Effect of Sample Size on the Heat Release Rate of Charring Materials.
Effect of Sample Size on the Heat Release Rate of
Ritchie, S. J.; Steckler, K. D.; Hamins, A.; Cleary, T.
G.; Yang, J. C.; Kashiwagi, T.
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), 177-188 pp, 1997.
fire research; fire safety; fire science; char; burning
rate; heat release rate; model studies; small scale fire
The burning of a horizontal wood slab situated atop an
insulating substrate was modeled using three coupled
submodels for the gas-phase, wood, and substrate
processes. A global analytical model was used to
determine the radiative and convective heat feedback
from the gas-phase combustion to the wood surface. The
char-forming wood model was a one-dimensional numerical
computation of the density change as a function of
position and time. The backside boundary condition of
the wood was treated as conductive heat loss into a
substrate material modeled by the heat conduction
equation. The condensed-phase model results were tested
by exposing Douglas Fir samples to an external flux in a
nitrogen environment (no combustion). Heat release rate
calculations are compared to experimental results for
Douglas Fir samples of 0.1 m and 0.6 m diameter. Both
theory and experiments show that, for the conditions
studied, the heat release rate is nearly independent of
the specimen diameter except for the initial peak and
the affect of this peak on the first portion of the
quasi-steady settling period. Model predictions also
indicate that the second peak, which follows the
settling period, is very sensitive to the thicknes of
the insulating substrate.