DO NOT HEAT LIQUIDS IN A MICROWAVE FOR MORE THAN 2 MINUTES




'A 26-year old person 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 told me 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 instantly 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 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. It is however a much safer choice to boil the water in a 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 a 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."

I alwyas prepare my tea or coffe or hot chocolate in a microwave but never had such things happened.

Intersting..... I heard that the risk of superheating water in microwave can be easily eliminated by using a metal (preferably steel) kettle. When you heat water in a kette in microwave, metal in the kettle absorbs the excessive heat from water and water can boil without superheating.









































FYI Do not try this in your kitchen.

u_day: says, FYI Do not try this in your kitchen


so try in others kitchen......? hehehehe

naviN!
That was a joke. you didn't get it???

I don't know how true it is but I have heard that it is very bad to put metallic objects in microwave. I don't know how good the idea of heating water in a kettle (or any metallic holder) in microwave is.

About superheating, the best thing to do is to make sure that water surface is not even. Ceramic objects, cups have very smooth surfaces that denies water molecules of any surface to form bubbles (same phenomenon as how dirt is needed to form rain, in which case saturated clouds need a point of contact to liquify). Heat water with a straw in it, or stir it with a spoon with your hand stretched before taking it out of microwave. I always do the latter.

I had already written this stuff (such possibility) in Sajha.com long time ago.
(I believe).

Similarly, don't put egg (uncooked) with "bokra" inside the microwave. It
will result the same. Thats terrible.

Why you should not do it?

Microwave works by tuning the water molecules plus and minus charges
upside down and doing this in cycles the molecules vibrate and internal
energy of liquid molecules are increased. Microwave's heating
mechanism is not supported by the convection type of heat transfer,
as it usually happens when we heat water on kettle over electric
heater. so, there is not rotation of hot and cold water inside
microwave, because the heating was so fast that water molecules
don't have enough time to follow convection mechanism and neither
they can follow conduction method to transfer heat to get uniform
temperature. Thus, the dT/dx (T=temperature, x is distance) is
so high that the k (heat conduction coefficient is very very low
almost like an insulator), thus dQ/dt = kA dT/dx (the rate of heat
flow is too low) across the depth of water inside a cup or inside
a unboiled egg. Thus, these molecules have extremely high heat
while outer surface does not have, so these items are very
very fragile for even a slight shaking or vibration, slight vibration
creates a route so that dQ/dt becomes extremely high and
it transfer like micro bomb.

What is the solution?
My own idea is to put some acrylik balls so that when they are also
heated along with water then these balls will vibrate and moved up
and down in such a way that heat can not accumulate at one place.
The other solution might be to use flatter utensils (bowls) compared
to deep cups. Deep cups are extremely dangerous, some time deadly.
Unboiled egg should never be tested inside microwave.

Remember microwave does not if it does not have liquid, especially
water. It uses the mechanism as mentioned in first part of this
posting.

If you want to kill the RAAG ko Pyaj, you can microwave for 10-20
seconds, then it becomes kachai khana hune, use it in chatar matar.
Similarly, if you want to eat Lasoon (Garlic) for some somach or
for extra potassium intake, then you can kill the RAAG of lasoon
by microwaving for 10-30 seconds depending on power of the
microwave. It becomes excellent, no raag no worry.

Use and don't misuse science "laws of physics". Thats it.

GP

I like the explanations GP and Cardinal put. I was thinking more of Nucleae Boiling, when hot steam or even hot layer of water puts out an insulating surface in topmost layer. Well, my theory is right, but the explanation GP put is the way this layer is created.

Nucleae=Nucleate