Water boiled in Microwaves can Explode
Nancree
heated past boiling, can explode.
---------------
When you heat pure water in a smooth cup using a microwave oven, there is
virtually nothing present to help nucleation occur. The water can heat right
past its boiling temperature without boiling. The water then superheats--its
temperature rising above its boiling temperature. When you shake the cup or
sprinkle something like sugar or salt into it, you initiate nucleation and the
water then boils violently.
----------------------------
From "Ask Jeeves How Stuff Works"
Kris Hildrum
Ward Stewart <wste...@hawaii.rr.com> wrote:
>superheated I cannot imagine water so pure, a container so smooth or a
>micro-wave oven so entirely motion and vibration free as to allow this
>to happen in the real world.
I'm not a physicist, but when I was in highschool chemistry, we
used boiling chips to provide a place for bubbles to form when boiling
water.
Kris
Siobhan Perricone
wrote:
>Ward Stewart wrote:
>
>> Let's ask if there is a physicist in our group -- while water may be
>> superheated I cannot imagine water so pure, a container so smooth or a
>> micro-wave oven so entirely motion and vibration free as to allow this
>> to happen in the real world.
>
>
>Let's ask the scars on my hand left over from the calm-looking water
>that I heated in the microwave that virtually 'blew up' when I gently
>lowered a tea bag into it years ago. Never again...
Microwaves get water to boiling without convection and what that does is,
when you put something in the water, all the air that's in there that would
have normally boiled to the surface due to convection is still in there.
So when you put something into the water, all that air releases all at
once.
The water isn't any hotter, it's just releasing the air all at once. In a
kettle, the water is heated from the bottom, so the hot water rises, the
colder water sinks, and because there's movement, the air gets released as
it bubbles. In a microwave, there is no water movement, it gets heated on
all sides, so the air doesn't have anywhere to go until you disturb it.
It's not superheated, it's just full of hot air.
--
Siobhan Perricone
"Truth decays into beauty, while beauty soon becomes merely charm. Charm
ends up as strangeness, and even that doesn't last, but up and down are
forever." - The Laws of Physics
Ward Stewart
>A few weeks ago there was a discussion here on why water that is boiled, or
>heated past boiling, can explode.
>---------------
> When you heat pure water in a smooth cup using a microwave oven, there is
>virtually nothing present to help nucleation occur. The water can heat right
>past its boiling temperature without boiling. The water then superheats--its
>temperature rising above its boiling temperature. When you shake the cup or
>sprinkle something like sugar or salt into it, you initiate nucleation and the
>water then boils violently.
>----------------------------
>From "Ask Jeeves How Stuff Works"
>
>
Let's ask if there is a physicist in our group -- while water may be
superheated I cannot imagine water so pure, a container so smooth or a
micro-wave oven so entirely motion and vibration free as to allow this
to happen in the real world.
ward
-------------------------------------------------
Orohippus, Mesohippus, Miohippus, Protohippus,
Pliohippus, Equus. Evolution is just a theory.
So is gravity.*
-------------------------------------------------
Steve Kramer
> Let's ask if there is a physicist in our group -- while water may be
> superheated I cannot imagine water so pure, a container so smooth or a
> micro-wave oven so entirely motion and vibration free as to allow this
> to happen in the real world.
Let's ask the scars on my hand left over from the calm-looking water
that I heated in the microwave that virtually 'blew up' when I gently
lowered a tea bag into it years ago. Never again...
Steve
Osaka, Japan
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PENMART10
Stewart) writes:
>On 28 Jun 2000 23:33:57 GMT, nan...@aol.com (Nancree) wrote:
>
>>A few weeks ago there was a discussion here on why water that is boiled, or
>>heated past boiling, can explode.
>>---------------
>> When you heat pure water in a smooth cup using a microwave oven, there is
>>virtually nothing present to help nucleation occur. The water can heat right
>>past its boiling temperature without boiling. The water then superheats--its
>>temperature rising above its boiling temperature. When you shake the cup or
>>sprinkle something like sugar or salt into it, you initiate nucleation and
the
>>water then boils violently.
>>----------------------------
>>From "Ask Jeeves How Stuff Works"
>Let's ask if there is a physicist in our group -- while water may be
>superheated I cannot imagine water so pure, a container so smooth or a
>micro-wave oven so entirely motion and vibration free as to allow this
>to happen in the real world.
>
>ward
Don't bet on it, you'd lose.
Louis A. Bloomfield, Professor of Physics, The University of Virginia
http://howthingswork.virginia.edu
(Q) I always thought that pure water cannot exceed 100° Celsius at atmospheric
pressure without first turning into its gaseous state. How is it that the water
heated in the microwave oven can superheat and exceed 100° Celsius? -- AC
(A) The relative stabilities of liquid and gaseous water depend on both
temperature and pressure. To understand this, consider what is going on at the
surface of a glass of water. Water molecules in the liquid water are leaving
the water's surface to become gas above it and water molecules in the gas are
landing and joining the liquid water below. It's like a busy airport, with lots
of take-offs and landings. If the glass of water is sitting in an enclosed
space, the arrangement will eventually reach equilibrium--the point at which
there is no net transfer of molecules between the liquid in the glass and the
gas above it. In that case, there will be enough water molecules in the gas to
ensure that they land as often as they leave.
The leaving rate (the rate at which molecules break free from the liquid water)
depends on the temperature. The hotter the water is, the more frequently water
molecules will be able to break away from their buddies and float off into the
gas. The landing rate (the rate at which molecules land on the water's surface
and stick) depends on the density of molecules in the gas. The more dense the
water vapor, the more frequently water molecules will bump into the liquid's
surface and land.
