Chaotic amplification?

Factual Questions
1

I recently bought a clear glass kettle which has a flat plate element; it’s fascinating to watch it boil (and yes, it does actually boil when watched).

I happened to notice that if I switch it on to boil when the water inside is still, the water will be still when it is finished boiling (after the bubbles subside); no surprise, you might be saying.

But I also happened to notice that if the water is sloshing(for want of a better word) from side to side when it is switched on, the water will be sloshing from side to side more when it finishes.

If the water is sloshing around in a circular motion (the vessel is almost spherical in shape), again, the movement will be greater when the water is finished boiling.

It is interesting that even though the water can be moving quite considerably when the kettle is switched on, this will have damped down to very little by the time the water starts to bubble

I have three hypotheses:
1: The chaotic bubbling of the boiling water somehow amplifies existing motion.
2: when the water sloshes to the left, the thinner layer of water remaining at the right heats up quicker than the thick layer of water at the left and vice versa. The increased heat on one side causes convection currents (or expansion, or something) causing forces that contribute to the motion of the water.
3: It is an observational fluke and/or Mangetout is going mildly insane, but I have observed this quite a few times now.

2

I think I recognise most of the words.

I think they comprise some sentences.

I think my head hurts.

3

[bump]
Maybe I should have framed a question:

Is there such a thing as chaotic amplification and how does it work?

4

I vote for 3. 1 and 2 might be happening, but I don’t see any obvious way that the initial sloshing or swirling would be preserved through prolonged boiling. Boiling can drive oscillatory processes though. Geysers are a good example of this, but you can also see an oscillation when a liquid boils in a container with sloping sides. Do you have a Wok ?

5

Hmmm, so it looks as if I have a weekend of kettle observation ahead of me.

6

Well, if it’s raining and there are no convenient apple trees to sit under in hopes of inspiration :slight_smile:

7

My first thought: 3:. crackpot. Mods, you can close this thread now.
My second thought: Do I get closer to my brain if I put my finger in my nose or in my ear :confused:
Then I made tea … and I saw nothing but bubbly water.

Anyway, it does not violate any laws of thermodynamics to build up motion, since you push a lot of energy through the water.

If anything, i’d vote for the geyser effect, you know, where a column of hot water is prevented from boiling by it’s own hydrostatic pressure, until the steam pushes the water up, lowering pressure and boiling point, more steam pushes more water… chuff, chuff, wooosh! :smiley:

Of course not that violent in your kettle, but probably it can create or intensify an oscillation.

In the Do bathtubs drain counterclockwise in the Northern Hemisphere?-column the water kept it’s initial motion for hours,
so a bit of sloshing will certainly have an effect: as much as coriolis on the bathtub.
If there will be an oscillation, it builds up anyway.

…Yep, 3:. :slight_smile:

Oh, instead of ‘sloshing’ try ‘chaotic multiphase flow dynamics of nucleate boiling’.

[ul][li]Someone creates true random numbers from the video of a lava lamp.[/li][li]Here’s a schlieren photo of a water kettle.[/li][li]And if it helps, here’s a site showing you’re not the only bubble-counter.[/li][/ul]
Combine the imaging method of the one with the statistics of the other, sprinkle it with the insanity of the remaining, and maybe…

Mangetout, whatever you have, it’s contagious. :frowning:

8

Mangetout, i will go with (d), none of the above, but actually (1).

here’s what i’m imagining: the water is still, and you put it on to boil. the currents that arise are going in a (for want of a better term) inside-out doughnut. the only real motion is away from the center, initially up but bending over backwards (still away from the center) and then moving down along the side of the pot.

you dig? like a torus.

now, let’s look at a pot of water that’s ‘sloshing’. from above, the water is going clockwise. when boiling starts, the doughnut-torus pattern arises, but it’s also rotating clockwise.

so it’s less that the clockwise motion is amplified, as much as it is sustained.

i think.
jb

9

Ah! Toroidal convection, that made me think of Why do the bubbles in Guinness Stout float down?, though I think a less viscous fluid like water will produce something more local, like Rayleigh-Bénard convection cells.

This site shows that they can produce pretty spiral patterns, which one could translate to ‘sloshing around’, but that’s a rather calm bubble-less convection, not the chaotic kettle we’re talking about.

A rotating torus may be stable, but if you additionally turn that system you’ll introduce a Coriolis force (this time the ‘real’ one) on the already distressed particles. There will come out something at least as contorted as the field of a tokamak.

If anyone can solve that, maybe the fluid dynamics guy who computed the Guinness bubbles, or the one from Cecil’s shower curtain vortex.
Eat this: The Spatial Structure of Turbulent Rayleigh-Benard Convection

casdave, now my head is hurting, too.