Characterization of fire sprinkler sprays using particle image velocimetry

Although fire sprinklers have been used for over a century for fire suppression, little is known about the character of the spray. Particle image velocimetry was used to measure the droplet velocity near the sprinkler in sprays generated from several typical fire sprinklers. The spray near the sprinkler is essentially radial, with a virtual origin for the spray velocity that is between the orifice and the deflector for pendant sprinklers and between the orifice and 0.05 m above the deflector for upright sprinklers. The maximum radial velocity in the spray ranges from 5.8 to 14.1 m/s, depending on the sprinkler and the pressure in the sprinkler pipe. The spray velocity profiles near sprinklers are dependent on the azimuthal angle and the elevation angle, though not strongly dependent. There is very little difference in the velocity profiles for pendant and upright sprinklers. However, in some cases the measured velocity can be related to sprinkler features such as notches in the deflector. Scaling the radial velocity using the water density and pressure as U _r(ρ/P)^1/2 collapses the droplet velocity profiles over a wide range of pressures. The average radial velocity at a distance 20 cm from the sprinkler is approximately 0.6 (P/ρ)^1/2, while the maximum radial velocity in the spray 20 cm from the sprinkler is 1.0(P/ρ) ^1/2. The spray velocity profiles reported here are available for use in the National Institute of Standards and Technology's "Fire Dynamics Simulator," a computational model for fires and fire suppression based on large-eddy simulation techniques.