Noiseless teapot

[jimon]

Had a brain-fart today, why nobody makes noiseless teapots ?

As I understand actual noise is created because water close to heated surface heat up to 100 C and create small bubbles, which goes up a bit and collapse with ~100 Hz sound, while this is happening - surround water is still <100 C.

So why don't we put two thermocouples: 1) on a heater itself 2) somewhere close to top of water level. And we just regulate current through heating element so heater will not go over threshold temperature (let's say 70-90 C) until second thermocouples reach threshold temperature. Then we just go full throttle util we reach 100 C (with a bit of noise, but you can't make noiseless boiling water, so it's ok)

I see one reason why it will not work : to maintain heater at temperature X we need to cool down it with surrounding water by dissipating power without boiling off water close to header itself, and amount of power can be really small which will make boiling process really slow.

PS. What is the simplest compact way to control mains voltage for application like this ? (It's ~10 Amps)

[c4757p]

Easier way, perhaps: circulate the water.

But... why?

[jimon]

But... why?

In some cases teapots create too much noise (like boiling water in 2 AM for example), but it's more brain-fart idea =)

[Ian.M]

Take  a 3KW dimmer and an electric kettle and see how far you actually have to reduce the power to eliminate the noise.  To a first approximation, the time to boil from cold is  proportional to the volume of water divided by the applied power, and most people vastly prefer as short a boiling time as possible and don't really care about the noise.

I suspect that a better way of eliminating excessive noise would be to add a magnetic stirrer + make the element with a much larger surface area.

[Mr.B]

...make the element with a much larger surface area.

I have a Breville "Quiet Boil"
http://www.breville.com.au/the-quiet-kettle-bke490bs.html

It appears to achieve this using a combination of a larger surface area and "a special coating to make bubbles smaller"

It really does work. It is very quiet indeed.

[Jeroen3]

So why don't we put two thermocouples: 1) on a heater itself 2) somewhere close to top of water level. And we just regulate current through heating element so heater will not go over threshold temperature (let's say 70-90 C) until second thermocouples reach threshold temperature. Then we just go full throttle util we reach 100 C (with a bit of noise, but you can't make noiseless boiling water, so it's ok)

Expensive... kettles only have a heating element a latching switch and a thermal cutoff element. Try competing with that.

You do know there are taps with instant boiling water?

[Ian.M]

Anodized aluminium is *CHEAP* compared to adding electronics.  Simply make the element surface area large enough and shape it to encourage maximum convection currents (e.g. its diameter should be no more than 70% of the base to encourage a return down flow at the sides) so that its surface temperature doesn't exceed 100 deg C till the water is nearly boiling.  Maybe Teflon coat it to discourage scale from sticking.   It also keeps the boiling time short and makes it more resistant to damage if boiled dry as the increased thermal mass reduces the risk of hot-spotting before the cutout trips.

[IanB]

I was slightly confused by your subject title since my teapots have never made any noise 

On reading, I realized it was a language problem and you are referring to electric kettles. Yes, they make a sound, but the sound is a pleasant sound that bothers me not at all.

[Ian.M]

[hamster_nz]

But isn't the problem that the sound isn't caused by the rolling boil, but by the formation of small bubbles of steam on the element (that must be over 100C to transfer heat), that rise through the cooler water and then collapse causing the noise?

If I had to produce a silent water boiler I would make the heating element surface area big, keep the water in motion close to the element, and most importantly of all pressurize the system to raise the boiling point of water. At about 70 PSI you could have the heater at 150C without the water boiling (and therefore making noise), and as long as you don't heat the water above 100C it can't flash to steam when you pour it out.

[Deathwish]

wear ear protectors problem solved

[IanB]

I think the issue is that the heating element inside a kettle gets very hot (in my kettle it is trying to transfer 3 kW into the water). If you consider thermal gradients in terms of degrees Celsius per watt and think what gradient is needed to transfer 3 kW across the surface, it is clear that the heating surface is going to get very hot indeed. The sound is caused by cavitation: minute bubbles of steam form in contact with the heating surface and then collapse almost immediately as they contact the cooler surrounding water.

There isn't an easy way to make the process quieter without some cost in terms of longer boiling times or more complexity in the design. Longer boiling times worsen the user experience and increased complexity leads to higher costs and more potential points of failure.

I can live with the sound my kettle makes.

[Bob F.]

The sound of the kettle boiling is telling me that I have a nice cup of tea coming soon.  I like the sound   

[suicidaleggroll]

If it's 2am and you don't want it to make a sound, then put the water in a pot on the stove instead.

[Someone]

So why don't we put two thermocouples: 1) on a heater itself 2) somewhere close to top of water level. And we just regulate current through heating element so heater will not go over threshold temperature (let's say 70-90 C) until second thermocouples reach threshold temperature. Then we just go full throttle util we reach 100 C (with a bit of noise, but you can't make noiseless boiling water, so it's ok)

Expensive... kettles only have a heating element a latching switch and a thermal cutoff element. Try competing with that.

The entire "thermostat" of a kettle is very elegant, its a snappy bimetal contact that is heated by a small fraction of steam carefully channelled past it (you can fool most kettles by blocking the spout when they are on and they will terminate heating early).

