Why aren't kettles highly insulated?
I was distracted by the phone this morning and kettle had cooled a bit before I poured my cuppa.
Made me think how convenient and energy efficient kettles would be if they could keep the water in them near boiling for some time.
Worse still is the current fashion for stainless steel kettles - these take ages to boil. A few years back we were given a stainless kettle and toaster matching set. The performance of both was awful. We've gone back to using nice plastic ones, which boil quickly.
I've wondered about this as well. The insulation would probably need to be something like
Thinking along the lines if efficiency, the amount of energy needed to boil water depends on the temperature differential between the starting temperature and finishing temperature. Maybe keep several litres of water on a sunny windowsill to warm up before using. Also, not all beverages need boiling water. Monitoring the temperature of the water in the kettle and then turning it off when the desired temperature has been reached would be a good idea.
But was that the material or the power rating? It seems a bit surprising that stainless steel can radiate/convect *that* much heat to make much of a difference with a 2-3kW heat source.
This puzzled me at the time. The stainless kettle was a Morphy Richards
3.1kW, which replaced a (much faster) 3kW Kenwood.To start with I thought it might be thermal mass, but raising 300 grams of stainless steel from 20C to 80C takes about 9kJ, which the element can do in 3 seconds, so that's not the issue. I therefore assumed that it must be convective losses from the surface.
My kettle has several settings. One for tea, coffee and one for lukewarm drinks which is supposedly the right temperature for adding to yeast for bread.
I believe there are now kettles with a 'coffee' setting for such a purpose.
Owain
Lidl did a nice plastic 3kw kettle with an additional stat for hot water rather than boiling for £9.99. It works OK but you have to remember to switch it off if you are using the stat or it will keep it hot until you do.
I wonder if one could work out the convection and radiation losses for both.
The energy equation is pretty simple. We know that there is not an issue of the heat being transferred into the water since it has nowhere else to go. Therefore if one takes a given amount of water in both cases and heats it from temperature T to 100 then the energy used in the time difference would account for the difference in loss.
It's not possible that there was less water in the plastic kettle? These tend to be jugs whereas the metal ones are usually more traditional kettle shaped. Hmm.... thinks difference in surface area of short squat cylinder vs. tall one?
As for the toaster, I think it's harder to work out. Here the heat transferred to the bread would depend on what's behind the element (insulation and reflection of some kind?) and proximity of element to bread.
I guess one possibility is that the stainless was lying about the power rating...
No, it was a jug one, a little like this (but without the windows)
The toaster was bad for different reasons - it seemed incapable to irradiating the bread evenly, so you always ended up with some burnt bits and some untoasted bits. I think that was just poor design, and not related to the casing material.
It really shouldn't be hard to get that right....
Okay I'll start the ball rolling
Tefal Elegance 3000W stainless jug
500ml water, start temp 16.5°C 79.8 secs to auto stopOkay so they shut off at different temps, but this is probably more pertinent since I expect most people wait for it to shut off and certainly don't use a thermometer.
I have a Siemens kettle which is perhaps 6 years old, and is insulated. Outside is brushed stainless steel, inside is plastic except for the flat bottomed element. One issue with an insulated kettle is you can't quickly tell if it's already boiled, or if you forgot to switch it on in the first place.
It was designed by Porsche -- he might be able to design cars, but as with many designers, he completely failed to design a spout which can pour properly. Otherwise, it works fine.
We have a kettle at work which has a "keep hot" switch on it, which maintains the temperature just below boiling when the boil switch is off. It's a large industrial thing though, with a hopelessly underpowered element for its size.
They could always combine the stainless kettle with a stainless thermos flask. How the latter manage to keep things warm so effectively is a mystery to me!
On the kettle theme, having just used around a pound of citric acid to get all the clinker out of our stainless kettle (which boils v quickly - Phillips), I wonder about those little bundles of wire I used to see in old ladies kettles, that somehow stop the furring up: how do they work, and what are they made of? (This is a bigger problem than it used to be, since we started taking note of the water levels in order not to waste energy: the result is a thick ring of clinker at the 'two cups' level! The clinker also blocks up the level tube entrance which foolishly happens to be at about the same level!)
S
Forget the insulation. An energy efficient kettle is the one that is controlled properly by the user. This requires only boiling the required amount of water that is needed and not over filling. For the very few times you are interupted in making a cup of tea the heat loss is irrelevant.
Adam
Oh, how AWFUL!>
I can't think of anything worse ...
Remember to add the milk immediately after the hot water, to slow the subsequent heat loss...
Not necessarily, in our case it depends on the bread. I make ours and if I use a lean dough the crusts and towards them brown more quickly than the rest. If I make a rich dough it toasts far more evenly.
Exactly the same happens if I toast under the grill.
Mary
Leaving aside the fact I don't like boiled toast I'll warrant both your plastic toaster and kettle will fall apart long before stainless steel ones. Plastics simply don't like heat long term.
The lid fell off my stainless steel one.. the plastic hinges broke.
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