Small Business Innovation Research/Small Business Tech Transfer
A Novel Electrode Material for Thermionic Power Generation
Project Description
The conversion of heat to power has proven to be vital in flight missions where solar power generation is not an option. Radioisotope thermoelectric generators that converted heat produced by a decaying nuclear source to power have been used on missions such as Cassini, New Horizons, Galileo, Ulysses and the Mars Science Laboratory. Although never flown by the United States, thermionic converters have also been investigated for space applications. Their improved efficiency over thermoelectric generators makes them an attractive option, but the high operating temperatures required have thus far been a significant obstacle to their use. Thermionic generators convert heat energy directly into electrical power. An emitter electrode on a heat source emits electrons across a vacuum gap to a cold electrode. The generated current is pumped through a load where it can do useful work before it is returned to the emitter. Thermionic generators do not use any moving parts or working fluid, which results in highly reliable devices that do not need frequent maintenance. Unlike thermoelectric generators, which have exhibited efficiencies only up to about 8%, state-of-the-art thermionic generators operate with efficiencies approaching 20%. This proposal seeks to study the use of the nanomaterial C12A7 electride as an electrode material. C12A7 electride has been shown to emit stably at temperatures in excess of 1600 degrees C and has a measured work function between 0.8-2.1 eV. Due to its low work function, C12A7 electride has the potential to greatly improve the efficiency of the state-of-the-art in thermionic energy conversion as well as enable device operation at much lower temperatures than is currently possible. Busek previously has investigated C12A7 electride in thermionic emission configurations for space propulsion hollow cathode applications. In the proposed work, Busek will evaluate the potential benefits of a C12A7 electride thermionic converter electrode.
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Anticipated Benefits
The space market is a niche yet lucrative market for thermionic devices. NASA's deep-space missions might replace or augment radioisotope thermoelectric generation systems with thermionic systems, while in near-space, it may be possible to harvest thermal energy off monopropellant and bi-propellant propulsion systems (depending upon operating temperature/duration). Such energy generation technology can be utilized for continuous or pulsed-power generation for a variety of spacecraft, rover vehicles, and basecamp power needs. While Busek does not have experience with radioisotope generation systems, it does have design and development experience with small chemical thruster systems (<20N green monopropellant systems). Such systems have been known to initiate and run at temperatures close to or exceeding the forecasted thermionic power generation threshold of 700k (800 degrees F/ 427 degrees C). Coupling power generation with chemical propulsion warrants further exploration for both spacecraft as well as missile systems; such systems potentially being coupled with pulsed-power electronics, another area where Busek has design and development experience.
In the commercial space market, roughly 20 GEO launches and 25 non-GEO launches occur on an annual basis (excludes micro/nano-satellites), with most spacecraft having a number of chemical thrusters aboard for orbit-raising and station-keeping. In addition to Busek's own chemical propulsion systems, potential space customers include chemical thruster manufacturers such as Rafael, EADS, ECAPS, Northrop Grumman, Moog (AMPAC), Aerojet. Collectively, these firms represent the large majority of chemical systems flow in the industry. Potential customers for radioisotope power generation include ESA missions and NATO customers. The largest terrestrial market in terms of economic benefit, is industrial thermal energy recovery. The United States industrial sector uses one third of the country's energy. Improved waste heat recovery technology, in which some of the used energy could be "recycled", would lead to lower operating costs and decreased environmental impact and is therefore of great interest. Applications in which bulky, complex heat engines cannot be used need compact, solid-state devices that require little to no maintenance. The potential improvements enabled by a C12A7 electride thermionic generator device, in both efficiency and flexibility of use, could lead to a significant decrease in costs for industries such as glass manufacturing, cement manufacturing, iron and steel manufacturing, aluminum production, and metal casting. More »
In the commercial space market, roughly 20 GEO launches and 25 non-GEO launches occur on an annual basis (excludes micro/nano-satellites), with most spacecraft having a number of chemical thrusters aboard for orbit-raising and station-keeping. In addition to Busek's own chemical propulsion systems, potential space customers include chemical thruster manufacturers such as Rafael, EADS, ECAPS, Northrop Grumman, Moog (AMPAC), Aerojet. Collectively, these firms represent the large majority of chemical systems flow in the industry. Potential customers for radioisotope power generation include ESA missions and NATO customers. The largest terrestrial market in terms of economic benefit, is industrial thermal energy recovery. The United States industrial sector uses one third of the country's energy. Improved waste heat recovery technology, in which some of the used energy could be "recycled", would lead to lower operating costs and decreased environmental impact and is therefore of great interest. Applications in which bulky, complex heat engines cannot be used need compact, solid-state devices that require little to no maintenance. The potential improvements enabled by a C12A7 electride thermionic generator device, in both efficiency and flexibility of use, could lead to a significant decrease in costs for industries such as glass manufacturing, cement manufacturing, iron and steel manufacturing, aluminum production, and metal casting. More »
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Primary U.S. Work Locations and Key Partners
| Organizations Performing Work | Role | Type | Location |
|---|---|---|---|
| Busek Company, Inc. | Lead Organization |
Industry
Women-Owned Small Business (WOSB)
|
Natick, Massachusetts |
Johnson Space Center
(JSC)
|
Supporting Organization | NASA Center | Houston, Texas |
Primary U.S. Work Locations
-
Massachusetts
-
Texas
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