson, best known for his invention of the super soaker squirt gun, has recently designed a new type of solar energy technology that he says can achieve a conversion efficiency rate of more than 60 percent. Considering that the best solar energy systems today have an efficiency of 30-40 percent, Johnson´s method could cut the cost of solar energy nearly in half.
A recent article in Popular Mechanics describes how Johnson´s system would work. Rather than use photovoltaic cells, where silicon converts light into electricity, the new system works like a heat engine. But instead of using heat to turn an axle, it uses heat to force hydrogen ions through a membrane-electrode, and create electricity.
The system, called the Johnson Thermoelectric Energy Converting System (JTEC) consists of two stacks of electrodes --- a high-temperature stack heated by the sun (and by concentrated mirrors) and a low-temperature stack.
An electrical jolt triggers a voltage across the electrode stacks, with the low-temperature stack pumping out hydrogen from low to high pressure in order to maintain the pressure differential. As the hydrogen passes through the high-temperature stack of electrodes, it generates power. In a sense, the system works similar to a fuel cell.
Johnson plans to build a system whose high temperature reaches 600 degrees centrigrade, within the current solar concentration ability of parabolic mirrors, which can produce temperatures of more than 800 degrees centigrade. At 600 degrees, the system would have an efficiency of close to 60 percent. At higher temperatures, the efficiency would increase even more.
The system should be able to produce several megawatts of power, according to Johnson. It could also harvest waste heat from internal combustion engines, turbines, and even the human body.
Johnson, a former NASA employee, funds his work with the millions of dollars he made from inventing the super soaker.
http://www.popularmechanics.com/science/earth/4243793.html
Popular Mechanics ( Jan. 8, 2008)
Super Soaker Inventor Aims to Cut Solar Costs in Half
by
Logan Ward
Solar energy technology is enjoying its day in the sun with the advent of innovations from flexible photovoltaic (PV) materials to thermal power plants that concentrate the sun’s heat to drive turbines. But even the best system converts only about 30 percent of received solar energy into electricity—making solar more expensive than burning coal or oil. That will change if Lonnie Johnson’s invention works. The Atlanta-based independent inventor of the Super Soaker squirt gun (a true technological milestone) says he can achieve a conversion efficiency rate that tops 60 percent with a new solid-state heat engine. It represents a breakthrough new way to turn heat into power.
Johnson, a nuclear engineer who holds more than 100 patents, calls his invention the Johnson Thermoelectric Energy Conversion System, or JTEC for short. This is not PV technology, in which semiconducting silicon converts light into electricity. And unlike a Stirling engine, in which pistons are powered by the expansion and compression of a contained gas, there are no moving parts in the JTEC. It’s sort of like a fuel cell: JTEC circulates hydrogen between two membrane-electrode assemblies (MEA). Unlike a fuel cell, however, JTEC is a closed system. No external hydrogen source. No oxygen input. No wastewater output. Other than a jolt of electricity that acts like the ignition spark in an internal-combustion engine, the only input is heat.
Here’s how it works: One MEA stack is coupled to a high- temperature heat source (such as solar heat concentrated by mirrors), and the other to a low-temperature heat sink (ambient air). The low-temperature stack acts as the compressor stage while the high-temperature stack functions as the power stage. Once the cycle is started by the electrical jolt, the resulting pressure differential produces voltage across each of the MEA stacks. The higher voltage at the high-temperature stack forces the low-temperature stack to pump hydrogen from low pressure to high pressure, maintaining the pressure differential. Meanwhile hydrogen passing through the high-temperature stack generates power.
“It’s like a conventional heat engine,” explains Paul Werbos, program director at the National Science Foundation, which has provided funding for JTEC. “It still uses temperature differences to create pressure gradients. Only instead of using those pressure gradients to move an axle or wheel, he’s using them to force ions through a membrane. It’s a totally new way of generating electricity from heat.”
The bigger the temperature differential, the higher the efficiency. With the help of Heshmat Aglan, a professor of mechanical engineering at Alabama’s Tuskegee University, Johnson hopes to have a low-temperature prototype (200-degree centigrade) completed within a year’s time. The pair is experimenting with high-temperature membranes made of a novel ceramic material of micron-scale thickness. Johnson envisions a first-generation system capable of handling temperatures up to 600 degrees. (Currently, solar concentration using parabolic mirrors tops 800 degrees centigrade.) Based on the theoretical Carnot thermodynamic cycle, at 600 degrees efficiency rates approach 60 percent, twice those of today’s solar Stirling engines.
This engine, Johnson says, can operate on tiny scales, or generate megawatts of power. If it proves feasible, drastically reducing the cost of solar power would only be a start. JTEC could potentially harvest waste heat from internal combustion engines and combustion turbines, perhaps even the human body. And no moving parts means no friction and fewer mechanical failures.
As an engineer, Johnson says he has always been interested in energy conversion. In fact, it was while working on an idea for an environmentally friendly heat pump (one that would not require Freon) that he came up with the Super Soaker, which earned him millions of dollars in royalties. That money allowed Johnson to quit NASA’s Jet Propulsion Lab (where he worked on the Galileo Mission, among other projects) and go independent. His toy profits have funded his research in advanced battery technology, specifically thin-film lithium-ion conductive membranes. And that work sparked the idea for JTEC. Besides, he jokes, “All inventors have to have an engine. It’s like a rite of passage.”
National Science Foundation
http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=0646367
Award Number: 0646367
Johnson ThermoElectrochemical Converter (JTEC) Solar Powered Cell Tower Generator
ABSTRACT --- JTEC SOLAR POWERED CELL TOWER GENERATOR
This project will attempt to resolve the key technical issues
and uncertainties regarding a breakthrough concept for low-cost
high-efficiency solar power. The proposed approach is based on a
conceptual system for providing independent power for cell
towers that will allow them to function even after emergencies
like hurricane Katrina. The solar engine is based on the Johnson
ThermoElectrochemical Converter (JTEC) concept for converting
heat to electricity invented by (Lonnie) Johnson, who will be
available to assist Tuskegee University in carrying out this
work. Except for the working fluid, JTEC is an all solid state
engine that does not have mechanical moving parts. Different
from conventional solid state thermoelectric devices, it does
not have inherent parasitic heat loss paths. JTEC uses Membrane
Electrode Assemblies (MEA) similar to those used in fuel cells;
however, it does not require oxygen or a special fuel, only
heat. The availability of a range of proton conductive membrane
materials that operate from room temperature up to and exceeding
1200 C suggests that JTEC could generate electricity from
practically any heat source, from very small, just a few
degrees, to very large temperature differences. JTEC
approximates the Ericsson thermodynamic cycle which is Carnot
equivalent. Research on this technology offers the potential for
achieving solar power efficiency of 50% in the short-term and
80% in the long-term, far beyond what is expected from
photovoltaics both in efficiency and in cost.
(1) Intellectual merit of the proposed activity
JTEC is a fundamentally new solid state engine concept. Critical research is needed to enable a credible analysis of its potential. Research is needed into the properties of proton conductive materials needed to make a working system. The materials are similar those being studied in fuel cell research, but new material properties must be investigated in order to optimize the choices for this application. Research is needed to model, simulate and optimize an integrated systems design for cost-effective recharge power for cell towers.
(2) Broader impacts resulting from the proposed activity:
Cell towers running out of battery power were a crucial problem in the wake of Katrina and resulted unnecessary deaths and destruction. This project, with follow-on research, could provide un-interruptible, cost effective power for communications in areas threatened by hurricanes and other disasters that is not limited by battery life. The proposed engine technology will have major impacts on the international energy economy particularly with respect to the need for economical, green, renewable energy. This research is consistent with NSF goals for minority education and outreach. Tuskegee University is a HBCU institution and Johnson Research is a minority owned small business.
http://www.wikipedia.org
The Ericsson Cycle is named after inventor John Ericsson. John
Ericsson designed and built many unique heat engines based on
various thermodynamic
cycles. He is credited with inventing two unique heat engine
cycles and developing practical engines based on these cycles.
His first cycle is very similar to what we now call the "Brayton
Cycle" except that it was external combustion. His second cycle
we now call the "Ericsson Cycle".
Ideal Ericsson Cycle
The following is a list of the four processes that occur between the four stages of the ideal Ericsson cycle:
Process 1 -> 2: Isothermal Compression. The compression space is assumed to be intercooled, so the gas undergoes isothermal compression. The compressed air flows into a storage tank at constant pressure. In the ideal cycle, there is no heat transfer across the tank walls.
Process 2 -> 3: Isobaric Heat-addition. From the tank, the
compressed air flows through the regenerator and picks-up heat
at a high constant-pressure
on the way to the heated power-cylinder.
Process 3 -> 4: Isothermal Expansion. The power-cylinder expansion-space is heated externally, and the gas undergoes isothermal expansion.
Process 4 -> 1: Isobaric Heat removal. Before the air is released as exhaust, it is passed back through the regenerator, thus cooling the gas at a low constant pressure, and heating the regenerator for the next cycle.
Comparison with Stirling, Carnot and Brayton cycles
The Ericsson Cycle is often compared to the Stirling cycle,
since the engine designs based on these respective cycles are
both external combustion
engines with regenerators. The Ericsson is perhaps most similar
to the so called "double-acting" type of Stirling engine, in
which the displacer piston also acts as the power piston.
Theoretically, both of these cycles have so called "ideal"
efficiency, which is the highest allowed by the Second law of
thermodynamics. The most well known ideal cycle is the Carnot
cycle, although ironically, a real Carnot Engine is not known to
have been invented.
Comparison with the Brayton Cycle
The first cycle Ericsson developed, is now called the "Brayton Cycle", commonly applied to the rotary jet engines for airplanes.
The second Ericsson cycle is the cycle most commonly referred to as simply the "Ericsson cycle". The (second) Ericsson cycle is also the limit of ideal gas-turbine Brayton cycle, operating with multistage intercooled compression, and multistage expansion with reheat and regeneration. Compared to the Brayton cycle which uses adiabatic compression and expansion, the second Ericsson cycle uses isothermal compression and expansion, thus producing more net work per stroke. Also the use of regeneration in the Ericsson cycle increases efficiency by reducing the required heat input. For further comparisons of thermodynamic cycles, see Heat engine.
Ericsson Engine
The Ericsson engine, (see figure), is based on the Ericsson cycle, and is known as an "external combustion engine", because it is externally heated. To improve efficiency, the engine has a regenerator or recuperator between the compressor and the expander. The engine can be run open-cycle or closed-cycle. Expansion occurs simultaneously with compression, on opposite sides of the piston.
The Regenerator
Ericsson coined the term "regenerator" for his independent invention of the mixed-flow counter-current heat-exchanger. However, Rev. Robert Stirling had invented the same device, prior to Ericsson, so the invention is credited to Stirling. Stirling called it an "economiser" or "economizer", because it increased the fuel economy of various types of heat processes. The invention was found to be useful, in many other devices and systems, where it became more widely used, since other types of engines became favored over the Stirling engine. Interestingly, the term "regenerator" is now the name given to the component in the Stirling Engine!
The term "recuperator" refers to a separated-flow, counter-current heat exchanger. As if this weren't confusing enough, a mixed-flow regenerator is sometimes used as a quasi-separated-flow recuperator. This can be done through the use of moving valves, or by a rotating regenerator with fixed baffles, or by the use of other moving parts. When heat is recovered from exhaust gases and used to preheat combustion air, typically the term recuperator is used, because the two flows are separate.
History
In 1791, before Ericsson, Barber proposed a similar engine. The Barber engine used a bellows compressor and a turbine expander, but it lacked a regenerator/recuperator. There are no records of a working Barber engine. Ericsson invented and patented his first engine using an external version of the Brayton Cycle in 1833 (number 6409/1833 British). This was 18 years before Joule and 43 years before Brayton. Brayton engines were all piston engines and for the most part, internal combustion versions of the un-recuperated Ericsson engine. The "Brayton Cycle" is now known as the gas turbine cycle, which differs from the original "Brayton Cycle" in the use of a turbine compressor and expander. The gas turbine cycle is used for all modern gas turbine and turbojet engines, however simple cycle turbines are often recuperated to improve efficiency and these recuperated turbines more closely resemble Ericsson's work.
Ericsson eventually abandoned the open cycle in favor of the traditional closed Stirling cycle.
The Ericsson Cycle Engine (The second of the two discussed here) was used to power a 2000 ton ship, The Caloric Ship Ericsson and the engine ran flawlessly for 73 hours. The combination engine produced about 300 horsepower. It had a combination of 4 dual-piston engines; the larger expansion piston/cylinder, at 4.267 meters or 14 feet in diameter, was perhaps the largest piston ever built. Rumor has it that tables were placed on top of those pistons and dinner was served and eaten, while the engine was running at full power. At 6.5 RPM the pressure was limited to 8 psi. The one sea trial proved that even though the engine ran well it was underpowered. ometime after the trials the Ericsson sank. When it was raised the Ericsson cycle engine was removed and a steam engine took its place.
Ericsson designed and built a very great number of engines running on various cycles including steam, Stirling, Brayton, externally heated diesel air fluid cycle. He ran his engines on a great variety of fuels including coal and solar heat.
Ericsson also was the inventor of the screw propeller for ship propulsion, in the USS Princeton.
