With the advent of space exploration, fire safety aboard space vehicles including space capsules, the Space Shuttle, and the permanent space station presents new challenges. The low-gravity combustion experiments of thermoplastic PMMA (polymethylmethacrylate), PP (polypropylene), and PS (polystyrene) spheres reveal interesting phenomena, which are not observed in normal gravity. Whereas dripping of a polymer melt can pose a fire hazard in normal gravity, in the case of PP, the random and violent ejection of burning material in microgravity represents a nontrivial fire safety challenge. The three thermoplastic types used in the reduced gravity experiments exhibited very different combustion characteristics. The two types of bubble bursting phenomena, the release of a gas jet and the ejection of condensed-phase material from the break-up of a bubble jet, offer a plausible explanation for the dynamic ejection events during combustion of the three types of polymers studied here. The average mass burning rates of PMMA were found to increase with the initial sphere diameter and oxygen concentration and were not affected significantly by pressure. Under the same initial conditions, the average mass burning rate of PP was lower than PMMA, whereas the mass burning rate of PS was similar to PMMA. Calculations show that during burning, a large fraction of the sphere is composed of gaseous bubbles that nucleate, grow and escape from the polymer, causing sputtering of molten burning solid polymer. Unlike liquid droplets, diameter expansion of the molten fuel occurs mainly due to the in-depth formation and growth of bubbles, whereas the decreased density accompanying polymer heating also contributes. Sputtering and the escape of bubbles from the sphere surface acts to enhance the mass loss rate of polymer burning.


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    Titel :

    Reduced gravity combustion of thermoplastic spheres


    Beteiligte:
    Yang, J.C. (Autor:in) / Hamins, A. (Autor:in) / Donnelly, M.K. (Autor:in)

    Erschienen in:

    Combustion and Flame ; 120 , 1/2 ; 61-74


    Erscheinungsdatum :

    2000


    Format / Umfang :

    14 Seiten, 8 Bilder, 3 Tabellen, 38 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch






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