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Spray Characteristics of Fire Sprinklers.


pdf icon Spray Characteristics of Fire Sprinklers. (2455 K)
Sheppard, D. T.

NIST GCR 02-838; Thesis; 204 p. June 2002.
Order number: PB2003-100879

Keywords:

sprinklers; sprays; water distribution; droplets; drop sizes; lasers; experiments; velocity; pressure effect

Abstract:

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 velocity 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 54% of the water velocity through the orifice with a 0.8% 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.