Here’s one of the coolest 10-second YouTube clips you’re likely to see. It’s the researchers at the Pentagon’s Defense Advanced Research Projects Agency putting out a fire with sound.
How did they do it? Well, as the DARPA website explains, traditional approaches to extinguishing have always focused on the chemical side of fire. However, researchers have long theorized that fires could also be put out by bringing physics into the equation.
In the video test, two dynamics were at play:
First, the acoustic field increases the air velocity. As the velocity goes up, the flame boundary layer, where combustion occurs, thins, making it easier to disrupt the flame. Second, by disturbing the pool surface, the acoustic field leads to higher fuel vaporization, which widens the flame, but also drops the overall flame temperature. Combustion is disrupted as the same amount of heat is spread over a larger area.
DARPA isn’t yet sure how to scale this sort of thing down to the point where it’s practical and usable. But, with the rate at which technology improves, perhaps the inevitable iPhone 10 will feature a fire-extinguishing app.