INVESTIGATION OF GAS PRESSURE BUILDUP IN THERMOELECTRIC SNAP GENERATORS

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The program for investigating gas pressure buildup in thermoelectric generators was initiated in February 1963 and continued through December 1963. The program objectives were to determine the source(s) of internal gas pressure increase in SNAP thermoelectric generators, establish methods of alleviating or eliminating the condition, and conduct a proof-of-principle test on an electrically heated 60-watt thermoelectric SNAP generator to determine the effectiveness of the procedures developed to control or eliminate the condition. The gas pressure increase in the generators that were initially filled with dry inert gas results from decomposition of the phenol-formaldehyde resin that is used as a binder ... continued below

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Pages: 43

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McDonald, W.A. & McGrew, J. January 1, 1964.

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Description

The program for investigating gas pressure buildup in thermoelectric generators was initiated in February 1963 and continued through December 1963. The program objectives were to determine the source(s) of internal gas pressure increase in SNAP thermoelectric generators, establish methods of alleviating or eliminating the condition, and conduct a proof-of-principle test on an electrically heated 60-watt thermoelectric SNAP generator to determine the effectiveness of the procedures developed to control or eliminate the condition. The gas pressure increase in the generators that were initially filled with dry inert gas results from decomposition of the phenol-formaldehyde resin that is used as a binder in the Min-K 1301 thermal insulation and desorption of atmospheric gases and water vapor that adsorb on the surface of the insulation. The degree of gas release in both cases was determined to be temperature and pressure dependent. The recommended procedure to control gas pressure buildup for all future generators is: (1) precondition the Min-K by burning off the phenolic resin binder; (2) vacuum outgas the insulation at a temperature above its maximum operating temperature; and (3) install a gas getter (zirconium) to absorb any gases that may be released during subsequent generator operation. The complete recommended procedure to control this pressure buildup could not be employed in the 60-watt thermoelectric SNAP generator test since the generator had been previously constructed and assembled using Min-K that had not been preconditioned by outgassing. Therefore, a modified outgassing procedure was established for the generator when the test was initiated. The procedure, in essence, specified that the generator be maintained on continuous evacuation while the thermoelement hot junction temperature was slowly increased to approximates 525 deg F, and that the generator be subjected to frequent rapid evacuations and gas changes as the temperature was increased to 960 deg F. (Lead telluride thermoelements begin to sublime in a vacuum at elevated temperatures in the 950 to 1000 deg F range.) An amount of 2,143 grams of zirconium sponge were inserted in the hottest region of the generator to react with getterable gases that remained after the outgassing and evacuation procedure. The 60-watt electrically heated SNAP generator was then maintained on a stability test for two months. The generator internal gas fill pressure remained essentially constant throughout the period, demonstrating that the recommended control procedure will alleviate the internal gas pressure buildup condition. (auth)

Physical Description

Pages: 43

Source

  • Other Information: Orig. Receipt Date: 31-DEC-64

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  • Report No.: MND-3143-1
  • Grant Number: AT(30-1)-3143
  • DOI: 10.2172/4082219 | External Link
  • Office of Scientific & Technical Information Report Number: 4082219
  • Archival Resource Key: ark:/67531/metadc868109

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  • January 1, 1964

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  • Sept. 16, 2016, 12:32 a.m.

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  • Dec. 5, 2016, 9:29 p.m.

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McDonald, W.A. & McGrew, J. INVESTIGATION OF GAS PRESSURE BUILDUP IN THERMOELECTRIC SNAP GENERATORS, report, January 1, 1964; United States. (digital.library.unt.edu/ark:/67531/metadc868109/: accessed September 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.