LouB wrote in :

Bob F wrote:
LouB wrote:
RJ wrote:
It SEEMS
I can heat water faster in my microwave
than I can on my stovetop.

Is a microwave "more efficient" at heating water ?

If so, can anyone see a time where
the heat source for a home water heater
would be microwave rather than heating elements ?

The microwave heats faster cause there is no warm-up time.

No
AND be carefull to never heat plain water in a MW as it may damn
near "explode" when you go to use it due to surface tension issue.
I.E. put cocoa in before heating, ditto tea bag.

Excellent advice, if you like cocoa all over the inside of the
microwave. Otherwise - not so much.



I made what appears to be a rash assumption for some folks.
That the user is smart enough to not run the MW for too long a period.

Lou

Actually, superheating is a wellknown phenomenon. For water to boil, it
has to go to vapor phase (steam). That usually (in a pan on a fire of
some kind) at very hot places on the pan's surface. That's when the
water is starting to "sing". In a MW there is no such hot surface and
boiling has to start somewhere. This is then usually on a floating speck
of dust. The MW energy has heated the water in the meantime to higher
than the boiling temperature, so when a teensy "boil" starts, suddenly
this is the seed for much more water to become steam. Steam is also
much, muc more voluminous than water, hence the force of the boiling
water and steam.

When a chem student having to heat solvents on a heated water bath, it
was official policy to add "boiling stones" to the containers in order to
have a controlled boiling, rather than a little explosion. But that is
another story ...

Oh, yeah. 1 mole of water is 18 grams, just over half an ounce.
Visualize that volume. At "normal" conditions (0degrees C, 1 atmosphere
pressure), the volume of an ideal gas is 22.4 liters. Since pV=RT, that
volume would be 373/273 times as much at 100 degree C (boiling), or about
31 L, or close to 8 gallons. Visualize 18 milliliters expanding to 31
liters, roughly 2000 fold. That's the power of steam.

That explains why you eed be careful pulling the Saran wrap off of a
microwaved food container. Less than 4 tablespoons of water will convert
to 8 gallons of steam when overheated to boiling.

--
Best regards
Han
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