Dynamics and Suppression Effectiveness of Monodisperse Water Droplets in Non-Premixed Counterflow Flames
NAVAL RESEARCH LAB WASHINGTON DC CHEMISTRY DIV
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In situ measurements of velocity and size distributions of initially monodisperse water mists of initial diameters ranging from 14 micrometers to 42 micrometers seeded into the air stream of non-premixed propaneair counterflow flames are reported. Droplets were generated piezoelectrically, and the size and velocity distributions and the number density were determined by phase-Doppler particle anemometry. Droplets having initial diameters of 18 micrometers underwent complete vaporization in a counterflow flame at a strain rate of approximately 170 s-1, while droplets of 30 micrometers penetrated slightly beyond the visible flame zone. Measurements of the effect of water droplets on the extinction strain rates of propaneair counterflow flames were performed. Droplets having initial diameters of 14 micrometers and 30 micrometers were found to have similar suppression effectiveness, while droplets of 42 micrometers were substantially less effective at reducing the extinction strain rates. Both the 14 micrometer and 30 micrometer water droplets were found to be more effective, on a mass basis, than CF3Br. The present experimental results are in excellent agreement with the predictions of recent modeling studies exploring the behavior of various sized water droplets in counterflow flame.
- Combustion and Ignition
- Fluid Mechanics