The Atlanta Journal-Constitution
Inventor breaks through again -- Beyond Super Soaker :
Atlantan's energy game-changer earns honors.
Lonnie Johnson has some impressive hard science credentials.
He's worked for the Strategic Air Command and for NASA's Jet Propulsion Laboratory, outfitting missions to Mars, Jupiter and Saturn. He holds about 100 patents, many of them in that arcane spot where chemistry, electricity and physics cross into the marketplace. And his latest invention appears to do the impossible: generating electricity with no fuel and no moving parts.
But he's still known as Mr. Squirt Gun.
Even among the geniuses who gathered to honor him and his new thermo-electrochemical converter at a Breakthrough Awards banquet in Manhattan this month, the Atlanta scientist's new invention was ignored when his most famous device was revealed.
"What?" they cried. "You invented the Super Soaker?"
Johnson, 59, doesn't mind if he's better known for watery mayhem than rocket science. Perhaps that's because $1 billion worth of Super Soakers have sold since 1990. A billion dollars could buy most of a Galileo mission.
Johnson's share (he licensed the Soaker's design to Larami, later bought by Hasbro) won him the financial independence to pursue his own ideas, which is how the Johnson Thermo-electrochemical Converter system -- JTEC for short --- was born.
Using heat to force ions out of a hydrogen cell, the JTEC "is just a stunning insight," said Jerry Beilinson, deputy editor of Popular Mechanics magazine, which honors innovators in its current issue and sponsors the Breakthrough Awards. "I kind of thought we were finished; I didn't think there was a new way."
Beilinson groups Johnson with other great synthesists of science, including Henry Ford and Thomas Edison. He also points out that Johnson, a native of Mobile, flourished in a somewhat hostile environment.
˜A whole new technology"
In 1963 his governor stood up for segregation in Alabama, standing in the schoolhouse door. Five years later, Johnson, a high school senior, finished building a remote-controlled robot with a reel-to-reel tape player for a brain and jukebox solenoids controlling its pneumatic limbs. As a representative of Williamson High School, Johnson took his robot (nicknamed Linex) to a science fair at the University of Alabama.
The door wasn't exactly blocked, but no other black high schools participated in the event. On the strength of Linex, Williamson won. Teachers predicted Johnson would go far.
His robots went even farther. After graduating from Tuskegee University, Johnson joined the Air Force, worked at the Air Force Weapons Laboratory at Sandia, worked for NASA's Jet Propulsion Lab on the Galileo mission to Jupiter and the Mars Observer project, among others. He also helped design the Cassini robot probe that flew 740 million miles to Saturn.
In 1990, just before the Super Soaker made him wealthy, Johnson moved to Atlanta. In 2000, he began working in earnest on the JTEC. In 2006 that work came to the attention of Paul Werbos at the National Science Foundation, who recommended Johnson to Popular Mechanics.
"This is a whole new family of technology," said the NSF's Werbos. "It's like discovering a new continent. You don't know what's there, but you sure want to explore it to find out."
Johnson's device can potentially work with even modest temperature differentials -- say, between body heat and ambient air -- to power implanted medical devices such as pacemakers. If successful, at high heat it would generate Con Edison-scale output. It also would run backward for refrigeration purposes: put in electricity to generate heat loss for, say, wearable air conditioning.
Paired with a parabolic solar array to generate heat, it would create virtually limitless emission-free power.
Johnson, who projects earnings of $10 billion by 2013, claims a potential 60 percent efficiency rating, which doubles the efficiency of the current leader, the Stirling engine.
"It has a darn good chance," said Werbos, "of being the best thing on Earth."
˜Always an adventure"
This energy game-changer comes from unlikely quarters: a renovated factory on a formerly bleak stretch of Decatur Street.
With the help of a $3.9 million empowerment-zone loan from the city, Johnson's company bought, renovated and outfitted three adjacent buildings on the street. In addition to his workshop, he hosts a high school robotics team sponsored by the 100 Black Men of Atlanta and donates office space for the Georgia Alliance for Children, of which he is the chairman.
On a recent weekday, Johnson, impeccable in head-to-toe khaki, conducts a tour of the workshop, moving among shiny stainless steel deposition chambers and glove boxes where scientists can manipulate delicate materials isolated in a pure argon atmosphere.
Here the two dozen employees of his privately owned concern work on several projects at once, developing solid-state batteries and lithium-air batteries.
At one station Bill Rauch is working on solid-state batteries. "He's full of ideas," says Rauch, a Ph.D. in material science from Georgia Tech. "It's always an adventure."
Rauch says every now and then Johnson has a get-together at his Ansley Park home for the employees; they swim in the pool and squirt each other with off-the-shelf Super Soakers. Then Johnson comes out with a prototype water weapon not available to the public. He crushes the opposition.
Johnson's interest in thermal engines and heat pumps led to experiments using water vapor instead of Freon as a compressible liquid, which led, oddly enough, to the birth of the Super Soaker.
His work with batteries led to an interest in generating electricity electrochemically, instead of mechanically, which led to the JTEC. The JTEC completes the loop between heat pumps and batteries.
It;s freshman chemistry, said Karl Littau, a material scientist at Palo Alto Research Center, a California nursery for high-tech innovation. "Millions of people learn about that every year, yet he was the guy who put two and two together."
Most of his ideas are connected, said Johnson.
"Sometimes I think I'm still working on everything I ever invented."
HOW DOES IT WORK?
Most electricity is generated using heat to power a mechanical device, such as a piston or a turbine. The JTEC uses heat to force ions through a special membrane. "It's a totally new way of generating electricity from heat," Paul Werbos told Popular Mechanics. The JTEC includes two closed hydrogen cells or "stacks" attached to pairs of electrodes. One is a low-temperature stack, the other is high-temperature. Current compresses hydrogen in the low-temperature stack, ionizing the hydrogen and forcing its protons through the membrane to the high-temperature stack, where the hydrogen expands. Current is generated as electrons are freed. The high-temperature end generates more power than the low-temperature end uses -- creating an excess that can cool beer or run TVs and washing machines. Hydrogen is neither burned nor added, and emissions are zero.
LONNIE JOHNSON
> Born: Oct. 6, 1949, Mobile
> Residence: Ansley Park
> Family: Wife, Linda Moore, and four children
> Education: Tuskegee University, with degrees in mechanical
engineering and nuclear engineering
> Career: Research engineer with Oak Ridge National
Laboratories; engineer at NASA’s Jet Propulsion Laboratory;
nuclear safety engineer with U.S. Air Force; officer with the
Strategic Air Command; flight test engineer Edwards Air Force
Base.
> Businesses: Johnson Research and Development, Johnson
Electro-Mechanical Systems, Excellatron Solid State LLC
http://www.johnsonems.com/
Johnson Thermo-Electrochemical Converter System
Until now, thermodynamic engines that use compressible working fluids have generally been mechanical devices. These devices have inherent difficulties in achieving high compression ratios and in achieving the near constant temperature compression and expansion processes needed to approximate Carnot equivalent cycles. Solid-state thermoelectric converters that utilize semiconductor materials have only been able to achieve single digit conversion efficiency. Extensive resources have been applied toward Alkali Metal Thermoelectric Converters (AMTEC), which operate on a modified Rankine cycle and on the Stirling engine. However, because of inherent limitations, these systems have not achieved envisioned performance levels.
The JTEC is an all solid-state engine that operates on the Ericsson cycle. Equivalent to Carnot, the Ericsson cycle offers the maximum theoretical efficiency available from an engine operating between two temperatures. The JTEC system utilizes the electro-chemical potential of hydrogen pressure applied across a proton conductive membrane (PCM). The membrane and a pair of electrodes form a Membrane Electrode Assembly (MEA) similar to those used in fuel cells. On the high-pressure side of the MEA, hydrogen gas is oxidized resulting in the creation of protons and electrons. The pressure differential forces protons through the membrane causing the electrodes to conduct electrons through an external load. On the low-pressure side, the protons are reduced with the electrons to reform hydrogen gas. This process can also operate in reverse. If current is passed through the MEA a low-pressure gas can be "pumped" to a higher pressure.
The JTEC uses two membrane electrode assembly (MEA) stacks. One stack is coupled to a high temperature heat source and the other to a low temperature heat sink. Hydrogen circulates within the engine between the two MEA stacks via a counter flow regenerative heat exchanger. The engine does not require oxygen or a continuous fuel supply, only heat. Like a gas turbine engine, the low temperature MEA stack is the compressor stage and the high temperature MEA is the power stage. The MEA stacks will be designed for sufficient heat transfer with the heat source and sink to allow near constant temperature expansion and compression processes. This feature coupled with the use of a regenerative counter flow heat exchanger will allow the engine to approximate the Ericsson cycle.
The engine is scaleable and has applications ranging from supplying power for Micro Electro Mechanical Systems (MEMS) to power for large-scale applications such as fixed power plants. The technology is applicable to skid mounted, field generators, land vehicles, air vehicles and spacecraft. The JTEC could utilize heat from fuel combustion, solar, low grade industrial waste heat or waste heat from other power generation systems including fuel cells, internal combustion engines and combustion turbines. As a heat pump, the JTEC system could be used as a drop in replacement for existing HVAC equipment in residential, commercial, or industrial settings.
http://www.popularmechanics.com/science/environment/green-energy/4243793
Solar energy technology is enjoying its day in the sun with the advent of innovations from flexible photovoltaic (PV) materials to thermal power plants that concentrate the sun's heat to drive turbines. But even the best system converts only about 30 percent of received solar energy into electricity—making solar more expensive than burning coal or oil. That will change if Lonnie Johnson's invention works. The Atlanta-based independent inventor of the Super Soaker squirt gun (a true technological milestone) says he can achieve a conversion efficiency rate that tops 60 percent with a new solid-state heat engine. It represents a breakthrough new way to turn heat into power.
Johnson, a nuclear engineer who holds more than 100 patents, calls his invention the Johnson Thermoelectric Energy Conversion System, or JTEC for short. This is not PV technology, in which semiconducting silicon converts light into electricity. And unlike a Stirling engine, in which pistons are powered by the expansion and compression of a contained gas, there are no moving parts in the JTEC. It's sort of like a fuel cell: JTEC circulates hydrogen between two membrane-electrode assemblies (MEA). Unlike a fuel cell, however, JTEC is a closed system. No external hydrogen source. No oxygen input. No wastewater output. Other than a jolt of electricity that acts like the ignition spark in an internal-combustion engine, the only input is heat.
Here's how it works: One MEA stack is coupled to a high- temperature heat source (such as solar heat concentrated by mirrors), and the other to a low-temperature heat sink (ambient air). The low-temperature stack acts as the compressor stage while the high-temperature stack functions as the power stage. Once the cycle is started by the electrical jolt, the resulting pressure differential produces voltage across each of the MEA stacks. The higher voltage at the high-temperature stack forces the low-temperature stack to pump hydrogen from low pressure to high pressure, maintaining the pressure differential. Meanwhile hydrogen passing through the high-temperature stack generates power.
"It's like a conventional heat engine," explains Paul Werbos, program director at the National Science Foundation, which has provided funding for JTEC. "It still uses temperature differences to create pressure gradients. Only instead of using those pressure gradients to move an axle or wheel, he's using them to force ions through a membrane. It's a totally new way of generating electricity from heat."
The bigger the temperature differential, the higher the efficiency. With the help of Heshmat Aglan, a professor of mechanical engineering at Alabama's Tuskegee University, Johnson hopes to have a low-temperature prototype (200-degree centigrade) completed within a year's time. The pair is experimenting with high-temperature membranes made of a novel ceramic material of micron-scale thickness. Johnson envisions a first-generation system capable of handling temperatures up to 600 degrees. (Currently, solar concentration using parabolic mirrors tops 800 degrees centigrade.) Based on the theoretical Carnot thermodynamic cycle, at 600 degrees efficiency rates approach 60 percent, twice those of today's solar Stirling engines.
This engine, Johnson says, can operate on tiny scales, or generate megawatts of power. If it proves feasible, drastically reducing the cost of solar power would only be a start. JTEC could potentially harvest waste heat from internal combustion engines and combustion turbines, perhaps even the human body. And no moving parts means no friction and fewer mechanical failures.
As an engineer, Johnson says he has always been interested in energy conversion. In fact, it was while working on an idea for an environmentally friendly heat pump (one that would not require Freon) that he came up with the Super Soaker, which earned him millions of dollars in royalties. That money allowed Johnson to quit NASA's Jet Propulsion Lab (where he worked on the Galileo Mission, among other projects) and go independent. His toy profits have funded his research in advanced battery technology, specifically thin-film lithium-ion conductive membranes. And that work sparked the idea for JTEC. Besides, he jokes, "All inventors have to have an engine. It's like a rite of passage."
http://www.theatlantic.com/magazine/archive/2010/11/shooting-for-the-sun/8268/1/
By Logan Ward
From his childhood in segregated Mobile, Alabama, to his run-ins with a nay-saying scientific establishment, the engineer Lonnie Johnson has never paid much heed to those who told him what he could and couldn’t accomplish. Best known for creating the state-of-the-art Super Soaker squirt gun, Johnson believes he now holds the key to affordable solar power.