As you raise the temperature of the water in your glass, the leaving rate
increases and the equilibrium shifts toward higher vapor density and less
liquid water. By the time you reach 100° Celsius, the equilibrium vapor
pressure is atmospheric pressure, which is why water tends to boil at this
temperature (it can form and sustain steam bubbles). Above this temperature the
equilibrium vapor pressure exceeds atmospheric pressure. The liquid water and
the gas above it can reach equilibrium, but only if you allow the pressure in
your enclosed system to exceed atmospheric pressure. However, if you open up
your enclosed system, the water vapor will spread out into atmosphere as a
whole and there will be a never-ending stream of gaseous water molecules
leaving the glass. Above 100° C, liquid water can't exist in equilibrium with
atmospheric pressure gas, even if that gas is pure water vapor.
So how can you superheat water? Don't wait for equilibrium! The road to
equilibrium may be slow; it may take minutes or hours for the liquid water to
evaporate away to nothing. In the meantime, the system will be out of
equilibrium, but that's ok. It happens all the time: a snowman can't exist in
equilibrium on a hot summer day, but that doesn't mean that you can't have a
snowman at the beach... for a while. Superheated water isn't in equilibrium
and, if you're patient, something will change. But in the short run, you can
have strange arrangements like this without any problem.
(Q) When I heat a cup of water in my microwave oven to 200 degrees, then put a
spoonful of instant coffee in the hot water, it foams up. Hot water from a
coffee maker does not do this. Why does water heated in a microwave oven do
this? -- WAH, Library, Pennsylvania
(A) The microwave oven is superheating the water to a temperature slightly
above its boiling temperature. It can do this because it doesn't help water
boil the way a normal coffee maker does. For water to boil, two things must
occur. First, the water must reach or exceed its boiling temperature--the
temperature at which a bubble of pure steam inside the water becomes sturdy
enough to avoid being crushed by atmospheric pressure. Second, bubbles of pure
steam must begin to nucleate inside the water. It's the latter requirement
that's not being met in the water you're heating with the microwave. Steam
bubbles rarely form of their own accord unless the water is far above its
boiling temperature. That's because a pure nucleation event requires several
water molecules to break free of their neighbors simultaneously to form a tiny
steam bubble and that's very unlikely at water's boiling temperature. Instead,
most steam bubbles form either at hot spots, or at impurities or
imperfections--scratches in a metal pot, the edge of a sugar crystal, a piece
of floating debris. When you heat clean water in a glass container using a
microwave oven, there are no hot spots and almost no impurities or
imperfections that would assist boiling. As a result, the water has trouble
boiling. But as soon as you add a powder to the superheated water, you trigger
the formation of steam bubbles and the liquid boils madly.
(Q) We heated a cup of water in a microwave oven for 2-1/2 minutes and then
added a spoonful of sugar to it. A rush of tiny bubbles ensued. Did the sugar
crystals nucleate boiling water molecules that were trapped by surrounding
cooler molecules or did they nucleate the release of dissolved air? -- VC
(A) When you heated the water in the microwave oven, you raised its temperature
above its boiling temperature, yet it did not boil. While the water was hot
enough to boil--that is, any steam bubble that formed in this hot water would
have a pressure at least equal to atmospheric pressure and would not be crushed
by the surrounding air--the water was having a difficult time forming steam
bubbles. For a bubble to appear, several water molecules must simultaneously
break free of their neighbors to form a bubble nucleus. Once this nucleation
has occurred, additional water molecules can evaporate into the bubble, making
it grow. This nucleation is rare in pure water near its boiling temperature; in
most cases it is assisted by hot spots at the bottom of a pot on the stove or
by imperfections in the container holding the water. But when you heat water in
a glass or glazed ceramic container in a microwave oven, there are no hot spots
or surface imperfections to nucleate the bubbles. The water superheats above
its boiling temperature. When you add sugar crystals to this superheated water,
the crystal's sharp edges and points assist the nucleation of steam bubbles and
the water boils violently.
Your suggestions for why the bubbles appear raise two interesting points.
First, in a thermal system such as hot water, you can't identify some molecules
as being boiling hot and others as being cooler--temperature is a property of
the entire system and not of individual molecules. However, at a given instant,
there are molecules with more energy than their neighbors and it is these
energetic molecules that may break free of their neighbors to form a bubble
nucleus.
Second, water often contains dissolved gases and these gases come out of
solution when the water is heated. While many of the gas molecules leave
through the water's surface, some of them may leave as bubbles from within the
water. This gas bubble formation requires nucleation as well, which is why
these bubbles often appear on the inner surfaces of a metal pot on the
stove--flaws in the pot's surface assist bubble nucleation. But these gas
bubbles aren't what you observed; there just isn't that much dissolve gas. You
can prove that the bubbles you observe are steam: repeat the experiment several
times with the same water. Each time you heat the water and add sugar, it
bubbles wildly--something that wouldn't be possible if you were simply
releasing dissolved gases from the water.
---
Sheldon
````````````
On a recent Night Court rerun, Judge Harry Stone had a wonderful line:
"I try to keep an open mind, but not so open that my brains fall out."
