Spray Measurements of an Upright Fire Sprinkler

Abstract

Measurements were conducted to characterize the spray patterns of an upright fire sprinkler in the near and far field of the sprinkler. The spatial distribution of droplet size, velocity and number density in the spray was measured using a laser-based shadow-imaging system. The water volume flux distribution was measured by an array of pressure-transducer-equipped water collection tubes and containers. A large-scale traverse was constructed to move the laser optics and water collection tubes and containers to the designated measurement locations. An upright fire sprinkler with a K-factor of 162 lpm/bar1/2, installed with its deflector 0.17 m below a flat horizontal ceiling, was characterized at two discharge pressures, i.e., 0.76 bar and 1.31 bar. In the near field at 0.76 m from the sprinkler, measurements were performed in a spherical coordinate at different azimuthal and elevation angles with respect to the sprinkler deflector. In the far field, the sprays were mapped out in a 110° circular sector at 3.05 m and 4.57 m below the ceiling. The shadow-imaging based water flux measurements were verified by the measurements obtained from water collection containers. Except for the pipe effect, the azimuthal distributions of the flow rate showed that the spray pattern was more influenced by the frame arms than by the deflector tines and slots. The gross droplet size distribution was expressed as a combination of a log-normal function and Rosin–Rammler function. The median droplet diameter was correlated as an empirical function of the sprinkler orifice diameter and operating pressure. The near-field distributions of the droplet size, velocity and flux can be used to prescribe the starting spray conditions for numerical simulations of spray transport. The far-field measurements are useful in evaluating the spray transport calculations.