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Understanding Sprinkler Sprays: Trajectory Analysis.

pdf icon 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.


National Institute of Standards and Technology, Gaithersburg, MD

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fire safety; fire research; sprinkler systems; water sprays; water distribution; droplets; sprinklers; experiments


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.