In March 2003, the independent inventor Lonnie Johnson faced a roomful of high-level military scientists at the Office of Naval Research in Arlington, Virginia. Johnson had traveled there from his home in Atlanta, seeking research funding for an advanced heat engine he calls the Johnson Thermoelectric Energy Converter, or JTEC (pronounced “jay-tek”). At the time, the JTEC was only a set of mathematical equations and the beginnings of a prototype, but Johnson had made the tantalizing claim that his device would be able to turn solar heat into electricity with twice the efficiency of a photovoltaic cell, and the Office of Naval Research wanted to hear more.
Projected onto the wall was a PowerPoint collage summing up some highlights of Johnson’s career: risk assessment he’d done for the space shuttle Atlantis; work on the nuclear power source for NASA’s Galileo spacecraft; engineering help on the tests that led to the first flight of the B-2 stealth bomber; the development of an energy-dense ceramic battery; and the invention of a remarkable, game-changing weapon that had made him millions of dollars—a weapon that at least one of the men in the room, the father of two small children, recognized immediately as the Super Soaker squirt gun.
Mild-mannered and bespectacled, Johnson opened his presentation by describing the idea behind the JTEC. The device, he explained, would split hydrogen atoms into protons and electrons, and in so doing would convert heat into electricity. Most radically, it would do so without the help of any moving parts. Johnson planned to tell his audience that the JTEC could produce electricity so efficiently that it might make solar power competitive with coal, and perhaps at last fulfill the promise of renewable solar energy. But before he reached that part of his presentation, Richard Carlin, then the head of the Office of Naval Research’s mechanics and energy conversion division, rose from his chair and dismissed Johnson’s brainchild outright. The whole premise for the device relied on a concept that had proven impractical, Carlin claimed, citing a 1981 report co-written by his mentor, the highly regarded electrochemist Robert Osteryoung. Go read the Osteryoung report, Carlin said, and you will see.
End of meeting.
Concerned about what he might have missed in the literature, Johnson returned home and read the inch-thick report, concluding that it addressed an approach quite different from his own. Carlin, it seems, had rejected the concept before fully comprehending it. (When I reached Carlin by phone recently, he said he did not remember the meeting, but he is familiar with the JTEC concept and now thinks that the “principles are fine.”) Nor was Carlin alone at the time. Wherever Johnson pitched the JTEC, the reaction seemed to be the same: no engine could convert heat to electricity at such high efficiency rates without the use of moving parts.
Johnson believed otherwise. He felt that what had doomed his presentation to the Office of Naval Research—and others as well—was a collective failure of imagination. It didn’t help that he was best known as a toy inventor, nor that he was working outside the usual channels of the scientific establishment. Johnson was stuck in a Catch-22: to prove his idea would work, he needed a more robust prototype, one able to withstand the extreme heat of concentrated sunlight. But he couldn’t build such a prototype without research funding. What he needed was a new pitch. Instead of presenting the JTEC as an engine, he would frame it as a high-temperature hydrogen fuel cell, a device that produces electricity chemically rather than mechanically, by stripping hydrogen atoms of their electrons. The description was only partially apt: though both devices use similar components, fuel cells require a constant supply of hydrogen; the JTEC, by contrast, contains a fixed amount of hydrogen sealed in a chamber, and needs only heat to operate. Still, in the fuel-cell context, the device’s lack of moving parts would no longer be a conceptual stumbling block.
Indeed, Johnson had begun trying out this new pitch two months before his naval presentation, in a written proposal he submitted to the Air Force Research Laboratory’s peer-review panel. The reaction, when it came that May, couldn’t have been more different. “Funded just like that,” he told me, snapping his fingers, “because they understood fuel cells—the technology, the references, the literature. The others couldn’t get past this new engine concept.” The Air Force gave Johnson $100,000 for membrane research, and in August 2003 sent a program manager to Johnson’s Atlanta laboratory. “We make a presentation about the JTEC, and he says”—here Johnson, who is black, puts on a Bill-Cosby-doing-a-white-guy voice—“‘Wow, this is exciting!’” A year later, after Johnson had proved he could make a ceramic membrane capable of withstanding temperatures above 400 degrees Celsius, the Air Force gave him an additional $750,000 in funding.
The key to the JTEC is the second law of thermodynamics. Simply put, the law says that temperature differences tend to even out—for instance, when a hot mug of coffee disperses its heat into the cool air of a room. As the heat levels of the mug and the room come into balance, there is a transfer of energy.
Work can be extracted from that transfer. The most common way of doing this is with some form of heat engine. A steam engine, for example, converts heat into electricity by using steam to spin a turbine. Steam engines—powered predominantly by coal, but also by natural gas, nuclear materials, and other fuels—generate 90 percent of all U.S. electricity. But though they have been refined over the centuries, most are still clanking, hissing, exhaust-spewing machines that rely on moving parts, and so are relatively inefficient and prone to mechanical breakdown.
Johnson’s latest JTEC prototype, which looks like a desktop model for a next-generation moonshine still, features two fuel-cell-like stacks, or chambers, filled with hydrogen gas and connected by steel tubes with round pressure gauges. Where a steam engine uses the heat generated by burning coal to create steam pressure and move mechanical elements, the JTEC uses heat (from the sun, for instance) to expand hydrogen atoms in one stack. The expanding atoms, each made up of a proton and an electron, split apart, and the freed electrons travel through an external circuit as electric current, charging a battery or performing some other useful work. Meanwhile the positively charged protons, also known as ions, squeeze through a specially designed proton-exchange membrane (one of the JTEC elements borrowed from fuel cells) and combine with the electrons on the other side, reconstituting the hydrogen, which is compressed and pumped back into the hot stack. As long as heat is supplied, the cycle continues indefinitely.
“Lonnie’s using temperature differences to create pressure gradients,” says Paul Werbos, an energy expert and program director of the National Science Foundation. “Only instead of using those pressure gradients to move an axle or a wheel, he’s forcing ions through a membrane.” Werbos, who spent months vetting the JTEC and eventually awarded Johnson’s team a $75,000 research grant in 2006, describes the JTEC as “a fundamentally new way, a fundamentally well-grounded way, to convert heat to electricity.” Regarding its potential to revolutionize energy production on a global scale, he says, “It has a darn good chance of being the best thing on Earth.”
Johnson is a member of what seems to be a vanishing breed: the self-invented inventor. Born the third of six children in Mobile, Alabama, in 1949, he came into the world a black male in the Deep South during the days of lawful segregation. His father, David, who died in 1984, was a World War II veteran and a civilian driver for nearby Air Force bases. According to his mother, Arline, who is 86 and still lives in Mobile (in a house remodeled with Super Soaker profits), the family was poor but happy. All eight lived in a three-bedroom, one-bathroom house near Mobile Bay, in a neighborhood then being bisected by the construction of Interstate 10.
As a boy, Johnson was quiet and curious, and early on, he developed a fascination with how things worked. “Lonnie tore up his sister’s baby doll to see what made the eyes close,” his mother recalls. As he grew older, he began making things, including rockets powered by fuel cooked up in his mother’s saucepans. At 13, he bolted a discarded lawn-mower engine onto a homemade go-cart and took it atop the I-10 construction site—only to have a bemused policeman escort him back down. It was around then that Johnson learned that “engineers were the people who did the kind of things that I wanted to do.”
It was hardly an obvious career path: then, as now, the profession was dominated by whites. (As recently as 2004, only 1.6 percent of the engineering doctorates awarded in the United States went to blacks.) In high school, a standardized test from the Junior Engineering Technical Society informed Johnson that he had little aptitude for engineering; but he persevered and, as a senior, became the first student from his all-black high school ever to enter the society’s regional engineering fair. The fair was held at the University of Alabama at Tuscaloosa, just five years after then-Governor George Wallace had tried, in 1963, to physically block two black students from enrolling there. Johnson’s entry in the competition was a creation he called Linex: a compressed-air-powered robot assembled from electromagnetic switches he’d salvaged from an old jukebox, and solenoid valves he’d fashioned out of copper tubing and rubber stoppers. The finished product wowed the judges, who awarded him first prize: $250 and a plaque. Unsurprisingly, university officials didn’t trumpet the news that a black boy had won top honors. “The only thing anybody from the university said to us during the entire competition,” Johnson remembers, “was ‘Goodbye, and y’all drive safe, now.’”
Johnson went on to win math and Air Force ROTC scholarships to Tuskegee University, where he received a bachelor’s degree in mechanical engineering and a master’s in nuclear engineering. He joined the Air Force in 1975 and subsequently held jobs at the Air Force Weapons Laboratory, NASA’s Jet Propulsion Laboratory, and the Strategic Air Command—solid, respectable positions that made him a part of the scientific establishment. But at each stop, he felt that his creativity was stifled, and in 1987, at the age of 38, he could take it no longer. He would go into business for himself, he decided, focusing on his own projects, which included a thermodynamic heat pump, a centrifugal-force engine, and a pressure-action water gun. “All I needed was one to hit,” he says, “and I’d be fine.”
The idea for the water gun had come to him one weekend afternoon in 1982, while he was tinkering with an idea for an environmentally friendly heat pump that would use water instead of Freon. He’d built a prototype pump, attached some rubber tubing, and brought it into a bathroom. Aiming the nozzle at the tub, he turned it on, and produced a blast of water so powerful that the mere wind from the spray ruffled the curtains. This, he thought, would make a great water gun. It took Johnson seven uncertain and stressful years, but he acquired the patents and eventually found a company interested in manufacturing his Super Soaker: the Larami Corporation, which licensed the rights to the gun in a deal that would ultimately make Johnson rich.
Hoping to offer society something more significant than enhanced squirt-gun firepower, Johnson began plowing his Super Soaker profits into energy-related R&D. While continuing to work on mechanical devices such as his heat pump, he also studied battery technology. When what he taught himself about electrochemistry collided with his longtime obsession with the second law of thermodynamics, Johnson had his eureka moment: why not use temperature differences rather than a chemical reaction to force the flow of ions through a cell? The JTEC concept was born.
Today, Johnson and his family live in Atlanta’s upscale Ansley Park neighborhood. The business he launched more than two decades ago, Johnson Research and Development Company, now employs two dozen people, including designers, marketers, and research scientists. Once again, however, Johnson faces financial worries. “There was a time in my life,” he says, “when I was independently wealthy.” But that time has passed: Super Soaker profits have eroded thanks to a host of knockoffs, and now bring in only about a third of his company’s operating budget. For the rest, he relies on grants and commissions—and in the aftermath of the dot-com bust and the recent economic crisis, they’ve been drying up. He’s begun borrowing money to keep his research going—and he’s betting much of it, millions of dollars in all, on the JTEC.
In the winter of 2008, Johnson received a promising call from Karl Littau, a materials scientist with the Palo Alto Research Center (known as PARC), a subsidiary of Xerox. PARC, which gave the world the laser printer, Ethernet, and many other groundbreaking technologies, had expanded into alternative-energy research, and this had led Littau to the JTEC. Like Paul Werbos, Littau initially feared that the device sounded too good to be true, but he and several other PARC scientists set up elaborate three-dimensional computer models to analyze fluidics and heat-flow behavior in the JTEC under various conditions, and they came away from those experiments, he says, “really impressed.” Littau, like Werbos, is now a convert. The JTEC, he says, is “a very clever way to extract energy from a heat engine … It’s incredibly elegant.”
When I spoke to Littau, he ticked off the potential advantages of the JTEC over typical heat engines: no moving parts, which means the engine is more reliable and virtually silent; the safety of hydrogen, which is essentially benign (unlike, say, Freon); and the lack of waste produced (the JTEC gives off no carbon or—unlike a fuel cell—even water, which, although environmentally harmless, can corrode equipment). All of these advantages mean longer-lasting performance and potentially higher energy-conversion efficiencies.
Commercial photovoltaic solar cells convert approximately 20 percent of received solar energy into electricity. The best solar-energy systems today—thermal-power plants that concentrate the sun’s heat to drive turbines—operate at a rate of about 30 percent efficiency. The JTEC, Johnson claims, could double that figure, cutting the cost of producing solar power in half from its current average of 25 cents per kilowatt-hour, and making it competitive with coal.
“There’s a lot of debate in Washington about carbon emissions and energy,” Paul Werbos says—“about coal, nuclear power, and oil, what I call the three horsemen of the apocalypse. If we can cut the cost of solar energy in half, it becomes possible to escape from the three horsemen. The importance of this is just unbelievable.”
But having wowed PARC, Johnson is now wrestling once again with the difficulties of working within the confines of the scientific establishment. PARC wants to publish a paper about the JTEC in a peer-reviewed scientific journal, both to provide legitimacy and to encourage members of the scientific community to advance the technologies involved. But Johnson is unconvinced. “Peer review is fine,” he says, “as long as you’re making incremental improvements to a technology.” But Johnson dreams of advancing by leaps and bounds.
Adding to Johnson’s worries is tension with PARC over intellectual-property rights. Only recently did Johnson, with much reluctance, give PARC permission to file for patent protection for the problems solved in its lab. After more than two decades as his own boss, Johnson isn’t sure how much ownership interest—and potential profit—he is willing to give up. “All of a sudden, I have other people inventing stuff that I don’t have control over anymore,” Johnson says. “They could put patents in place for things I would need to implement in my engine. I’d have to pay them for my own idea!”
