superheated water

Mike T., Swampeast MO

Actually it was the super-heated water thing that made me find that site in the first place.

Had "double heated" a teapot full of water in a commercial dual magnetron microwave by accident. Water wasn't boiling when I added the tea bag. I was burned by the steam (and nearly by the water) when it instantly began boiling and overflowing quite violently.

Earthfire

superheated water

Finally got around to checking email today,and this was sent to me. I usally just do 20 seconds on plain water. Is this an internet myth or fact?




: Fw: Microwave

A 26-year old man decided to have a cup of coffee. He
took a cup of water and put it in the microwave to
heat it up (something that he had done numerous times before). I am
not sure how long he set the timer for, but he wanted to bring the
water to a boil. When the timer shut the oven off, he removed the
cup from the oven.


As he looked into the cup, he noted that the water was
not boiling, but suddenly the water in the cup "blew
up" into his face. The cup remained intact until he
threw it out of his hand, but all the water had flown
out into his face due to the build up of energy. His
whole face is blistered and he has 1st and 2nd degree
burns to his face which may leave scarring.

He also may have lost partial sight in his left eye.
While at the hospital, the doctor who was attending to
him stated that this is a fairly common occurrence and
water (alone) should never be heated in a microwave
oven. If water is heated in this manner, something
should be placed in the cup to diffuse the energy such
as a wooden stir stick, tea bag, etc. (nothing metal).

It is however a much safer choice to boil the water in
a tea kettle.

GENERAL ELECTRIC's RESPONSE:

Thanks for contacting us, I will be happy to assist
you. The e-mail that you received is correct.
Microwaved water and other liquids do not always
bubble when they reach the boiling point. They can
actually get superheated and not bubble at all. The superheated
liquid will bubble up out of the cup when it is moved or when
something like a spoon or tea bag is put into it.

To prevent this from happening and causing injury, do
not heat any liquid for more than two minutes per cup.
After heating, let the cup stand in the microwave for
thirty seconds before moving it or adding anything
into it.

Here is what our local science teacher had to say on
the matter: "Thanks for the microwave warning. I have
seen this happen before. It is caused by a phenomenon
known as super heating. It can occur anytime water is
heated and will particularly occur if the vessel that
the water is heated in is new, or when heating a small amount of
water (less than half a cup).

What happens is that the water heats faster than the
vapor bubbles can form. If the cup is very new then it
is unlikely to have small surface scratches inside it
that provide a place for the bubbles to form. As the
bubbles cannot form and release some of the heat that
has built up, the liquid does not boil, and the liquid continues
to heat up well past its boiling point.

What then usually happens is that the liquid is bumped
or jarred, which is just enough of a shock to cause the bubbles
to rapidly form and expel the hot liquid. The rapid formation of
bubbles is also why a carbonated beverage spews when opened after
having been shaken."

kevin coppinger_4

myth (nm)

Chris_7

yes this could happen under the right conditions

Yes, this situation could happend under the right conditions. They tested this theory on a show called Myth Busters on the Discovery channel. It can happen if you used distilled water. You would have to super heat the distilled water and then introduce something to the water like a spoon and that will wake the water explode out of the cup.

Uni R

Read this...

http://www.straightdope.com/mailbag/mmicroboil.html

It's a response to the same story and it is from 2000. One part truth, 9 parts embellished.

Partial quote...

Campbell explains that microwaving water can indeed be dangerous under certain circumstances, but not to the extent mentioned in the e-mail legend. When you think of boiling water, you think of bubbles coming to the top. Where do the bubbles come from? They form at a nucleation site. Usually this consists of a small flaw in the container or a seam--say, where the sides meet the bottom--but Campbell notes that it could also be turbulence in the water due to convection. Such a flaw or turbulence is common in teapots or saucepans used to boil water on the stove. However, when you are boiling water in a microwave, you are probably using a ceramic mug, which is much smoother and may not have a good starting point for nucleation. On top of that, a microwave oven heats more or less uniformly, so the amount of convection and turbulence in the water is greatly reduced. Without nucleation, the water just gets hotter and eventually becomes superheated; that is, it exceeds the normal boiling point for water without actually boiling.

This is when things can get touchy. If you move the cup around a bit, or drop a teabag into it, or put your spoon in to stir it, or whatever, you can provide the nucleation site the water has been looking for. So it turns from a superheated liquid to a boiling one--quickly. Usually, this will just mean it boils over the top of the cup, in which case you'll only be burned if you happen to be holding it (such as if you took it out of the microwave and jostled it enough to start it going). It could also splatter a bit, just as a pot of boiling water occasionally throws up some scalding drops. But it's not going to "blow up" and throw all the water into your face, as described in the e-mail message. At least, it won't unless you're sitting there with your face an inch away from the water, staring at it (if that's the case, perhaps getting burned isn't your biggest problem).

Mike T., Swampeast MO

Microwave Oven \"Experiments\"

http://www.eskimo.com/~billb/weird/microexp.html

Guess I'm just too curious for my own good sometimes, but I have "verified" many of these...

The super-heated water is interesting. I haven't seen it "launch" itself out of the container, but it can boil over with extreme intensity. The "double heating" thing seems to get it REALLY going.

Uni R

Oh boy...

*****
My 8" fluorescent tube isn't the only light producer. Another classic u-oven experiment is to cook a standard incandescent bulb briefly on "high". A 100W bulb will light up with more than normal brightness.

If you have a newer oven with rating over 800W, include a glass of water in the oven, otherwise the filament support wires will instantly melt and spoil your fun. Even with the water, don't run this for very long, since ALL the lightbulb wires glow white hot, not just the filament. This could shatter the bulb. For best results, buy a transparent bulb rather than a frosted bulb, then watch what happens inside.
*****

I'm glad to see you have found a nice hobby Mike.
I'm afraid to read any more... j/k