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Effect of Sample Size on the Heat Release Rate of Charring Materials.


pdf icon Effect of Sample Size on the Heat Release Rate of Charring Materials. (718 K)
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.

Keywords:

fire research; fire safety; fire science; char; burning rate; heat release rate; model studies; small scale fire tests; wood

Abstract:

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.