On water mist fire suppression mechanisms in a gaseous diffusion flame

Ndubizu, C. C.; Ananth, Ramagopal; Tatem, Patricia A.; Motevalli, Vahid

doi:10.1016/s0379-7112(98)00007-1

Cited by 72 publications

(32 citation statements)

References 8 publications

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“…It is interesting that the computer simulations show that the water extinction concentration (mass %) is about one third that of nitrogen. This is consistent with the thermodynamic argument made by Ndubizu et al [7], which showed that the oxygen dilution effect is about one third of the total.…”

Section: Resultssupporting

confidence: 93%

“…Evaporation of water drops includes three effects: oxygen dilution, latent heat absorption, and extra sensible heat absorption due to the higher specific heat of water vapor than air [7,9]. Therefore, the evaporation rate plays a key role that is absent for gaseous extinction agents.…”

Section: Resultsmentioning

confidence: 99%

“…Measurements of fuel temperature, composition, and velocity at the exit of the inner tube are not yet available. However, Ndubizu et al [7] measured a fuel temperature of about 623 K at the exit of a slot burner filled with sand. This is because of heat feed back upstream by conduction and radiation from the flame to the sand particles at low fuel velocities, which are typically encountered in co-flow burners.…”

Section: Theoreticalmentioning

confidence: 99%

“…Most previous fire suppression studies [2][3][4] with water droplets have considered droplets from sprinklers and high pressure spray nozzles [5][6]. Ndubizu et al [7] conducted experimental studies of water mist suppression of co-flow, methane diffusion flames formed in a slot burner (Wolfhard-Parker burner) and for pool fires [8]. They used high-pressure nozzles to form mists with Sauter mean diameter (SMD) of 30 to 66 μm.…”

mentioning

confidence: 99%

“…They showed that the flame temperature is reduced significantly at 7% mass fraction of water (SMD 66 μm) in the inlet air used for co-flow. Prasad et al [9] modeled the experiments of Ndubizu et al [7] by solving full Navier-Stokes (NS) equations, and using Eulerian-Eulerian sectional approach. The model predicted that the extinction concentration increases monotonically from 17.5 to more than 50% by mass as the drop size is increased from 50 to 150 μm.…”

mentioning

confidence: 99%

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Extinction Dynamics of a Co-flow Diffusion Flame by Very Small Water Droplets Injected into the Air Stream

Ananth¹,

Mowrey²

2008

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Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Computations are performed to examine the effectiveness of mono-disperse water droplets in extinguishing a co-flow, propane diffusion flame by injecting the droplets into the air stream. The calculations show that the droplets entrained into the reaction kernel at the flame base are crucial for extinction. The reaction kernel detaches from the burner rim and blows-off when the droplet concentration is increased to a critical value (extinction concentration). At the critical value, the maximum chain-branching reaction (H2+O=OH+H) rate in the reaction kernel was found to be reduced by a factor of 5 in our computations. A large decrease in the reaction rate indicates that the maximum heat generations rate and Damkholer number are too low to sustain the flame, and cause the flame blow-off. Large drops are more effective than small drops, and the extinction concentration of water increases from 10.5% to 15% by mass as the size is reduced from 32 to 4 micro m. As the droplet size is increased further (>32 micro m), the trend will reverse as the evaporation rates get too small despite increased penetration of flame core by the drops. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S ACRONYM(S) 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S REPORT NUMBER(S) 28-07-2008Memorandum Report

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Section: Resultssupporting

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Theoreticalmentioning

confidence: 99%