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Why are Pool Fires Anchored?


pdf icon Why are Pool Fires Anchored? (176 K)
Venkatesh, S.; Ito, A.; Saito, K.

NISTIR 5904; October 1996.

National Institute of Standards and Technology. Annual Conference on Fire Research: Book of Abstracts. October 28-31, 1996, Gaithersburg, MD, 37-38 pp, 1996.

Sponsor:

NASA Kennedy Space Center, KSC, FL

Available from:

National Technical Information Service
Order number: PB97-153514

Keywords:

fire research; fire science; pool fires; flow visualization

Abstract:

This paper attempts to answer the question, "Why are small scale pool fires anchored?" by providing and interpreting a new set of experimental data. For momentum-controlled, high Reynolds (Re) number turbulent-jet diffusion flames, the formation of a premixing zone is suggested as the primary reason for the flame anchoring. For buoyancy-controlled pool fires, however, the existence of the premixing zone at the flame base is not clear because both Re and Fr (Froude number) are low. To improve our understanding of the flame anchoring mechanism and structure of buoyancy-controlled liquid pool fires, we employed small scale pool fires whose diameters range between 1.5 - 20 cm. Our measurements include flow visualization by a particle-trace laser-sheet technique (PTLS) combined with a high speed video camera and temperature profiles by a fine thermocouple. We found from those measurements that major air entrainment occurred through the primary anchoring zone, PAZ, which consists of a small area covering approximately 1 cm high and around the circumference just above the dark zone; while air entraiment through the quenching zone (a dark zone formed between the visible flame edge and the burner port) was negligible. The structure of the PAZ was found to be premixed flame (another interpretation may be it is similar to counter-diffusion flame). This enables the pool fires to anchor at the burner port. In addition, we visualized the existence of a vortex ring at a stagnation zone in the fuel vapor phase for both propanol and hexane pool fires, in agreement with qualitative observation by other workers.