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-fonning 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 thickness of the insulating substrate.
A study was made of the thermal and flow environment within a corridor subject to a room fire of intensities of 300 to 1500 kW approximately. A corresponding model study was done under 1/7th geometric scale. Dimensionless groups were derived from the conservation equations governing the gas and solid phases. A subset of dimensionless groups was identified as significant to establish criteria to maintain partial dynamic scaling between the model and prototype experiments. Good results were achieved between the model and prototype for the convective process. i.e., gas temperature, velocity, and convective heat transfer. Radiant heat transfer did not scale, but an analysis of the data explains the lack of agreement in terms of dimensionless groups that were not preserved in scaling. A secondary result yielded corridor convective heat transfer coefficients which could be correlated by a general relationship.
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