Opposed-Flow Flame Spread Over Polymeric Materials: Influence of Phase Change.
Opposed-Flow Flame Spread Over Polymeric Materials:
Influence of Phase Change.
(730 K)
Zheng, G.; Wichman, I. S.; Benard, A.
Combustion and Flame, Vol. 124, No. 3, 387-408,
February 2001.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Keywords:
flame spread; numerical models; thermal properties;
formulation; equations; flame spread rate; heat flux;
flame structure; heat transfer
Abstract:
A numerical model for flame spread over polymeric
surfaces is constructed. The dependence of the flame
spread rate on phase change and thermal properties is
investigated by varying three non-dimensional
parameters. Quantitative comparisons indicate that the
numerical model provides excellent agreement to an
analytical formula in the cases of variable latent heat
of the phase change, variable liquid thermal capacity,
and variable thermal conductivity. However, the deRis
formula yields a constant spread rate higher than the
numerical result and is independent of phase change.
Qualitatively, with the increase, or with the decrease
of the flame spread rate increases. In addition, the
strongest determinant of the influence of the thickness
of the liquid region. The mechanisms of flame spread at
the steady state are interpreted by applying an energy
balance principle for the control volume upstream of the
flame leading edge. It is found that a ratio between the
total heat applied to the condensed material upstream of
the flame leading edge and the spread rate reveals the
physical mechanisms that control the preheating of the
condensed material to the ignition temperature. The
dependence of flame structure is studied. It is found
that with the increase or with the decrease, the size of
the flame increases. These results indicate that flame
size dependence follows the magnitude of the spread rate
when the properties of the condensed material are
variable.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899