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Numerical Model for Combustion of Bubbling Thermoplastic Materials in Microgravity.


pdf icon Numerical Model for Combustion of Bubbling Thermoplastic Materials in Microgravity. (1761 K)
Butler, K. M.

NISTIR 6894; 67 p. August 2002.

Sponsor:

NASA-John H. Glenn Research Center at Lewis Field, Cleveland, OH

Available from:

: National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
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Keywords:

thermoplastics; combustion; microgravity; numerical models; bubbles; pyrolysis; finite element model; polymethyl methacrylate; polypropylene

Abstract:

A numerical model is demonstrated for the pyrolysis of a spherical thermoplastic sample in microgravity including effects of bubbles. The model combines nucleation, growth, and migration of individual bubbles in 3-D space with a finite element model that solves the 1-D radial equation for the temperature field. Energy calculations include surface losses due to radiation and convection, conductive heat transfer through the mixture of gaseous and condensed phase material, and the chemistry of gasification. Gases released by bursting bubbles determine the mass loss rate from the sample. Results demonstrate the thermally insulating properties of bubbles as they transport gases to the suface of a heated polymeric sample. The mass loss rate is particularly sensitive to the bursting process, since slow drainage from the thin film definign the bubble at the surface maintains gases of low thermal conductivity as a thermal barrier to slow the transport of heat. The behaviors of pyrolyzing PMMA and PP spheres are investigated.