[Phys-L] how to make superheated water explosions

[Bill Norwood <bnorwood111@gmail.com>]

Hi Phys-L,
A few factors, some of which will be old info to you:
- At least for my mw oven, the magnetron does not start until 2 or 3
seconds after pressing start, but the fan and light start immediately.
- I can tell when the magnetron starts, because at that time the fan motor
slows and the cooking chamber light dims, both actions signaling a voltage
drop due to the heavy loading of the power line by the magnetron.
- I am suspecting that the iron in the iron-rich blackstrap molasses is
reacting to the microwaves, but I do not understand what is going on,
especially the overloading of the magnetron.
- This effect persisted even with a half cup of water accompanying the
bottle in the mw oven.
- I tried to get a video of this flashing, but with the oven atop the
fridge, and with my fumbling with camera and oven controls in a 2-4 second
interval I was afraid that a mishap might cause injury to myself or the
magnetron. Seems like a 2-person job.
- There was no heating of the bottle.
- I would gladly send anyone a pic of the bottle.
- I would gladly mail the bottle to anyone wishing to examine and
experiment with it and keep it. I do not want to take any more risks with
my oven.
- My cheapness started this problem, I was hoping that the last few drops
would easily pour out if I heated the bottle.
- For most of my runs I had wiped away all of the molasses I could access
at the neck and mouth of the bottle.
Thanks for any enlightenment.
Bill Norwood, U of MD at College Park

---------- Forwarded message ----------
From: "Bill Norwood" <bnorwood111@gmail.com>
Date: Dec 25, 2017 4:47 PM
Subject: Re: [Phys-L] how to make superheated water explosions
To: <Phys-L@phys-l.org>
Cc: "bnorwood111" <bnorwood111@gmail.com>

- So, what's going on in a microwave when one gets brilliant flashes inside
a plastic molasses bottle which has only a thin film of molasses inside and
which has a loose cap.
- Notably this commences as soon as the magnetron commences, which would be
about 3 seconds. Also the magnetron gets overloaded, and mine seemed to, so
I stopped the trials at less than 2 seconds.
- By the way, this has already made the rounds on TAP-L
Bill Norwood, U of MD at College Park.

On Dec 25, 2017 3:25 PM, "John Denker via Phys-l" <phys-l@mail.phys-l.org>
wrote:

> Y'all can probably guess what I'm about to say.......
>
> Scaling laws!
>
> I reckon scaling laws are easier and more grade-
> appropriate than most of the stuff that gets
> taught in traditional physics classes ... and
> more useful.
>
> Nucleation is the poster child for scaling laws:
>  -- The energy associated with pressure inside the
>   bubble scales like volume, i.e. like radius cubed.
>  -- The energy associated with surface tension
>   scales like surface area, i.e. like radius squared.
>  ==> Therefore small bubbles get crushed, whereas
>   large bubbles grow.
>
>
> Safety suggestion:  If you're going to experiment
> with superheated water, please please please use
> small amounts in a shallow dish, and use full
> chem-lab-style blast protection.  The problem is
> that these experiments work too well.  If the
> superheated water nucleates at the bottom of a
> tall vessel, it could very well launch most of
> the contents.  It could burn you right through
> your clothes, not to mention what happens to
> unprotected skin.
>
> Diet coke and mentos is safer than superheated
> water.
>
> For adult audiences:  For centuries it has been
> traditional to serve Pilsener beer in tall fire-
> polished glasses, with a small nick in the bottom
> to serve as a nucleation site.  Nowadays it is
> trendy for breweries to laser-etch their logo at
> the bottom of the glass, so for example you can
> get some Heineken with a star-shaped column of
> tiny bubbles rising through it.
>
> For safety reasons I don't recommend it, but if
> you insist on experimenting with superheated water,
> you don't need fancy fire-polished glassware.  A
> thin layer of cooking oil suffices to fill the
> innumerable tiny scratches in ordinary household
> glassware.  Add some water, boil it once (in the
> microwave) to get rid of the dissolved gases, then
> reheat it.  You can superheat it by a considerable
> margin.  If you drop in a boiling chip it will
> instantly boil.  If you keep heating it until it
> boils without a boiling chip, it will be unpredictable
> but likely quite violent.
>
> Popcorn is not what I consider an example of nucleation,
> but it is on-topic for this thread, because it does
> involve the sudden release of superheated steam (along
> with molten cornstarch).
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