Last year, I visited the four-acre commercial property that Johnson owns on the south side of downtown Atlanta. Wearing pleated khakis and a long-sleeved polo shirt with a turtleneck underneath, Johnson took me on a tour of a meticulously refurbished three-story brick loft space featuring soaring ceilings and antique wood floors. Johnson intends to transform the building into a high-tech manufacturing center that will train and employ workers from the area; however, because of research delays and the recent economic downturn, those plans are on hold.
Until he can scale up, Johnson is instead leasing his beautiful loft space to a city agency, while he and his employees—including a handful of scientists with doctorates in chemistry, materials science, and engineering—hunker down in a low-slung, windowless warehouse across the parking lot. It’s a no-frills space, with galvanized electrical conduit descending from the ceiling through gaps where acoustic tiles are missing. On one wall of his office is a promotional poster created by the retail chain Target that features Johnson’s face amid a pantheon of 19th- and 20th-century African American inventors. Along another wall is a row of plaques commemorating a dozen of Johnson’s 100-odd patents, including those for his water-pressure heat pump, his ceramic battery, hair rollers that dry and set without heat, a diaper that plays a musical nursery-rhyme alarm when the baby is wet, and the electrochemical conversion system at the heart of the JTEC. And hanging crooked above his desk is a cheap black frame that contains an inspirational quote that has been attributed to Calvin Coolidge. Under the heading Press On, it reads:
Nothing in the world can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education alone will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent.
After we toured the office cubicles, Johnson swiped a card to unlock a door, and we entered a cavernous laboratory abuzz with fluorescent fixtures and thrumming with high-tech equipment. We stepped across a sticky mat, meant to grab dust from our shoes, and followed a yellow-paint path across the warehouse floor, past shelves of chemicals, airtight glove boxes, and banks of machines bristling with wires, charging and discharging batteries. Technicians in long blue lab coats and protective goggles milled about. Some of the equipment stations were housed beneath plastic clean-room tents topped with large fans and aluminum ductwork that snaked off toward the ceiling. The lab looked like a disheveled, family-garage version of a computer-microchip factory, and the resemblance wasn’t coincidental: to develop his proton-exchange membrane and ceramic batteries, Johnson has borrowed processes developed by the semiconductor industry for depositing materials, often atom by atom, onto various substrates. Beaming as he showed me his latest acquisition—a pricey-looking X-ray photoelectron spectrometer that lets him analyze a material’s atomic makeup—Johnson was clearly in his element.
US2012064419
RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
TECHNICAL FIELD
[0003] This invention relates to energy harvesting mechanisms for generating electrical power, and more particularly, the invention relates to a thermo-electrochemical device that utilizes hydrogen to convert heat energy from an environment in which the device is located into electrical power.
BACKGROUND OF THE INVENTION
[0004] It has long been a goal to develop an engine that operates on thermal energy that is freely available in the ambient environment. Consistent with the second law of thermodynamics, prior attempts at such thermal-energy-harvesting devices required two distinct sources of thermal energy, namely, a heat source and a heat sink for supplying and removing heat, respectively, at different temperatures simultaneously. A heat-source and heat-sink pair having two distinct, spaced-apart temperatures typically does not occur naturally and/or plentifully, and thus are generally difficult to access. Therefore, because ambient heat at a single atmospheric temperature is more abundant and available than a simultaneous dual-heat source, a device for harnessing single-source ambient heat is more desirable than a device that requires a dual-heat source.
[0005] The present inventor disclosed a device in U.S. Pat. No. 6,899,967. That device relies on cyclic temperature changes in the environment to produce the needed simultaneous dual-heat source. The needed temperature difference was provided through the use of a mass of material that has significant heat capacity. The prior device is a thermo-electrochemical converter that operates on a pressure difference between two metal-hydride chambers separated by a membrane electrode assembly (MEA). In the prior invention, one metal-hydride chamber is exposed to the ambient environment while the other is insulated and thermally stabilized. A thermal mass is coupled to the stabilized chamber to act as a heat source/sink material. Insulation may be used to thermally isolate the thermal-mass material from the environment in order to enhance the temperature difference produced. It absorbs heat and stores it during periods of elevated ambient temperature and releases that heat to function as an elevated-temperature heat source during periods of reduced ambient temperatures. As such, changes in the temperature of the thermal mass will always lag temperature changes in its environment. Thus a converter coupled between the thermal mass and the environment will be subjected to a simultaneous temperature differential needed for the device to operate.
[0006] The open-circuit electrical potential due to a hydrogen pressure differential across a proton-conductive membrane electrode assembly (MEA) is a linear function of temperature and proportional to the natural logarithm of the hydrogen pressure ratio and can be calculated using the Nernst equation (Fuel Cell Handbook, Fourth Edition, 1999, by J. H. Hirschenhofer, D. B. Stauffer, R. R. Engleman, and M. G. Klett, at pp. 2-5:
[0000]
VOC= RT/2F ln(PHi/PLow) Equation 1
[0000] where VOC is open circuit voltage, R is the universal gas constant, T is the cell absolute temperature in degrees Kelvin, F is Faraday's constant, PHi is the hydrogen pressure on the high-pressure side and PLow is the hydrogen pressure on the low-pressure side.
[0007] The hydrogen pressure produced by a metal-hydride bed depends on temperature. When the ambient metal-hydride chamber is at a higher temperature, H2 gas is desorbed from its metal hydride content and flows through the MEA into the thermally stabilized chamber, thus generating power. During the next half cycle, when the temperature of the ambient chamber falls below the temperature of the insulated chamber, the opposite takes place, hydrogen flows through the MEA back to the ambient temperature chamber. Hydrogen thus cycles back and forth under a pressure differential across the proton-conductive membrane generating power in the process.
[0008] A major limitation encountered with the prior invention is associated with the need to have a device that is capable of scavenging power in a relatively efficient manner. A major limitation in achieving efficient operation is associated with the difficulty of creating a significant temperature difference between components. This is particularly true for a small device. The close proximity of the components in a small device allows parasitic heat transfer losses between the two metal-hydride beds that are too high whenever a significant temperature gradient is present. In larger devices, the need for insulation and heat sink/source material can result in a large, bulky device that is difficult to implement. Thus it can be appreciated that a need remains for a device for producing electrical power using heat from its ambient environment that overcomes the disadvantages and shortcomings of previous chemical and thermal converters that need a simultaneous temperature difference in order to operate.
SUMMARY OF THE INVENTION
[0009] According to an embodiment of the present invention, an electrochemical conversion system has a thermally-conductive housing. The interior of the housing is divided into a high-pressure chamber and a low-pressure chamber by a substantially gas-impermeable membrane. An ionically-conductive, electrical-energy-generating mechanism forms at least a portion of the substantially gas-impermeable membrane. A first hydrogen-storage medium is disposed within the high-pressure chamber. A second hydrogen-storage medium is disposed within the low-pressure chamber. The characteristics of the hydrogen-storage mediums are such that at any given temperature, the first hydrogen-storage medium stores hydrogen at a first average storage pressure that is higher than a second average storage pressure at which the second hydrogen-storage medium stores hydrogen. The housing contains an initial quantity of hydrogen. An electrical-energy storage device connected to the ionically-conductive, electrical-energy-generating mechanism is selectively operable between a charge condition and a discharge condition.
[0010] The Johnson Ambient-Heat Engine (JANE) (an electrochemical conversion system) uses thermal transients that naturally occur in its ambient environment to generate electrical power. During selected periods of high temperature, the electrochemical conversion system naturally produces a high voltage output for a given pressure ratio between the high-pressure and low-pressure chambers. The electrical-energy storage device is charged by allowing hydrogen to expand from the high-pressure chamber into the low-pressure chamber during periods of high temperature and thereby high voltage. Conversely, the electrochemical conversion system produces low voltage during periods of low temperature. The electrical-energy storage device is discharged during selected low voltage periods to compress hydrogen from the low-pressure chamber back into the high-pressure chamber. Given two electrons per hydrogen molecule, returning the hydrogen to the high-pressure chamber requires the same amount of current as that generated when it transitioned to the low-pressure chamber. However, less energy is required since the hydrogen is returned during periods when the voltage of the electrochemical conversion system is low. The difference in energy produced during high-temperature expansion versus low temperature-compression is retained within the electrical-energy storage device and is available for supply to an external load.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic illustration of an electrochemical conversion system in accordance with an embodiment of the invention.
[0012] FIG. 2 is a data plot showing the voltage potential of a proton-conductive Membrane-Electrode Assembly (MEA) cell as a function of temperature for selected ranges of hydrogen pressure ratios across the MEA.
[0013] FIG. 3 is a data plot showing hydrogen pressure as a function of hydrogen content for a representative type and brand of metal hydride at selected temperatures.
[0014] FIG. 4 is a data plot showing midpoint hydrogen pressure as a function of temperature for selected representative metal hydrides suitable for use in of an electrochemical conversion system in accordance with an embodiment of the invention.
[0015] FIG. 5 is a data plot of Nernst voltage change as a function of temperature for three example metal-hydride pairings wherein the metal-hydride pairs are selected based upon predicted, advantageous pressure differentials.
[0016] FIG. 6 is a schematic illustration of an electrochemical conversion system in accordance with an embodiment of the invention depicting high/low-temperature operation at high ambient temperature.
[0017] FIG. 7 is a schematic illustration of an electrochemical conversion system in accordance with an embodiment of the invention depicting high/low-temperature operation at low ambient temperature.
[0018] FIG. 8 is a Temperature-Entropy diagram representing ideal operation of an electrochemical conversion system in accordance with embodiments of the invention, viewed as an Ambient-Heat Engine operating on a Sterling thermodynamic cycle.
[0019] FIG. 9 is a schematic illustration of an electrochemical conversion system in accordance with an embodiment of the invention showing metal-hydride beds, MEA arrays or stacks, battery and controller system under example operating conditions.
[0020] FIG. 10 is a schematic illustration of an electrochemical conversion system in accordance with an embodiment of the invention showing metal-hydride beds, MEA array or stack, battery integrated with controller system for dynamic operation over a range of mean temperatures.
DETAILED DESCRIPTION
[0021] Embodiments of the present invention are described herein. The disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms, and combinations thereof. As used herein, the word "exemplary" is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. In other instances, well-known components, systems, materials, or methods have not been described in detail in order to avoid obscuring the present invention. Therefore, at least some specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention.
Overview
[0022] As an overview, the invention teaches a system and methodology for generating electrical energy, which electrical energy can be applied to devices requiring electric power. The concept and overall embodiments of the invention are referred to herein generally as the Johnson Ambient-Heat Engine. The Johnson Ambient-Heat Engine is an apparatus that is powered by thermal transients in its environment. It utilizes thermodynamic principles of heat engines and electrochemical-cell principles in combination to generate electrical energy.
[0023] The apparatus performs through a combination of a thermodynamic processes and complementary electrochemical reactions. The phrase electrochemical conversion system will be used throughout this description and claims to generally refer to the invention. The invention also may be considered an "energy harvester," and more particularly may be considered a "thermal energy harvester." Thus the invention as described and claimed herein may be referred to alternatively as the Johnson Ambient-Heat Engine, an electrochemical conversion system and an energy harvester.
INVENTION DESCRIBED IN DETAIL
[0024] Referring now to the drawings, wherein like numerals indicate like elements throughout the several views, the drawings illustrate certain of the various aspects of exemplary embodiments.
[0025] Referring first to FIG. 1, therein is illustrated a schematic representation of an electrochemical conversion system 10 in accordance with an embodiment of the invention. A thermally-conductive housing 20 encloses a high-pressure chamber 22 and a low-pressure chamber 24 that are separated from one another by a substantially gas-impermeable barrier 26. An ionically-conductive, electrical-energy-generating mechanism forms at least a portion of the substantially gas-impermeable barrier 26. In the basic embodiment of FIG. 1, the entire barrier 26 is formed of an ionically-conductive, electrical-energy-generating mechanism. The central component of the ionically-conductive, electrical-energy-generating mechanism is an electrochemical cell 30 formed of electrodes 32, 34 that sandwich an electrolyte medium 36. The electrolyte medium is substantially impermeable. The key elements of the electrochemical cell, namely, electrodes 32, 34 and an electrolyte medium 36, may be referred to as a Membrane-Electrode Assembly (MEA) 30. There may be more than one cell, or MEA, however, in the embodiment illustrated in FIG. 1, a single cell (or MEA) forms the substantially impermeable barrier.
[0026] When the electrolyte medium 36 is a proton-conductive membrane, a first hydrogen-storage medium 42 is disposed within the high-pressure chamber 22. A second hydrogen-storage medium 44 is disposed within the low-pressure chamber 24. In a closed volume, as in the chambers of the invention, the hydrogen gas will attain an equilibrium pressure in each chamber which depends on the temperature and the amount of hydrogen contained within the metal-hydride of that respective chamber. The equilibrium pressure of a given metal hydride will vary in accordance with the temperature to which it is subjected. The equilibrium pressure will increase with increases in temperature and decrease with decreases in temperature. Although there is hysteresis, the equilibrium pressure may be considered a tipping point for absorption and desorption of hydrogen. At a given equilibrium pressure, the pressure of hydrogen gas above the equilibrium pressure will cause hydrogen to be absorbed by the hydride and, conversely, hydrogen pressure below the given equilibrium pressure will cause hydrogen to be released (desorbed) by the hydride.
