Electric Kettles

[sunder]

mmotyka at lsil.com wrote:
> 
> Why boil water for tea on a stove or in an electric "kettle" when you
> can put a mug of water in the microwave and have it on the verge of
> boiling in 60 seconds? Probably uses less energy too.

Bad idea:

http://rabi.phys.virginia.edu/HTW//microwave_ovens.html

"Why does water react  in a violent and dangerous way when overheated in a microwave oven? CA

Water doesn't always boil when it is heated above its normal boiling temperature (100 0C or 212 0F). The only thing that is certain
is that above that temperature, a steam bubble that forms inside the body of the liquid will be able to withstand the crushing
effects of atmospheric pressure. If no bubbles form, then boiling will simply remain a possibility, not a reality. Something has to
trigger the formation of steam bubbles, a process known as "nucleation." If there is no nucleation of steam bubbles, there will be
no boiling and therefore no effective limit to how hot the water can become.

Nucleation usually occurs at hot spots during stovetop cooking or at defects in the surfaces of cooking vessels. Glass containers
have few or no such defects. When you cook water in a smooth glass container, using a microwave oven, it is quite possible that
there will be no nucleation on the walls of the container and the water will superheat. This situation becomes even worse if the top
surface of the water is "sealed" by a thin layer of oil or fat so that evaporation can't occur, either. Superheated water is
extremely dangerous and people have been severely injured by such water. All it takes is some trigger to create the first bubble-a
fork or spoon opening up the inner surface of the water or striking the bottom of the container-and an explosion follows. I recently
filmed such explosions in my own microwave (low-quality movie (749KB), medium-quality movie (5.5MB)), or high-quality movie
(16.2MB)). As you'll hear in my flustered remarks after "Experiment 13," I was a bit shaken up by the ferocity of the explosion I
had triggered, despite every expectation that it would occur. After that surprise, you'll notice that I became much more concerned
about yanking my hand out of the oven before the fork reached the water. I recommend against trying this dangerous experiment, but
if you must, be extremely careful and don't superheat more than a few ounces of water. You can easily get burned or worse. For a
reader's story about a burn he received from superheated water in a microwave, touch here."




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