What Causes the Pinging Sounds When Boiling Water in a Kettle?

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Discussion Overview

The discussion revolves around the phenomenon of pinging sounds produced when boiling water in a kettle. Participants explore the underlying causes of these sounds, including the role of bubble dynamics and temperature changes, as well as variations in kettle design and water volume. The scope includes both conceptual and experimental aspects of boiling water.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the pinging sounds occur as the water approaches boiling, suggesting a phase transition when the kettle begins to whistle.
  • Another participant proposes that the sounds may be related to the degassing of water and the behavior of bubbles, which affect sound propagation.
  • A different viewpoint describes the popping of small, local steam bubbles that collapse due to cooling, likening it to cavitation but with different causes.
  • One participant shares an observation that when boiling a smaller amount of water, the boiling sounds become louder instead of quieting down, inferring that the pinging may be due to bubbles detaching from the kettle's metal surface.
  • Another participant elaborates on the factors influencing the sounds, including the temperature at which degassing occurs, the power supplied for boiling, and the kettle's design, which can amplify certain sounds.
  • There is mention of distinct 'cracking' sounds at the onset of boiling, particularly with freshly drawn water, indicating variability based on conditions.

Areas of Agreement / Disagreement

Participants express various hypotheses regarding the causes of the pinging sounds, with no consensus reached. Multiple competing views remain on the specific mechanisms involved.

Contextual Notes

Participants acknowledge that factors such as water volume, kettle design, and thermal contact may influence the sounds produced, but these aspects remain unresolved and are subject to individual interpretation.

Who May Find This Useful

This discussion may be of interest to those curious about the physics of boiling, sound propagation in liquids, and the effects of different kettle designs on boiling behavior.

Hornbein
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I boil water in a tea kettle. When it's starting to boil there are pinging sounds. These grow louder until there is some sort of phase transition and they quiet down. That's about when the tea kettle starts to whistle. What's going on?
 
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Yes, that's how it goes. I don't have a real answer, only a guess: it is related to the water degassing (solubility of gases goes down with the temperature) and size/presence of the bubbles in water (which change the way sound propagates in water).
 
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As far as I know it's about small, local bubbles of steam popping up and then collapsing when cooling down due their expansion and rise. Kind of like (mechanical) cavitation, just different reason.
When the energy available is finally enough to keep the bubbles going it quiets down (and start boiling).
 
To make coffee I pour a cup of water into the tea kettle and boil that. In this case the boiling doesn't quiet down, instead it gets louder. I (infer?deduce?) that the pinging sound comes from bubbles detaching from the metal surface of the kettle. If the water is deep enough then most of the later bubbles form away from the surface. If the water is shallow then most of the bubbles continue to detach from the metal.
 
Hornbein said:
To make coffee I pour a cup of water into the tea kettle and boil that. In this case the boiling doesn't quiet down, instead it gets louder.
It seems to me that there are at least two factors here. De-gassing takes place at relatively low temperatures (singing kettle due to many small bubbles) and actual boiling will happen at around 100C. The rate of boiling, after 100C, will depend on the power supplied and the noise will depend on the specific surface and even details of thermal contact between element and water. 'Bumping' is the descriptive term for what you can get under some conditions. Also, the size of a typical kettle can give resonances to the sound inside it and sound louder for some kettles than others

Your small mass of water probably goes quickly through the stages. A kettle full of water (or even an urn) can produce the different effects at noticeably different times. I notice our kettle starts of (a few seconds after switch on) with distinct 'cracking' sounds for a short time, particularly with freshly drawn water.

You should take care, here. You could get addicted to the sounds plus the taste of coffee/.
 
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