Take  a 3KW dimmer and an electric kettle and see how far you actually have to reduce the power to eliminate the noise.  To a first approximation, the time to boil from cold is  proportional to the volume of water divided by the applied power, and most people vastly prefer as short a boiling time as possible and don't really care about the noise.

I suspect that a better way of eliminating excessive noise would be to add a magnetic stirrer + make the element with a much larger surface area.

Heating the large quantities of water as in a kettle with a magnetically stirred hotplate is similarly noisy but they haven't been optimised for quietness.

...make the element with a much larger surface area.

I have a Breville "Quiet Boil"
http://www.breville.com.au/the-quiet-kettle-bke490bs.html

It appears to achieve this using a combination of a larger surface area and "a special coating to make bubbles smaller"

It really does work. It is very quiet indeed.

Its a classic corporate solution to the problem, a special kettle which requires regular cleaning with their proprietary "Breville Kettle Cleaner" solution so you're on the hook for ongoing costs (and income for them). They don't add other basic noise reduction solutions like insulation or damping to the vessel.

I have a quiet kettle, simply reduced power in the element by half and chose a kettle with a solid design that has insulation around the sides and over the top. It uses one of the large plate type heating elements but run at a lower temperature, and guests enjoy being able to watch the convection currents in the water as it heats.

[Mr.B]

Its a classic corporate solution to the problem, a special kettle which requires regular cleaning with their proprietary "Breville Kettle Cleaner" solution so you're on the hook for ongoing costs (and income for them). They don't add other basic noise reduction solutions like insulation or damping to the vessel.

I don't know what you are on about.
There is no mention about proprietary cleaners in my instruction manual.
I have had it at least 5 years and never cleaned it, mind you I have hardly any calcium in my water.
Also, it does have good noise reduction with quality rubber feet and such like.
It just works as advertised.
And, no, I don't work for breville or any of its distributors.

[T3sl4co1l]

Put it under pressure.  Seal the kettle, pressurize it to several atmospheres (this is safe to do when it's only water, no airspace at all), then begin heating (this is not so safe).

As long as the temperature cannot exceed 105C or so, the partial pressure will not be much above atmospheric.  So, if you open the kettle to atmospheric, the overpressure will be fairly gentle, so that it could be released into a modest surge tank or something, and voila, instant boiling water.  It would even be self-propelled, if you put the vent at the bottom.

You're also guaranteed to get a good cup of tea, even on the top of Mt. Everest.....but you need to do the brewing while in the pressure chamber.  It'll boil and splatter a whole lot if you just vent it at that altitude.

Tim

[Someone]

Its a classic corporate solution to the problem, a special kettle which requires regular cleaning with their proprietary "Breville Kettle Cleaner" solution so you're on the hook for ongoing costs (and income for them). They don't add other basic noise reduction solutions like insulation or damping to the vessel.

I don't know what you are on about.
There is no mention about proprietary cleaners in my instruction manual.
I have had it at least 5 years and never cleaned it, mind you I have hardly any calcium in my water.
Also, it does have good noise reduction with quality rubber feet and such like.
It just works as advertised.
And, no, I don't work for breville or any of its distributors.

Several members of the family have tried those Breville kettles they all got noisy, perhaps there have been several different revisions of the design, and as you say water quality varies wildly across Australia, but the reviews are very mixed and from personal experience (sitting next to one in use) I'm not impressed.

Does anyone remember the solid ceramic jugs?

[Mr.B]

Several members of the family have tried those Breville kettles they all got noisy...

Maybe, for once in my life, I didn't get the one made on a Friday... 

[BravoV]

Though I am not sure the explanation, has anyone observed the water used for boiling ?

1st, fill the pot with water and boil it, observe the noise.

2nd round, fill it again, then leave the water overnight or even more to let it "settled", boil it again, the noise will substantially different or should I say "quieter".

Not very sure why ? 

[hamster_nz]

Though I am not sure the explanation, has anyone observed the water used for boiling ?

1st, fill the pot with water and boil it, observe the noise.

2nd round, fill it again, then leave the water overnight or even more to let it "settled", boil it again, the noise will substantially different or should I say "quieter".

Not very sure why ? 

Darn that google is good!

http://physics.stackexchange.com/questions/46655/why-is-boiling-water-the-second-time-more-quiet-than-boiling-it-the-first-time

[B.B.Bubby]

Does anyone remember the solid ceramic jugs?

Fondly,  they're a really good stein substitute for when some good German beer is to be drunked.   O0

[rs20]

Use a magnetron instead of a heating element? Safety optional.

[Circlotron]

Does anyone remember the solid ceramic jugs?

Yeah the ones with exposed wire element. I put 415 V on one of those once and it really got  it moving! Would've been exactly three times the normal 240V wattage but the element had broken and been shortened and twisted together several times so was shorter than normal so the power would have been even higher. So was the noise it made. 

[android]

I have a Breville "Quiet Boil"
http://www.breville.com.au/the-quiet-kettle-bke490bs.html

Me too. Unfortunately the engineers chose to make it go "BEEP...BEEP...f*****g BEEEEEP" when the water was ready. Go figure. Judicious application of a pair of wire snips fixed it