Talk:Kettle

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'

Ajrobb (talk) 04:19, 11 October 2008 (UTC)

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)

History

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.

Rogerwho? (talk) 20:28, 10 December 2008 (UTC)

please flag this article as needing cleanup

it is exceptionally poorly written. 70.112.237.136 (talk) 05:43, 10 April 2009 (UTC)

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 :-( --83.38.126.5 (talk) 14:38, 11 May 2010 (UTC)