Download or read book EMITTER MATERIALS STUDY THERMIONIC ENERGY CONVERTERS written by and published by . This book was released on 1962 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental program was conducted on selected emitter materials to determine their potential for use in low-temperature thermionic energy converters. One oxide emitter and four different dispenser types were evaluated in parallel plate and cylindrical geometry in both glass and metal ceramic construction. With respect to power density the various dispenser emitter types showed suitable and reasonably similar performance. Performance degradation was reversed in some of these diodes and its mechanism explored and explained.
Download or read book Thermionic Energy Converter written by Dr. Walter L. Knecht and published by . This book was released on 1960 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research and Development for Barium Vapor filled Thermionic Energy Conversion Technology written by Martin Company and published by . This book was released on 1964 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research on Materials Processes and Devices Related to Energy Conversion written by and published by . This book was released on 1962 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research is reported in five major divisions: I. Subcontracting Materials and Systems, II. Electrochemical Energy Conversion Research, III. High temperature Metallurgy Research on Thermoelectric and Thermionic Materials, IV. Solid State Energy Converters, V. The Development of Thermionic Emitter Materials.
Download or read book High Voltage Thermionic Converters written by General Motors Corporation. Allison Division and published by . This book was released on 1964 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several emitter materials, tantalum, tungsten and rhenium, and two emitter geometries, planar and excess area were evaluated in a flexible laboratory thermionic converter design. Results are reported from six converters that were tested for a total of 1070 hr. Experimental results from the excess area emitter converters did not exhibit the current enhancement observed in multicapillary and slotted emitter converters developed on a previous Air Force contract. While the electron currents in the passive mode at relatively low cesium pressure were in qualitative agreement with theory, the actual current densities obtained were not high enough to produce practical power densities at high output voltage. The method of emitter fabrication which used a niobium braze material appears to be a primary reason for the low performance.
Download or read book Microfabricated Thermionic Energy Converters written by Jae Hyung Lee and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermionic energy converters (TECs) are heat engines that convert heat directly to electricity at very high temperatures. This energy conversion process is based on thermionic emission--the evaporation of electrons from conductors at high temperatures. In its simplest form, the converter consists of two electrodes in the parallel plate capacitor geometry, and it uses the thermionically emitted current to drive an electrical load. This dissertation presents research on five key areas of microfabricated thermionic energy converters ([mu]-TECs). First, the numerical calculation of the emitter-collector gap that maximizes the power conversion efficiency of thermionic energy converters (TECs) is discussed. Thermionic energy converters require emitter and collector work-functions that are relatively low, to reach useful efficiencies at typical operating temperatures of 1000 - 1500 oC. The optimum arises because efficiency drops both at very large gaps, due to space-charge limitations on the TEC current, and at very small gaps, due to the increased heat loss via near-field radiative heat transfer. The numerical calculation results show that, for typical TECs made with cesiated tungsten electrodes, the optimal gaps range from 900 nm to 3 [micrometers]. I then discuss several prototypes of mechanically and thermally robust [mu]-TECs, including the stress-relieved emitter design, emitter-collector structural design, as well as a recent approach for the stand-alone (encapsulated) [mu]-TECs. Thermionic emission from the SiC emitter was demonstrated for the first time. The stress-relieved design emitters were analyzed, and the work-function of the SiC emitter was estimated at temperatures of up to 2900K. Also described are both the planar and the U-shaped suspension for microfabricated TECs ([mu]-TECs). Our initial planar [mu]-TECs achieved emitter temperatures of over 2000 K with incident optical intensity of approximately 1 W/mm2 (equivalent to 1000 Suns), remained structurally stable under thermal cycling, and maintained a temperature difference between the emitter and the collector of over 1000 K. Conformal sidewall deposition of poly-SiC on a sacrificial mold is used to fabricate stiff suspension legs with U-shaped cross sections, which increases the out-of-plane rigidity and prevents contact with the substrate during the heating of the suspended emitter. By extending the conventional technique of cesium coatings to SiC, we reduce the work-function from 4 eV to 1.65 eV at room temperature. Subsequently, we tested [mu]-TECs with both barium and barium oxide coatings. The coatings reduced the work-function of the SiC emitter to as low as ~2.14 eV and increased the thermionic current by 5-6 orders of magnitude, which is a key step toward realizing a efficient thermionic energy converter. Encapsulation of [mu]-TEC was achieved by an anodic bond between pyrex and the silicon substrate with via feedthroughs. Last, I introduce the photon-enhanced thermionic emission (PETE) concept, and show why a single crystal photo-emitter is needed. I cover my recent fabrication development of smart-cut layer transfer using Spin-on-Glass (SoG). In addition, a novel layer transfer technology that can transfer any device materials onto the glass substrate, which I call "Anything on Glass, " is briefly described. I, then, describe how the first demonstration of the photon-enhanced thermionic emission (PETE) from the microfabricated emitter was achieved. The p-type SiC emitter was used to demonstrate PETE in an uncesiated and microfabricated sample, bringing this energy conversion approach closer to practical applications.