[0027] The characteristics of the hydrogen-storage mediums 42, 44 are such that at any given temperature, the first hydrogen-storage medium 42 stores hydrogen at a first average storage pressure that is higher than a second average storage pressure at which the second hydrogen-storage medium 44 stores hydrogen. Effective hydrogen-storage mediums 42, 44 are metal-hydrides (also referred to herein as metal-hydride materials). Thus effective hydrogen-storage mediums are a high-pressure metal-hydride material and a low-pressure metal-hydride material, respectively. The housing 20 contains an initial quantity of hydrogen. A sufficient quantity will have to be aggregated under pressure in the high-pressure chamber 22 to begin the process of generating electrical energy.
[0028] Electrical conductors 46, 48 extend from respective electrodes 32, 34 of the MEA 30 (or other electrochemical cell configuration) to complete the electrical circuit that is necessary for operation of the invention. The circuit may be completed by components such as a simple electronic load or a controller system, or a combination of components 50. The invention teaches connection of the MEA 30 (or other cell) to an electrical-energy storage device, such as a capacitor or battery. The electrical-energy storage device is selectively operable between a charge condition and a discharge condition. More particularly, the invention teaches connection of conductors 46, 48 to a rechargeable battery. The load 50 may be a combination of a rechargeable battery and controller system that selectively places the battery component in a charge condition when certain parameters are met and in a discharge condition when other parameters are met.
[0029] The chemical reactions that take place in the high-pressure chamber 22 and low-pressure chamber 24, respectively, are written out in the chambers 22, 24 in FIG. 1.
[0030] Ideally, the various components comprising the thermo-electrochemical converter, particularly the environment, the housing, high-temperature metal-hydride bed, the MEA and the low-temperature metal-hydride bed are tightly coupled thermally such that all of the components are maintained at or near a single uniform temperature. Ideally, the uniform temperature is the temperature of the environment existing at the time when an expansion or compression event occurs. As a given metal-hydride bed undergoes the endothermic process of releasing hydrogen or exothermic process of absorbing hydrogen, heat is conducted between it and other components so as to maintain the relatively uniform temperature. As hydrogen is compressed or expanded through the MEA heat is removed or supplied respectively so as to maintain the uniform temperature. The thermal energy needed or removed to maintain the temperature of the system (including MEA, cells, hydrides and hydrogen) as hydrogen expands or undergoes compression respectively is thermal energy supplied to or from the environment. It is energy that is conducted through the housing 20 to or from the MEA 36, the high-pressure chamber 22 and low-pressure chamber 24. This thermal energy from the environment is considered "ambient" thermal energy. "Ambient" in this context is considered to mean heat from the environment where the housing is located. In a "local sense," the ambient environment is any enclosure wherein the housing 20 is subjected to the temperature level and temperature transients occurring in the enclosure. Applicable enclosures include but are not limited to a building, a room in a building structure, or a compartment or enclosure in close proximity to a combustion engine. A local ambient environment also encompasses a combustion engine (or other heat-producing instrumentality) itself. The housing 20 may be mounted upon such ambient environment. In a more general sense, the ambient environment may be the atmosphere of the great outdoors wherein thermal energy and temperature transients are provided by the sun.
[0031] The materials of the high-pressure and low-pressure beds have been selected such that at any given temperature the storage pressure of the high-pressure storage medium 42 is greater than that of the low-pressure storage medium 44. And, further, because hydrogen is aggregated under pressure in the high-pressure chamber 22, a greater hydrogen pressure will be exerted in the high-pressure chamber 42 than in the low-pressure chamber 24.
[0032] The "Load/Controller system" 50 includes a battery or other electrical-energy storage device. When the circuit with the MEA 30 (or other electrical-energy-generating mechanism) is closed electrical power is produced as hydrogen, under pressure and as ions, migrates from the high-pressure chamber to the low-pressure chamber. In the case where the electrical-energy-generating mechanism is a hydrogen conductive MEA, hydrogen undergoes oxidation at the high-pressure electrode 32-electrolyte membrane 36 interface. Electrons are conducted through the circuit as the hydrogen ions (protons) are conducted through electrolyte membrane 36. In the MEA electrode 34 in the low-pressure chamber 24, the hydrogen ions being conducted through the membrane combine with the electrons conducted through the closed circuit to "reconstitute" hydrogen molecules. The hydrogen reconstituted in the low-pressure electrode exits the electrode and becomes substantially absorbed within the second hydrogen-storage medium 44 that is disposed within the low-pressure chamber 24 as the second hydrogen storage medium functions to maintain a low-pressure within the chamber 24.
[0033] Hydrogen is returned to the high-pressure chamber 22 from the low-pressure chamber 24 by applying a voltage of sufficient magnitude to reverse the current across the MEA 30 or other electrical-energy-generating mechanism. In this case, hydrogen is conducted from the low-pressure chamber 24 to high-pressure chamber 22. Under the reverse current, electrons are striped from protons in the low-pressure chamber at the low-pressure electrode 34-electrolyte 36 interface and combined with protons in the high-pressure chamber at high pressure electrode 32-electrolyte 36 interface as the protons are conducted through membrane 36. The current and voltage are provided by the capacitor, battery or other electrical-energy storage device.
[0034] FIG. 2 shows the voltage across a proton conductive Membrane Electrode Assembly (MEA) as a function of temperature as calculated using the Nernst equation for selected hydrogen pressure ratios. For a given pressure ratio, the MEA voltage is high when the temperature is high and low when the MEA temperature is low. The controller 50 operates to select charge and discharge events under temperature conditions such that less electrical energy is required to return hydrogen to the high-pressure chamber than is produced to charge the battery. The difference between voltage generated during high-temperature migration and voltage required to facilitate low-temperature migration is useable electrical energy that is retained in the electrical-energy storage device.
[0035] Referring now to FIG. 3, a data plot shows the pressure and temperature relationship versus hydrogen content for an example metal hydride. This particular chart is for a metal hydride commercially marketed as Hy-Stor(R) 207 that has a chemical formula LaNi4.7Al0.3. The product is believed to be sold and distributed by Hera USA Inc., a Delaware Corporation, having a contact address at C/O Corporation Svc. Company, 2711 Centerville, Road Suite 400 Wilmington Del. 19808. OMEGA, the quantity along the x-axis, is the amount of hydrogen in the metal hydride as a ratio to the maximum amount of hydrogen that the hydride can absorb. As can be seen from the data plot, metal hydrides exhibit pressure plateaus that are a function of temperature whereby, at a given temperature, the majority of the hydrogen is stored with minimal increase in pressure. The pressure level of the plateau increases with increasing temperature. The "midpoint pressure" for a given temperature is defined as the pressure at which the hydride contains 50% (0.50) of its storage capacity. The midpoint pressure may be used as a representative value for comparison of pressures of different hydrogen-ladened metal-hydride materials at a given temperature.
[0036] Referring now to FIG. 4, therein is shown a plot of the variation of the midpoint pressure versus temperature for several selected commercially available metal hydrides. The name Hydralloy(R)C5 is a trademark for the metal hydride having chemical formula: Ti0.98Zr0.02V0.43Fe0.09Cr0.05Mn1.5. The product is believed to be sold and distributed by GfE Gesellschaft fur Elektrometallurgie mbH Ltd Liab Co, Fed Rep Germany, Hofener Strasse 45, 8500 Nurnberg 1 Fed Rep Germany, a subsidiary of AMG Advanced Metallurgical Group N.V., Netherlands. FIG. 3 highlights the fact that metal hydrides can be selectively paired with each other based on how their midpoint pressures change with temperature. The data provided by the metal hydride suppliers indicate that the midpoint pressures of some of the metal hydrides converge toward each other with increasing temperature (that is, increasing temperature transients) whereas others diverge. Thus selected metal hydrides can be paired together as high-pressure and low-pressure beds for optimum performance in the ambient-heat engine application. The power produced as hydrogen passes from the high-pressure bed to the low-pressure bed through the MEA increases as the pressure ratios between the two beds increase. Similarly, the power required to recompress hydrogen from the low-pressure hydride bed to the high-pressure hydride bed decreases as the pressure ratio decreases. Therefore, higher performance is achieved by the ambient-heat engine for the case where the average pressures of the high- and low-pressure metal-hydride beds diverge with increasing temperature.
[0037] Referring now to FIG. 5, therein is shown a plot of an increase in Nernst voltage versus increase in temperature above a starting temperature of 300 degrees K for three example metal-hydride pairs at their midpoint pressure ratios. The pairs include MnNi3Co2 paired with Hy-Stor(R) 207, MnNi3Co2 paired with Pd0.7Ag0.3, and TiCo paired with Pd0.7Ag0.3. The change in voltage with change in temperature is greatest for the TiCo and Pd0.7Ag0.3 pair.
[0038] Referring now simultaneously to FIGS. 6, 7 and 8, these figures illustrate ideal operation of an ambient-heat engine (electrochemical conversion system) 12 in accordance with an embodiment of the present invention. The term ambient-heat engine as used herein refers to that electrochemical conversion system that has a thermal-heat component as described herein. The engine/system 12 described operates under the same combined thermal and electrochemical principles as the system 10 illustrated in FIG. 1 and discussed above. Like elements operate in the same manner as previously described herein. Referring now particularly to FIGS. 6 and 7, the engine includes a housing 60, heat-conductive baffle 66 and MEA array or stack 68. The baffle 66 and MEA array 68 form a substantially gas-impermeable barrier that separates the housing 60 into a high-pressure chamber 62 and a low-pressure chamber 64. The MEA array 68 is an ionically-conductive, electrical-energy-generating mechanism. Although the ionically-conductive, electrical-energy-generating mechanism 68 could comprise a single electrochemical cell as illustrated and described with respect to FIG. 1, the embodiment of FIGS. 6 and 7 teaches a multiple-cell array or stack in which each cell 70 is a Membrane Electrode Assembly (MEA) comprised of a pair of electrodes 72, 74 and a proton-conductive electrolyte medium 76. The electrodes 72 and 74 are configured on opposite sides of the proton-conductive electrolyte medium 76 such that the medium is sandwiched between the two electrodes. The electrolyte medium 76 may be a single, contiguous, elongated structure or it may be a series of smaller structures placed end-to-end or stacked. Each approach effectively forms a set of multiple membrane electrode assemblies each having an electrolyte layer sandwiched between a pair of opposing electrodes 72, 74. The high-pressure chamber 62 contains first hydrogen-storage medium in the form of a high-pressure metal hydride 82. The electrodes 72, 74 of the multiple cells 70 are connected in series (anode/negative electrode to cathode/positive electrode) to respective conductors 92, 94. The low-pressure chamber 64 contains a second storage medium in the form of low-pressure metal hydride 84. A controller system 90 that includes a combined controller and electrical-energy storage device is electrically coupled to the MEA array 68 through conductors 92, 94. Controller system 90 contains an electrical-energy storage device such as a battery or capacitor.
[0039] Referring now also to FIG. 8, the Temperature-Entropy (T-S) diagram of FIG. 8 represents operation of the AHE device illustrated in FIGS. 6 and 7. The indicators QHT and QLT denote the high-temperature and low-temperature heat quantities described with respect to the engines/systems illustrated in FIGS. 6 and 7. Beginning at high-temperature, high-pressure State 1, represented in FIG. 6 as "DAY" operation, hydrogen expands to low-pressure state 2 under, ideally, constant-temperature conditions as the engine extracts the needed heat of expansion as heat QHT from the engine's environment.
[0040] When high-temperature heat, denoted as QHT with direction arrow 80 in FIG. 6, from the engine environment (ambient thermal energy or ambient heat) is available to the engine, the controller system 90 applies a load to the MEA array 68. Electrical current is produced as hydrogen passes from the high-pressure, metal-hydride bed 82 and high-pressure chamber 62 (as H2) through the proton-conductive membrane 76 (as H<+>) to the low-pressure chamber 64 and low-pressure, metal-hydride bed 84 (as H2) as illustrated by direction arrows 78. Freed electrons flow through the conductor 92 to the electrical-energy storage device (battery) that is part of the controller system 90 in the direction shown by direction arrow 96. Useful electrical energy generated by the engine is stored within an electrical-energy-storage device (battery) that is a part of the combined battery and controller system 90. Hydrogen released from the high-pressure metal-hydride bed, after passing through the MEA by becoming ions H<+> and then being reconstituted as hydrogen molecules H2, is absorbed by the low-pressure metal-hydride bed on the low-pressure side of the MEA stack 68.
[0041] Referring again to the temperature entropy diagram shown in FIG. 8, once high-temperature, low-pressure State 2 is achieved, operation stops and the engine transitions from State 2 to State 3 (from the elevated temperature conditions depicted in FIG. 6 to the low-temperature state represented in FIG. 7). This temperature change takes place over an interval of time and represents a decrease in ambient temperature. This transition from State 2 to State 3 is essentially a constant volume process with no movement of the hydrogen or change in state during the transition. Ideally, the absorbed hydrogen substantially remains absorbed in the metal-hydride bed on the low-pressure side of the engine.
