Solid Fuel Flame Spread and Mass Burning in Turbulent Flow.
Solid Fuel Flame Spread and Mass Burning in Turbulent
Flow.
(3354 K)
Zhou, L.
NIST GCR 92-602; 232 p. March 1992.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Available from:
National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
Telephone:
1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900; Rush
Service (Telephone Orders Only) 800-553-6847;
Website:
http://www.ntis.gov
Order number: PB92-181049
Keywords:
solid fuels; flame spread; turbulent flow; ceilings;
floors; paper; plastics; polymethyl methacrylate;
regression rate
Abstract:
An experimental study has been carried out to
investigate the controlling mechanisms of solid fuel
flame spread and mass burning in turbulent flows. The
effects of flow velocity, turbulence intensity and
buoyancy on concurrent and opposed flame spread rate and
surface regression rate have been examined in both flow
and ceiling configurations. It is found that for
opposed flows, the flame spread rate of thermally thick
PMMA sheet increases initially with the flow velocity,
reaches a peak value and then decreases as the flow
velocity increases further. The flow turbulence effect
is to increase the flame spread rate initially and then
decreases it at higher turbulence intensity. The flame
spread rate of thermally thin paper sheet in an opposed
flow decreases monotonically with the flow velocity and
turbulence intensity. The flow turbulence also has a
significant effecton the flame extinction conditions,
resulting in a smaller extinction velocity for larger
flow turbulence intensity. For concurrent flow flame
spread, it is found that the flow turbulence decreases
the flame spread rate for both floor and ceiling
geometries, mainly as a result of the flame length
shortening at high turbulence intensity. I is also
found that flow velocity intensifies the spread of the
flame. The experimental data of flame spread rate,
flame length and surface heat flux agree well with the
formula obtained from a simplified thermal model,
indicating that the heat transfer from flame to solid
surface is the dominant controlling mechanism in the
turbulent concurrent flame spread and, that the gas
phase chemical reaction is of secondary importance. For
solid fuel mass burning, it is found that the solid fuel
surface regression rate decreases with the downstream
distance and the flow velocity in both floor and ceiling
configurations. The flow turbulence increases the
surface regression by enhancing the mixing and bringing
the flame closer to the solid surface. Empirical
correlations betwen the non-dimensional surface
regression rate and the non-dimensional flow parameter
are obtained, which indicates the possibility of
incorporating the flow turbulence intensity explicitly
in a non-dimensional analysis or a numerical simulation
of the problem. The results from floor and ceiling
geometries are compared to determine the effect of
buoyancy on flame spread and mass burning. It is shown
that for ceiling configuration, buoyancy enhances the
heat transfer from the flame to the solid surface by
pushing the flame closer to the wall. However, it also
causes the gas phase chemical reactions to proceed less
completely through insufficient gas mixing and surface
quenching.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899