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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Heat and mass transfer 28 (1993), S. 397-409 
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Abstract A model was developed to determine the radiative heat transfer in bubbling fluidized beds taking the bubble and suspension contact at the wall into account. The bubble radiation can be regarded as the heat exchange between two isothermal surfaces. The suspension radiation is described between single particles of the near wall particle layer and the wall during suspension contact at the wall. The two mechanisms particle convection and suspension radiation are simultaneous effects which both results in a decrease of the temperature at the particle surface. The time dependent particle surface temperature can be determined from heat balances of the particle and at the particle surface which are simultaneously influenced by convection and radiation. From this information the suspension radiation can be evaluated. The model results and experimental data were compared and a relatively good agreement was found. The discrepancies are small and no systematic deviations were observed. The model results show not only the expected influence of the bed temperature on the radiative heat transfer but also a strong influence of the particle diameter. Increasing particle diameter increases the radiative heat exchange. The fluidizing velocity influences the radiation via the bubble volume fraction within the bed. Furthermore the radiation is effected by the wall temperature. The system pressure has a minor influence on the radiation by the pressure dependency of the particle convection. Since the application of the radiation model presented here is rather complicated an empirical equation was developed to determine the radiative heat exchange. This equation is easy to handle and represents the results of the complete model as well as all influences which are discussed here. This equation fits the experimental results with a maximum deviation of 20%. The radiation model is verified in a wide range of different parameters so that it includes not only applications of pressurized fluidized bed combustion but includes also other applications for example fluidized beds with metallic bed material.
    Notes: Zusammenfassung Zur Beschreibung des Strahlungswärmeübergangs in blasenbildenden Wirbelschichten wird ein Berechnungsmodell für den Wärmeübergang bei Blasen- und Suspensionskontakt entwickelt. Während die Blasenstrahlung als Strahlungsaustausch zweier isothermer Körper behandelt werden kann, wird die Suspensionsstrahlung als Strahlungswärmeaustausch zwischen den Partikeln der wandnächsten Partikellage und der Wand zuzüglich der Hintergrundstrahlung tieferer Suspensionsschichten beschrieben. Die beiden parallel ablaufenden Mechanismen Partikelkonvektion und Strahlung führen zu einem Abkühlen der Partikel während des Partikel-Wand-Kontaktes. Durch Wärmebilanzen für das Partikel und an der Partikeloberfläche wird der stationäre Verlauf der Partikeloberflächentemperatur bei gleichzeitigem Konvektions-und Strahlungswärmeaustausch bestimmt und daraus die Suspensionsstrahlung ermittelt. Zur Verifikation des Modells wurden die Modellergebnisse mit Meßdaten verglichen. Hierbei ergab sich eine recht gute Übereinstimmung. Die Modellrechnungen zeigen, daß neben der Bettemperatur auch der Partikeldurchmesser eine starke Auswirkung auf die Strahlung hat. Mit steigendem Partikeldurchmesser steigt der Strahlungswärmeübergang an. Die Fluidisierungsgeschwindigkeit beeinflußt über den Fluidisierungszustand des Bettes den Strahlungswärmeaustausch, und auch die Wandtemperatur hat einen nicht vernachlässigbaren Einfluß. Der Systemdruck hat lediglich über die Druckabhängigkeit der Partikelkonvektion Auswirkungen auf die Strahlung, so daß dieser Effekt nicht sehr stark ausgeprägt ist. Die Auswertung der vollständigen Modellgleichungen erfordert das numerische, iterative Lösen mehrerer Differentialgleichungen und ist damit in der Handhabung sehr aufwendig. Aus diesem Grund wurde eine verkürzte Berechnungsvorschrift für den Strahlungswärmeübergang hergeleitet, die alle hier beschriebenen Einflüsse mit guter Genauigkeit darstellt und einfach in der Anwendung ist. Diese Gleichung gibt alle hier vorgestellten Meßdaten mit einer Abweichung von maximal ±20% wieder. Der für das Berechnungsmodell überprüfte Bereich der untersuchten Einflußparameter umfaßt weite Anwendungsgebiete der Wirbelschichttechnik. Dabei erstreckt sich die Gültigkeit der entwickelten Berechnungsvorschrift nicht nur auf die Druckwirbelschichtfeuerungstechnik, sondern schließt auch weitere Anwendungen mit zum Beispiel metallischen Wirbelgütern ein.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 65 (1993), S. 1110-1110 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 69 (1997), S. 1262-1263 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 65 (1993), S. 1106-1107 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 66 (1994), S. 1196-1196 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 66 (1994), S. 1251-1252 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0009-286X
    Keywords: Wärmeübergang ; Stoffübergang ; Filmkondensation ; Turbulenz ; Rohrströmung ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 68 (1996), S. 1067-1068 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A two-color pyrometer has been developed to measure the temperature of surfaces with unknown emissivities during high speed turning processes. Quartz fibers enable measurements at locations with limited optical access. The sensitivity of the pyrometer has to be high enough to measure temperatures down to 300 °C of an aluminum alloy with an emissivity as low as 0.2. The accuracy of the two-color pyrometer has been compared with the accuracy of monochromatic pyrometers for different metallic surfaces. The different arguments for the choice of the two pyrometer wavelengths 1.7 and 2.0 μm are explained. The influences of the surface emissivities, the digitization, and the noise on the absolute and relative measurement error have been determined. Fast amplifiers and data acquisition allow a maximum time resolution of a few microseconds and a local resolution of ∼0.5 mm2. Some test measurements of an aluminum alloy surface are presented. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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