Abstract
Characteristics of single sprinkler sprays for two Early Suppression Fast Response (ESFR) sprinklers were investigated. The water density, drop size and velocity distributions were measured at an elevation 2.85 m (9 ft 4 in.) below the sprinkler deflector for two water discharge pressures, 1.72 bar (25 psig) and 3.45 bar (50 psig). Measurements began at 0.61 m (2 ft) from the sprinkler axis and extended to near spray boundary. For every 0.61 m (2 ft) increment, the measurements were performed for 10 azimuthal angles with 45 degree intervals. The drop size and velocity distributions were measured with a PMS (Particle Measuring Systems, Inc.) optical imaging probe which can measure drop size ranging from 0.1 to 6.2 mm with a resolution of 0.1 mm.
The results of the water density measurements indicate that the water densities for the two sprinkler models diminish with increasing radial distance from the sprinkler axis. Based on the local measured density data, the gross density distributions in term of volume fraction for the entire sprinkler sprays were derived. It was found that the gross density distributions were well represented by the Rosin-Rammler equation. The distribution curves for the two sprinkler models discharging at 3.45 bar (50 psig) were close to each other.
From the drop size measurements, it was found that larger drops tended to be projected to near the spray boundary rather than towards the sprinkler axis. The average droplet velocity for each drop size was found to be very close to the experimental terminal velocity for a singlewater droplet traveling through air. The gross drop size distribution curves for the two sprinkler models were similar, with one model drop size distribution being uniformly smaller than the other. Each gross drop size distribution can be expressed as a combination of the log-normal equation and the Rosin- Rammler equation.
Get full access to this article
View all access options for this article.