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Wjousts wrote: The water molecules aren't reacting (well they might be, but that would be cooking rather than defrosting).
Which is what happens when you leave the kitty mouse Insta-Noodles in there for too long.
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Wjousts wrote: but evaporation is a cooling process not a heating process
That would imply that I could evaporate water by cooling it? A gas, isn't that just a heated form of a solid? With very fast vibrating molecules?
Sounds logical that if a lot of fast molecules escape, that the sum of all vibrations goes down. It's true that water becomes cooler when a bit evaporates. It's not true that evaporation is 'caused' by the cooling - it's rather a side-effect of the initial heating.
Something like a ball coming back down, once you throw it up in the air 
--edit--
Throwing up is something quite different.
I are Troll 
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Eddy Vluggen wrote: That would imply that I could evaporate water by cooling it?
Not at all. Evaporation removes energy from a liquid, hence it cools the liquid. Hence you have to supply energy for it to continue happening.
You have to supply energy for evaporation to happen, but what you'll notice at a phase transition (e.g. water to steam) is that the temperature of the liquid doesn't change because evaporation is removing energy from the liquid.
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You did notice his sig, right? So don't feed him.
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"Not all that glitters is gold, and not all who wander are lost"
The word "Troll" has multiple meanings, and it's also the name of a race in World of Warcraft. It's a suggestive sig without that particular part of information.
..and there you got the hardest part of our profession. It's easy to create a table to save some information on employees. Now the user has a different idea on what an employee is then I do, and that's the hard part.
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Wjousts wrote: You have to supply energy for evaporation to happen
You don't have to supply energy to get evaporation. Unless it's cooled to 0K, it will have energy, in the form of warmth. At 0K there won't be evaporation simply by definition.
Wjousts wrote: you'll notice at a phase transition (e.g. water to steam) is that the temperature of the liquid doesn't change because evaporation is removing energy from the liquid.
A cooling-process from the viewpoint of a water-droplet, a heating-process if you happen to be a molecule that's part of the gassy collection?
From a logical viewpoint, it would be neither.
I are Troll
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Now let's see if I can describe this without posting a text wall...
Eddy Vluggen wrote: That would imply that I could evaporate water by cooling it? A gas, isn't that just a heated form of a solid? With very fast vibrating molecules?
Not quite. And the initial description was not 100% accurate either. The first law of thermodynamics (also known as Principle of Conservation of Energy) states that you simply can't win: you can't produce energy from nothing. The alcohol molecules lying in liquid state on your hand, need some extra energy to make the transition to gas state. They take it from your hand and the air around them. Since some (thermal) energy is drawn from your hand, you feel it's getting colder there as the molecules leave the liquid state. So the cooling process is on your hand, not the alcohol evaporation. The evaporation requires energy to happen. No extra energy means no evaporation (actually this is an oversimplification of things, as some molecules will evaporate. And if the alcohol is not in a sealed box (so that some of the runaway molecules return to the liquid state), eventually it will dry off. Blowing on it, simple desaturates the air around the liquid alcohol, thus reducing the amount of molecules returning to liquid from gas state, thus making the process faster -and your hand colder).
Now a gas is certainly NOT a heated form of a liquid. There are forces at play in liquid form that are too weak in gas state, and a "normal" liquid has drastically different behaviour than a gas (or a solid for that matter). If a gas was simply a heated liquid, then the trasition between the two states would not be a violent one (as in boiling, or droplets of water on a cold glass surface when you blow on it).
Eddy Vluggen wrote: It's true that water becomes cooler when a bit evaporates.
Hm, only under particular circumstances. If you seal the water off (in terms of energy exchange with its environment) and also if you somehow remove the molecules that escape the liquid state WITHOUT interacting with the liquid, then the remaining molecules in the water will have a smaller mean kinetic energy, meaning the liquid will have a lower temperature. However, those are two big if's there...
As for the original post, well, what happened to that guard should give you a hint on the viability of such a contraption
Yiannis
Φευ! Εδόμεθα υπό ρηννοσχήμων λύκων!
(Alas! We're devoured by lamb-guised wolves!)
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yiangos wrote: If a gas was simply a heated liquid, then the trasition between the two states would not be a violent one
I'll stop calling a gas a heated liquid. Somehow they remind me of different view for the same table - just different representations.
The way you're explaining it, it's not a different representation, but a conversion. Something like going from HTML to RTF.
My gratitude for the explanation 
I are Troll
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Eddy Vluggen wrote: The way you're explaining it, it's not a different representation, but a conversion. Something like going from HTML to RTF.
It's a conversion, it's deterministic macroscopically, and it has a rather simple (but not too simple) conversion function. Sort of like a switch with 3 cases per transition.
Check this:
http://en.wikipedia.org/wiki/Cooling_curve[^]
This graph shows what happens to the temperature of a material(the temperature is related to the mean kinetic energy of the molecules, irrespective of state) as it goes from liquid (far left, smooth decline) to solid (far right, smooth decline again). Notice the sharp angle and the plateau that occurs at "freezing" temperature. Sharp angles in physics denote violent changes. Here, when the liquid (say, water) reaches this temperature (for water, 273 Kelvin), the temperature in the water stops dropping although we continue to pump heat out of it (by using e.g. a freezer). In this transient state, both ice and water co-exist, as some molecules have so little internal energy left, that the binding forces that keep them together forcefully bind them to a lattice, stopping any "attempt" to escape or move freely. Other molecules still have enough energh to overcome this attraction, and still move as if they're liquid. The heat taken from water to convert it from water of 273 Kelvin (or 0C, or 32F) to ice of the same temperature is called latent heat, and it's a distinct characteristic of the material itself.
