Investigation of Droplet Penetrations Through Complex Openings of Compartments.
Investigation of Droplet Penetrations Through Complex
Openings of Compartments.
(5560 K)
Yao, S. C.; Hung, L. S.
NIST GCR 98-759; 78 p. November 1998.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Available from:
National Technical Information Service
Order number: PB99-105132
Keywords:
compartments; droplets; penetration; computational fluid
dynamics; fire suppression; water mist
Abstract:
The use of fine water mist as one of the possible Halon
1301 replacements has been identified for certain fire
suppression situations in equipment compartments. One
current research effort is to apply the water mist
sprays to suppress the fire occurring in hidden location
behind obstructions or inside the equipment
compartments. Since the mist usually contains a
spectrum of drop sizes, the smaller mist droplets may
follow the gas streams closely and penetrate directly
through the slots of the obstructions while the larger
droplets may be intercepted or impacted by the
obstructions. When the mist droplets are approaching
the structures, the overall penetrating process of the
mist flow through the obstruction depends strongly on
the transport of the mist droplets in the gas streams,
the ability of the droplets flowing through the
obstruction, and the behavior of droplets subsequent to
the impaction. The present research presents an
integrated approach to model the penetration of water
mist through the obstructions for fire suppression
applications. Firstly, numerical investigations
employing the two-phase Navier-Stokes equations are
achieved using computational fluid dynamics (CFD) to
evaluate the overall transport of droplets in the
vicinity of the openings, which include rectangular
strips and a 3-D screen object. In particular, the
motions of the droplets coupled with the gas flow field
around the objects are analyzed. The deposition of
droplets on the objects and their penetration through
the spacing of the objects are also formulated. Then,
experimental investigations are performed to address the
actual impacting phenomena of droplets on objects.
Droplet generators are designed to generate droplets in
a variety of operating conditions. Structures such as
cylindrical wires and mesh screens are examined in the
impaction experiments. Images of the impacting
phenomena are analyzed through digital image processing.
Non-dimensional regime maps and the correlations of the
impaction outcome are also developed. The conclusions
from both the numerical and experimental investigations
are integrated to provide an overall understanding to
the complex interaction phenomena and to establish a
procedure for predicting the outcome of similar
processes.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899