Flame Spread in a Vitiated Concurrent Flow.
Flame Spread in a Vitiated Concurrent Flow.
(215 K)
Chao, Y. H.; Fernandez-Pello, A. C.
American Society of Mechanical Engineers (ASME). Heat
Transfer in Fire and Combustion Systems. HTD-Vol. 199.
Book No. H00757-1992. 1992, Am. Soc. of Mechanical
Engineers, New York, NY, Kanury, A. M.; Brewster, M. Q.,
Editor(s)(s), 135-142 pp, 1992.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Keywords:
flame spread; solid surfaces; experiments; gas flow;
oxygen concentraton; velocity; oxygen concentration
Abstract:
Experiments have been conducted to study the effects of
forced gas flow velocity and oxygen concentration on the
flow assisted flame spread over a flat solid combustible
surface. All the tests are performed with thick PMMA
Sheets as fuel and mixtures of oxygen and nitrogen as
oxidizer. The spread rate is measured for flow velocity
ranging from 0.5 to 2.0 m/sec and oxygen mass fraction
from 0.19 to 0.23. It is found that the flame spread
rate increases linearly with the main flow velocity and
the oxygen concentration within the experimental
conditions. In order to determine the effect of
buoyance on the flame spread rate, data in the ceiling
and floor configurations are compared. The exhaust gas
composition are also measured to detect possible
buoyancy effects on the chemical reactions in the flame.
Despite the overall similarity between the
characteristics of ceiling and floor surface flame
spread, some substantial differences have been observed.
The experimental results indicatethat buoyancy has two
main effects in the ceiling case, one is the enhancement
of heat transfer from the flame to the solid surface,
and the other is the flame quenching through cold wall
effect. For large flow velocities, the enhanced heat
transfer is found to be dominant and results in a faster
flame propagation in the ceiling than in the floor. For
low flow velocities, the flame quenching effect becomes
more important and the opposite result is observed. The
transition velocity decreases as the oxygen mass
fraction decreases.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899