Understanding Sprinkler Sprays: Trajectory Analysis.
Understanding Sprinkler Sprays: Trajectory Analysis.
(801 K)
Sheppard, D. T.; Gandhi, P. D.; Lueptow, R. M.
NISTIR 6588; November 2000.
U.S./Japan Government Cooperative Program on Natural
Resources (UJNR). Fire Research and Safety. 15th Joint
Panel Meeting. Volume 1. Proceedings. March 1-7, 2000,
San Antonio, TX, Bryner, S. L., Editor(s), 281-288 pp,
2000.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
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Order number: PB2001-101517
Keywords:
fire safety; fire research; sprinkler systems; water
sprays; water distribution; droplets; sprinklers;
experiments
Abstract:
Previous research on the characterization of sprinkler
water spray has concentrated on understanding the
droplet and velocity size distributions. However,
previous research appears not have used the droplet and
velocity distributions to determine the delivered
density of water at a specific distance below the
sprinkler, and thus the results, while interesting, do
not provide an analysis of the local delivered density.
This is an important factor in control and suppression
of fires. In this paper, an analytical trajectory
analysis is combined with the results of experiments
conducted with a laser measurement technique called
Particle Image Velocimetry (PIV). The trajectory
analysis is used to predict the path of individual
droplets. Particle Image Velocimetry (PIV) is used to
develop a description of the droplet velocities and
water densities leaving the sprinkler. The trajectory
analysis provided several insights into the physics of
sprinkler sprays. For example, it was found that larger
droplets always travel farther horizontally from the
sprinkler than smaller droplets. This phenomena is
caused by the momentum of larger droplets being
proportionally larger than the drag force. The
experimental study has shown that the droplet velocities
and water fluxes are different at different angles from
the sprinkler. It was found that, for the sprinkler
studied, the droplet velocities could be characterized
as a purely radial flow at a radial distance ranging
from 175 to 300 mm depending on the sprinkler. Further,
it was also found that the angular dependence of the
spray characteristics produce different delivered water
densities and that the sprinkler sprays can not be
characterized as axisymmetric flows. The combination of
the trajectory analysis and the experimental study was
used to predict the water density measured in the
traditional pan distribution tests. The results of this
comparison provided good preliminary results. Further
refinement of the analysis and experimental techniques
will be required to provide acceptable engineering
results.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899