- Author
- Parker, W. J.
- Title
- Prediction of the Heat Release Rate of Wood.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
- Thesis, April 1988, 176 p.
- Keywords
- wood | heat release | combustion | char | chemical composition | thermochemistry | thermophysical properties | heat transfer | thermal diffusivity
- Abstract
- A model for the heat release rate of wood during flaming combustion was developed during this research. It incluedes the effects of char shrinkage, multiple chemical components, adsorbed moisture, internal convective cooling and the variation of the thermophysical and thermochemical properties with temperature the the mass retention fraction of the char. It does not include char oxidation or diffusion of moisture and volatile pyrolysis products toward the rear surface. It calculates the time to ignition, mass burning rate, heat release rate, heat of combustion, heat of gasification and depth of char. An important part of this research was the determination of the thermochemical and thermophysical properties required by the model. An apparatus was developed for determining the kinetic parameters and the heat of combustion of the volatiles under conditions similar to those in the interior of a flaming slab of wood. Data have been obtained on each of the four major chemical components present in Douglas fir. Thermal diffusivity measurements on Douglas fir and its char yielded an average value of 2.1 x 10-7 m2/s which was nearly independent of temperature and mass retention fraction of the char for temperatures up to 550 deg C and for mass retention fractions above 0.30. The calculations for a vertical slab of oven dry Douglas fir exposed at a constant external radiant flux of 25 kW/m2 agreed within 20 percent over most of the flaming period with the heat release rate, mas loss rate, heat of combustion and the rear surface temperature history measured in the cone calorimeter. This agreement deteriorated at higher incident heat fluxes. Both thermophysical and thermochemical property data are needed in the temperature range above 600 deg C.