[0042] As depicted in FIG. 7, when the environment reaches a predetermined low temperature as detected and registered by controller system 90, controller system 90 supplies power by means of charged battery to MEA array 68 as illustrated by direction arrow 98 to electronically "pump" hydrogen from the low-pressure side of the engine back to the high-pressure side as illustrated by direction arrows 87. The compression process transitions the engine from State 3 to State 4 of the T-S diagram of FIG. 8. This is, ideally, a constant-temperature compression process as heat of compression QLT is dissipated to the engine's environment as illustrated by direction arrow 89. The transition from state 4 back to state 1 to complete the cycle is a constant-volume process as the hydrogen remains substantially absorbed in the high-pressure, metal-hydride bed, thus the cycle continues with changes in the temperature of the engine's environment.
[0043] As an example, consider a daily thermal environment cycle of 10[deg.] C., that is, during a 24-hour period the difference between a high and a low ambient temperature is 10[deg.] C. During long thermal transitions such as day-night cycles, even a relatively large engine could have time to come into thermal equilibrium with its environment. Assume an engine, as taught by the invention, that uses the Pd0.7Ag0.3 and TiCo metal-hydride pair. Referring back momentarily to FIG. 5, the voltage change for this pair over a temperature change of 10[deg.] C. is about 1.6 mV. This value is derived under the condition that the midpoint pressure ratios represent an average of the pressure ratio maintained during transition of the hydrogen between hydride beds. A reasonable hydrogen capacity per unit volume of an average metal hydride is equivalent to about 1.86 Ah/cc in electrons. Assume that the high-pressure and low-pressure chambers each contain 1 cc of metal hydride. Given these conditions, the expansion process occurs at 1.6 mV higher voltage than the compression process thus a difference in energy of 2.98 mWh/cc (that is, 1.86 Ah/cc*1.6 mV). This amount of energy is available for powering an external load. If averaged over a period of 24 hours, the average level of continuous available power would be about 0.124 mW per cubic centimeter (that is, 2.98 mWh/cc/24 h=0.124 mW/cc) of metal hydride.
[0044] Given practical implementation constraints, assume an average power output of 0.1 mW/cm<3 >for this system. Additional thermal cycles result in the generation of additional power. Multiple daily cycles are possible and the controller system may be programmed to anticipate and respond to thermal transients that may be greater than or less than the 10[deg.] C. example transient disclosed herein. Consider one possible application wherein a portable electronic device that may be carried on one's person into and out of buildings or other situations that change the engine's thermal environment.
[0045] To achieve useful output voltage levels, the MEA may be configured as an array or stack of MEA cells with electrical interconnects connecting the cells in series. A single common membrane for the cells in the array or multiple membranes may be aligned to achieve a desired number of cells and voltage level. The amount of hydrogen cycled back and forth across the MEA stack remains constant on average during operation of the engine. Therefore, the difference in energy is extracted based on a difference in cell voltage between the expansion and compression half cycles of the engine.
[0046] Referring now to FIG. 9, therein is illustrated schematically an electrochemical conversion system 14 in accordance with another embodiment of the invention. A thermally-conductive housing 100 is separated into a high-pressure chamber 102 and a low-pressure chamber 104 by a substantially gas-impermeable barrier. Ambient heat of the environment QE and heat from within the housing 100 are interchanged through the housing 100, as denoted by the bi-directional arrow 120. As with the systems 10, 12 illustrated and previously described herein, at least a portion of the substantially gas-impermeable barrier comprises an ionically-conductive, electrical-energy-generating mechanism. A particularly suitable ionically-conductive, electrical-energy-generating mechanism is at least one membrane-electrode assembly type of electrochemical cell. The MEA and constituent elements described previously herein are also suitable for use in the embodiment of FIG. 9. As before, the membrane of the MEA provides the substantially gas-impermeable barrier. Somewhat similar to the embodiment of FIGS. 6 and 7, the present embodiment uses multiple MEA's connected in series. For convenience, the illustration of FIG. 9 uses a graphic icon to represent MEA cells. The icon is denoted by the numeral 112 and consists of the symbol for a cell (positive and negative electrode) inscribed within a circle as a symbol for at least one MEA. The icon is also used to represent one or a grouping of more than one MEA. Further, the groupings of the graphic MEA icon 112 are used herein to represent an array, or stack, 110 of individual MEA cells 112. The array, or stack, 110 is comprised of two MEA sub-arrays or stacks 116, 118 with all the individual cells connected in series. One sub-array contains more MEA's than the other. In an example, the array, or stack, 110, comprises 142 MEA cells all connected in series and segmented into a first sub-array 116 of 138 cells and a second sub-array 118 of 4 cells. A first hydrogen-storage medium, in the form of a high-pressure, metal-hydride bed 122 is disposed in the high-pressure chamber 102. A second hydrogen-storage medium, in the form of a low-pressure, metal-hydride bed 124, is disposed in the low-pressure chamber 104. Operation of the arrays is such that the hydrogen passes across the cells uniformly. Since all the cells are connected in series, the current through each and therefore the hydrogen flow across each must be the same. Assuming operation over a 10[deg.] C. temperature swing between 20[deg.] C. and 30[deg.] C. and the Pd0.7Ag0.3 and TiCo metal-hydride pair, the Nernst voltage at 20[deg.] C. is 0.02762V and at 30[deg.] C. is 0.02926V at the midpoint pressures for these materials.
[0047] The system 14 further includes controller system 130, battery 132, normally-open charge control switch 140 and normally-open regeneration control switch 142. Operation of the system 14 is such that when the temperature is high, say 30[deg.] C., the 138 cells in group 116 produce a voltage of 4.03V (that is, 138 cells*0.02926 V/cell). Output power from MEA array group 116 is supplied at this voltage and controller system 130 closes switch 140 to charge battery 132. The resulting current flow allows hydrogen to expand from high-pressure bed 102 to low-pressure bed 104. Assume that each bed is sized to supply and absorb an amount of hydrogen equivalent to 1.86 Ah of current capacity. The geometry of the system (that is, cells, chambers, etc.) is such that the hydrogen transfer is divided over the number of MEA cells in the stack or array. This alignment results in each cell transferring an amount of hydrogen equivalent to an electrical charge of 13.5 mAh (that is, 1.86 Ah/138 cells). Therefore, 13.5 mAh of charge is supplied to battery 132 at a voltage of 4.03 Volts.
[0048] Switch 140 is returned to an open state after charging stops. For battery-charging condition, electric current is dissipated from the larger MEA sub-array 116 through a connector 134 and the closed switch 140 in the direction of the direction arrow 144. When the system is in a discharge-battery configuration, current flows from the battery 132 through closed switch 142 and connector 136 into the full MEA array 110 in the direction shown by direction arrow 146.
[0049] Optimally, battery discharge to "recharge" hydrogen in the high-pressure chamber will be effected when the temperature is low, say 20[deg.] C. At that temperature, the voltage of the individual cells is reduced to 0.02762V, as given by the Nernst equation. Under this condition, controller system 130 closes switch 142 and thereby connects rechargeable battery 132 in series with the four cells that are in group, or sub-array, 118 and the 138 cells of group, or sub-array, 116. At 20[deg.] C., the 142 MEA cells connected in series produce a voltage of only 3.92V (that is, 142 cells*0.02762 V/cell). Conversely, this is the amount of voltage that is necessary to return (or pump) the same quantity of hydrogen back across the membrane(s) at the lower temperature and associated pressure ratio. The battery, having been previously charged to 4.03 volts, now supplies power to the full MEA array 110 to pump hydrogen back from low-pressure bed 124 to high-pressure bed 122. Return of the equivalent of 1.86 Ah of hydrogen to the high-pressure chamber is now divided over 142 cells requiring an application of electrical energy from the battery of only 10.3 mAh (that is, 1.86 Ah/142 cells). In this simple example, 3.1 mAh (that is, 13.5 mAh-10.3 mAh) of residual capacity of electrical energy charge remains available in the battery 132 after the hydrogen has been pumped back to the high-pressure side of the engine. This residual, thus harvested, energy can be used for external applications and the ambient-heat engine is now ready for the follow-on power half cycle.
[0050] Charging is initiated after an increasing temperature transient has occurred in the ambient environment. Such charge initiation can be facilitated through use of a sensing system and detector that work in conjunction with the controller system 130 to recognize when charging may be conducted effectively. For example, a temperature sensor may detect the ending, stabilization or leveling off of an increasing temperature transient. If the controller 130 determines that the configuration of the engine and the magnitude of the temperature change are suitable for a charge or discharge event, then it will initiate such an event. Similarly, the event may be initiated upon the detection of a temperature change at the housing or in the ambient environment of a predetermined magnitude over a predetermined period of time. As another example, a pressure sensor may detect that a predetermined pressure in the high-pressure chamber 102 has been reached or that a predetermined pressure differential between the high-pressure chamber 102 and the low-pressure chamber 104 has been reached. Charging may be stopped when the battery 132 has been charged to a predetermined level. For example, a voltage sensor and detecting system may be used in conjunction with the controller system 130.
[0051] The battery 132 may be placed in a discharge condition for at least two purposes. One purpose is to provide electrical energy to an external load. The battery 132 may also be placed in a discharge condition for the purpose of providing current through and a voltage potential across the MEA so as to cause hydrogen to migrate from the low-pressure chamber 104 to the high-pressure chamber 102. This is in effect a "recharging" of the high-pressure chamber 102 with hydrogen. Discharge of battery 132 to recharge the hydrogen may be facilitated through use of sensor and detection systems in conjunction with the controller system 130. Battery discharge is terminated when a sufficient amount of hydrogen has been placed in or returned to the high-pressure chamber 102 and hydride bed 122. The "recharged" hydrogen condition in the high-pressure chamber 102 and associated hydride bed may be detected by a sensing mechanism that works in conjunction with the controller system 130 to recognize that sufficient hydrogen is now in the high-pressure chamber. For example, and not by way of limitation, a pressure sensor may detect that a predetermined hydrogen pressure has been achieved. As a further example, and also not by way of limitation, a charge sensor to integrate current during the charge period as a part of the controller system may detect and determine that that at least as many hydrogen ions as migrated from the high-pressure chamber to the low-pressure chamber during the battery 132 charging have been returned to the high-pressure chamber.
[0052] Referring now to FIG. 10, an electrochemical conversion system 16 has several elements similar to the systems 10, 12, 14 previously illustrated and described herein. A thermally-conductive housing 160 defines an interior that is divided into a high-pressure chamber 162 and a low-pressure chamber 164 by a substantially gas-impermeable barrier that is formed at least in-part by an ionically-conductive, electrical-energy-generating mechanism. Ambient heat of the environment QE and heat from within the housing 160 are interchangeable through the housing 160, as denoted by the bi-directional arrow 180. A particularly suitable ionically-conductive, electrical-energy-generating mechanism is at least one membrane-electrode assembly (MEA) type of electrochemical cell. The MEA and constituent elements described previously herein are also suitable for use in the embodiment of FIG. 10. As before, the membrane of the MEA provides the substantially gas-impermeable barrier. The ionically-conductive, electrical-energy-generating mechanism comprises an MEA array, or stack 170. The array/stack 170 comprises individual MEA's electrically connected in series. As in the case of the embodiment of FIG. 14, for convenience, the illustration of FIG. 10 uses a graphic icon to represent MEA cells. The icon is denoted by the numeral 172 and consists of the symbol for a cell (positive and negative electrode) inscribed within a circle as a symbol for at least one MEA. The icon is used to represent one or a grouping of more than one MEA. Further, the grouping of the graphic MEA icons 172 is used herein to represent an array, or stack, 170 of individual MEA cells 172. A first hydrogen-storage medium, in the form of a high-pressure, metal-hydride bed 182 is disposed in the high-pressure chamber 162. A second hydrogen-storage medium, in the form of a low-pressure, metal-hydride bed 184, is disposed in the low-pressure chamber 164. Operation of the array, or stack, 170 is such that the hydrogen passes across all of the cells uniformly.
[0053] A charge controller system 190 includes a rechargeable battery, electrical circuit components, sensing components, switching components, battery and discharge charge circuitry, and software components including but not limited to pattern recognition software. Internal logic of the charge controller system 190 enables it to selectively extract power from the MEA array/stack 170 to charge the battery and/or to direct electrical power elsewhere or to supply power to the MEA array/stack 170 to regenerate the metal-hydride beds 182, 184. The pattern recognition software allows the charge controller system 190 to recognize patterns in temperature transients and hydrogen pressure transients and thereby anticipate peaks and ebbs in temperature so as to identify optimum times at which to initiate a battery charge or metal-hydride regeneration event. The battery charge circuitry allows the charge controller system 190 to operate efficiently over a wide range of MEA array open circuit voltages. As such it can perform a battery charge or hydride-bed regeneration event independent of the mean environmental temperature or associated mean operating voltage of the MEA array. This feature gives the engine the versatility to operate about a mean environmental temperature of 10[deg.] C., 40[deg.] C. or other mean that the environmental temperature may dictate.