PENMART10
<ast...@sover.net> writes:
>On Thu, 29 Jun 2000 09:46:34 +0900, Steve Kramer <stev...@osb.att.ne.jp>
>wrote:
>
>>Ward Stewart wrote:
>>
>>> Let's ask if there is a physicist in our group -- while water may be
>>> superheated I cannot imagine water so pure, a container so smooth or a
>>> micro-wave oven so entirely motion and vibration free as to allow this
>>> to happen in the real world.
>>
>>
>>Let's ask the scars on my hand left over from the calm-looking water
>>that I heated in the microwave that virtually 'blew up' when I gently
>>lowered a tea bag into it years ago. Never again...
>
>Microwaves get water to boiling without convection and what that does is,
>when you put something in the water, all the air that's in there that would
>have normally boiled to the surface due to convection is still in there.
>So when you put something into the water, all that air releases all at
>once.
>
>The water isn't any hotter, it's just releasing the air all at once. In a
>kettle, the water is heated from the bottom, so the hot water rises, the
>colder water sinks, and because there's movement, the air gets released as
>it bubbles. In a microwave, there is no water movement, it gets heated on
>all sides, so the air doesn't have anywhere to go until you disturb it.
>
>It's not superheated, it's just full of hot air.
Like you.
Science was not your favorite subject.
Nancree
<"The water isn't any hotter, it's just <releasing the air all at once. In a
kettle, the water is heated from the <bottom"
----------------------------------
Yes, it is hotter. For all you ever wanted to know about microwaves, go to
<howthingswork.virginia.edu> and type "microwave ovens" in the Search Box.
Nancree
David Carnell
Yes, dust in water, scratches on the container, dissolved air, etc. will all work
against superheating water. I boil water in the nuker as standard practice. The
whole idea that water will get superheated to where it will boil suddenly (not
explode) id pretty far-fetched.
Ward Stewart wrote:
> On 28 Jun 2000 23:33:57 GMT, nan...@aol.com (Nancree) wrote:
>
> >A few weeks ago there was a discussion here on why water that is boiled, or
> >heated past boiling, can explode.
> >---------------
> > When you heat pure water in a smooth cup using a microwave oven, there is
> >virtually nothing present to help nucleation occur. The water can heat right
> >past its boiling temperature without boiling. The water then superheats--its
> >temperature rising above its boiling temperature. When you shake the cup or
> >sprinkle something like sugar or salt into it, you initiate nucleation and the
> >water then boils violently.
> >----------------------------
> >From "Ask Jeeves How Stuff Works"
> >
> >
> Let's ask if there is a physicist in our group -- while water may be
> superheated I cannot imagine water so pure, a container so smooth or a
> micro-wave oven so entirely motion and vibration free as to allow this
> to happen in the real world.
>
Siobhan Perricone
>>>> Let's ask if there is a physicist in our group -- while water may be
>>>> superheated I cannot imagine water so pure, a container so smooth or a
>>>> micro-wave oven so entirely motion and vibration free as to allow this
>>>> to happen in the real world.
>>>
>>>
>>>Let's ask the scars on my hand left over from the calm-looking water
>>>that I heated in the microwave that virtually 'blew up' when I gently
>>>lowered a tea bag into it years ago. Never again...
>>
>>Microwaves get water to boiling without convection and what that does is,
>>when you put something in the water, all the air that's in there that would
>>have normally boiled to the surface due to convection is still in there.
>>So when you put something into the water, all that air releases all at
>>once.
>>
>>The water isn't any hotter, it's just releasing the air all at once. In a
>>kettle, the water is heated from the bottom, so the hot water rises, the
>>colder water sinks, and because there's movement, the air gets released as
>>it bubbles. In a microwave, there is no water movement, it gets heated on
>>all sides, so the air doesn't have anywhere to go until you disturb it.
>>
>>It's not superheated, it's just full of hot air.
>
>Like you.
>
>Science was not your favorite subject.
*sigh* I just looked up "superheat" and it doesn't mean what I thought it
meant. So yes, the water is superheated. However, if you'll bother to
look at the rest of what I said, I'm correct. The whole point is, in a
microwave the water is still, so the air doesn't get released until
something stirs it up, when the air gets released all at once.
Why do you have to be such a jerk about things? Why couldn't you have
pointed that out to me nicely? It's not like I was being an idiot or
anything, I made one simple mistake in an otherwise correct statement.
Nancree
Dave wrote
>The whole idea that water will get superheated to where it will boil suddenly
>(not
>explode) id pretty far-fetched.
Hi, Dave,
Here is a fascinating article by a Professor of Physics at U. of Virginia. It
gives his version of "superheated water". Also, click on the hyperlink to a
man's description of what happened to him when water "exploded" (or supply your
own word), and burnt his arm, leaving only drops in the cup. (I've had a
similar experience, though not hurt so badly). The water does just "leap", or
"spout", or whatever, out of the container, under certain circumstances.
===============================
Quoted below from http://howthingswork.virginia.edu/
Type "Microwave ovens" into the Search Box.
The third question down deals with this superheated water phenomenon. The
author is Louis A. Bloomfield, Prof. of Physics, U. of Virginia.
================================
There is a story circulating by email about a 26 year old man who heated a cup
of water in a microwave oven and had it "explode in his face" when he took it
out. He suffered serious burns as a result. Is this possible and, if so, how
did it happen? -- JJ, Kirksville, Missouri
Yes, this sort of accident can happen. The water superheated and then boiled
violently when disturbed. Here's how it works:
Water can always evaporate into dry air, but it normally only does so at its
surface. When water molecules leave the surface faster than they return, the
quantity of liquid water gradually diminishes. That's ordinary evaporation.
