Mixed Layer Model for Pyrolysis of Bubbling Thermoplastic Materials.
Mixed Layer Model for Pyrolysis of Bubbling
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
fire research; fire science; fire suppression;
thermoplastics; pyrolysis; heat flux; bubbles
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