Metal Hydrides' Role in Operation of Ambient-Heat Engine
[0054] Metal hydrides are metallic substances that are capable of absorbing hydrogen gas when exposed to the hydrogen gas at certain pressures and temperatures. The terminology used in discussing metal hydrides is sometimes confusing. A primary reason for the confusion is that the term metal hydride can be used to refer to the hydrogen-absorptive material both before and after it has absorbed hydrogen. Therefore, for purposes of explanation herein, the pre-absorption material generally will be referred to as "metal hydride" or "metal-hydride material," or, simply, "hydride." After the metal hydride, or metal-hydride material, has absorbed hydrogen gas, for clarity, the resulting product sometimes is referred to herein as a hydrogen-ladened metal-hydride." The "hydrogen-ladened" adjective is not used where from the context the state or condition of hydrogen absorption is clear. In the hydrogen-ladened metal hydride, hydrogen is distributed throughout the metal-lattice structure of the metal hydride. The metal-hydride material is typically provided in a crushed or other configuration that maximizes the surface area to be contacted by hydrogen gas.
[0055] Ideally, if the pressure of the hydrogen gas rises above the equilibrium pressure, then hydrogen will be absorbed into the metal hydride. Absorption is exothermic since heat will be released during the process. If sufficient heat is not transferred away from the metal hydride to support continued hydrogen absorption at a stable temperature, then the temperature will increase to a point where a new, higher equilibrium pressure state is attained. On the other hand, if the pressure of hydrogen gas drops below the equilibrium pressure, hydrogen gas will be released from the hydrogen-ladened metal-hydride material. The hydrogen-release process is endothermic since heat input is required to maintain the desorption process. If sufficient heat is not available to support continued hydrogen evolution at a stable temperature, then the temperature will drop to a point where a new lower equilibrium pressure is attained. In practice, for a given material, the equilibrium pressures and temperatures for absorption are different from the equilibrium pressures and temperatures for desorption by finite amounts. This difference is generally referred to as the hysteresis property of the material and must be accounted for by appropriately selecting metal hydrides for use in the JAHE.
[0056] The ambient-heat engine 10, 12, 14, 16 operates cyclically and, as such, any point or region in the cycle that is illustrated in the temperature-entropy diagram of FIG. 8 can be chosen as a starting point. Certain conditions will exist in the engine at any one of the four points of the diagram. For example, consider the condition of an increasing environment temperature when the hydrogen gas that is used in the engine is predominantly contained in the high-pressure chamber. The temperature transient of the high-pressure hydrogen terminates at point "1" on the diagram. As previously discussed herein, the metal-hydride materials are chosen such that at any given temperature, the midpoint equilibrium pressure in the high-pressure chamber 22, 62, 102, 162 will be greater than the midpoint equilibrium pressure in the low-pressure chamber 24, 64, 104, 164. As the ambient temperature increases, the equilibrium pressures of both metal-hydride beds 42/44, 82/84, 122/124, 182/184 of each engine 10, 12, 14, 16 respectively increase.
[0057] Phase 1-2: The portion of the cycle of FIG. 8 from point 1 to point 2 represents, the expansion of hydrogen from the high-pressure chamber 22, 62, 102, 162 and passage of the hydrogen from the high-pressure chamber to the low-pressure chamber 44, 64, 104, 164. Electrical energy is generated during this portion of the cycle. Several things occur simultaneously, in Phase 1-2. Heat is absorbed in the high-pressure chamber as hydrogen is released and heat is released by the low-pressure chamber as the metal hydride contained therein absorbs hydrogen. The engine may be configured to facilitate heat transfer between the two chambers so as to minimize the amount of heat that must be extracted from or transferred to the environment. However, the overall effect of expansion of hydrogen from the high-pressure bed to the low-pressure bed is endothermic due to the net decrease in energy state of the hydrogen and heat is absorbed by the engine from the elevated temperature ambient environment. The transition of the hydrogen from state 1 to state 2 is associated with the closing of a circuit that includes the ionically-conductive membrane and the electrical-energy storage device. With closing of the circuit hydrogen ions H<+> are conducted across the membrane and electrons freed from the hydrogen flow through the circuit into the electrical-energy storage device. During Phase 1-2, hydrogen (that has been reconstituted from migrated hydrogen ions H+ and received electrons) is received in the opposing low-pressure chamber 24, 64, 104, 164 where it is ready to be absorbed into the associated metal-hydride beds 44, 84, 124, 184.
[0058] Phase 2-3: With the hydrogen now substantially contained by the low-pressure metal-hydride chamber 24, 64, 104, 164, the portion of the cycle of FIG. 8 from point 2 to point 3 represents a decreasing temperature transient (which may be a succession of decreasing temperature transients) associated with the engine's environment. Note that at point 2, the temperature of each metal-hydride bed has been substantially stabilized to the high temperature (THT) of the ambient environment. Between points 2 and 3, as ambient environment temperature decreases, heat is transferred through the housing 20, 60, 100, 160 of the engine 10, 12, 14, 16 to what is now a low-temperature ambient environment (QLT, QE) causing both the temperature and the equilibrium pressures of the metal-hydride beds 42/44, 82/84, 122/124, 182/184 of each engine 10, 12, 14, 16 respectively to decrease. Phase 2-3 may be considered to be carried out under the constant volume of the low-pressure chamber 24, 64, 104, 164.
[0059] At point 3, the predominance of hydrogen in the engine system is in the low-pressure chamber 24, 64, 104, 164 and in equilibrium with the low-temperature point of the ambient environment, TLT.
[0060] Phase 3-4: During this phase of the cycle of FIG. 8 represented by point 3 to point 4, the high-pressure chamber 22, 62, 102, 162 of the engine system is "recharged" with hydrogen. The electrical-energy storage device is energized to complete a circuit (that includes the MEA 30, 70, 116, 170) and thereby cause hydrogen (H2) to be conducted through the MEA as hydrogen ions (H<+>) from low-pressure chambers 24, 64, 104, 164 to high-pressure chambers 22, 62, 102, 162 respectively. The MEA performs a pumping process to recompress the hydrogen. At point 4 of the diagram of FIG. 8, hydrogen predominantly has been aggregated in the high-pressure chamber under some pressure. Electrical energy is consumed during this portion of the cycle. Heat is absorbed in the low-pressure chamber as hydrogen is released and heat is released by the high-pressure chamber as the metal hydride contained therein absorbs hydrogen. The overall effect of compression of hydrogen from the low-pressure bed to the high-pressure bed is exothermic due to the net increase in energy state of the hydrogen and heat is released by the engine to the now lower temperature ambient environment.
[0061] Phase 4-1: The portion of the cycle of FIG. 8 from point 4 to point 1 represents an increasing temperature transient (which may include a succession of lesser increasing temperature transients). Note that at point 4 hydrogen has been aggregated in the high-pressure chamber 22, 62, 102, 162. As ambient environment temperature increases, heat is transferred through the housing 20, 60, 100, 160 of the engine 10, 12, 14, 16 causing both the temperature and equilibrium pressures of the metal-hydride beds to increase, with the high-pressure bed maintaining a higher equilibrium pressure than that of the low pressure bed.
Additional Features of the Invention
[0062] In a broad embodiment, the invention is practiced without first and second hydrogen-storage mediums, and more particularly, without metal-hydride materials. In this embodiment, at least a first portion of the hydrogen that is placed in the housing is initially placed in the high-pressure chamber at a higher pressure than a second quantity of hydrogen that is initially placed in the low-pressure chamber. The invention still operates by the previously-described mechanism of selecting between a charge condition and a discharge condition. The addition of hydrogen-storage mediums such as metal hydrides increases the amount of hydrogen that can be stored at a given pressure in a given volume and therefore the amount of electronic charge that can be produced.
[0063] A capacitor may be used instead of a battery as an electrical-energy-storage device that can be successively charged and discharged.
[0064] Each electrode may include a porous current collector to help facilitate the flow of hydrogen and hydrogen ions while still conducting a flow of electrons.
[0065] Each electrode may include a catalyst such as platinum to help facilitate the hydrogen reaction at each respective electrode.
[0066] Many variations and modifications may be made to the above-described embodiments without departing from the scope of the claims. All such modifications, combinations, and variations are included herein by the scope of this disclosure and the following claims.
US7943250
REFERENCE TO RELATED APPLICATION
This is a continuation-in-part of U.S. Patent Application Ser. No. 60/569,890 filed May 11, 2004. This is also a continuation-in-part of U.S. patent application Ser. No. 10/425,067, filed Apr. 28, 2003, now U.S. Pat. No. 7,160,639 which is a continuation-in-part of U.S. patent application Ser. No. 09/627,721, filed Jul. 28, 2000 now abandoned.
TECHNICAL FIELD
This invention relates to the conversion of heat energy to electrical energy or electrical energy to heat energy utilizing multiple electrochemical cells.
BACKGROUND OF THE INVENTION
The conversion of heat energy or chemical energy to electrical energy, or visa-versa, may be accomplished in a variety of ways. It is known that electrochemical cells or batteries rely on redox reactions wherein electrons from a reactant being oxidized are transferred to a reactant being reduced. With the separation of the reactants from each other, it is possible to cause the electrons to flow through an external circuit where they can be used to perform work.
Electrochemical cells however have had a problem of exhausting the reactants. Although cells can be designed to be recharged by applying a reverse polarity voltage across the electrodes, such recharging requires a separate electrical source. During the recharging of the cell the cell typically is not usable.
Fuel cells have been developed in an effort to overcome problems associated with electrochemical cells. Typically, fuel cells operate by passing an ionized species across a selective electrolyte which blocks the passage of the non-ionized species. By placing porous electrodes on either side of the electrolyte, a current may be induced in an external circuit connecting the electrodes. The most common type of fuel cell is a hydrogen-oxygen fuel cell which passes hydrogen through one of the electrodes while oxygen is passed through the other electrode. The hydrogen and oxygen combine at the electrolyte-electrode interface to produce water. By continuously removing the water, a concentration gradient is maintained to induce the flow of hydrogen and oxygen to the cell.
These types of fuel cells however suffer from a number of disadvantages. These cells must be continuously supplied with a reactant in order to produce electricity continuously. Additionally, these cells produce a continuous product stream which must be removed, the removal of which may pose a problem. The porous electrodes of these fuel cells must allow the passage of the reactant entering the cell. However, over time these porous electrodes can become fouled or plugged so as to slow or even prevent the passage of the reactant. Such slowing of the reactant flow reduces the production of electricity. Lastly, the selection of an appropriate electrolyte is not always easy. The electrolyte must rapidly transport the ionized species in order to increase the current production. Frequently, the limited migration of the ionized species through the electrolyte is a limiting factor on the amount of current produced.
In an effort to avoid the problems inherent with the previously described fuel cells, thermoelectric conversion cells have been designed. These thermoelectric conversion cells utilize heat to produce a pressure gradient to induce the flow of a reactant, such as molten sodium, across a solid electrolyte. A current is generated as sodium atoms lose electrons upon entering the electrolyte and gain electrons upon leaving the electrolyte. These cells however also suffer from the plugging of the porous electrodes required to pass the sodium ions. Furthermore, the diffusion of the sodium ions through the solid electrolytes has proven to be slow, thereby limiting the amount of current produced by the cell. These cells also utilize alkali metals which is difficult to use in these types of applications because of they are highly corrosive. Lastly, these types of fuel cells operate at extremely high temperatures, typically in a range between 1,200-1,500 degrees Kelvin, thus making them impractical for many uses.
Accordingly, it is seen that a need remains for an electrochemical conversion system that does not require a continuous source of reactant, which does not require an electrolyte which may be plugged over time and which may be operated at relatively low temperatures. It is the provision of such therefore that the present invention is primarily directed.
SUMMARY OF THE INVENTION
In a preferred form of the invention an electrochemical conversion system for managing energy comprises a first electrochemical cell having a first ion conductive material, a first electrode mounted upon one side of the first ion conductive material, and a second electrode mounted upon one side of the first ion conductive material opposite the first electrode, a second electrochemical cell having a second ion conductive material, a third electrode mounted upon one side of the second ion conductive material, and a fourth electrode mounted upon one side of the second ion conductive material opposite the third electrode, and a third electrochemical cell having a third ion conductive material, a fifth electrode mounted upon one side of the third ion conductive material, and a sixth electrode mounted upon one side of the third ion conductive material opposite the fifth electrode. The system also includes a conduit system having a first conduit, second conduit and third conduit. The first conduit is in fluid communication with the first electrochemical cell second electrode and the second electrochemical cell third electrode. The second conduit is in fluid communication with the second electrochemical cell fourth electrode and the third electrochemical cell fifth electrode. The third conduit is in fluid communication with the third electrochemical cell sixth electrode and the first electrochemical cell first electrode. The system also includes a first heat exchanger for exchanging heat between the first conduit adjacent the first electrochemical cell and the third conduit adjacent the first electrochemical cell, and a second heat exchanger for exchanging heat between the first conduit adjacent the second electrochemical cell and the second conduit adjacent the second electrochemical cell. A supply of ionizable gas is contained within the conduit system and an electrical circuit coupled to the first electrode, the second electrode, the third electrode, the fourth electrode, the fifth electrode and the sixth electrode. The electrical circuit includes an electrical energy storage device.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic view of a reversible heat engine in a preferred form of the invention, shown in a heat engine configuration.
FIG. 2 is a theoretical, temperature entropy diagram of the reversible heat engine of FIG. 1.
FIG. 3 is a schematic view of a reversible heat engine in a preferred form of the invention, shown in a heat pump configuration.