However, when water is heated to its boiling temperature, it can begin to
evaporate not only from its surface, but also from within. If a steam bubble
forms inside the hot water, water molecules can evaporate into that steam
bubble and make it grow larger and larger. The high temperature is necessary
because the pressure inside the bubble depends on the temperature. At low
temperature, the bubble pressure is too low and the surrounding atmospheric
pressure smashes it. That's why boiling only occurs at or above water's boiling
temperature. Since pressure is involved, boiling temperature depends on air
pressure. At high altitude, boiling occurs at lower temperature than at sea
level.
But pay attention to the phrase "If a steam bubble forms" in the previous
paragraph. That's easier said than done. Forming the initial steam bubble into
which water molecules can evaporate is a process known as "nucleation." It
requires a good number of water molecules to spontaneously and simultaneously
break apart from one another to form a gas. That's a rare event. Even in a cup
of water at several degrees above the boiling temperature, you might have to
wait minutes before such a rare event occurred. In reality, it usually occurs
at a defect in the cup or an impurity in the water--anything that can help
those first few water molecules form the seed bubble. When you heat water on
the stove, the hot spots at the bottom of the pot or defects in the pot bottom
usually assist nucleation so that boiling occurs soon after the boiling
temperature is reached. But when you heat pure water in a smooth cup using a
microwave oven, there is virtually nothing present to help nucleation occur.
The water can heat right past its boiling temperature without boiling. The
water then superheats--its temperature rising above its boiling temperature.
When you shake the cup or sprinkle something like sugar or salt into it, you
initiate nucleation and the water then boils violently.
Fortunately, serious microwave superheating accidents are unusual--this is the
first injury I've ever heard about. You could minimize the chance of this sort
of problem by deliberately nucleating boiling before removing the cup from the
microwave. Inserting a metal spoon or almost any food into the water should
trigger boiling in superheated water. A pinch of sugar will do the trick,
something I've often noticed when I heat tea in the microwave.
For a reader's story about a burn he received from superheated water in a
microwave, touch here.
Nancree
====================
Since this "link" didn't copy from my previous post, here is the report of the
man who burned his arm badly from superheated water "exploding" from the
microwave container.
Below quotation is from;
http://howthingswork.virginia.edu/
(Search for "microwave ovens)
==============================
I received the following story of someone who was burned by water superheated
in a microwave oven. I hope you find it useful. -- Lou Bloomfield
--------------------------------------------------------------------------
------
The reader sent in the following note:
"I am a 44-year-old man who was injured by exploding water. Here is how it
happened:
I was boiling about two cups of water for tea in my microwave in a clear
Pyrex-type measuring cup, and when I didn't see it boiling, cranked up the
microwave for another few minutes. I somewhat absent-mindedly did this SEVERAL
TIMES, and when it never boiled, figured there must be something wrong with the
oven. Thankfully, it crossed my mind that I should be cautious, and reached in
for the cup with my face away from the door; because the water literally
exploded out of the cup. It instantly covered from half of my hand to midway up
my upper arm -- and I'm six and a half feet tall. Only a few drops of water
were left in the cup.
I called the emergency room, I called the Optim Nurse Line, and I called a
friend who I knew had an aloe vera plant. I ended up self-treating with
fresh-squeezed aloe juice several times a day, followed with clean bandages,
but it was very painful for quite a while. I ended up with just a little
blistering, and a reddish tint that faded over a few months' time.
I'm sure that my experience was not "reported." In fact, I didn't talk about it
much, because it was so weird and incredible. Some people looked at me like
they weren't sure they believed me, so I shut up. I am very glad I found some
validation for my experience, so I can show it to them. It could be that many
cases of this occur but go officially unreported.
I'm also glad that I ran across your scientific explanation, because it totally
baffled me and the few I asked about it.
If it is of any interest to you or anyone else, I will put you in contact with
people who saw my burns and helped me treat them, and I will gladly give you my
address, etc."
PENMART10
<ast...@sover.net> writes:
>>Microwaves get water to boiling without convection and what that does is,
>>>when you put something in the water, all the air that's in there that would
>>>have normally boiled to the surface due to convection is still in there.
>>>So when you put something into the water, all that air releases all at
>>>once.
>>>
>>>The water isn't any hotter, it's just releasing the air all at once. In a
>>>kettle, the water is heated from the bottom, so the hot water rises, the
>>>colder water sinks, and because there's movement, the air gets released as
>>>it bubbles. In a microwave, there is no water movement, it gets heated on
>>>all sides, so the air doesn't have anywhere to go until you disturb it.
>>>
>>>It's not superheated, it's just full of hot air.
>>
>>Like you.
>>
>>Science was not your favorite subject.
>
>*sigh* I just looked up "superheat" and it doesn't mean what I thought it
>meant. So yes, the water is superheated. However, if you'll bother to
>look at the rest of what I said, I'm correct.
>Why couldn't you have pointed that out to me nicely?
I was nice, actually I was exceptionally kind!
> It's not like I was being an idiot or anything,
You really don't want me to go there.
>Siobhan Perricone
No part of what you said is correct. You could not have displayed less
ignorance had you worked on that debauchery for a year. All I stated is
"Science was not your favorite subject." I stand by my statement, plus now
add: educating yourself was/is not your favorite pastime. Stick to what you
excel at: FM shoes! ;)
gzywicki
>
>*sigh* I just looked up "superheat" and it doesn't mean what I
>thought it meant. So yes, the water is superheated. However,
>if you'll bother to look at the rest of what I said, I'm
>so the air doesn't get released until something stirs it up,
>when the air gets released all at once.
