Minimum Mass Flux Requirements to Suppress Burning Surfaces With Water Sprays.
Minimum Mass Flux Requirements to Suppress Burning
Surfaces With Water Sprays.
Yang, J. C.; Boyer, C. I.; Grosshandler, W. L.
NISTIR 5795; 50 p. April 1996.
Sponsor:Federal Emergency Management Agency, Emmitsburg, MD
Available from: National Technical Information Service
Order number: PB96-183181
drop sizes; extinguishment times; fire suppression;
mist; sprays; polymethyl methacrylate; polystyrene
Experimental measurements of extinguishment times of
burning solid fuels using water were conducted using a
prototype micronozzle array and a piezoelectric droplet
generator. Solid fuels considered included solid white
pine, polymethylmethacrylate, and polystyrene foam.
External heat flux was applied to the sample surface
during burning. The effects of drop size, sample
orientation with respect to the nozzle, and nozzle
distance from the sample surface on extinguishment time
were examined. The extinguishment time was found to
decrease with increasing water flow rate. For a given
water flow rate, significant reduction in extinguishment
time was observed when smaller droplets were used. At
low water flow rates, the extinguishment time decreased
when the nozzle was positioned further from the sample
surface. At high flow rates, the extinguishment was
independent of the nozzle-to-sample distance. When the
droplet stream was 45DG relative to the sample, the
extinguishment time was not affected by the
nozzle-to-sample distance. The other component of the
project was to evaluate a commercial low pressure, high
momentum pendant water mist nozzle using an optical
array probe droplet analyzer. The pendant nozzle used
in this study is currently being evaluated by listing
organizations for fire suppression in residential and
light hazard occupancies. The objective of this study
was to determine drop size and velocity distributions at
various locations in the spray. Experiments were
conducted at delivery pressures of 621 kPa + 14 kPa
(90.0 psi + 2.0 psi) and 448 kPa + 14 kPa (65.0 psi +
2.0 psi). The droplet diameters from the experiments
were found to range from less than 36 mm to 1230 mm for
the experiments conducted at 448 kPa + 14 kPa (65.0 psi
+ 2.0 psi,) and to range from less than 36 mm to 1155 mm
for the experiments conducted at 621 kPa + 14 kPa (90.0
psi + 2.0 psi). The velocities of the water droplets
were calculated based on the time required for each
individual drop to pass through the probe image field.
The range of droplet velocities was found to be
approximately 0.19 m/s to 1.58 m/s (0.62 ft/s to 5.18
ft/s) from the experiments conducted at 448 kPa + 14 kPa
(65.0 psi + 2.0 psi). For the measurements taken at 621
kPa + 14 kPa (90.0 psi + 2.0 psi), the droplet
velocities ranged from approximately 0.25 m/s to 1.9 m/s
(0.82 ft/s to 6.23 ft/s).