A new concept for the electric kettle

[poor mystic]

Hi People
Lots of you will know that both coffee and tea are best made with water that is not actually boiling, but only hot. I will add that boiling water is not really necessary for many domestic applications except for childbirth, and that it is a waste of money to boil water unnecessarily when hot water will make a better job. Besides, I drink my tea, and instant coffee, black.
My idea is for an electric kettle which, rather than switching off when the water has boiled, will switch off when the kettle makes a sound which is characteristic of the kettle for the water temperature that is wanted.
The first job is to find out exactly what sound the kettle makes at different temperatures.
I think that a small processor could do the job. It would get its input data from a microphone and control the kettle using a triac. A potentiometer would be graduated for temperature. The kettle I propose is better than the kettles on the market because the user has greater control over the final temperature of the water that the kettle heats.
This invention is free for anyone to develop, and I hope it happens soon, since I am sick of too-hot coffee and tea.
Mark

 

[davenn]

Hey Mark
Good to see ya

sounds like a good plan to save power

cheers
Dave

 

[KMoffett]

That sounds sort of Rube Goldberg'ish. Since water temperature is what you're concerned about, why not just monitor/control the water temperature? Or am I missing something.

Ken

 

[davelectronic]

Kettle concept

Hello Mark. Yes its a good concept, more for coffee lovers than tea, a lot of people say boiled water wrecks the flavour, i am a tea fan, i prefer well brewed tea, so heats more beneficial. I like the idea of looking to improve, or re invent an existing product. I find myself looking at things in production being improved, go for it, and i will watch this space.
Dave.

 

[jackorocko]

That sounds sort of Rube Goldberg'ish. Since water temperature is what you're concerned about, why not just monitor/control the water temperature? Or am I missing something.

Ken

right on, cause no two kettles are the same, but water temperature stays the same. I am almost betting you could retro fit a retail model off the shelf pretty easily. Go buy one and take it apart...

 

[poor mystic]

That sounds sort of Rube Goldberg'ish. Since water temperature is what you're concerned about, why not just monitor/control the water temperature? Or am I missing something.

Ken

Yes, maybe there is something more to say...
I think that while no 2 brands of kettle might be quite the same, individual kettles from the same line should be very similar.
I also think that measuring water temperature is very difficult to do accurately (just try it!) and I think that listening to the kettle might really be the cheapest, most foolproof way to go about it. I think that small bubbles are made at the element when the water is relatively cool, and that as the water heats the bubbles become larger, so that the characteristic frequency detected by the microphone should become lower as temperature rises.

 

[MattyMatt]

Another thought occurred to me reading down the posts... I agree with Mark on this... at least to accurately measure the temperature of the water, it does require multiple thermometers placed at different levels, and areas... but it really does depend on how accurate you want to be.

I am also a bit of a coffee, and tea lover... I am known for an occasional espresso... not the kind you get at the local Starbucks (BIG chain place) either... I'm talkin mom&pop shop.... 190F seems to be pretty ideal (about 87C) from what I hear.

I would say you could explore the possibility of using some sort of pressure transducer, that may give you a good idea of temps... but that would require some calibration... IE, you would need to know at what temperatures would give you the correct pressures....

Just a thought....
Matty-

 

[KMoffett]

How is a sound detector or a pressure sensor going to be more accurate than a temperature sensor/controller, when water "temperature" is the goal?

Ken

 

[MattyMatt]

Well if anything else, using 1 thermometer in conjunction with any of the other devices would give you a more accurate reading, provided that other device is basing its readings on a known value.

Measuring the temp of water VERY accurately can be difficult, which is why the suggestion is out there... not to mention, it does make for quite a nifty project

Matty-

 

[KMoffett]

Measuring the temp of water VERY accurately can be difficult, .....

Matty-

Can you elaborate on that?

Ken

 

[MattyMatt]

Because water is very dynamic when it comes to heating it... it does not heat evenly, as in places within the kettle could be a few degrees different from where it is that you are measuring...

how much different I don't know...

