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Re: microwave, RF heating

¶ (1) I thought it was safe enuff, because I was convinced that the olive oil would
absorb, and it's mass was ~ that of one glass. Note that the temp of the glass was near
that of the oil (36 C deg + 21 deg C) an ideal calorimeter! I've never read (oven
instructions or elsewhere) that one should include an absorber (or never operate an oven
mty.). However, I was told this long before I owned one, so when checking house wares for
"safeness", I include a mug of water. That's how I discovered that "melmac" was not
"safe." Not so incidentally, (I pray I'm not repeating) melmac is melamine resin probably
with a filler (cellulose or mineral fiber?). melamine = cyanamide trimer + formaldehyde =
melamine resin, and, therefore, has C=O bonds.



¶ (2) As an experiment, I was only interested in the relative absorption. The diff. in
absorption is greater than the data indicates, as the other glass heated the mineral oil.

bc


P.s. note that in the previous xpt. (dry milk and sugar), wherein I had no idea of their
absorbency, I did include a mug of water.



John Denker wrote:

At 11:00 PM 5/30/00 -0700, Bernard G. Cleyet & Nancy Ann Seese wrote:

In two identical (well, from the same mold) goblets
equal masses of U.S.P. mineral oil
(edible) and olive oil 108 g.

temp rises (respectively) four C. degs. and 36
(note the glasses absorb, as the bases of
both were quite warm (~ 45 C.)

This situation is best avoided, for two reasons. Remember, ovens put out
constant power (to a reasonable approximation). So if you put in samples
none of which has a high absorption coefficient, the power still goes
_somewhere_. The standing-wave voltage (i.e. the energy density) builds up
to very high levels, until it can attack whatever weak absorbers are around.
1) If the energy goes into the stem or base of a typical glass, the
consequences can be shattering. I've seen it done.
2) Also in this case you don't learn nearly as much about the
sample(s). In particular the results are hard to compare with other runs
where the voltage was different.

The right strategy is to regulate the "effective source impedance" by
always including a known amount of a good absorber. That gives you
something closer to a constant-voltage (rather than constant-power)
situation, improving safety and making the results easier to interpret.