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Mark_Wallace wrote: Well, I'll be buggered!
That's something I'd not want you to post a picture of - but feel free to enjoy![^]
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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Welcome to your own discover of "superheating" !
I first experienced this years ago - without even a microwave - but a brand new tea kettle on a gas stove.
You can look up all the grisly details you'd find interesting, but the basic requirements for this are heating in a brand new container without any internal flaws (micro-scratches from normal use). With no irregularities, the water reaches it boiling point (not enough reason to boil, by the way) and then, added energy would cause the conversion from liquid-to-gas.
But where ? ? ? ? The microscopic scratches are places that lower the energy required to cross that gas/liquid boundary. Suppose there aren't any?
If the container's "flawless" from the point of view of the heating content, then it will just keep getting hotter, even exceeding it's boiling point at the ambient pressure. Then - you move it or the energy content gets high enough it can jump that barrier.
Once it starts - chain reaction - watch it!
This is not related to microwave heating, in particular, but the way and what we heat things in a microwave oven lends itself to this phenomenon.
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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I experienced it with the heater that serve my whole house, 3 storeys. The valve that should have opened when the water reached 70°C (in order to make it flow through the radiators) jammed, me and my dad were away for less than an hour... we found half of the heater plumbings torn apart and a crapton of water next to the heater building.
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Not (or shouldn't be!) the same thing.
You kept putting energy into the water in your system without any way for it to vent. The water boiled (probably normally, except for the pressure) creating steam. As more heat was added, more steam was created and the pressure above the water kept increasing. Eventually something has to give.
Many moons ago, whilst studying German, one of the textbooks actually had bomb-making instructions (really!) - it was sealing a metal container with water and heating it until it exploded. Alternatively, think of a jammed vent on a pressure cooker (hence why they have a safety plug).
Superheating (in the context we're using) differs in that the container isn't sealed - the liquid exceeds its boiling point but is not constrained by a sealed container. It just doesn't have whats called a nucleation point to begin the phase change in a (comparatively) orderly manner.
Glad you were out !
| Ravings en masse^ |
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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Well, sadly I'm cut off from such time-wasting facilities such as YouTube during the day, so I'll just have to use my imagination, but....
W∴ Balboos wrote: the water reaches it boiling point (not enough reason to boil, by the way)
Why's that then? Presuming we are at normal atmospheric pressure I'm struggling to see what else it would do.
Regards,
Rob Philpott.
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Rob Philpott wrote: Presuming we are at normal atmospheric pressure I'm struggling to see what else it would d
First thought for you:
at 100C (212F), what is water's state? Liquid? Gas?
Actually, both - to go from liquid to gas, you need to add an additional >2260 J/g. That energy, then can manifest itself with the body (i.e., water) more than one way.
It can boil, disippating the extra energy.
The water's temperature can increase its temperature, a mere 4.2 J/g per deg C
What to do? What to do?
As it turns out, nature loves producing location of higher and lower potential energy. Sharp point rough things are good at this - very smooth things are schizophrenic about it. If a tiny rough area exist (or, for example, a grain of sand or tea leaf), the reduced potential required to change phase in that area lets the energy be dissipated via liquid->gas, i.e., boiling. In the absence of such a location, the energy does what entropy demands: disperses as much as possible - so the water temperature goes above it's boiling point. It wants to boil - oh so much - but doesn't have a location where it can.
We can lump all such phenomena into a single one: Activation Energy. At certain locations, the activation energy, an excess over that actually needed for the transformation, is lower.
Another example: Mix Hydrogen and Oxygen gases at room temperture. OK - what happens?
If you said 'boom' - you are wrong. Put a spark in the mixture - to get the molecules in that spot above the activation energy - then "boom" - as the chain reaction spreads, the reaction supplying even more activation energy. Alternatively, put a spec of palladium dust in contact with the two gases, even at room temperature: Boom! Its surface lowers the activation energy (messes with the Hydrogen, in particular) and the chain starts.
So - it's not enough to simply have enough. You either need an extra push over that Activation Energy wall or something to lower the wall or . . . . . . . . you just wait.
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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I need to have words with my physics teacher. I remember talk of 'latent heat of vapourisation', and triple points at weird pressures, but nothing of activation energy, and my kettle just boils water rather than blowing it up. Probably a good thing actually.
I remember rumours on TV that microwave ovens could super heat things, such that when you stuck your spoon in, a rather unpleasant burn could result. I like to stick a spoon in everything I microwave, and so far, nothing so my doubts were growing. Perhaps this is related.
Thanks for the lengthy explanation. I will be sure to remove the tray of palladium in my garage off the hydrogen cylinder!
Regards,
Rob Philpott.