>
*sigh*, unfortunately as you're seeing, no, you're not correct.
The whole point is that there aren't many good sources for
the formation of steam bubbles. When you add sugar or tea or a
spoon or whatever, you suddenly present sites for all those
bubbles that have wanted to form for the time the water was 100
degrees to the time you added something, at which point the temp
may be 3, 4, or 5 degrees higher. Yes, you're also going to
nucleate disolved gasses, but there's not so much dissolved gas
that it's taking it to a rolling boil, and the process would be
the same even if you were to start with water that has had the
dissolved gasses removed. Water boils because it changes to
steam. How you missed this essential point of physical chemistry
is intriguing.
Yes, the lack of convection does play some part, but not much.
It's not like boiling a large pot on the stove where you should
stir because the heat capacity of the big mass of water is so
large that just heating from the bottom takes longer. Microwaves
excite the water from all directions - top, bottom, and sides.
The only limit is how far they can penetrate, which is determined
by the density of the food being heated and the time you nuke it.
With water, I don't think that's much of a limit. From my
understanding, the microwaves permeate and excite the entire mug
of water pretty quickly.
Another note to all - water will boil in a microwave, as all have
probably seen. The fact that water _can_ superheat without
boiling doesn't mean that it won't boil if you let it continue to
heat. If you're worried about it, just use a container that's
big enough to contain rapidly boiling water (such as a pyrex
measuring cup that hasn't been filled beyond the top measure) and
heat it until it boils. It can't "explode" into a boil if it's
already boiling.
Greg Zywicki
>Why do you have to be such a jerk about things? Why couldn't
you have
>pointed that out to me nicely? It's not like I was being an
idiot or
>anything, I made one simple mistake in an otherwise correct
statement.
>
>--
>Siobhan Perricone
>"Truth decays into beauty, while beauty soon becomes merely
charm. Charm
> ends up as strangeness, and even that doesn't last, but up and
down are
> forever." - The Laws of Physics
>
>
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Got questions? Get answers over the phone at Keen.com.
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notbob
Nancree wrote:
>
> A few weeks ago there was a discussion here on why water that is boiled, or
> heated past boiling, can explode.
> ---------------
> When you heat pure water in a smooth cup using a microwave oven, there is
> virtually nothing present to help nucleation occur. The water can heat right
> past its boiling temperature without boiling. The water then superheats--its
> temperature rising above its boiling temperature. When you shake the cup or
> sprinkle something like sugar or salt into it, you initiate nucleation and the
> water then boils violently.
> ----------------------------
> From "Ask Jeeves How Stuff Works"
This is quite fascinating. But, the learned professor's explanation
raises more questions than it answers. I also regularly boil water in
my microwave in a pyrex measuring cup. It boils ...big ol fat bubbles
that will push the water right out of the cup onto the turntable. Is
this because the water is agitated by the rotating turntable? Maybe
it's the crud in my water, which is actually quite hard in our area.
Also, why isn't this phenomena more well known?
Microwave ovens have been used by millions of people for a couple of
decades now. I would think the shear numbers would have caused many
occurrences of this phenomena. Also, that this would have generated
enough lawsuits that every microwave sold would have huge warnings on
the door and lengthy explanations in the manual and Ronco and Popiel
would be hawking scientifically designed cups with "nuclear" surfaces to
save us all from this potential catastrophe. And, 60 Minutes should
have done at least one expose. As it is, this hasn't even generated a
decent urban legend. "Entire family scalded to death by exploding cup
of coffee while Elvis' two headed Martian baby sleeps in bedroom"!!
Don't get me wrong. I'm not doubting anyone's veracity or disputing the
Prof.'s info. And, I have no doubt Steve's injury is quite real. I'm
just amazed this isn't common knowledge. Like I said, it's all quite
fascinating and I'm just doing my curious thing. You can be sure I'll
be eyeing my next cup of of hot water a little more warily.
nb
Paul M. Cook┊
turned to high and waited. Yup, water boils, really big bubbles and
everything. Nothing superheated about it, just no hotter than on the stove.
Paul
"notbob" <not...@NOThome.com> wrote in message
news:395B5450...@NOThome.com...
Ayeesha Patel
What a fascinating story! Please allow me to share my opinion.
notbob wrote:
> This is quite fascinating. But, the learned professor's explanation
> raises more questions than it answers. I also regularly boil water in
> my microwave in a pyrex measuring cup. It boils ...big ol fat bubbles
> that will push the water right out of the cup onto the turntable. Is
> this because the water is agitated by the rotating turntable? Maybe
> it's the crud in my water, which is actually quite hard in our area.
> Also, why isn't this phenomena more well known?
After reading the explanation of the Prof's, I'd say that in your cup of
water, there are plenty of nucleation site, sites that will enable the
heated water to form bubble. It can be from the impurities of your water
(perhaps mineral dissolved in it), tiny scratches on the surface of your
pyrex, and also from the motion you introduce with the turntable.
I'd think that perfectly pure body of water in a perfect container is a
rare occasion in regular household situation. Even water that we drink
day by day is not pure at all, left alone the container that we use the
water in (e.g. those white-ish spots of minerals on glass/goblets after
they are dried in the dishwashing machine can contribute as nucleation
sites, dust, etc.).
