Spray characterization measurements of a pendent fire sprinkler

Abstract

The spray patterns of a pendent fire sprinkler were characterized through experimental measurements in the near and far field of the sprinkler. A laser-based shadow-imaging system was used to measure the droplet size, velocity and number density in the spray. An array of pressure-transducer-equipped water collection tubes and containers provided a separate set of water volume flux measurements. A large-scale traverse was constructed to move the laser optics and water collection tubes and containers to the designated measurement locations. A pendent fire sprinkler with K-factor of 205lpm/bar1/2 (14.2gpm/psi1/2) was characterized at two discharge pressures 3.5bar and 5.2bar (50 and 75psi). In the near field at 0.76m 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 3.05m and 4.57m below the ceiling. The shadow-imaging based water flux measurements were verified by the measurements obtained from water collection containers. The measurements show that the spatial distributions of water volume flux, droplet size and velocity of sprinkler sprays are strongly influenced by the sprinkler frame arms and the configuration of sprinkler deflector’s tines and slots. For the purpose of fire protection analysis, empirical correlations were developed from the near-field measurements to prescribe the spray starting conditions for the numerical modeling of spray transport through fire plumes. The far-field measurements can be used to evaluate the spray transport calculations.