Download or read book Research Studies on Thermionic Converters Emitter Shell Phase Report Number 5 written by G. Y. Eastman and published by . This book was released on 1965 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Survey of Materials for Thermionic Converters written by Arthur L. Smith and published by . This book was released on 1970 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1975 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt: NSA is a comprehensive collection of international nuclear science and technology literature for the period 1948 through 1976, pre-dating the prestigious INIS database, which began in 1970. NSA existed as a printed product (Volumes 1-33) initially, created by DOE's predecessor, the U.S. Atomic Energy Commission (AEC). NSA includes citations to scientific and technical reports from the AEC, the U.S. Energy Research and Development Administration and its contractors, plus other agencies and international organizations, universities, and industrial and research organizations. References to books, conference proceedings, papers, patents, dissertations, engineering drawings, and journal articles from worldwide sources are also included. Abstracts and full text are provided if available.
Download or read book High temperature High power density Thermionic Energy Conversion for Space written by James F. Morris and published by . This book was released on 1977 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Thermionics Quo Vadis written by National Research Council and published by National Academies Press. This book was released on 2001-12-18 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report evaluates the Defense Threat Reduction Agency prior and present sponsored efforts; assess the present state of the art in thermionic energy conversion systems; assess the technical challenges to the development of viable thermionic energy conversion systems for both space and terrestrial applications; and recommend a prioritized set of objectives for a future research and development program for advanced thermionic systems for space and terrestrial applications.
Download or read book Research on Materials Processes and Devices Related to Energy Conversion written by MASSACHUSETTS INST OF TECH CAMBRIDGE ENERGY CONVERSION AND SEMICONDUCTOR LAB. and published by . This book was released on 1963 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Contents: Superconducting materials and systems Electrochemical energy conversion research High temperature metallurgy research on thermo electric and thermionic materials Solid state energy converters Development of thermionic emitter materials.
Download or read book The Development of a Thermionic Converter Module Suitable for Liquid Metal Heating written by G. Y. Eastman and published by . This book was released on 1964 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Effort was continued to improve performance and increase the reliability of thermionic energy converters for space applications. The particular objectives include optimization of geometry and ceramic insulation between emitters and heat source. This work will include the development of a thermionic generator module to develop 3.0 volts of potential from a liquid metal heat source. The overall concept of the 3-volt generator has been established. Before final design and fabrication of the generator, the more difficult problems are being solved by fabricating and testing prototype 3-converter modules. During this period, four 3-converter modules were assembled. A number of subassemblies were successfully tested and techniques for assembling a series of converters within a single envelope were perfected. A method of bonding the center heat source tubing has been tentatively selected and materials for detailed evaluation of the method have been ordered. Life testing of one Type A1198B converter was concluded after 1010 hours. Another converter of this type has since completed 600 hours of a life test with a constant output of 46 watts. (Author).
Download or read book RESEARCH STUDIES ON THERMIONIC CONVERTERS EMITTER SHELL PHASE written by and published by . This book was released on 1965 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the program was the development of a barrier shell to protect thermionic energy converters from the combustion products of a fossil fuel flame. Two material properties are of prime importance; impermeability, and corrosion resistance. Three types of materials were selected for extensive testing; alumina, beryllia and silicon carbide. Equipment of very high sensitivity (10) to the minus 12th power liter torr/sq cm second) was developed which permitted the determination of gas permeation rates. The identification of individual gases was made possible by the latest mass spectrometer equipment. It was determined that high purity alumina has the lowest permeation rate, the highest material strength, good thermal shock resistance and is resistant to corrosion. Beryllium oxide had a poor corrosion resistance and a high permeation rate for carbon monoxide. The pyrolytic silicon carbide samples obtained for this program evidenced high permeation rates for carbon monoxide and showed a tendency toward unpredictable fracture after extended periods at elevated temperatures.
