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Velocity and droplet concentration measurements of downward directed water mist suppressing a diffusion flame
R. Karthikeyan, , S.R. Chakravarthy
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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, for 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 methane fed circular burner generates a diffusion flame. Pressurized water fed into a Delavan nozzle generates the water mist and is positioned right above the burner at a fixed 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 spray 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 velocity field results indicate that the droplets are slowed down very close to the nozzle due to the flame. Also, a recirculation zone is observed at the periphery of the spray cone, very close to the nozzle. It is a toroidal vortex that is generated due to the interaction, and the droplets thrown away from the spray cone gets trapped into this flow. The flow structure is present in a highly turbulent region and is identifiable only in the mean flow. Another finding is that close to the burner, fine droplets that could make it to the base, gets entrained into the flame. It is expected that the droplets to be greatly entrained into the larger flame, as the entrainment is stronger for large flame, compared to the smaller flame. But the PIV results indicate otherwise. Also, an increased droplet number density near the spray edge indicates widening of the spray in the presence of a flame. These results will add to the repository of data that can validate various fire suppression models being developed. © 2018 Solar Turbines Incorporated.
About the journal
JournalICLASS 2018 - 14th International Conference on Liquid Atomization and Spray Systems
Open AccessFalse