Condensed-phase pyrolysis heat conduction

The FDS5 pyrolysis model is used here to qualitatively illustrate the complexity associated with material property estimation. Each condensed-phase species (i.e., virgin wood, char, ash, etc.) must be characterized in terms of its bulk density, thermal properties (thermal conductivity and specific heat capacity, both of which are usually temperature-dependent), emissivity, and in-depth radiation absorption coefficient. Similarly, each condensed-phase reaction must be quantified through specification of its kinetic triplet (preexponential factor, activation energy, reaction order), heat of reaction, and the reactant/product species. For a simple charring material with temperature-invariant thermal properties that degrades by a single-step first order reaction, this amounts to -11 parameters that must be specified (two kinetic parameters, one heat of reaction, two thermal conductivities, two specific heat capacities, two emissivities, and two in-depth radiation absorption coefficients). 

The pyrolysis equations above are based on an assumed which is not generally known from condensed phase considerations alone. To proceed further and obtain a solution for mass flux requires information about the conductive heat feedback to the surface from the gas phase qc which must be supplied by the gas... 

These results are reasonable since B—N is reportedly synthesized by heating the condensation product of orthoboric acid and urea in a stream of ammonia till 1650 C [25]. However, when the pyrolysis were conducted in argon, a black residue was left, indicative of sigmficant amount of carbon in the char. The weight loss was approximately 70%. Initial characterization by XRD of the former residues indicate the presence of a graphite phase, a small amount of BN and other complex B—N—C phases. 

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