28 Sep
2012
28 Sep
'12
10:55 a.m.
At 12:00 -0500 9/28/12, Rob wrote:
Many years ago, I actually had a microwave
intermittently turn on by
itself... We (usually) took to leaving a jug of water in it while
quickly sourcing a replacement.
This may not be the best idea, unless your water is "dirty"
(in the sense of having something suspended that forms nucleation
sites for steam bubbles). Our water is "clean", and my wife once
decided to try to heat some up in our microwave. It superheated by a
noticeable amount, then finally boiled off catastrophically. Big
cloud of steam, microwave door blown open, loud noise, 100 C water
splashing around the kitchen. There was some damage apparent later in
the switch that should normally turn the thing off when the door is
open, which I eventually had to replace, but otherwise the microwave
itself was OK.
Maybe this is an unusual event and almost certainly it
depends on what container the water is in, but I'd use a little
caution with that approach given our experience.
Howzabout a pile of CD's or marshmallows or a crate of eggs
in there instead? ;-) OK seriously, wet towel or wheel of cheese in a
bowl or something that won't superheat and has not much mechanical
integrity? Physics majors, any good suggestions? Oatmeal in the water?
--
- Mark 210-379-4635
-----------------------------------------------------------------------
Large Asteroids headed toward planets
inhabited by beings that don't have
technology adequate to stop them:
Think of it as Evolution in Fast-Forward.
28 Sep
28 Sep
11:17 a.m.
On Sep 28, 2012, at 1:55 PM, Mark Tapley wrote:
At 12:00 -0500 9/28/12, Rob wrote:
I was always under the impression that that sort of story was an urban
legend. The physics isn't out of the question, I just can't imagine
any container in a household that wouldn't provide a sufficiently
rough surface to nucleate. Surprised to hear it's a thing!
Either way, though, leaving the water jug in there would provide a
sufficient microwave energy sink to take the "heat" for a few minutes
in case it catches you by surprise; a jug of hot water is a lot better
than a fire. I don't think the intent was to then remove the jug and
use the water.
- Dave
Many years ago, I actually had a microwave
intermittently turn on by
itself... We (usually) took to leaving a jug of water in it while
quickly sourcing a replacement.
This may not be the best idea, unless your water is "dirty" (in the sense of
having something suspended that forms nucleation sites for steam bubbles). Our water is
"clean", and my wife once decided to try to heat some up in our microwave. It
superheated by a noticeable amount, then finally boiled off catastrophically. Big cloud of
steam, microwave door blown open, loud noise, 100 C water splashing around the kitchen.
There was some damage apparent later in the switch that should normally turn the thing off
when the door is open, which I eventually had to replace, but otherwise the microwave
itself was OK. 
11:32 a.m.
New subject: Microwave sink
On 9/28/12 1:17 PM, David Riley wrote:
On Sep 28, 2012, at 1:55 PM, Mark Tapley wrote:
A common canning jar is smooth enough to superheat "soft" water.
Personal experience, trip to the opthamologist, etc...
Doc
At 12:00 -0500 9/28/12, Rob wrote:
I was always under the impression that that sort of story was an
urban legend. The physics isn't out of the question, I just can't
imagine any container in a household that wouldn't provide a
sufficiently rough surface to nucleate. Surprised to hear it's a
thing! Many years ago, I actually had a microwave
intermittently turn on
by itself... We (usually) took to leaving a jug of water in it
while quickly sourcing a replacement.
This may not be the best idea, unless your water is "dirty" (in the
sense of having something suspended that forms nucleation sites for
steam bubbles). Our water is "clean", and my wife once decided to
try to heat some up in our microwave. It superheated by a
noticeable amount, then finally boiled off catastrophically. Big
cloud of steam, microwave door blown open, loud noise, 100 C water
splashing around the kitchen. There was some damage apparent later
in the switch that should normally turn the thing off when the door
is open, which I eventually had to replace, but otherwise the
microwave itself was OK. 
3:04 p.m.
New subject: Microwave sink
On 28/09/2012 19:32, Doc Shipley wrote:
I once got superheated coffee in my favourite mug. I mis-set the timer,
and although I thought the mug handle seemed unusually hot when I took
it out, it wasn't until I added the sugar that I found out why. That
was very messy.
--
Pete Peter Turnbull
Network Manager
University of York
On 9/28/12 1:17 PM, David Riley wrote:
I was always
under the impression that that sort of story was an
urban legend. The physics isn't out of the question, I just can't
imagine any container in a household that wouldn't provide a
sufficiently rough surface to nucleate. Surprised to hear it's a
thing!
A common canning jar is smooth enough to superheat "soft" water.
Personal experience, trip to the opthamologist, etc... 
4:05 p.m.
New subject: Microwave sink
On 09/28/2012 03:04 PM, Pete Turnbull wrote:
I once got superheated coffee in my favourite mug. I
mis-set the timer,
and although I thought the mug handle seemed unusually hot when I took
it out, it wasn't until I added the sugar that I found out why. That
was very messy.
That's how I learned to make microwave tea with the teabag in the water
before the cup goes into the mouth of the beast, instead of after.
One other microwave-related burn was microwaving a cup of potato-leek
instant soup-in-a-paper cup. I miscalculated the temperature and
involuntarily squeezed the cup when I pulled it out of the oven. My
face was an ugly mess (not that it isn't usually) for a couple of weeks
after that.
I've since made it a rule not to microwave soups, noodles, etc. in the
cups that are part of the packaging.
