On Jul 3, 11:03?am, Dirty Sick Pig > wrote:

> That "Status: true, but rare" takes this out of urban legends! Hey,
> Roughrider, thanks!

The subject of superheated water tweaked my curiousity as a steam
plant engineer. But we usually talk about superheated *steam* in the
industry.

Water that is heated to a fraction of a degree above 212 degrees at
sea level air pressure of 14.7 PSI is superheated water all right,
it's actually *heat saturated* and cannot exist in the liquid state,
it has to intaneously change to a gaseous state, *flashing* into
steam.

Walking around a steam plant at night is a weird experience. Steam in
the pipes overhead cools down below the temperature at which it is a
gas and turns into water again.

Then the control room operator needs to send a lot of steam through
the pipes to some process that needs steam, that adds heat to the
water and the water heats up and flashes into steam again with a loud
BANG!

But nobody ever talked about bubbles forming in the water and somebody
getting a faceful of superheated scalding water, the steam was in the
pipes where it belonged.

>From a thermodynamic viewpoint, a British Thermal Unit is the amount
of heat required to raise the temperature of one pound of water one
degree Fahrenheit.

We're talking about a teacup full of water here, about 0.25 pounds,
and the water out of the tap is about 55 degrees. To bring the water
to boiling, we have to raise the temperature 212 minus 55 = 157
degrees.

157 X 0.25 pounds = 39.25 BTU's. That's still too much energy to be
putting into the water.

Why do microwave users want to pour so much excess energy into the
water that they are boiling? Why boil a cup of water to stir
a spoonful of instant coffee mix into it and then have to wait for the
water to cool down so they can drink their coffee without burning
their mouth?

Well, they aren't just heating the water, they have to heat the cup
too, and the specific heat of the cup's material is different from the
specific heat of water, which is 1.0.

To convert microwave wattage to BTU's, multiply times 0.0586.

My microwave puts out 900 watts on high, so it is pouring 900 X 0.0586
= 52.7 BTU's into the tea cup full of water in a minute.

The water absorbs heat because the molecules of water are polarized
and the alternating electromagnetic field of the microwaves sends the
molecules spinning and bumping into each other.

52.7 divided by 0.25 = 211 degrees, if the water was all that was
being heated, instead of the water *and* the cup.