Analysis of emitter material transport in thermionic converter. Paramonov, D.V. (Institute for Space and Nuclear Power Studies, Chemical and Nuclear Engineering Department, University of New Mexico, Albuquerque, New Mexico 87131 (United States)); El-Genk, M.S. AIP Conference Proceedings; 361 (1): 1137-1148 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Output power and efficiency of a thermionic converter depend on temperatures, cesiated work functions, and emissivities of electrodes as well as the interelectrode gap size. Operation lifetime of a thermionic converter is directly related to the values as well as the stability of these parameters, which can be seriously altered by the transport of emitter material to the collector during operation. Loss rate of tungsten, a preferred emitter material, by sublimation at typical operating temperatures is small (about 3{times}10{sup 7} atom/cm{sup 2}sec at 2000 K). The loss rate, however, can be several orders of magnitude higher in the presence of gaseous contaminants. Accelerated transport of emitter material to collector surface changes the effective emissivity and work functions of the electrodes, resulting in performance degradation. A phenomenological model was developed to simulate emitter material transport to the collector in the presence of oxygen, water vapor, and carbon oxide contaminants. The model accounts for interaction of these contaminants with both emitter and collector. Model results were in agreement with experimental data and theoretical results of other investigators. An analysis was performed to determine steady-state chemical composition of deposited material onto the collector surface in the presence of H{sub 2}O, O{sub 2}, and H{sub 2} gaseous contaminants. {copyright} {ital 1996 American Institute of Physics.}

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WAIS Entry Date:
11/30/1996
Document Type Text:
Journal Article
Literary Indicator Text:
Conference literature, either as published proceedings or individual papers
Publication Date:
03/01/1996
Packed Report Number:
CONF960109
EDB Subject Category Text:
THERMIONIC CONVERTERS
EDB Subject Categories:
300400
Keywords:
THERMIONIC CONVERTERS/contamination; CONTAMINATION; TUNGSTEN; MASS TRANSFER; OXYGEN; WATER; CARBON OXIDES; HYDROGEN; DESORPTION; THERMIONIC COLLECTORS; THERMIONIC EMISSION

Effect of oxygen on performance and mass transport in a single-cell thermionic fuel element. Paramonov, D.V. (Univ. of New Mexico, Albuquerque, NM (United States)); El-Genk, M.S. pp. 945-950 of Proceedings of the 31. intersociety energy conversion engineering conference. Volume 2: Conversion technologies, electro-chemical technologies, stirling engines, thermal management. Chetty, P.R.K.; Jackson, W.D.; Dicks, E.B. (eds.). Inst. of Electrical and Electronics Engineers, Piscataway, NJ (United States) (1996). 867p. Sponsored by Department of the Air Force, Washington, DC (United States). (CONF-960805--: 31. intersociety energy conversion engineering conference, Washington, DC (United States), 9-14 Aug 1996).

The introduction of tracer amounts of oxygen into the interelectrode gap of a thermionic converter has been shown to improve converter performance. Excess oxygen, however, increases the loss rate of emitter material, reducing the converter performance and shortening its lifetime, owing to the increase in the effective emissivity of the electrodes, the change in the collector work function, and the deposition of emitter material oxides on spacers and insulators. In this paper, a model was developed, which calculated the emitter material loss rate, composition of the emitter material deposits on the collector surface and investigated the effect on performance of a single-cell Thermionic Fuel Element (TFE) in the presence of oxygen and cesium oxides in the interelectrode gap. The amount of oxygen and the cesium pressure in the interelectrode gap were varied parametrically and the TFE volt-ampere characteristics, and axial distributions of current density and emitter material loss rate along the TFE were calculated.

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WAIS Entry Date:
04/12/1997
Document Type Text:
Book Analytic
Literary Indicator Text:
Conference literature, either as published proceedings or individual papers
Publication Date:
01/01/1996
Packed Report Number:
CONF960805
EDB Subject Category Text:
PERFORMANCE AND TESTING;POWER REACTORS, MOBILE, PROPULSION, PACKAGE, AND TRANSPORTABLE
EDB Subject Categories:
300402;210600
Keywords:
THERMIONIC FUEL ELEMENTS; THERMIONIC EMITTERS; PERFORMANCE; MASS TRANSFER; OXYGEN; MATHEMATICAL MODELS; PARAMETRIC ANALYSIS; TOPAZ REACTOR

A review of cesium thermionic converters with developed emitter surfaces. Paramonov, D.V. (Institute for Space and Nuclear Power Studies, Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico 87131 (United States)); El-Genk, M.S. AIP Conference Proceedings; 361 (1): 1305-1314 (Mar 1996). (CONF-960109--: STAIF 96: space technology and applications international forum, Albuquerque, NM (United States), 7-11 Jan 1996).

Studies from US and Russian literature on experimental and theoretical investigations of thermionic converters with developed emitter surfaces are reviewed and analyzed. Experimental data for these converters is compared with that for close-spaced and traditional Cs arc converters. The former is most advantageous at low temperatures from 1300 to 1700 K, with the power gain increasing as the emitter temperature decreases and/or its emission properties deteriorate. This power gain is attainable at a larger load voltage and at a significantly larger optimum interelectrode gap size than traditional converters. Additional experiments and mathematical modeling are needed to understand the physical processes taking place and assess the performance of thermionic converters with developed emitter surfaces, compared to traditional ones operating under identical conditions. {copyright} {ital 1996 American Institute of Physics.}

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WAIS Entry Date:
11/30/1996
Document Type Text:
Journal Article
Literary Indicator Text:
Conference literature, either as published proceedings or individual papers
Publication Date:
03/01/1996
Packed Report Number:
CONF960109
EDB Subject Category Text:
PERFORMANCE AND TESTING
EDB Subject Categories:
300402
Keywords:
THERMIONIC CONVERTERS/performance; PERFORMANCE; CESIUM; ENERGY CONVERSION; THERMIONIC EMISSION; ELECTRIC CONDUCTIVITY; POWER DENSITY