Experimental investigation on spray morphology in dual pitch spiral nozzle.

This study investigates dual-spiral-pitch nozzles, which are essential for high-discharge applications like deluge fire suppression systems (5–4000 L/min). Such nozzles produce multi-sprays, which have received little attention in the past. In the present research, experiments quantified the relationship between inlet pressure (0.2–3.4 bar), mass flow rate, and spray characteristics. Results reveal three distinct spray morphologies linked to inlet pressure: a gradual mass flow rate increase across 0.2–1 bar inlet pressure, a dramatic surge exceeding 1000% between 1 and 3 bar, and an approach to hydraulic saturation (maximum achievable flow) at 3.4 bar, due to geometric constraints. In addition, the results indicated that at 0.2 bar inlet pressure, the nozzle produces single, coarse droplets. As pressure increases to 1.6 bar and above, the spray pattern evolves into two distinct, separate jets: an outer spray (Spray 1) and an inner spray (Spray 2). While increasing the inlet pressure from 1.6 to 3.4 bar causes the outer spray cone angle to expand significantly (from 64° to 121°), the inner spray cone angle remains remarkably stable at approximately 30°. These experimental findings can be used to rigorously verify the accuracy of the corresponding CFD simulations, providing necessary experimental validation for the models.