That's probably why noone tried to design such a container with enough
nucleation site, just in case we need to heat perfectly pure water
safely :) and why this phenomena is not well known. As in rare occasion
with Steve, the moment he removed the glass from the microwave (thus
introducing movement to the body of water), the water started bubbles up
like crazy that it exploded.
Very fascinating, thanks to Sheldon for sharing the article!
Ayeesha Patel
PENMART10
> I also regularly boil water in
>my microwave in a pyrex measuring cup. It boils ...big ol fat bubbles
>that will push the water right out of the cup onto the turntable. Is
>this because the water is agitated by the rotating turntable? Maybe
>it's the crud in my water, which is actually quite hard in our area.
>Also, why isn't this phenomena more well known?
Probably because folks do not to read/comprehend the manual. My GE microwave
oven manual lists several precautions in the "Important Safety Instructions"
section, one of which plainly states thusly:
• Spontaneous Boiling---Under certain special circumstances, liquids may
start to boil during or shortly after removal from the microwave oven. To
prevent burns from splashing liquid, stir the liquid briefly before removing
the container from the microwave oven.
b.s.f. lo
(using stoneware, but not Pyrex), I have nothing to add to this thread.
But I do have a microwave related question. Sometimes when I heat "dry" food on
a stoneware plate in the microwave, the plate will crack. Not crack into pieces,
but I'll hear a pop sound, and there will be a crack in the plate that wasn't
there before. (This usually happens when I microwave for more than 2-3 minutes.)
"Dry" food includes plain cooked rice, cheese and other foods that don't have a
lot of sauce or generate their own steam. This does not occur when I use Corelle
plates, or when I put a small cup of water in the oven with the plate.
Anyone know what's happening here ?
Ward Stewart
>>Water boiled in Microwaves can Explode
>====================
>Since this "link" didn't copy from my previous post, here is the report of the
>man who burned his arm badly from superheated water "exploding" from the
>microwave container.
>Below quotation is from;
>http://howthingswork.virginia.edu/
>(Search for "microwave ovens)
>==============================
>
I stand corrected -- I am also grateful for the link above --
wonderful!
ward
************************************************
"The Jews are a frightened people. Nineteen centuries
of Christian love has broken down their nerves."
Israel Zangwill
*************************************************
Nancree
"Maybe
it's the crud in my water, which is actually quite hard in our area. "
Probably so. I use filtered (reverse osmosis) water
================
NotBob also said:
"> I also regularly boil water in
>my microwave in a pyrex measuring cup. It boils ...big ol fat bubbles
>that will push the water right out of the cup onto the turntable."
Yes, this can happen. I think it's the *timing* of the heating that
matters--just the right (wrong?) moment, and it can erupt over your hand.
Again, I refer you to <howthingswork.virginia.edu> and enter the words
"Microwave oven". More than you ever wanted to know "about penguins" (Forgive
me, it's an old family joke.)
~Nancree~
Nancree
>on
>a stoneware plate in the microwave, the plate will crack. Not crack into
>pieces,
>but I'll hear a pop sound, and there will be a crack in the plate that wasn't
>there before. (This usually happens when I microwave for more than 2-3
>minutes.)
>"Dry" food includes plain cooked rice, cheese and other foods that don't have
>a
>lot of sauce or generate their own steam. This does not occur when I use
>Corelle
>plates, or when I put a small cup of water in the oven with the plate.
>
>Anyone know what's happening here ?
Yes. Not enough moisture. It could harm your magnetron.
Quote below is also from
http://howthingswork.virginia.edu/
Search for "Microwave Ovens"
(this particular question is near the end of
the Physics professor's series of answers)
================
What happens if you start the microwave oven with nothing inside?
The magnetron creates microwaves that travel into the cooking chamber and
should be absorbed there. If there is no food (or rather no water-containing
food), those microwaves will not be absorbed and will eventually find their way
back to the magnetron. Eventually the magnetron will absorb as many microwaves
as it emits. This situation is hard on the magnetron, which works best when it
has very little radiation returning to it. That's why you should never run a
microwave empty for more than a second or two.
=================
Ergo, you must have something moist in the micro while using it, or risk harm
to the magnetron.
~Nancree~
Jim Yanik
>
>Aside from saying I've also experienced "exploding" water in the microwave
>(using stoneware, but not Pyrex), I have nothing to add to this thread.
>
on
>a stoneware plate in the microwave, the plate will crack. Not crack into
pieces,
>but I'll hear a pop sound, and there will be a crack in the plate that wasn't
>there before. (This usually happens when I microwave for more than 2-3
minutes.)
>"Dry" food includes plain cooked rice, cheese and other foods that don't have
a
>lot of sauce or generate their own steam. This does not occur when I use
Corelle
>plates, or when I put a small cup of water in the oven with the plate.
>
>Anyone know what's happening here ?
I speculate that the finish coating on yout stoneware is not keeping out water
from the porous interior. Then when you heat it in the microwave,the resulting
steam bubbles crack your plate. Corelle is a tempered glass that is not
porous.I love the stuff,it's very durable.
Jim Yanik,NRA member
Lawrence Rottersman
penm...@aol.com says...
> In article <qlcmlsgnfmlvl36lj...@4ax.com>, Siobhan Perricone
> <ast...@sover.net> writes:
>
> >>Microwaves get water to boiling without convection and what that does is,
> >>>when you put something in the water, all the air that's in there that would
> >>>have normally boiled to the surface due to convection is still in there.
> >>>So when you put something into the water, all that air releases all at
> >>>once.