Download or read book Thermionic Converter Research Studies written by J. M. Houston and published by . This book was released on 1964 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work accomplished covered research studies of a cesium thermionic converter incorporating a thorium dispenser cathode, studies of electrode materials both polycrystalline and single crystal, and the development of research techniques associated with the thermionic converters. (Author).
Download or read book Thermionic Emitter Materials Research Program written by and published by . This book was released on 1961 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The experimental work necessary to complete the studie o the characteristics of T A AND Mo as emitters in thermionic converters was complete . the para etric experiments during this period were performed with greater accuracy and rapidit e t the method of observing and recording data. the data n t a an o emitters was carefully reduced and analyzed. Parametric curves hic faces, Metal coatings, High temper ature research. Identifiers: Energy conversion. The experimental work necessary to complete the studie can be used by diode designers are presented. The results of experiment and analysis of surface characteristics which are currently being used to guide the development of a comprehensive theory of the cesium converter are included. (Author).
Download or read book Application of Semiconductors to Thermionic Energy Converters written by Daniel C. Riley and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermionic energy conversion (TEC) is a direct heat-to-electricity conversion technology with the potential to leapfrog state-of-the-art solid-state conversion in efficiency and power density. In a thermionic energy converter, electrons evaporate from a hot electrode, the cathode, into a vacuum gap and are collected by a cooler electrode, the anode, to generate electric current. In the 1960s-1970s numerous groups reported thermionic converters with power densities above 10 W/cm^2 and conversion efficiencies of ~15%. However most of this work was tied to the US space-nuclear program which ended in 1973, and thermionics research has never fully recovered. As a result two central challenges yet remain in thermionics: (1) High operating temperatures necessary to produce electric current result in difficult materials challenges, and (2) low operating voltages due to losses associated with space charge and high anode work functions. However, new opportunities to tackle these challenges are available as a result of the breathtaking rise of semiconductor fabrication technology. In this work I present a new physical mechanism called photon enhanced thermionic emission (PETE). This concept is an improvement on thermionic emission by using light to boost the average energy of carriers in a hot p-type semiconductor cathode. Additionally, unlike in a photovoltaic cell, the waste heat from recombination losses and sub-bandgap light absorption is utilized to heat the cathode. Thus a PETE cathode can produce efficient electron emission at lower temperatures than a thermionic cathode. I will describe theoretical calculations showing that a PETE device may exceed 40% solar power conversion efficiency, and the conversion efficiency may exceed 50% if a PETE device is used in tandem with a solar thermal backing cycle. I will also describe an experimental demonstration of the PETE effect in an ultra-high vacuum photoemission measurement. In the cathode of an energy converter based on photon-enhanced thermionic emission (PETE) photoexcited carriers may need to encounter the emissive surface numerous times before having sufficient thermal energy to escape into vacuum and therefore should be confined close to the surface. However, in a traditional planar geometry, a thin cathode results in incomplete light absorption. Nanostructuring has the potential to increase light capture and boost emission by decoupling the lengths associated with photon absorption and electron emission. Nanostructures may complicate the properties of the emissive surface; therefore, the effect of nanostructuring on emission efficiency needs to be studied. In this work I describe results from a suite of simulation tools we have developed to capture the full photoemission process: photon absorption, carrier transport within the active material, and electron ballistics following emission. I show that the theoretical efficiency of a negative electron affinity emitter may be increased with nanostructures if light absorption and electron escape ballistics are considered. I then describe measurements of the photoemission efficiency of fabricated nanostructures that were designed based on the results of the simulation suite. I will also present a fundamentally new method to increase the operating voltage of a TEC by lowering the anode work function using the surface photovoltage effect. When a semiconductor surface is illuminated, photo-excited carriers form an internal dipole, or surface photovoltage (SPV), in the band-bending region and begin to flatten the bands near the surface. This SPV is analogous to the photovoltage in a photovoltaic cell and can reduce the effective work function of the material. I will describe an experimental demonstration using the SPV effect to produce a low work function surface. I will also describe a proof-of-concept demonstration of the SPV effect applied to improve the I-V characteristics of thermionic device. This generic physical process extends across materials systems and forms a realistic path to ultra-low work functions in devices to enable efficient thermionic energy conversion.
