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Flame Spread in a Vitiated Concurrent Flow.


pdf icon Flame Spread in a Vitiated Concurrent Flow. (215 K)
Chao, Y. H.; Fernandez-Pello, A. C.

American Society of Mechanical Engineers (ASME). Heat Transfer in Fire and Combustion Systems. HTD-Vol. 199. Book No. H00757-1992. 1992, Am. Soc. of Mechanical Engineers, New York, NY, Kanury, A. M.; Brewster, M. Q., Editor(s)(s), 135-142 pp, 1992.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Keywords:

flame spread; solid surfaces; experiments; gas flow; oxygen concentraton; velocity; oxygen concentration

Abstract:

Experiments have been conducted to study the effects of forced gas flow velocity and oxygen concentration on the flow assisted flame spread over a flat solid combustible surface. All the tests are performed with thick PMMA Sheets as fuel and mixtures of oxygen and nitrogen as oxidizer. The spread rate is measured for flow velocity ranging from 0.5 to 2.0 m/sec and oxygen mass fraction from 0.19 to 0.23. It is found that the flame spread rate increases linearly with the main flow velocity and the oxygen concentration within the experimental conditions. In order to determine the effect of buoyance on the flame spread rate, data in the ceiling and floor configurations are compared. The exhaust gas composition are also measured to detect possible buoyancy effects on the chemical reactions in the flame. Despite the overall similarity between the characteristics of ceiling and floor surface flame spread, some substantial differences have been observed. The experimental results indicatethat buoyancy has two main effects in the ceiling case, one is the enhancement of heat transfer from the flame to the solid surface, and the other is the flame quenching through cold wall effect. For large flow velocities, the enhanced heat transfer is found to be dominant and results in a faster flame propagation in the ceiling than in the floor. For low flow velocities, the flame quenching effect becomes more important and the opposite result is observed. The transition velocity decreases as the oxygen mass fraction decreases.