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Mixed Layer Model for Pyrolysis of Bubbling Thermoplastic Materials.


pdf icon Mixed Layer Model for Pyrolysis of Bubbling Thermoplastic Materials. (257 K)
Butler, K. M.

NISTIR 6242; October 1998.

National Institute of Standards and Technology. Annual Conference on Fire Research: Book of Abstracts. November 2-5, 1998, Gaithersburg, MD, Beall, K. A., Editor(s), 31-32 pp, 1998.

Available from:

National Technical Information Service
Order number: PB99-102519

Keywords:

fire research; fire science; fire suppression; thermoplastics; pyrolysis; heat flux; bubbles

Abstract:

For many thermoplastic materials exposed to a strong heat flux from above, a layer of bubbles forms in the melted region near the upper surface. The action of these bubbles is observed to range from slow growth and bursting to vigorous boiling behavior. Although the bubbles appear to have a significant effect on the macroscopic thermal and mechanical properties of the material, the mechanisms by which a bubbling layer affects heat and mass transfer are not well understood. Since the thermal conductivity of a gas is much lower than the thermal conductivity of a liquid, we might expect the transport of heat to be slowed considerably in the presence of bubbles. Alternatively, vigorous boiling behavior could be mixing the upper layer of melted thermoplastic material, resulting in a nearly uniform temperature throughout the bubling layer. How would these seemingly contradictory mechanisms affect heat and mass transfer, and which dominates behavior during pryolysis?