Snow and physics
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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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0x3c0 wrote:
A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules.
Wrong. Microwaves excite the vibrational modes of water molecules causing them to heat up (the energy of the excited modes is translated into heat as the molecules relax back to the ground state). If they get hot enough, they will evaporate, but evaporation is a cooling process not a heating process. Try putting a little rubbing alcohol on your skin and blow on it.
modified on Tuesday, January 5, 2010 1:41 PM
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 :suss:
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That's an interesting read; thanks. By the way, CP uses HTML, not BBCode, so your tag hasn't shown up properly.
Wjousts wrote:
the energy of the excited modes is translated into heat as the molecules relax back to the ground state
Release of energy as molecules fall down by a state. That sounds a lot like electrons - my chemistry teacher taught the class that most reactions are caused by atoms losing electrons (and thus a charge); the atoms then fall down a state, releasing energy (sometimes photons). It's been far too long since I did GCSE Chemistry though, so I could very easily be wrong.
OSDev :)
0x3c0 wrote:
By the way, CP uses HTML, not BBCode, so your tag hasn't shown up properly.
I always manage to mix up which forums use which. Thanks.
0x3c0 wrote:
Release of energy as molecules fall down by a state. That sounds a lot like electrons
It's not electrons. It's vibrational modes not electronic modes. Molecules have different types of energy modes all of which are quantized. In order of how big the gaps in different energy levels are: Electronic > vibrational > rotational > translational. So the thing your chemistry teacher didn't tell you when he drew a neat little diagram of a ladder of electronic states is that each of those states also has vibrational modes superimposed on it, and each of those has rotational modes and each of those has translational modes. They don't show you that because it tends to muddy the point about neatly quantized energy states if they show you how they are blurred by all this additional energy in different modes. Also, in the case of atoms rather than molecules, their are no vibrational or rotational states to worry about, so the picture is essentially correct.
0x3c0 wrote:
my chemistry teacher taught the class that most reactions are caused by atoms losing electrons (and thus a charge);
Mostly correct (but over simplified), but we are talking about physics rather than chemistry here. The water molecules aren't reacting (well they might be, but that would be cooking rather than defrosting).
0x3c0 wrote:
the atoms then fall down a state, releasing energy (sometimes photons).
Yes, this is how something like neon produces light, by electrically excited atoms returning to their ground state releasing a photon. In our case (the microwave and water molecules), since the gaps in rotational states are much smaller, the corresponding photons tend to fall in the IR region, i.e. heat.
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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 :suss:
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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 :suss:
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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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 :suss:
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
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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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
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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0x3c0 wrote:
By the way, CP uses HTML, not BBCode, so your tag hasn't shown up properly.
I always manage to mix up which forums use which. Thanks.
0x3c0 wrote:
Release of energy as molecules fall down by a state. That sounds a lot like electrons
It's not electrons. It's vibrational modes not electronic modes. Molecules have different types of energy modes all of which are quantized. In order of how big the gaps in different energy levels are: Electronic > vibrational > rotational > translational. So the thing your chemistry teacher didn't tell you when he drew a neat little diagram of a ladder of electronic states is that each of those states also has vibrational modes superimposed on it, and each of those has rotational modes and each of those has translational modes. They don't show you that because it tends to muddy the point about neatly quantized energy states if they show you how they are blurred by all this additional energy in different modes. Also, in the case of atoms rather than molecules, their are no vibrational or rotational states to worry about, so the picture is essentially correct.
0x3c0 wrote:
my chemistry teacher taught the class that most reactions are caused by atoms losing electrons (and thus a charge);
Mostly correct (but over simplified), but we are talking about physics rather than chemistry here. The water molecules aren't reacting (well they might be, but that would be cooking rather than defrosting).
0x3c0 wrote:
the atoms then fall down a state, releasing energy (sometimes photons).
Yes, this is how something like neon produces light, by electrically excited atoms returning to their ground state releasing a photon. In our case (the microwave and water molecules), since the gaps in rotational states are much smaller, the corresponding photons tend to fall in the IR region, i.e. heat.