> >>>
> >>>The water isn't any hotter, it's just releasing the air all at once. In a
> >>>kettle, the water is heated from the bottom, so the hot water rises, the
> >>>colder water sinks, and because there's movement, the air gets released as
> >>>it bubbles. In a microwave, there is no water movement, it gets heated on
> >>>all sides, so the air doesn't have anywhere to go until you disturb it.
> >>>
> >>>It's not superheated, it's just full of hot air.
> >>
> >>Like you.
> >>
> >>Science was not your favorite subject.
> >
> >meant. So yes, the water is superheated. However, if you'll bother to
> >look at the rest of what I said, I'm correct.
>
>
>
>
Actually, you should just get lost; you are rude; pompous; and an
asshole. It's no wonder lurkers do not want to stick their heads out in
the face of such superior knowledge.
PENMART10
<lawr...@teleport.com> writes:
>In article <20000629094303...@nso-cq.aol.com>,
>penm...@aol.com says...
>> In article <qlcmlsgnfmlvl36lj...@4ax.com>, Siobhan Perricone
>> <ast...@sover.net> writes:
>> You really don't want me to go there.
>>
>
> It's no wonder lurkers do not want to stick their heads out in
>the face of such superior knowledge.
You betcha!
Hey, what kind a goofy name is that... Larrrrry Rutabagaman! :::hehehe:::
Now get back under your mulch, you ignorant root vegetable... poke that pointy
protuberance out again I'll lop it off like a turnip! <G>
Larrrrry... Larrrrry Rutabagaman... Ahahahahahahahahahahaha. . . .
• TURNIP CAKE • (LAW BOCK GOW)
This is the delicious savory cake served in dim sum houses throughout the year
and, most auspiciously, on New Year's Day as a symbol of prosperity and rising
fortunes. Turnip cake is made with Chinese turnip, law bock, which is a type of
daikon radish. There is also a daikon radish called Japanese daikon radish,
which is similar to the Chinese turnip in appearance. To make matters more
confusing, law bock, translated into English, means turnip. Some produce
vendors do not realize there is a distinction, but the Chinese turnip is more
blemished looking than the Japanese daikon, which has a creamier white color.
Although Chinese turnip is best for this recipe, whichever one you use, choose
a firm heavy vegetable. The turnip should ideally be 8 to 12 inches long and
about 4 inches wide.
Some people remove only the rind of the Chinese bacon and finely chop the whole
piece, using all the fat. But I find this too rich, so I discard the layer of
fat under the rind. In recipes that call for Chinese bacon to be sliced, all
that is required is a sturdy cook's knife or cleaver. However, when the bacon
needs to be finely chopped, as in this recipe, the bacon should be steamed
first to make it easier. Make sure to use rice flour and not glutinous rice
flour.
I've never met anyone who served the entire cake at once. During the first ten
days of the New Year's celebration a few slices of all the different New Year's
cakes are fried every morning for breakfast or when friends or family stop by.
The cake will keep nicely in the refrigerator for ten days if wrapped in
plastic wrap.
6 ounces Chinese bacon (lop yok), store bought or homemade
1 large Chinese white turnip, about 2 pounds
8 Chinese dried mushrooms
1/2 cup Chinese dried shrimp, about 1 1/4 ounces
2 teaspoons Shao Hsing rice cooking wine
1 teaspoon sugar
2 cups rice flour
Cut the bacon into 3 equal pieces and place in a 9-inch shallow heatproof bowl.
Bring water to a boil over high heat in a covered steamer large enough to fit
the bowl without touching the sides of the steamer. Carefully place the bowl
into steamer, cover, reduce heat to medium, and steam 15 to 20 minutes, or just
until the bacon is softened and there are juices in the dish. Check the water
level from time to time and replenish, if necessary, with boiling water.
Carefully remove the dish from the steamer and set aside to cool.
Peel the turnip and grate to make about 4 1/2 cups. In a 3-quart saucepan,
combine grated turnip and about 1 quart cold water, and bring to a boil over
high heat. Reduce heat to low, cover, and simmer 30 minutes, or until very
tender. Drain, reserving the cooking liquid.
Meanwhile, in a medium bowl, soak the mushrooms in 1/2 cup cold water 30
minutes, or until softened. Drain and squeeze dry, reserving the soaking
liquid. Cut off and discard stems and mince the caps. In a small bowl, soak the
dried shrimp in 1/2 cup cold water for 30 minutes, or until softened. Drain,
reserving soaking liquid. Finely chop shrimp and set aside.
Remove the bacon from its dish and reserve the juices. Cut off and discard the
rind and the thick layer of fat. Cut the remaining meat into paper-thin slices
and then finely chop. In a 14-inch flat-bottomed wok or skillet, stir-fry the
chopped bacon over medium heat for 2 to 3 minutes, or until meat releases fat
and just begins to brown. Add the minced mushrooms and shrimp, and stir-fry 2
to 3 minutes. Add the rice wine, sugar, and pan juices from the bacon, and stir
to combine. Remove from heat.
Return the cooked, drained turnip to the saucepan, add the bacon and mushroom
mixture, and stir to combine. In a large bowl, combine the rice flour and the
reserved mushroom and shrimp soaking liquids, stirring until smooth. Stir in 1
cup of the hot turnip broth. Pour this batter into the saucepan, add the salt,
and stir until combined. The consistency will resemble that of rice pudding.
Pour mixture into a heatproof 8-inch round, 3- to 4-inch-deep, straight-sided
bowl, such as a soufflé dish.
