|This article is of interest to the following WikiProjects:|
- 1 electric kettle efficiency
- 2 The kettle principle
- 3 History
- 4 Electric kettle boiling time
- 5 Lloyd's Patent Table Kettle
- 6 Tea pot?
- 7 Do not look like teapots
- 8 Automatic switch off and boil dry protection not even described let alone explained
- 9 Svenska language link links to wrong English article
- 10 Advantages
electric kettle efficiency
While an electric heating element is 100% efficient at converting electrical energy into heat, not all of this heat gets into the required water. A significant proportion is used to heat the kettle itself. Also, the minimum volume mark might be at a much larger volume than required. A 1.5 l plastic jug kettle with an exposed element might have a heat capacity equivalent to an additional 105 ml of water. A stainless steel squat kettle (non-jug) with a concealed element might have a heat capacity equivalent to an additional 230 ml of water.
The effective heat capacity of a kettle can be determined experimentally by boiling the minimum and the maximum volumes of water in the kettle from cold. Plot the 2 times against the volumes and draw a line between them, extending it until it crosses the volume axis. This should be a negative volume. The absolute value of that volume is equivalent to the effective heat capacity. Where the line crosses the time axis, this should be a positive value and indicates how much longer you have to wait just to heat up the kettle. You can check your experimental technique by repeating the measurements or by boiling another known volume of water somewhere between minimum and maximum. The resulting (volume,time) co-ordinates should lie on the same straight line.
An 'efficiency' value for a kettle can be defined as the ratio of the energy required to heat a desired volume of water (e.g. 220 ml standard cup) to the energy required to boil the kettle.
For the plastic kettle, the minimum volume mark corresponded to 350 ml. Add to this the additional volume for the heat capacity (105 ml) and the efficiency for a 220 ml cup full can be calculated as 220 / (350 + 105) or 48%.
For the metal kettle, the minimum volume mark corresponded to 550 ml. For a 220 ml cup, its efficiency is 220 / (550 + 230) or 28%.
(The above figures were derived from actual kettles. I ignored heat losses from the kettle, which might be 5-10%, as they are insignificant compared to the heat capacity of the kettle and extra water. The heat loss from a plastic kettle will be less than from a metal kettle as the outside surface temperatures are much lower for plastic. Also, kettles are often filled well above the minimum mark. Both of these factors will combine to reduce the above efficiency values still further. I have also ignored simple methods of reducing energy consumption; such as immediately refilling the kettle to the minimum mark after use so that the kettle starts warmer next time.)
There are several reasons the metal kettle has the higher heat capacity:
- the metal kettle is heavier
- stainless steel is a poor insulator, so the entire thickness of the kettle wall gets heated to the same temperature as the water
- plastic is a reasonable insulator, so there will be a large temperature gradient between the inside and the outside of the kettle meaning the average temperature of the kettle body will be lower than for metal (I can comfortably hold a plastic kettle full of boiled water by it body. I would get badly scalded if I tried the same with a metal kettle.)
- the concealed heating element might be heavier than the exposed element (?) - it takes much longer to start 'singing'
The kettle principle
Should there be something in this article giving the principles of the kettle? Obviously one of those principles is that it allows water to be exposed to a source of heat. However shouldn't there also be something along the lines of "Thermodynamically isolate the system to stop convection and conduction from equalizing the inside temperature with the outside temperature?" After all the article on Solar greenhouse gives exactly that as the first principle of the greenhouse. Or do you feel that it is the greenhouse article that inappropriately overemphasizes the significance of this isolation principle? --Vaughan Pratt (talk) 04:53, 7 November 2009 (UTC)
According to this article, http://www.wickedlocal.com/carver/archive/x1713644944/Carver-home-of-the-teakettle Carver, Massachusetts claims to have produced the first tea kettle.
Electric kettle boiling time
What are the factors involved in time taken by electric kettles to boil a cup of water? I'm always amazed in the variation in time taken by different kettles. Unfortunately, my current model is the slowest I've ever seen :-( --220.127.116.11 (talk) 14:38, 11 May 2010 (UTC)
Lloyd's Patent Table Kettle
An editor posted me a link to a 1800 advertisement for the Lloyd's Patent Table Kettle and suggested it might be added to the article Kettle. I am not sure exactly how this could be done or what a table kettle looks like (maybe like this?). Here is the text:
SINGLE LADIES or GENTLEMEN living in Apartments, at Breakfaſt or Tea-time, after Supper, at any time of the day or night, from one quart to one gallon of Boiling Water may be had on the Table every Ten Minutes, for leſs than One Penny expence, by means of LLOYD'S PATENT TABLE KETTLE, which, for Sick Rooms, is declared to be truly invaluable. - To be had only of the Inventor and Patentee, No 178, Strand, two doors Weſt of Norfolk-∫treet , where it may be ∫een in actual uſe.— The Times, 29 May 1800
> "A kettle, sometimes called tea kettle, teakettle or tea pot" I don't think this is correct - does anyone call a kettle a "tea pot"? Tea pots are for putting tea in, surely, not for heating the water. Dictionaries seem to agree with me so I've corrected this unless someone can cite a reliable reference.Gymnophoria (talk) 20:43, 23 June 2011 (UTC)
- I'm getting the impression that Americans often confuse kettles with teapots. I understand that kettles are rare in the US, because their low voltage means they take forever to heat up. 18.104.22.168 (talk) 21:27, 28 June 2011 (UTC)
Do not look like teapots
Automatic switch off and boil dry protection not even described let alone explained
The automatic switch off mechanism after boiling of most modern kettles, along with any secondary boil dry mechanism also, are not even mentioned let alone decribed and explained in this or related articles.
I first I thought that the primary mechanism was a bimetallic switch it is clear however that the vertical post with a hole in it is likely an capilliary to an air pressure sensor switch that gets triggered either by the -ve vacuum produced by the escaping steam or +ve pressure of same into the tube. Any self-resetting bimetalic switch is liekly to be used inline and attached immediately adjacent to the element for overheat or boil dry protection.
For whomever most cares for this page, please know that the Svenska language link links to the wrong English article. This English "kettle" article links to a Svenska "kittel" article. Though the words are obviously etymologically related, Swedish "kittle" means "cauldron", NOT "kettle". To the best of my ability, I believe the Swedish word for kettle is "vattenkokare". However, the Swedish wiki entry for "vattenkokare" focuses only on / and links to "electric water boilers". Though one could exist, I haven't found a kettle article in Swedish. I'll post on the Swedish sites as well, since things perhaps need to be untangled on that end. :) Pillartopost (talk) 14:57, 1 August 2012 (UTC)