Critical Mass Pyrolysis Rate for Extinction of Fires Over Solid Materials.
Critical Mass Pyrolysis Rate for Extinction of Fires
Over Solid Materials.
Delichatsios, M. A.; Delichatsios, M. M.
International Association for Fire Safety Science. Fire
Safety Science. Proceedings. Fifth (5th) International
Symposium. March 3-7, 1997, Melbourne, Australia, Intl.
Assoc. for Fire Safety Science, Boston, MA, Hasemi, Y.,
Editor(s), 153-164 pp, 1997.
Sponsor:National Institute of Standards and Technology,
fire research; fire safety; fire science; extinction;
pyrolysis rate; combustion; convective heat transfer;
heat flux; fire extinguishment; heat transfer; solid
New flame extinction conditions for the critical mass
pyrolysis rate are developed when extinction occurs by
interaction of flames with the pyrolyzing surface of a
condensed material. The extinction conditions provide
the critical mass pyrolysis rate and the corresponding
convective heat flux to the surface. A novel
formulation shows that the sum of fuel mass fraction
near the surface and the ambient oxygen mass fraction
corrected for stoichiometry and incompleteness of
combustion is constant. The extinction conditions are
derived from simple analysis of combustion and heat
transfer, and they are shown to be applicable for
various experimental conditions such as fuel dilution by
inert gas, oxygen dilution by inert gas, effects of
external heat flux, material preheating, transient
(charring) pyrolysis, including geometric effects which
influence the critical mass pyrolysis rate through an
effective heat transfer coefficient. Additional
validation of the proposed extinction conditions is
provided by numerical simulation reported in the
literaturein the regime of low straining rates for a
stagnation flow on a cylinder. The present approach can
be used to obtain the critical extinction conditions
from measurements in a standard flammability apparatus.