A similar curve exists for the transition between liquid and gas.
The funny thing is that under pressure, the width of the plateau in that graph changes, and also the temperature at which it occurs changes. For instance, gas inside a can of spray is at such high pressure, that even in room temperature, it's a liquid. Above a certain value of pressure (dependent on the material as well) it actually vanishes. At such high pressure, it makes no sense to talk about gas, liquid or solid state. There's no real distinction between the three. We believe that this is what goes on deep inside the gas giant planets of the solar system.
By the way, it's fun th check out the qualities of superfluids[^], such as liquid helium
Gasp, another wall of text! Ok, I'll shut up now...
Φευ! Εδόμεθα υπό ρηννοσχήμων λύκων!
(Alas! We're devoured by lamb-guised wolves!)
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yiangos wrote: Sort of like a switch with 3 cases per transition
That "sort of" made me somewhat uneasy, but you were referring to the number of states that a substance can have. And there are more states than the three that I learned at school.
..but liquids that climb up a wall and "escape" from a cup? Sounded more like voodoo than physics!
Thanks for the explanation
I are Troll
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I think some Big Ass Heat-lamps would be much simpler and probably consume less power.
And above all things, never think that you're not good enough yourself. A man should never think that. My belief is that in life people will take you at your own reckoning. --Isaac Asimov
Avoid the crowd. Do your own thinking independently. Be the chess player, not the chess piece. --Ralph Charell
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Flame war, maybe?
Go and boil your bottoms, sons of a silly person.
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The real problem I see with this solution is that snow (ice) melts into water which tends to turn back into ice and usually a more dangerous form of it. Places like where I live (we haven't seen > 0C temps for ~2weeks), it doesn't do any good to melt the snow.
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Microwaves only act on polar molecules that are free to spin back and forth. Water molecules in ice are rigidly bound and can't spin. The reason you can thaw your food out is that a few molecules of water on the surface melt due to the higher ambient temperature outside the freezer and other polar molecules in the water. Snow in a snowstorm won't melt effectively this way as a result.
3x12=36
2x12=24
1x12=12
0x12=18
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nice point
Ravie Busie
Coding is my birth-right and bugs are part of feature my code has!
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Actually, this rigidity only reduces the effect, and does not eliminate it completely. Or, if you have infintely rigid bonds in your ice, let me know, and we can win a Nobel Peace Prize together.
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Or, you could use a multi spectral source at a relatively low power density to warm the snow and evaporate the water residue.
Oh wait - that's called sunshine.....
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I'd be willing to bet that every hardcore software developer on earth that lives in a snowy climate has thought of a zillion different alternative schemes to get rid of it while shovelling.
My top three I've considered are lasers to zap individual flakes with some kind of optical tracking program for each flake as it falls, hot water heating under the driveway to melt it (highly inefficient but people actually do this), nanotech snow removal, you just open a bag of it (like road salt) and sprinkle some in the driveway and Bob's your lobster.
"Creating your own blog is about as easy as creating your own urine, and you're about as likely to find someone else interested in it." -- Lore Sjöberg
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"Set phasers on defrost"?
I wanna be a eunuchs developer! Pass me a bread knife!
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Sounds like what you want is one of them 1950's era microwave transmitters. They even have a convenient dish for directing the microwave beam. Bonus points if you figure out how to use paraffin lenses to focus the microwaves into a nice, tight little beam.
patbob
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Here buy something like this: http://www.wired.com/dangerroom/2010/01/sci-fi-weapons/3/
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The wavelength on microwaves is rather long 3cm or so, while water and especially water vapor are very very good ad absorbing the energy(why we didnt put microwave radar on our ships, our meaning the US, was because the humidity reduced the range to uselessness). You would have to heat the water to the evaporation point which if its snow or ice would require quite a bit of energy. Put an ice cube in your microwave and see how long it takes to boil it away. your best bet would be to use a short wavelength laser(shorter wavelength = more energy generally)x rays would be better but they're ionizing and thats always bad. Theres a bunch of ways to power up lasers, they make some on chips the size of the end of a pen that can cut through soda cans w/ no problem. Once you have a laser powerful enough(couple hundred watts prolly) you need a diffuser to spread it out in a line then just fire it in front of you while you walk. or mount it under the front bumper of your car to clear paths for your tires.
I have no idea if that will work, but it sounds good, and fun to build.
Please remember to rate helpful or unhelpful answers, it lets us and people reading the forums know if our answers are any good.
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Unless you want cataracts, don't start fooling around trying to defeat your microwave oven's safety features. It's optical output is really high, and can kill a bird at fifty paces. It's already directional, and you can't predict how it's going to reflect. Sure it's fun to think about, but leave it at that.
- Owen -
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