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Re: microwave, RF heating



At 13:04 5/29/00 -0400, you wrote:
At 08:26 AM 5/29/00 -0400, Chuck Britton wrote:
We had a MicroWave/IR spectroscopist PhD working for us as a
long-term sub, a coupla years back.
He INSISTED that MicroWave heating is ENTIRELY a conductivity effect
and that there are NO significant resonances anywhere near the 2.4
GHz household MicroWave frequency.

Here's an experiment folks can do:

Put some cold ice (T=-5C) in a styrofoam cup. Put some cold water (T=1C)
in another cup. Put both in the microwave oven at the same time. Cook
until the water begins to boil, indicating you have imparted about 99 cal/g
to the water.

What do you think happens to the ice?
A) If you believe in the "OH bond stretching" explanation recently put
forth in this thread, you presumably expect the ice to have picked up
roughly 99 cal/g also. Since melting the ice only requires (80+5) cal/g,
the ice should all be melted.
B) If you believe in the "conductivity" explanation, you presumably
expect that the ice is hardly affected at all.

I'm afraid some well-intended experimenters will be led astray by this
excellent experimental proposal unless they remember that microwave ovens
are notorious for their uneven heating effects, which is why the canny
experimenter will ensure that there is an internal turntable rotating
often enough to integrate the spatial inhomogeneity of the em field.

The ruling explanation for [at least one kind of] microwave absorption
is bond rotation - rather than molecular 'hand clapping' or stretching.
Can one on prior principle, deduce if bond rotation is hindered in
a crystal lattice, I ask myself?


brian whatcott <inet@intellisys.net>
Altus OK