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Extinction Studies of Propane/Air Counterflow Diffusion Flames: The Effectiveness of Aerosols
Rept. for 12-14 May 1998
NAVAL RESEARCH LAB WASHINGTON DC
Pagination or Media Count:
The fire suppression effectiveness of solid aerosols as suitable halon replacements has examined. Experiments were performed in a counterflow diffusion burner, consisting of two 1 cm i.d. tubes separated by 1 cm. Aerosols were delivered to propaneair flames in the air flow. Both sodium bicarbonate NaHCO3 and potassium bicarbonate KHCO3 powders were examined. The NaHCo3 and KHCO3 powders were separated into various size groupings 38 , 38-45 , 45-53 , 53-63 , and 63-75 using a commercial sieving system. The agent delivery system incorporated a variable orifice for gross adjustment of the delivery rate, and a variable frequency vibration unit for fine adjustments and to maintain powder flow. Light scattering using a modulated HeNe laser beam and a lock-in amplifier was used to monitor the amount of powder exiting the air tube and entering the flame. Extinction concentrations were determined for each agent sample as a function of the strain rate of the uninhibited flame. In general, suppression effectiveness increased with decreasing particle size or increasing strain rate for the size range studied. Potassium powders were 2.5 times by weight more effective than sodium powders. The suppression effectiveness of these powders as a function of particle size can be interpreted using a simplified model of the behavior of particle in counterflow steams.
APPROVED FOR PUBLIC RELEASE