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One more beating for the dead horse:
It shows itself more with microwave heating not so much because it's microwaves doing the heating as it is the unique vessels used to cook in the microwave oven. A nice shiny new mug or glass, fresh the the kiln, except perhaps for a rinse or sponge wipe. A good chance it's perfectly smooth and ready for super heating. Won't happen with your old worn stuff.
It's the opportunities afforded by microwave cooking, not the microwave heating, that gets ya.
For me, this was part of chemistry (even the beginner's classes) - not physics. Maybe that's why his perspective on it was different.
| Ravings en masse^ |
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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Super-cooled water is pretty interesting as well. I have seen a bottle of water be below the freezing point but still liquid until it gets bumped. Watching ice crystals fill the entire bottle in seconds is mesmerizing.
if (Object.DividedByZero == true) { Universe.Implode(); }
Meus ratio ex fortis machina. Simplicitatis de formae ac munus. -Foothill, 2016
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Yes, and now imagine the same effect when you open a bottle of beer
The language is JavaScript. that of Mordor, which I will not utter here
This is Javascript. If you put big wheels and a racing stripe on a golf cart, it's still a f***ing golf cart.
"I don't know, extraterrestrial?"
"You mean like from space?"
"No, from Canada."
If software development were a circus, we would all be the clowns.
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I would be amazed and heartbroken at the same time.
if (Object.DividedByZero == true) { Universe.Implode(); }
Meus ratio ex fortis machina. Simplicitatis de formae ac munus. -Foothill, 2016
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Back when we were still in school, we hid a whole case of beer in the bushes on the campus. The temperatures outside were still below zero and we got nice cold beer. Until we popped the cap. The plan was good, but...
The language is JavaScript. that of Mordor, which I will not utter here
This is Javascript. If you put big wheels and a racing stripe on a golf cart, it's still a f***ing golf cart.
"I don't know, extraterrestrial?"
"You mean like from space?"
"No, from Canada."
If software development were a circus, we would all be the clowns.
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just leave a teaspoon in the cup - that'll stop it superheating.
Sin tack
the any key okay
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If that's a metal teaspoon in a microwave oven . . . you bet it will!
| Ravings en masse^ |
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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Bud I wanna da fok in da micawave!
I wanna be a eunuchs developer! Pass me a bread knife!
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Years ago I was into those flavored instant coffee powders for a while. I nuked some water in the microwave, took out the cup and started to pour in powder. Boom, the thing exploded all over me.
What amazed me was, when repeating the experiment (hey, I'm a geek!), I realized how lucky I was not to have set the water off when I picked the cup up. Must not have jarred it in the right way.
Marc
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The microvawe is spying on you ... Just ask Kellyanne.
modified 20-Oct-19 21:02pm.
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Out of curiosity, what was your internal calculation for the amount of time to microwave the water vis-a-viz the volume of water and the relative power (efficiency) of the microwave?
Did you overshoot this time by a wide margin and therefore overheat? Or you really needed scolding hot water? Or was something "new" at this point (microwave, cup, amount of water, desired heat)?
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No solid experimental number for you, but it was something along these lines...
- Glass bowl; extremely plain (jibes with the scientists here)
- Volume if full: one pint
- Quantity in bowl: 11 or 12 ounces
- First heating: 6 minutes
- Ooops distracted time: 8 minutes
- Reheat setting: 5 minutes
- Explosion momment: 3 or 4 minutes
All times and quantities are complete and utter guesses with zero accuracy; fifty percent margin of error would not surprise me.
Oh, the initial 6 minute thing is what I normally use. It's a big microwave; a thousand watts or so, built in above the regular stove, so that number is probably correct.
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wow, so I usually make my coffee in 90 seconds, about 10 oz.
Not too hot.
2 minutes would be HOT.
3 minutes would be near boiling for sure, in a similar microwave.
I found this:
Time to bring to boil 3 cups of room temperature water in a microwave, by watts:
1000 watts: 5 min 57 sec
so, that is 3 cups, you had maybe 2 cups (2 minutes less time) Jives with my experience.
(back of the envelope, right).
So, you clearly boiled it the first time.
then it started out hot, and 8 minutes... you super boiled it.
Yep. You over boiled the water. Clearly.
During this time, you did not open the microwave and touch it to see if it was good enough?
(I would assume not).
You have the personality of a programmer (clearly distractable for many minutes, and a touch of OCD in giving the details!) LOL 
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Just to clarify; yes, the water almost always boils in 6 minutes; I think it starts around 4 or 5.
An expert who was involved in the design of microwaves told me that the physical size of the device was the second most important factor in actual heating.
i.e., a lower powered device can produce superior heating if the internal volume is sufficiently small.
That's what the expert told me.
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User Friendly: Coffee[^]
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
modified 28-Mar-17 5:45am.
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