--Chuck
4:35 p.m.
New subject: Microwave sink
On Sep 28, 2012, at 6:04 PM, Pete Turnbull wrote:
I once got superheated coffee in my favourite mug. I
mis-set the timer,
and although I thought the mug handle seemed unusually hot when I took
it out, it wasn't until I added the sugar that I found out why. That
was very messy.
Further confirming my bias towards cold, black coffee. :-)
- Dave
11:38 a.m.
New subject: Microwave sink
On 09/28/2012 02:17 PM, David Riley wrote:
I was always under the impression that that sort of story was an urban
legend. The physics isn't out of the question, I just can't imagine
any container in a household that wouldn't provide a sufficiently
rough surface to nucleate. Surprised to hear it's a thing!
Nope, it's real. It happened to me with a glazed mug about 15 years
ago. I touched the mug and it virtually detonated. Fortunately it
wasn't very full, but it still hurt.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
Many years ago, I actually had a microwave
intermittently turn on by
itself... We (usually) took to leaving a jug of water in it while
quickly sourcing a replacement.
This may not be the best idea, unless your water is "dirty" (in the sense of
having something suspended that forms nucleation sites for steam bubbles). Our water is
"clean", and my wife once decided to try to heat some up in our microwave. It
superheated by a noticeable amount, then finally boiled off catastrophically. Big cloud of
steam, microwave door blown open, loud noise, 100 C water splashing around the kitchen.
There was some damage apparent later in the switch that should normally turn the thing off
when the door is open, which I eventually had to replace, but otherwise the microwave
itself was OK. 
11:51 a.m.
New subject: Microwave sink
On 9/28/12 11:38 AM, Dave McGuire wrote:
Nope, it's real. It happened to me with a
glazed mug about 15 years
ago. I touched the mug and it virtually detonated. Fortunately it
wasn't very full, but it still hurt.
Happened to me about a year ago in a glass mug.
1:11 p.m.
New subject: Microwave sink
super cooling is possible too. We did it with a water / sugar solution
back in the chemistry class day.
the superheating was done by the teacher for all to watch, so we didn't
toast anyone trying the experiment on their own. Also was not done with
microwave.
jim
On 9/28/2012 11:51 AM, Al Kossow wrote:
Happened to me about a year ago in a glass mug.
8:04 p.m.
New subject: Microwave sink
On Fri, Sep 28, 2012 at 2:38 PM, Dave McGuire <mcguire at neurotica.com> wrote:
I had an incident a few weeks ago at work - I was heating water for
tea in an ordinary (and somewhat new) ceramic coffee mug. I bumped it
getting it out (the microwave is on a shelf over the sink and above my
eye-level) and it roiled furiously with a whooshing hiss. No major
splashing or injury, but I was a bit startled.
-ethan
I was always
under the impression that that sort of story was an urban
legend. The physics isn't out of the question, I just can't imagine
any container in a household that wouldn't provide a sufficiently
rough surface to nucleate. Surprised to hear it's a thing!
Nope, it's real. It happened to me with a glazed mug about 15 years
ago. I touched the mug and it virtually detonated. Fortunately it
wasn't very full, but it still hurt. 
30 Sep
30 Sep
4:38 a.m.
On 28 September 2012 20:17, David Riley <fraveydank at gmail.com> wrote:
I was always under the impression that that sort of story was an urban
legend.
I have often boiled water in the microwave; when I had a Norwegian
fianc?e, she did not own a kettle & always boiled water in the
microwave. (Electricity is *very* cheap there, as they have lots of
hydroelectric plants.) The thing is, normally, the water just boils.
The physics isn't out of the question, I just
can't imagine
any container in a household that wouldn't provide a sufficiently
rough surface to nucleate. Surprised to hear it's a thing!
Almost any ordinary container has multiple nucleation points. Pour a
fizzy drink into any household object; every chain of bubbles rising
from the sides and bottom is coming from a nucleation
point.
In the case of water in a mug or something, it can get to a good few
degrees over 100?C (sorry, I cannot fathom Fahrenheit & have no clue
what boiling point is in it; I use SI units, like all sensible people)
and thus when you drop in a teabag or a spoonful of coffee, *FOOM*,
instant boiling and water all over the counter-top.
But getting hot enough to become superheated? That I have /never/
seen, even when someone set the timer wrong and the container boiled
dry.
Now, if it was a /sealed/ container, a reasonably strong one, able to
withstand a lot of pressure before it blew - OK.
But an open vessel? No, I don't believe it. Even scrupulously clean
laboratory glassware has lots of nucleation points; getting water to
supercool or superheat without crystallising or boiling is actually
quite hard to do. Supercooling is easier but still nontrivial; it can
happen by accident, but rarely.
Either way, the further the temperature goes past the normal
phase-change temperature, the smaller the imperfection needed to start
the transition.
--
Liam Proven ? Profile: http://lproven.livejournal.com/profile
Email: lproven at cix.co.uk ? GMail/G+/Twitter/Flickr/Facebook: lproven
MSN: lproven at hotmail.com ? Skype/AIM/Yahoo/LinkedIn: liamproven
Tel: +44 20-8685-0498 ? Cell: +44 7939-087884
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aek＠bitsavers.org -
cclist＠sydex.com -
doc＠vaxen.net -
ethan.dicks＠gmail.com -
fraveydank＠gmail.com -
jws＠jwsss.com -
lproven＠gmail.com -
mcguire＠neurotica.com -
mtapley＠swri.edu -
pete＠dunnington.plus.com