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Atomization and Sprays
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ISSN Imprimer: 1044-5110
ISSN En ligne: 1936-2684

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Atomization and Sprays

DOI: 10.1615/AtomizSpr.v15.i5.40
pages 545-566

INFLUENCE OF INERT SPRAYS ON EXTINCTION OF PREMIXED FLAMES PROPAGATING IN A DUCT WITH VARYING CROSS-SECTIONAL AREA

Chih-Hsin Tsai
Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan 70101, Republic of China
Ta-Hui Lin
Department of Mechanical Engineering, National Cheng Kung University, Tainan 70101, Taiwan ; Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 70101, Taiwan

RÉSUMÉ

The extinction of a premixed flame propagating in a duct with varying cross-sectional area under the influences of flame stretch, preferential diffusion, and water sprays is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode are identified on the basis of a critical value of the initial droplet size (rc′) for completing the vaporization process at the flame. The liquid loading and droplet size of the water spray induces internal heat loss through liquid vaporization. It is found that the burning intensity of a flame with water sprays is reduced with increasing liquid loading or decreasing initial droplet size, independent of the value of Lewis number (Le). Small droplets can absorb heat from the flame more effectively than large ones. However, it is not beneficial to reduce droplet size below the critical initial droplet size. The negative (or positive) stretch weakens (or strengthens) a Le < 1 flame but intensifies (or reduces) a Le > 1 flame. A positively stretched flame with Le > 1 or a negatively stretched flame with Le < 1 can be extinguished by increasing the effect of stretch, and this behavior is characterized by a C-shaped extinction curve. For a Le < 1 flame enduring positive stretch or a Le > 1 flame experiencing negative stretch, extinction does not occur for the completely prevaporized mode. However, for the partially prevaporized mode, the S-shaped extinction curve occurs if the liquid-loading water is large enough and the droplet size is also sufficiently large. Note that extinction characterized by a C-shaped curve is dominated by flame stretch; whereas extinction, characterized by an S-shaped curve, is governed by internal heat loss.


Articles with similar content:

INFLUENCE OF WATER SPRAYS AND HEAT LOSS ON NEGATIVELY AND POSITIVELY STRETCHED CURVED PREMIXED FLAMES
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EXCESS ENTHALPY THEORY OF SPRAY DEFLAGRATION
ICLASS 94
Proceedings of the Sixth International Conference on Liquid Atomization and Spray Systems, Vol.0, 1994, issue
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LEWIS NUMBER AND VAPORIZATION EFFECTS IN SPRAY DIFFUSION FLAMES
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GROUP COMBUSTION BEHAVIOR OF DROPLETS IN A PREMIXED-SPRAY FLAME
Atomization and Sprays, Vol.7, 1997, issue 2
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