Characterization of a simplex water mist nozzle and its performance in extinguishing liquid pool fire

Pressure swirl nozzles are often employed in water mist fire suppression systems. In the present work, a single head full cone simplex nozzle with X-type swirl-insert and an orifice diameter of 1.2 mm is used to produce water mist. The objectives are to experimentally measure different characteristics of the spray and investigate extinction performance of diesel pool fires of size 0.1, 0.2, and 0.3 m. Discharge coefficient and spray cone angle are measured and correlations are presented as functions of Reynolds numbers (Re, based on orifice diameter). Mass flux density of the spray is measured with a patternator designed considering possible asymmetry in the spray. Droplet size and velocity distributions are measured using a particle droplet image analyser (PDIA) system for 28,850 ≤ Re ≤ 35,800 and axial distances from the nozzle (0.75 ≤ z ≤ 1.75 m). Experimentally measured droplet number distributions are characterized by modified log-normal distribution. Rosin-Rammler and modified Rosin-Rammler model are presented to predict droplet volume distributions. Correlations are presented for calculating parameters of these models in order to describe droplet size distribution (DSD) for any combination of Re and z. Relative span factor (RSF), Sauter mean diameter (SMD), and average velocity of the spray are measured. Correlations for SMD and average velocity are presented as functions of experimental variables. The extinction performances are investigated through video recording for 28,850 ≤ Re ≤ 35,800 and various vertical distances between the nozzle and the fuel surface (0.75-2 m). Extinction performance of the nozzle in the present work is compared with the other performances of different water mist systems reported in the literature.