Johnson thermoelectric energy converter
Encyclopedia
A Johnson thermoelectric energy converter or JTEC is a type of solid-state heat engine
that relies on the photodecomposition and recombination of hydrogen
in a fuel cell
using an approximate Ericsson cycle
. It was invented by Lonnie Johnson
and is under investigation as a viable alternative to conventional photovoltaic cells. Johnson claims the converter exhibits an energy conversion efficiency of as much as 60% compared to 30% efficiency typical of the best photovoltaic cells, although this is a theoretical level based on comparison with a Carnot cycle
, and assuming a temperature gradient of 600C. It was originally proposed for funding to the Office of Naval Research
, but was refused. Johnson obtained later funding by framing the engine as a hydrogen fuel cell. Currently Johnson is collaborating with PARC on development of the engine.
(MEA). An MEA is a proprietary ceramic proton exchange membrane
(PEM) sandwiched between two electrodes.
In the high-temperature power stage, the heat energy is converted to electrical energy by expanding high pressure hydrogen, from the compression stage, through the MEA. As the high-temperature, high pressure hydrogen is forced through the PEM it is ionized
, producing protons and electrons. The protons pass through the membrane while the electrons are forced out, via the electrodes, through a load. After passing through the PEM, the protons recombine with the electrons to produce low pressure hydrogen gas, which flows out to the compression stage. From the perspective of the high-temperature stage, the load consists of the external load on the engine and the low-temperature compression stage. In the compression stage, electrical potential is applied across the MEA. This electrical potential forces protons to flow through the PEM to produce high pressure hydrogen. As the hydrogen travels between the stages, it passes through a heat exchanger
which helps keep the high-temperature stage hot and the low-temperature stage cool, increasing efficiency.
The amount of energy available to the external load is the difference in electrical potential between what is needed to compress hydrogen at low-temperature and that which is generated by expanding it at high-temperature. Unlike other heat pump devices, the JTEC requires an initial input of electrical energy to start the compression stage and initiate the cycle. The engine can also be operated in reverse, to convert electrical energy into a temperature differential, for example in HVAC applications. In the proposed application, the power stage would be heated by solar irradiance
, with the compression stage coupled to an ambient temperature heat sink
.
(MEMS), to functioning as large-scale power plants.
Since it functions as an external combustion engine
, the converter benefits from being able to use many diverse forms of fuel, without the need for fuel-specific customization as seen in internal combustion engines. This means it can be used to generate power from fuel combustion, solar irradiance, low grade waste heat from industry or from other power generation systems including fuel cells, internal combustion engines or turbines.
Heat engine
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...
that relies on the photodecomposition and recombination of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
in a fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
using an approximate Ericsson cycle
Ericsson cycle
The Ericsson cycle is named after inventor John Ericsson, who 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...
. It was invented by Lonnie Johnson
Lonnie Johnson (inventor)
Lonnie George Johnson is an American engineer best known as the inventor of the Super Soaker water gun, which was the top selling toy in the United States in 1991 and 1992.-Engineering firms:...
and is under investigation as a viable alternative to conventional photovoltaic cells. Johnson claims the converter exhibits an energy conversion efficiency of as much as 60% compared to 30% efficiency typical of the best photovoltaic cells, although this is a theoretical level based on comparison with a Carnot cycle
Carnot cycle
The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot in 1824 and expanded by Benoit Paul Émile Clapeyron in the 1830s and 40s. It can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work, or conversely,...
, and assuming a temperature gradient of 600C. It was originally proposed for funding to the Office of Naval Research
Office of Naval Research
The Office of Naval Research , headquartered in Arlington, Virginia , is the office within the United States Department of the Navy that coordinates, executes, and promotes the science and technology programs of the U.S...
, but was refused. Johnson obtained later funding by framing the engine as a hydrogen fuel cell. Currently Johnson is collaborating with PARC on development of the engine.
Mechanism of action
The JTEC converts heat into electrical energy by compressing and expanding hydrogen gas. It operates as a closed system, with no moving parts, requiring no input of fuel and creating no exhaust. The engine consists of two stages: A low-temperature compression stage and a high-temperature power stage. Each stage consists of a working fluid chamber bisected by a copper lined membrane electrode assemblyMembrane electrode assembly
A membrane electrode assembly is an assembled stack of proton exchange membranes or alkali anion exchange membrane , catalyst and flat plate electrode used in a fuel cell.-PEM-MEA:...
(MEA). An MEA is a proprietary ceramic proton exchange membrane
Proton exchange membrane
A proton exchange membrane or polymer electrolyte membrane is a semipermeable membrane generally made from ionomers and designed to conduct protons while being impermeable to gases such as oxygen or hydrogen...
(PEM) sandwiched between two electrodes.
In the high-temperature power stage, the heat energy is converted to electrical energy by expanding high pressure hydrogen, from the compression stage, through the MEA. As the high-temperature, high pressure hydrogen is forced through the PEM it is ionized
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
, producing protons and electrons. The protons pass through the membrane while the electrons are forced out, via the electrodes, through a load. After passing through the PEM, the protons recombine with the electrons to produce low pressure hydrogen gas, which flows out to the compression stage. From the perspective of the high-temperature stage, the load consists of the external load on the engine and the low-temperature compression stage. In the compression stage, electrical potential is applied across the MEA. This electrical potential forces protons to flow through the PEM to produce high pressure hydrogen. As the hydrogen travels between the stages, it passes through a heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
which helps keep the high-temperature stage hot and the low-temperature stage cool, increasing efficiency.
The amount of energy available to the external load is the difference in electrical potential between what is needed to compress hydrogen at low-temperature and that which is generated by expanding it at high-temperature. Unlike other heat pump devices, the JTEC requires an initial input of electrical energy to start the compression stage and initiate the cycle. The engine can also be operated in reverse, to convert electrical energy into a temperature differential, for example in HVAC applications. In the proposed application, the power stage would be heated by solar irradiance
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
, with the compression stage coupled to an ambient temperature heat sink
Heat sink
A heat sink is a term for a component or assembly that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems and the radiator in a car...
.
Applications
Since the engine is scalable, its developers claim it has potential applications ranging from providing power for microelectromechanical systemsMicroelectromechanical systems
Microelectromechanical systems is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems and nanotechnology...
(MEMS), to functioning as large-scale power plants.
Since it functions as an external combustion engine
External combustion engine
An external combustion engine is a heat engine where an working fluid is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work...
, the converter benefits from being able to use many diverse forms of fuel, without the need for fuel-specific customization as seen in internal combustion engines. This means it can be used to generate power from fuel combustion, solar irradiance, low grade waste heat from industry or from other power generation systems including fuel cells, internal combustion engines or turbines.