But using a digital temperature probe, moving it around (on all axis) in a pot of boiling, or near boiling water will show changes by a few degrees or so.... that I actually did in my physics class in highschool... which, admittingly, has been a while now.

Now, this could be due to inaccuracies of the probe, but honestly, it was pretty stable (within a few 10ths of a degree) when holding it in one place. I hope I made some sense here .

Matty-

 

[KMoffett]

Measuring on the bottom of the container vs the top center will show some variation. But heated water is turbulent and distributes the heat throughout the container. The closer the heat source temperature is the desired water temperature the less variation you will see. I can't see any way that listening to boiling water sounds or measuring a single pressure point will give you a more accurate measure of the "overall" water temperature.
If you want a very accurate water temperature, use a PID temperature controller (cheap on eBay) with a thermocouple probe to power the kettle. Remember as soon as you pour the heated water in a cup you immediately lose temperature.

Ken

 

[daddles]

Hi, Mark: It's an interesting idea and I know where you're coming from. Personally, I like my tea water to be boiling, the hotter the better (but I'm pretty much limited by basic physics ). I'd imagine you're thinking that a sound sensor could be retrofitted to a kettle and somehow trained to emit a signal at the appropriate moment. This, of course, screams out microcontroller.

However, if you're going to go that far, why not use closed-loop control on the parameter you're trying to control (temperature)? In this I agree with Ken. If you want an exact temperature, then it would make more sense to rig up a double boiler type setup with temperature measurement in the internal container. This would minimize the convective cells in the inner container and make the temperature measurements more uniform (but it's impossible to avoid some convection unless you change the molecular properties of water). In other words, think Reichsanstalt resistor in a mineral oil bath in a standards lab.

But before I would recommend such engineering effort, I would certainly want to know that the effort was worthwhile. This clearly needs a good double-blind study to demonstrate that it makes a significant difference. And, fortunately, the experimental protocol has already been described. I refer, of course, to the most famous design of experiments paper ever written, Fisher's "Mathematics of a Lady Tasting Tea". It should be mandatory reading for every scientist and engineer. If any of you have never read it, do so -- like Einstein's 1905 paper on relativity, the mathematics involved are elementary, but the ideas are among the most profound that mankind has generated. Like Einstein's paper, it should raise the hair on your arms when you read it.

 

[poor mystic]

Hi
When a vessel of water is heated from beneath, the water forms convection columns above the heating element. These convection columns rise to the surface and spread out, and the water descends once more towards the floor of the vessel.This results in uneven heating - not all the water in the vessel takes part in the convection cycle.
Because of the different temperature in different parts of the vessel, it is very hard to find a point at which a representative water temperature can be measured.
Mark

Daddles, you can get your tea water to 105*C by heating in the microwave. (The oscillating microwave field may add an extra force sticking the molecules together)


PPS I believe a microphone, microcontroller, and triac might be a cheap replacement for steam switches.

 

[daddles]

When a vessel of water is heated from beneath, the water forms convection columns above the heating element. These convection columns rise to the surface and spread out, and the water descends once more towards the floor of the vessel.This results in uneven heating - not all the water in the vessel takes part in the convection cycle.
Because of the different temperature in different parts of the vessel, it is very hard to find a point at which a representative water temperature can be measured.

I took a heat transfer course around 30 years ago and I don't remember the temperature gradients being terribly large in such conditions. The only way to know for sure is to stick a temperature sensor with a short response time (e.g., a thin film RTD) into some water and make actual measurements. My physical intuition tells me the differences will probably be on the order of 10 K under typical teapot conditions (and remember an enclosed space like a teapot will have an atmosphere over the water that will be at a somewhat higher temperature than an open pot).

Daddles, you can get your tea water to 105*C by heating in the microwave. (The oscillating microwave field may add an extra force sticking the molecules together)

Absolutely -- that's the way I've been heating my morning tea since the 70's. In fact, when I take the water out and stick the tea ball in, I get the usual violent boiling of superheated water -- but never enough to burn me (I figure I'm pretty good at estimating what's going to happen after 10,000 cups of tea or so ).