EFFECT OF EVAPORATION ON TRAJECTORY OF FIREFIGHTING WATER JET

Abstract

Water has become the most widely used fire-fighting agent because its fire suppression performance is hard to beat. The thermal characteristics of water make it ideally suitable as an extinguishing agent for most types of fire, whether it is used to extract heat directly from the flames, the hot products of combustion or from the surface of the fuel. The phase change from liquid water to water vapour (steam) is particularly effective in extracting thermal energy and the production of large quantities of water vapour may further contribute to fire extinguishment by reducing the oxygen concentration of the surrounding atmosphere, particularly where the fire is confined. Computer simulation of the water jet trajectories, with and without interference of air and flame temperature is developed and discussed. Both drag force, and evaporation loss were considered as interference due to air. Evaporation of water droplets was analyzed by solving simultaneous mass and energy conservation equations whereas momentum equation was used to account for the drag force. Effects of various other parameters like nozzle diameter, exit velocity, pressure, and surface tension of the liquid on the initial and final droplet size, and range of trajectory were also studied. The range of the trajectories was found to be 15 to 25 percent less than that predicted without air interference, because flame temperature and air temperature as well as velocity reduce the range of the trajectory. Also, it was observed that in case of interference with air and flame temperature, lower angle of nozzle from the horizontal gives the more effectiveness for fire extinguishment as compared to the larger angle.