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Can anyone tell me... (Get ready for Science!) - 4/13/2013 7:10:43 AM

tommonymous

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I've been thinking about this for the last couple of days, but I can't come up with any answer.

When I heat water for tea, I take the pot off the element after it's been whistling for a few seconds. (It's a fairly healthy whistle before I take it off, but by no means as loud as it gets.) Every time I slide the pot, the whistle gets just a little more shrill, or frantic, as the pot comes off the element. I'd say the peak volume is when the last quarter of the pot is being heated.

Why does this happen? Sometimes bad things happen to good teapots? Like I said, I've been thinking about this for a couple of days, and can't come up with anything, so it's time to ask. I'm feeling lazy this morning, so asking is happening before researching.

Thanks all.

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 7:14:01 AM

thezeppo

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You must have some kind of deadline coming up mate, you're procrastinating harder than me!

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 7:15:42 AM

kdsub

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Maybe it is as simple as the water splashing up on the super heated sides of the tea pot. Heat an open pot of water…just when it begins to boil shake the pot and see the instant production of steam as the water splashes up the sides.

Butch

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 7:21:12 AM

Toysinbabeland

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when the volume of water that is heated is jostled, it displaces more air from the pot in an accelerated ratio.
The acceleration is proportionately displayed.

Edited for typo

< Message edited by Toysinbabeland -- 4/13/2013 7:22:24 AM >

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 7:27:52 AM

tommonymous

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The super-heated sides and the jostling of the air in the pot both make a lot of sense. Thanks all!

thezeppo, believe it or not, I got my taxes done last night. (That's the big deadline right now in the States. Seriously, it gets ridiculous.) But yeah, that's definitely a procrastinator's question.

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 7:30:30 AM

ResidentSadist

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When you move the pot, water hits the hot sides and generates even more steam.

Mystery solved.

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 11:29:51 AM

FrostedFlake

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It's gremlins.

Except in California, where gremlins are illegal.

In California, it's illegal gremlins.

It seems a fine point, but I am given to understand that a good enough lawyer can explain the difference.

And a great lawyer can win, even in California.

I hope that helps.

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 12:59:42 PM

fringeview

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Motion of the liquid water wouldn't appreciably displace gas from the pot – the volume of the liquid isn't changing, hence no increase in pressure to force gas out. The heated sides may have an effect in some cases, but I suspect the effect is largely caused by other factors.

In the interest of Saturday morning science/procrastination, I boiled some water in a teapot on low heat with a thermometer placed against the external side of the pot a bit above the water level. The temperature reading when the pot began to whistle was still below the boiling point, which would preclude heat transfer from the pot to the fluid, but the increase in whistle intensity was still present when removing the pot from heat and sloshing the liquid around.

So, what might be causing it? At the boiling point, the water is able to change phase from a liquid to a gas, but the surface tension and viscosity of the liquid can slow the process down a bit. There's also a limited surface area for exchange of gas between the boiling, two-phase fluid in the bottom of the pot and the gas in the top. Jostling the pot while removing it from the heat probably disrupts some of the surface tension retarding bubble expansion, allowing gas bubbles to expand and rise more rapidly, and the sloshing surface opens up more area at the fluid interface for gas to escape into the top of the pot. The end result is a sudden, but brief, increase in the rate of gas released into the top of the pot, which in turn raises the pressure and forces gas out of the pot at a higher rate, increasing the whistle intensity.

At any rate, that explanation – and the cup of Lupicia rhubarb and strawberry tea produced along with it – satisfied me. :)

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 1:03:13 PM

mnottertail

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Let us not whistle dixie and walk past the motion of the otion.

What effect is produced by the wave in the water changing the size of the chamber and acoustics, and raising or lowering pitch, as well?

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 3:18:45 PM

PeonForHer

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quote:

ORIGINAL: tommonymous
Every time I slide the pot, the whistle gets just a little more shrill, or frantic, as the pot comes off the element.

You're probably not getting to know it on a vanilla level before trying to get it to boil, tommonymous.

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 4:04:42 PM

FrostedFlake

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Y'know, when I'm watching the pot ( I know, I know) I can get to to cook a bit faster by rotating it a bit. 20 or 30 degrees or somesuch. You can hear it get more excited right away. Seems to boil sooner, though that might be imaginary. It could also be the muttering, the scowling or the threats have some effect.

Any thoughts?

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 5:04:07 PM

MercTech

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Mechanical agitation can stimulate a more rapid departure from nucleate boiling and cause a momentary increase in steam pressure.

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RE: Can anyone tell me... (Get ready for Science!) - 4/13/2013 5:23:55 PM

PeonForHer

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quote:

ORIGINAL: FrostedFlake

Y'know, when I'm watching the pot ( I know, I know) I can get to to cook a bit faster by rotating it a bit. 20 or 30 degrees or somesuch. You can hear it get more excited right away. Seems to boil sooner, though that might be imaginary. It could also be the muttering, the scowling or the threats have some effect.

Any thoughts?

I think it warms to your friendly beard and sensitive forehead, FF.

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