Decode the 100-year mystery of the howling kettle

Researchers have finally deciphered why the whistle-boiled kettle boils - a puzzle for the scientific community for more than 100 years.

Two researchers from the University of Cambridge (UK) were able to describe how sound was produced inside a kettle with a whistle when the air flowed through the taps. They were then able to point out two separate mechanisms, which not only produced sounds but also warmed horns, instead of making loud noises like the steam created in other household products, such as hairdryer.

A basic whistle in a kettle consists of two metal plates that fit together, forming an empty cavity. Both metal plates have a hole in the middle, allowing steam to pass through.

Although the sound of a kettle with a whistle is understood to be due to fluctuations in the accumulation of water vapor, trying to escape, the scientists have tried to understand the exact mechanism of this process.

Photo: online.wsj.com

Ross Henrywood and Anurag Agarwal, two researchers from Cambridge University, began by making a few simplified horns, then testing them in a measuring device to force air through them. with different speeds and record the sound they create.

This allows them to map the frequency and amplitude of sound, then analyze these data to identify trends.

Finally, they used two microphones to determine the frequency inside the taps. The results show that, on a certain air flow rate, sound is produced from small vortices (swirling flow area).

When the steam rises on the warm tap, it encounters a hole at the head of the whistle, which is much narrower than many taps. This area shrinks the air stream as it enters the horn and creates a steam nozzle that passes through.

The unsustainable steam nozzle, like a sprinkler sprinkler, always begins to crumble into droplets when it reaches a certain distance. Therefore, when approaching the end of the horn, the steam nozzle is no longer a whole block, but a little disturbed. These unstable blocks cannot escape out of the horn completely and when approaching the second wall of the horn, they form a small pressure pulse.

Pressure pulses will cause the vapor to form vortices when escaping from the whistle. The vortices would then produce sound waves, leading to a siren formation.

The findings of the Henrywood and Agarwal researchers are expected to help engineers know how to prevent loud, offensive noise arising from a similar mechanism in household plumbing or toxic car exhaust exhaust pipe.