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A ‘Sound’ Experiment – DARPA Extinguishes Flames with Sound

Defense Advanced Research Projects Agency (DARPA) is showing off a new system that can put out flames using only sound [1]. It’s part of the U.S. defense agency’s Instant Fire Suppression program. Using two speakers arranged on either side of a pool fire, an acoustic field was emitted and engulfed the flame. The sound increases air velocity, which thins the boundary layer of the flame, making it weak and much easier to douse. “We have shown that the physics of combustion still has surprises in store for us” commented DARPA manager Matthew Goodman in a statement. “Perhaps these results will spur new ideas and applications in combustion research”. Lest you think this is really surprising, here are a couple of earlier mentions of the concept.

First, a Google search leads quickly to the Wikipedia entry for Charles Kellog [2] which cites the following from a 1926 newspaper article: “In The Sydney Morning Herald, Thursday, February 4, année 1926: Sound vibration – Extinguishes Fire: New-York, Feb. 2. 1926: Mr Charles Kellogg, a Californian scientist, give firemen here a demonstration of extinguishing a gas flame two feet high by tonal vibration. Mr Kellogg passed a bow, like an enlarged violin bow, swiftly across an aluminium tuning fork, producing a screech like an intense radio static. Instantly the yellow flame subsided to six inches and became a sputtering blue flare. Another movement of the bow completely extinguished the flame. Mr Kellogg claimed that in future buildings would have a scientifically-determined pitch, with a screech for extinguishing fires tuned in from a central firehouse, where it would be produced by a much larger bow. He said that the General Electric Company was experimenting with the matter”.

Second, from a book The Theory of Sound published in 1896 by Lord Rayleigh, 1904 Nobel Prize winner for Physics [3]: “Singing flames may sometimes replace electrically maintained tuning-forks for the production of pure tones, when absolute constancy of pitch is not insisted upon. In order to avoid progressive deterioration of the air, it is advisable to use a resonator open above as well as below. A bulbous chimney, such as are often used with paraffin lamps, meets this requirement, and at the same time emits a pure tone. Or an otherwise cylindrical pipe may be blocked in the middle by a loosely fitting plug (Phil. Mag. vol. vii. p. 149, 1879).

Vibrations capable of being maintained are not always self-starting. The initial impulse may be given by a blow administered to the resonator, or by a gentle blast directed across the mouth. In the striking experiments of Schaff’gotsch and Tyndall (Sound, 3rd edition, p. 224, 1875) a flame, previously silent, responds to a sound in unison with its own. In some cases the vibrations thus initiated rise to such intensity as to extinguish the flame.”

 

by Jack Watts. Fire Safety Institute, USA, and Associate Editor of Fire Safety Science News REFERENCES 1. Video: Darpa’s ‘Wall-of-Sound’ Fire Extinguisher, Wired, July 13, 2012. http://www.wired.com/dangerroom/2012/07/wall-of-sound-fire 2. Wikipedia contributors, ‘Charles Kellogg (naturalist)’, Wikipedia, The Free Encyclopedia, 26 June 2012, 20:24 UTC, http://en.wikipedia.org/w/index.php?title=Charles_Kellogg_(naturalist)[accessed 30 August 2012] 3. Rayleigh, John William Strutt, The Theory of Sound vol.II , 2nd ed., Macmillan, London, 1896, p. 228. —

 
 
 
 
 
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