Wjousts wrote:
The water molecules aren't reacting
I believe that they are, as they are mildly dipolar and have a resonant frequency that matches the microwave emissions of the oven. Heat is produced primarily by frictional energy losses through molecular collisions. It's quite possible to melt falling snow with microwave radiation, but terribly inefficient. Much simpler and cheaper to put salt on the road...
"A Journey of a Thousand Rest Stops Begins with a Single Movement"
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
"Set phasers on defrost"?
I wanna be a eunuchs developer! Pass me a bread knife!
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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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Yeah, I'd got a feeling that I would cause quite a bit of cellular damage by exposing myself to microwave radiation. I'm tempted to make it directional, put some interesting bits at the base to stop it backfiring and causing all the water in my body to evaporate, connect it to a motion detector and use it to melt a path through the ice. I've slipped so many times it's not funny anymore.
OSDev :)
Reminds me of one of the candidates for the Darwin awards a number of years back. I never could understand why the guy did this but... It seems that a guard at some facility whose job it was to guard the exterior was in the habit of sitting in front of a microwave tower because it kept him warm. One morning, I believe it was on a New Years Day, they found him dead. Apparently he'd taken some beers up with him to celebrate NYE. He'd fallen asleep and failed to remove himself when things got uncomfortable. The cans of beer that hadn't been consumed had exploded due to overheating. Obviously the guy had brain cell damage before he decided to undertake this practice.
I'm not a programmer but I play one at the office
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
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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Reminds me of one of the candidates for the Darwin awards a number of years back. I never could understand why the guy did this but... It seems that a guard at some facility whose job it was to guard the exterior was in the habit of sitting in front of a microwave tower because it kept him warm. One morning, I believe it was on a New Years Day, they found him dead. Apparently he'd taken some beers up with him to celebrate NYE. He'd fallen asleep and failed to remove himself when things got uncomfortable. The cans of beer that hadn't been consumed had exploded due to overheating. Obviously the guy had brain cell damage before he decided to undertake this practice.
I'm not a programmer but I play one at the office
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Lilith.C wrote:
Obviously the guy had brain cell damage before he decided to undertake this practice.
There, you forgot to Bold the pun. FTFY.
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0x3c0 wrote:
By the way, CP uses HTML, not BBCode, so your tag hasn't shown up properly.
I always manage to mix up which forums use which. Thanks.
0x3c0 wrote:
Release of energy as molecules fall down by a state. That sounds a lot like electrons
It's not electrons. It's vibrational modes not electronic modes. Molecules have different types of energy modes all of which are quantized. In order of how big the gaps in different energy levels are: Electronic > vibrational > rotational > translational. So the thing your chemistry teacher didn't tell you when he drew a neat little diagram of a ladder of electronic states is that each of those states also has vibrational modes superimposed on it, and each of those has rotational modes and each of those has translational modes. They don't show you that because it tends to muddy the point about neatly quantized energy states if they show you how they are blurred by all this additional energy in different modes. Also, in the case of atoms rather than molecules, their are no vibrational or rotational states to worry about, so the picture is essentially correct.
0x3c0 wrote:
my chemistry teacher taught the class that most reactions are caused by atoms losing electrons (and thus a charge);
Mostly correct (but over simplified), but we are talking about physics rather than chemistry here. The water molecules aren't reacting (well they might be, but that would be cooking rather than defrosting).
0x3c0 wrote:
the atoms then fall down a state, releasing energy (sometimes photons).
Yes, this is how something like neon produces light, by electrically excited atoms returning to their ground state releasing a photon. In our case (the microwave and water molecules), since the gaps in rotational states are much smaller, the corresponding photons tend to fall in the IR region, i.e. heat.
-
Wjousts wrote:
The water molecules aren't reacting
I believe that they are, as they are mildly dipolar and have a resonant frequency that matches the microwave emissions of the oven. Heat is produced primarily by frictional energy losses through molecular collisions. It's quite possible to melt falling snow with microwave radiation, but terribly inefficient. Much simpler and cheaper to put salt on the road...
"A Journey of a Thousand Rest Stops Begins with a Single Movement"
-
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