Transient Modeling of Thermal Degradation in Non-Charring Solids.
Transient Modeling of Thermal Degradation in
Non-Charring Solids.
(1321 K)
Sohn, Y.; Baek, S. W.; Kashiwagi, T.
Combustion Science and Technology, Vol. 145, 83-108,
1999.
Keywords:
solids; thermal degradation; mass loss; polymethyl
methacrylate; equations; radiation modeling
Abstract:
For a more extensive investigation of polymers, a better
understanding of its gasification process is extremely
essential. Especially compared with the extensive
studies in the gas phase, the solid phase received
rather little attention. Thus, the purpose of this paper
is in its comparison of several modeling approaches for
thermal degradation and systematic demonstration of the
effects of basic assump tions on the model results,
while taking account of in-depth radiation. For this
object, this study has examined in more detail the
degradation for a horizontally positioned polymer which
is exposed to external radiation. After a preliminary
study, three different solid degradation models were
chosen from the literature, and their corresponding mass
and energy conservation equations and boundary
conditions were assembled. The in-depth non-gray as well
as gray radiation was taken into account by solving
relevant radiative transfer equation. In order to
concentrate on the fundamental mechanisms of polymer
degradation, gas phase reactions and subsequent heat
feedback from the gas were neglected. This corresponds
to a nitrogen environment. Various other parameters such
as the polymer refractive index, polymer absorption
coefficient, convective heat loss, solid fuel thickness
and external radiative heat flux were changed to discuss
their effects on the quantitative as well as qualitative
change in the mass loss rate. While the effect of the
solid fuel thickness on the mass loss rate was
negligible for a thick sample, each parameter among the
polymer refractive index, polymer absorption
coefficient, convective heat loss, and external
radiative heat flux incurred a non-negligible change in
the results. Furthermore, the convection term in the
energy equation, which is usually neglected in the
in-depth pyrolysis by many other works, was shown to
account for 29% decrease in the mass loss rate. Finally,
depending on the solid degradation model used, the
addition of gray radiation to the energy equation was
shown to augment or diminish the mass loss rate. It was
further enhanced by taking account of the non-gray
radiation. This results from the fact that the inner
solid is more quickly heated due to the far-reaching
effects of radiation from the surface.
