On the trajectory and reach of fire-suppressant liquid nitrogen droplets released from a spray nozzle

Abstract

Liquid nitrogen (LN2) can be used to supplement or replace currently used fire extinguishers in challenging fire situations. This environmentally-benign cryogenic fluid can be produced readily from deep refrigeration of air. This manuscript addresses the application of liquid nitrogen to fires through a nozzle. Its aim is to investigate the survivability of LN2 droplets, following breakup of the jet exiting the nozzle, and the amount of liquid that reaches a target. Numerical simulations were carried out to explore the effects of relevant parameters, such as the initial droplet size and velocity, the droplet injection angle, and the thermal radiation on the droplet flight distance and the liquid droplet mass. The results indicate that all these parameters influence the fate of the LN2 droplets. Coarse atomization, high initial velocities, short nozzle-to-target distances, and shallow jet angles maximize the amount of the cryogen delivered to the target. A small-scale experiment was performed to test the results of the calculations. The comparison of the experimental results and the theoretical calculations was deemed satisfactory. In both cases the reach of the liquid droplets was in the order of 1 m from the nozzle, for an initial droplet velocity in the neighborhood of 20 m/s as measured in the experiments.