Spray characteristics of fire sprinklers

Although fire sprinklers have been in use for over 100 years there has been little progress toward developing analytical methods of calculating their effectiveness. This lack of progress is primarily due to absence of information about initial spray characteristics near sprinklers. In this study, experiments were conducted near a variety of sprinkler designs utilizing (1) a pulsed laser sheet and CCD camera and (2) phase Doppler interferometry.; Particle image velocimetry analysis of the CCD camera images has shown that velocities near the sprinklers can be described as a purely radial flow with the origin located between the orifice and deflector for pendant sprinklers and between the orifice and slightly above the deflector for upright sprinklers. The average radial droplet velocity at a distance 0.2m from the sprinkler orifice is 53% of the water velocity through the orifice with a 0.08% standard deviation. The maximum spray velocities ranged from 62% to 120% of the orifice water velocity with a statistically significant trend for higher maximum velocities from pendant sprinklers. The radial velocity is strongly dependent on the elevation angle and less dependent on the azimuthal angle. The radial velocity is a function of the specific sprinkler model, so a general description of the radial velocity independent of sprinkler model is not very accurate. The radial droplet velocity is proportional to square root of the water pressure entering the sprinkler.; The droplet size distribution can be measured by phase Doppler interferometry techniques close to the sprinkler. The median droplet diameter increases with elevation angle. The median droplet diameter decreases with increasing water pressure, and relationship that has been suggested for the median droplet diameter to be proportional to the −1/3 power of the Weber number was found valid, but the proportionality constant depends on the location in the spray.; The water flux can be calculated from the visible drops in the CCD images. The water flux is strongly dependent on the elevation angle and on the azimuthal angle. The measurement technique is able to discern measurable increases in water flux at locations coinciding with large notches in the sprinkler deflectors. The details of the water flux are somewhat dependent on the water pressure, although the general characteristics of the water flux remain independent of water pressure. The water flux distribution vary so much with pressure and sprinkler type that it is impossible to determine a universal water flux distribution or to assume axisymmetry for the water flux.