ID 202

Velocity and droplet concentration measurements of water mist suppressing a diffusion flame

 

Abstract:

Water mist, as an effective fire suppressant, works on the principle of oxygen dilution and flame cooling. The recent re-emergence of water mist is attributed to its candidacy as a Halon-replacer, as Halon is being phased out. Also, water mist systems use less water as compared to sprinklers. Deep insight into the physical process of mist-fire interaction is lacking but is crucial for developing suppression systems.

The present work concerns the interaction between water mist and a flame.  A simple methane fed circular burner generates a diffusion flame.  Pressurised water fed into a Delavan nozzle generates the water mist and is positioned right above the burner at a variable height.  A glass cubicle encloses the entire system to isolate experiments from the surroundings.  A camera mounted on a traverse captures the light scattered by those droplets passing through a laser sheet generated from a Nd:YAG laser. The variation of parameters includes the nozzle-burner separation distance, injection pressures and heat release rates from the burner.

Employing the PIV technique yielded the velocity field of the mist with and without the flame.  The presence of flame causes mist entrainment into flame, close to the burner mouth. Also, an increased droplet number density near the spray edge indicates widening of the spray in the presence of a flame. Furthermore, one can observe clustering of droplets near the flame tip. These results will add to the repository of data that can validate various fire suppression models being developed.