Water Mist Suppression of PMMA Boundary Layer Combustion - A Comparison of NanoMist and Spray Nozzle Performance

Ndubizu, Chuka C.; Ananth, Ramagopal; Williams, Frederick W.

doi:10.21236/ada426605

Cited by 6 publications

(17 citation statements)

References 19 publications

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“…Extrapolating their calculations to zero air velocity gives an extinction water concentration of 12.5 mass %. Extrapolation of the measurements by Ndubizu et al [18][19][20] of the extinction mist concentration also gives similar results. This extinction value for PMMA flame is only slightly smaller than the values shown in Figure 9a for 4 to 8 µm drops for the coflow geometry.…”

Section: Resultssupporting

confidence: 75%

“…Ndubizu et al [18][19][20] conducted experiments on the effects of UFM on a forced convection boundary layer flame formed over a burning polymethyl-methacrylate (PMMA) plate. They measured droplet distribution curves (volume frequency % vs diameter), which show a peak at 6 µm, SMD in the rage of 3 µm, and 90% (by volume) of the droplets have sizes below 20 µm.…”

mentioning

confidence: 99%

“…The water droplets are injected into the air flow over the burning plate. Ndubizu et al [18][19][20] showed that, at a fixed inlet air velocity, the flame detaches from the leading edge of the plate and blows off as the UFM mass fraction is increased to a critical value (extinction concentration). The extinction water mass fraction was shown to decrease linearly from 7 to 1.5% as the inlet air velocity is increased from 60 to 120 cm/sec.…”

mentioning

confidence: 99%

“…The extinction water mass fraction was shown to decrease linearly from 7 to 1.5% as the inlet air velocity is increased from 60 to 120 cm/sec. Ananth et al [21,22] modeled the PMMA experiments of Ndubizu et al [18][19][20] and obtained computational solutions of the time dependent Navier-Stokes equations for the extinction of the PMMA boundary layer flame due to the injection of monodispersed water droplets. They used an Eulerian-Eulerian sectional approach to model the droplet dynamics and showed that the degree of droplet evaporation near the leading edge of the flame plays a key role in extinguishing the flame.…”

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: 75%

mentioning

confidence: 99%

mentioning

confidence: 99%

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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“…Laboratory-scale studies on the effectiveness of UFM are lacking. Recently, Ndubizu et al [13] conducted suppression experiments on boundary layer flames over a PMMA plate. They studied the effects of flow velocity on the extinction concentration of UFM and showed that the extinction concentration decreases linearly with flow velocity.…”

Section: Introductionmentioning

confidence: 99%

Suppression and Extinguishment of Boundary Layer Flame over Communication Cable by `Gas-like' Water Mist in Cross-flow

Ndubizu

Ananth

Williams

2008

Journal of Fire Sciences

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Fire suppression experiments are performed with `gas-like' water mist in cross-flow on bare (without PVC jacket) communication cables to simulate a worst-case scenario. As fine water droplets are injected at low velocities, an initial envelope flame that engulfed the circumference of the cable recedes and forms a wake flame stabilized behind the cable. At high-mist concentration and/or high-air velocity, the flame is extinguished by shrinking rather than blowing-off, which is the case in flat plate boundary layer flames. The results show that ultra fine mist (UFM, Sauter mean droplet diameter, SMD = 3 μm) seems to be more effective in reducing the extinguishment time than high-pressure spray nozzle mist (SMD = 20 μm), which introduces spray-induced turbulence. The cable flame is extinguished rapidly after a threshold UFM concentration is exceeded. The threshold concentration decreases with increased air velocity. Finally, the copper cylindrical mesh, which is part of the cable, significantly enhances the effectiveness of UFM in flame extinguishment.

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Water mist suppression of a turbulent line fire

White

Verma

Keller

et al. 2017

Fire Safety Journal

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Water Mist Suppression of PMMA Boundary Layer Combustion - A Comparison of NanoMist and Spray Nozzle Performance

Cited by 6 publications

References 19 publications

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

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

Suppression and Extinguishment of Boundary Layer Flame over Communication Cable by `Gas-like' Water Mist in Cross-flow

Water mist suppression of a turbulent line fire

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