Numerical Model for Combustion of Bubbling Thermoplastic Materials in Microgravity.
Numerical Model for Combustion of Bubbling Thermoplastic
Materials in Microgravity.
Butler, K. M.
NISTIR 6894; 67 p. August 2002.
Sponsor:NASA-John H. Glenn Research Center at Lewis Field,
Available from:: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
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thermoplastics; combustion; microgravity; numerical
models; bubbles; pyrolysis; finite element model;
polymethyl methacrylate; polypropylene
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