2
$\begingroup$

You may have seen the recent story of a device that engineers claim can extinguish flames using sound frequency. An older article loosely explains the theory behind how this works:

Sound travels in waves, which are simply variations of pressure in a medium—whether solid, liquid or gas. The energy from vibrating objects, such as speaker membranes, moves from particle to particle in the air in a repeating pattern of high- and low-pressure zones that we perceive as sound. According to the ideal gas law, temperature, pressure and volume are related; therefore, a decrease in pressure can lead to a corresponding decrease in temperature, which may explain how sound can extinguish a flame.

Like most readers and the journalists sensationalizing this story, I don't have much understanding of the laws of physics that apply here. But it made me curious to ask those who know: Does it stand to reason that altering the frequency appropriately could increase air pressure or otherwise be used to create more ideal conditions needed for fire?

$\endgroup$
4
$\begingroup$

A reasonable sub woofer at sound power level of 130 dB would produce pressure fluctuations of 60 Pa. Compare this to the ambient pressure of 100'000 Pa and you will see that related temperature fluctuations would be negligible.

It extinguishes fire because it pushes the air back and forth. For the small fire in this video you could take a small air blower and blow off the flame much quicker. Of course, stronger flame will not be extinguished by an air blower (on the contrary!), but I'm afraid that for such flame a loudspeaker also won't do much.

In closed or semi-closed environments (furnaces, rocket engines) the reflected sound can resonate with the flame, leading to flame extinction or amplification. Such interactions are studied by thermoacoustics. But this has little to do with the demonstration in this video.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.