Bring water to a boil over high heat in a covered steamer large enough to fit
the dish without touching the sides of the steamer. Carefully place the dish
into the steamer, cover, reduce heat to medium-low, and steam 1 hour, or just
until cake is set and is firm to the touch. Check the water level and
replenish, if necessary, with boiling water. Carefully remove the bowl from the
steamer and allow to cool on a rack for about 1 hour. Cover and refrigerate at
least 3 to 4 hours.
Run a knife along the edge of the cake to loosen sides. Place a cake rack over
the bowl and invert to unmold. Flip the cake right-side up onto a cutting
board. Wrap the cake in plastic and refrigerate until ready to use.
When ready to eat, cut cake into quarters. Cut each quarter crosswise, not into
wedges, but into two 2-inch-wide strips. Cut each strip crosswise into scant
1/2-inch-thick slices. This is the typical way of slicing a cake Chinese style.
Heat a 14-inch flat-bottomed wok or skillet, over medium heat until hot but not
smoking. Add just enough oil to barely coat the wok. Add the turnip cake slices
in batches and cook 2 to 3 minutes per side, until golden brown. Serve
immediately, with oyster sauce.
Makes one 8-inch cake, about 48 slices.
Wisdom of the Chinese Kitchen
Grace Young - Simon & Schuster
Shankar Bhattacharyya
David Carnell <davec...@worldnet.att.net> wrote:
>Chemical engineer's opinion:
>
>Yes, dust in water, scratches on the container, dissolved air, etc. will
>all work
>against superheating water. I boil water in the nuker as standard
>whole idea that water will get superheated to where it will boil suddenly
>(not
>explode) id pretty far-fetched.
Chemist's opinion:
Not at all far-fetched. Superheating is fairly common. If you keep your
dishes clean and scrub them with non-abrasive pads and cleaners, where
are the scratches going to come from, certainly while the dishes are
new? Cups and such don't even see a lot of stirring and scraping
with metal implements. The most serious abrasion they see, most of the
time, is a little contact with a spoon as people mix sugar or milk
into coffee or tea. Most cups - certainly many - are clean enough to
support superheating some non-trivial fraction of the time.
I have seen water superheat and subsequently boil over in a microwave.
I sent the victim off to the doctor, wrote the accident report, wrote
procedures to keep people from having that happen again. Fortunately,
the damage was not serious.
I imagine that "exploding" is a rare phenomenon. That would take a
very large amount of stored energy. However, some moderate level of
superheating is not a rare phenomenon. I have seen superheated water
any number of times. I have seen superheated ethanol and methanol,
benzene, toluene and xylene, methylene chloride and chloroform. I
think I have seen superheated ammonia but there are other explanations
for what I saw.
My impression is that liquids with highish latent heat of vaporization
tend to show more superheating. Even so, liquids with low latent heat
will show it, too. We do pesticide analyses and in the extraction
process a common last step is the concentration of a petroleum ether
solution in a Kuderna-Danish concentrator. Every now and then the
solution superheats and pretty much blows up. Technicians try to
"fasten things securely" so that glassware does not fly all over the
place. I have had to demand that they not do that, so that if
something goes wrong the system can vent easily rather than blow up.
We have shattered some glassware because of the internal pressures.
Having sharp bits of glass fly around is far more dangerous than
losing a $60 Snyder trap.
Nucleation is an interesting phenomenon. If you look at the forces
acting on the surface of a bubble you will see that the surface
tension produces a resultant force directed towards the concave side
of the surface. The pressure inside a bubble is higher than the
pressure outside. The difference depends on the radius of curvature
and on the surface tension. An infinitesimally small bubble has
"infinitely higher" internal pressure. What this means is that such a
bubble has a hard time being formed. Once a small gas bubble is formed
in a liquid, it grows rapidly. That takes some work, since the surface
is being expanded with associated increase in the potential energy of
the surface but a source of energy is available in heated liquids.
Nucleation sites provide a non-zero lower limit on the curvature of a
bubble formed at the site. They therefore involve much lower initial
pressure requirements.
If one of my staff were to boil liquids in the lab without taking
precautions against the bumping that accompanies superheated liquids I
would have that person put on the rack we keep for egregious
violations of safe lab practice. I would fire someone for persisting
in that sort of habit.
- Shankar
Cyndi H
Why don't we just say that boiling water in a microwave is very hot and a
person should use extra care when extricating the water from the microwave
to another location? Jeez! This really isn't all that complicated. Maybe
there was an air bubble in the water container that just decided that
"today is the day that I'm going to escape by whatever means, necessary" or
maybe the kitchen gods decided that that was the day to teach a lesson in
kitchen tool respect. Who knows? Who cares anymore? Lets face it - if you
play in fire you might get hurt. If you play with glass you might get
cut...
Sorry, PMS moment...
Sheryl Rosen
>
>>But I do have a microwave related question. Sometimes when I heat "dry" food
>>on
>>a stoneware plate in the microwave, the plate will crack. Not crack into
>>pieces,
>>but I'll hear a pop sound, and there will be a crack in the plate that
>wasn't
>>there before.
My guess is that you've let the plate soak, it's absorbed water, and the steam
has expanded, causing the crack.
My Pfaltzgraff stoneware has a rimmed "foot" underneath which is unglazed. The
usage instructions on Pfaltzgraff specifically warn against soaking the dishes
in water for that reason. Best to just rinse immediately after eating.
Sheryl
Not a newbie. Just new to AOL.