FIG. 4 is a temperature entropy diagram of the reversible heat engine of FIG. 3.
FIG. 5 is a schematic view of an electrochemical conversion system for energy management in a preferred form of the invention.
FIG. 6 is a temperature entropy diagram of the reversible heat engine of FIG. 5.
FIG. 7 is a schematic view of another electrochemical conversion system for energy management in a preferred form of the invention.
DETAILED DESCRIPTION
With reference next to the drawings, there is shown in FIG. 1 a reversible engine 10 in a preferred form of the invention of a heat engine. The engine 10 has a conduit system 11, a first electrochemical cells 12, and a second electrochemical cell 13. The conduit system 11 is made of a non-reactive material such as stainless steel. The conduit system 11 includes a first conduit 15 extending from the first electrochemical cell 12 to the second electrochemical cell 13, and a second conduit 16 extending from the second electrochemical cell 13 to the first electrochemical cell 12.
The heat engine 10 also includes a heater 18 mounted in thermal communication with the conduit system 11 adjacent the second electrochemical cell 13, a cooler 19 mounted in thermal communication with the conduit system 11 adjacent the first electrochemical cell 12, and a heat regenerator or exchanger 20 thermally coupled to the first and second conduits 15 and 16 for the transfer of heat therebetween.
The first electrochemical cell 12 has a first gas diffusion electrode 22, a second gas diffusion electrode 23 and a first proton conductive membrane 24, such as Nafion made by E.I. du Pont de Nemours, mounted between the first and second gas diffusion electrodes 22 and 23. This type of electrochemical cell is available from E-Tek, Inc. of Somerset, N.J. The electrochemical cell electrodes 22 and 23 are electrically coupled to an external power supply 25.
Similarly, the second electrochemical cell 13 has a third gas diffusion electrode 28, a fourth gas diffusion electrode 29 and a second proton conductive membrane 30 mounted between the third and fourth gas diffusion electrodes 28 and 29. The electrochemical cell electrodes 28 and 29 are electrically coupled to an external load 31.
In use, the conduit system 11 is filled with an ionizable gas, such as hydrogen, oxygen or sodium hereinafter referred to simply as hydrogen H. With the operation of the heater 18 (QH) to transfer heat energy to the second electrochemical cell 13, or adjacent thereto, to maintain a constant temperature of the hydrogen gas ionized and passed therethrough, the operation of cooler 19 (QL) to transfer heat energy from, or from adjacent thereto, the first electrochemical cell 12, and the operation of the heat exchanger 20 to transfer heat energy from the hydrogen gas within the second conduit 16 to the hydrogen gas within the first conduit 15, and the passage of an electric current from the external power supply 25 to the first electrochemical cell 12, hydrogen gas H passes through the first electrochemical cell 12. The hydrogen gas H passes through the first electrochemical cell 12 as a result of the electric potential from the external power supply 25 between the first electrode 22 and the second electrode 23. The electric potential causes the hydrogen gas at the first electrode 22 to oxidize into hydrogen protons. The oxidation of the hydrogen gas causes the release of electrons which are passed to the second electrode 23. The hydrogen protons are drawn through the first proton conductive membrane 24 to the second electrode 23 by the negative charge at the second electrode 23. At the second electrode 23 the hydrogen protons are reduced into hydrogen gas. As such, the electric current through the first electrochemical cell 12 forces the passage of hydrogen gas from the second conduit 16 to the first conduit 15, thereby increasing the hydrogen gas pressure within the first conduit 15 while decreasing the hydrogen gas pressure within the second conduit 16, i.e., creating a hydrogen gas pressure differential between the second conduit 16 and the first conduit 15.
The passage of hydrogen gas H from the second conduit 16 to the first conduit 15 causes a pressure differential across the second electrochemical cell 13. As the hydrogen pressure differential between the first and second conduits 15 and 16 increases an electrical potential across the second electrochemical cell 13 is created and progressively increased. Hydrogen gas H at the higher pressure first conduit 15 adjacent the second electrochemical cell third electrode 28 is oxidized into hydrogen protons. These hydrogen protons are forced by the hydrogen pressure differential through the second proton conductive membrane 30 to the fourth electrode 29 at the lower pressure second conduit 16. At the fourth electrode 29 the hydrogen protons are reduced into hydrogen gas. As such, the oxidation of the hydrogen gas causes the release of electrons which are passed to the third electrode 28 while the reduction of protons into hydrogen gas causes the acceptance or receiving of electrons from the fourth electrode 29, thereby inducing an electric current through load 31 coupled to the second electrochemical cell 13.
The passage of hydrogen gas through the first and second electrochemical cells 12 and 13 creates a fluid stream or flow through the conduit system 11 as illustrated by the direction arrows in the drawings. The flow of hydrogen gas through the first conduit 15 from adjacent the first electrochemical cell 12 to adjacent the second electrochemical cell 13 is done so under constant pressure while the temperature of the gas increases. Similarly, the flow of hydrogen gas through the second conduit 16 from adjacent the second electrochemical cell 13 to adjacent the first electrochemical cell 12 is done so under constant pressure while the temperature decreases.
It should be understood that it takes less work to transfer the hydrogen gas across the first electrochemical cell from the low pressure region to the high pressure region at a low temperature than the work required to transfer the hydrogen gas across the second electrochemical cell from the high pressure region to the low pressure region at a high temperature. As such, the work input at the first electrochemical cell is less than the work output at the second electrochemical cell, with the additional work output energy being obtained from the conversion of the heat energy input (QH). The transfer of heat through the heat exchanger 20 aids in maintaining a temperature differential between the regions of the conduit system surrounding the two electrochemical cells 12 and 13 and thereby aid in maintaining a constant pressure during the process, and in improving the efficiency by conserving the heat energy within the system by transferring it from the high temperature gas leaving the high temperature region adjacent the second electrochemical cell to the lower temperature gas flowing to the first electrochemical cell.
The entropy diagram shown in FIG. 2 illustrates the theoretical change in entropy of the just described system during its operation in an ideal or perfect situation wherein the heat exchange is ideal or 100 percent efficient, i.e., wherein outside influences on the system are not considered. Obviously, the true entropy diagram of the system will be different once these outside influences are taken into consideration.
The system may also be operated in a reverse cycle as a heat pump, as shown in FIGS. 3 and 4. Here, the second electrochemical cell 13 is coupled to an external power supply 25 while the first electrochemical cell 12 is coupled to an external load 31. Also, the region adjacent the first electrochemical cell 12 is provided with heat energy (QL) by while heat energy is extracted (QH) from the region adjacent the second electrochemical cell 13. The operation of the device in this configuration is the extraction of heat energy (QL) from a low temperature source and supply it as heat energy (QH) to a higher temperature source, as illustrated in FIG. 3. The principles of the invention however remain the same as those previously described, with the system here providing a change in the heat energy.
The system may be operated at relatively small temperatures differences. As such, this system is both safe and manageable. Furthermore, this system converts energy without any mechanically moving parts, and as such is practically free of mechanical failure.
It should be understood that the previously described systems may utilize any form of heat source such as electric heaters, gas burning heaters, heated air, radiation heat sources, radiant heaters or other conventionally known means of producing heat. The system may also utilize any form of cooling means such as cooling water jackets, heat sinks, cooling radiators, heat dissipaters or another other conventionally known means of removing heat.
With reference next to FIG. 5, there is shown an electrochemical conversion system 40 for energy management which includes multi-node (three or more stacks) or electrochemical cells. The three-node system 40 (a thermally driven heat pump) is described in detail to provide a stepping-stone for multi-node (>3 nodes) operation. Principles for the thermally driven heat pump apply equally to all multi-node electrochemical conversion systems.
The system 40 is an innovative, solid-state heat engine which can operate on any thermal source, such as combustible fuels, concentrated solar energy, waste heat, or geothermal. In addition to power generation, the electrochemical conversion systems can be configured as a heat pump or as a combination heat pump/heat engine to provide thermal management for heating, cooling and electrical energy. Operating on the Ericsson cycle and using hydrogen as a working fluid, the electrochemical conversion system can efficiently transport heat to or from a desired location to effectively maintain a desired elevated or reduced temperature. The Ericsson cycle is Carnot equivalent, and therefore, offers the maximum theoretical efficiency available from an engine operating between two temperatures. The electrochemical conversion system uses electrochemical cells, also referred to as Membrane Electrode Assemblies (MEA), similar to those used in fuel cells; however, it does not require oxygen or a fuel supply, only heat.
The three-node system 40 is a thermally driven heat pump and is shown in FIG. 5 along with a Temperature-entropy (T-s) diagram of the cycle shown in FIG. 6. The thermodynamic states on the T-s diagram correspond to the same locations in the thermally driven heat pump schematic.
The system 40 includes a conduit system 41, an electrical system 42, first electrochemical cell 43, a second electrochemical cell 44, a third electrochemical cell 45, a first recuperative heat exchanger (RHX) 46, and a second recuperative heat exchanger 47. The conduit system 41, electrical system 42, heat exchangers, and electrochemical cells are all constructed and function in the same manner as previously described.
This version of the system 40 includes an additional, second recuperative heat exchanger 47 (RHX) (the two node system of FIGS. 1 and 3 include a single RHX) to thermally isolate the third electrochemical cell 45 or node from the other two, and an interface with the ambient environment for heat exchange (labeled as QC at temperature TA), a high temperature interface for heat exchange (labeled as Qs, at temperature TH>TA), and an interface to the refrigerated space for heat exchange (labeled as QR at TR<TA). As shown, the electrochemical cells 43, 44 and 45 are electrically and pneumatically connected in series so that the electrical current flow and the proton flow through the electrochemical cells are balanced.
Beginning at high temperature intermediate pressure state 1, electrical energy EO is generated at the high temperature MEA as hydrogen expands from state 1 to high temperature low-pressure state 2. The temperature of the hydrogen is maintained nearly constant by supplying heat QS from the source during the expansion process. The thin membrane (less than 10 [mu]m thick) within the electrochemical cell will not support a significant temperature gradient, so the near isothermal assumption for the process is valid, provided adequate heat is transferred from the membrane through its substrate. From state 2 to state 3, the hydrogen passes through the first recuperative heat exchanger (RHX) 46 under approximately constant pressure and is cooled by transferring heat to hydrogen flowing in the opposite direction to ambient temperature. From ambient temperature, low-pressure state 3, electrical energy (labeled as EC) is consumed as hydrogen is compressed nearly isothermally across the ambient temperature, third electrochemical cell 45 to high pressure, ambient temperature state 4. Heat QC generated during the compression process is rejected to the ambient environment to maintain the isothermal process. From ambient temperature, high-pressure state 4 the hydrogen passes through the second recuperative heat exchanger to low temperature, high-pressure state 5. The hydrogen flowing from state 4 to 5 is cooled by transferring heat to the hydrogen flowing in the opposite direction through the second recuperative heat exchanger flowing from the low temperature, first electrochemical cell 43 (state 6 to 7). Refrigeration is accomplished at the low temperature, first electrochemical cell 43 by extracting heat QR from the low temperature environment as hydrogen expands from low temperature, high-pressure state 5 to low temperature, low-pressure state 6 thereby generating energy ER. From state 6 to state 7, hydrogen flows through the second recuperative heat exchanger 47 wherein its temperature is increased by heat transfer from the hydrogen passing from state 4 to 5. The hydrogen continues through the first recuperative heat exchanger 46, where it is heated by hydrogen leaving the high temperature, second electrochemical cell 44 to return to high temperature, high-pressure state 1 completing the cycle.
With reference next to FIG. 7, there is shown a four-node electrochemical conversion system 60 in another preferred form of the invention. It should be noted that the electrochemical convention system of the present invention can be configured with N total nodes, where M (which must be less than N) of the nodes are connected to sources or sinks at non-ambient temperatures and at least one node interfaces with the ambient environment to satisfy thermodynamic requirements for a heat engine. The multi-node system can be designed for nearly any thermal management issues, and overall operation will of course depend on the number of nodes and the amount of heat available.
The four node system 60, is similar to the three-node system of FIGS. 5 and 6 except for the addition of a fourth electrochemical cell, the details of which will follow, and a third recuperative heat exchanger 63. Here, the system 60 includes a high temperature power generation electrochemical cell 64, a waste heat power generation electrochemical cell 65, a heat pump electrochemical cell 66, and an ambient interface electrochemical cell 67. Electrochemical cell 64 may operate on combustion or some other high quality heat source (concentrated solar, high quality waste heat, etc.), while electrochemical cell 65 may operate on a lower quality waste heat source, e.g. electronics. Electrochemical cell 66 can be used to provide space heating, while the electrochemical cell 67 rejects heat to the ambient as required for a heat engine or heat pump. All nodes or electrochemical cells do not need to operate simultaneously or at the same voltage and current, which is why the schematic shows a control processor and load leveling battery. The control processor ensures that proper voltages and currents are maintained at proper values, while the load leveling battery is used (as the name implies) to level the system loads for any combination of operating electrochemical cells.
It thus is seen that an electrochemical conversion system for heat management is now provided which is efficient. It should of course be understood that many modifications, in addition to those specifically recited herein, may be made to the specific embodiments described herein without departure from the spirit and scope of the invention as set forth in the following claims.