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So here is the thing, I searched all over the internet for this but all the sources say that I need wind because the process of evaporation goes as follow: Water particles at the top layer with highest levels of energy (which they take from lower layers) are trying to break free and jump up. When they meet air particles with enough energy, they take that energy and use it to break the bonds with the other liquid- thus escaping and turning into a gas.

Now my question is, what if I got no wind? What if instead I just put a heating coil close to the surface of the liquid which is in a barrel (i.e not touching the water)? Would my liquid just boil? Or maybe the energy from the coil would transfer to top layer first, giving it enough energy to escape (and cool the rest of the liquid)? What if the barrel closed? What if it is open?

All of the internet sources say that I have to have air movement, does this mean that my scenario won't work? Also, if it would, does that mean that the energy required to make the water dissapear with evaporation is lower than with boling?

Thank you very much!!!!

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Put water in Vacuum and it'll evaporate without even heat. –  Sachin Shekhar Jul 11 at 6:58
You ever left half a glass of water on the counter for a month? Don't bother answering, you haven't because by the time the month is up it's just a glass on the counter. It stopped being half a glass of water a long time ago. You need neither wind nor heat, you just need sufficiently dry air (or a sufficient lack of water in the space above your liquid water) –  Jim Jul 11 at 12:58
Also you might consider that if you had any kind of heater in an ideal environment with no wind, there will still be air movement due to convection. –  Phil Frost Jul 11 at 15:28

3 Answers 3

If you have water in an enclosed container with some air, then the evaporation will gradually slow down towards zero. That is because the rate that liquid water molecules gain energy and become water vapor will be balanced by the rate at which water vapor molecules lose energy and become bound to the liquid. The point at which that occurs is called the equilibrium vapor pressure, and it depends on the temperature, but not on the presence or content of the air. In an open container in an atmosphere where the vapor pressure of water is below the equilibrium, there will continue to be some evaporation without wind because the water vapor will diffuse away, but the diffusion will be very slow. Water vapor is also less dense than air and will create convection as it rises and thus creates wind.

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You say the content and presence of the air does not have an effect. Does air pressure not come into account simply because the materials are in the same temperature regions? –  Garet Claborn Sep 16 '12 at 23:13
@GaretClaborn The content and pressure will effect the equilibrium pressure, temperature and vapor pressure but will not fundamentally change the process at work. –  dmckee Sep 17 '12 at 0:27
@dmckee Makes perfect sense, thank you. –  Garet Claborn Sep 17 '12 at 0:30
Thank you guys for your help. Jcohen79, thank you, so you are saying that in an open container if we hang a heating lamp/coil above the water it would evaporate slower than if a wind carrying the same amount of energy hit the water. But why? If we have no vapor pressure outside?I'sn't the whole point of evaporation is surface molecules urging to break free and move with great speed and freedom out in the big world like a blonde girl from a small town arriving to Hollywood XD... (The wind from the evacuating molecules is no problem since it doesn't add any new heat to the water). –  question Sep 17 '12 at 17:35
Any sort of breeze will remove the saturated air near the water, and replace it with drier air from elsewhere, thus enabling additional evaporation. Lacking some air movement, only slow diffusion from the humid area into drier surroundings will permit further evaporation. The air in a sealed environment will quickly become saturated, preventing further evaporation. –  Phil Perry May 29 at 13:31

Just take a trip to high altitudes cities, for example, Peru, Bolivia, Tibet, Nepal, all those places see how water evaporates due to lack of enough atmospheric pressure.

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The atomic hypothesis describes processes, and so we shall look at vaporization from an atomic standpoint. We shall picture the molecules of water forming a body of liquid water (and the surface). Above the surface we see a number of things. First of all there are water molecules, as in steam. This is water vapor, which is always found above liquid water. (There is an equilibrium between the steam vapor and the water which will be described later.) In addition we find some other molecules—here two oxygen atoms stuck together by themselves, forming an oxygen molecule, there two nitrogen atoms also stuck together to make a nitrogen molecule. Air consists almost entirely of nitrogen, oxygen, some water vapor, and lesser amounts of carbon dioxide, argon, and other things. So above the water surface is the air, a gas, containing some water vapor.

The molecules in the water are always jiggling around. From time to time, one on the surface happens to be hit a little harder than usual, and gets knocked away. It is hard to see that happening in the picture because it is a still picture. But we can imagine that one molecule near the surface has just been hit and is flying out, or perhaps another one has been hit and is flying out. Thus, molecule by molecule, the water disappears— it evaporates. But if we close the vessel above, after a while we shall find a large number of molecules of water amongst the air molecules. From time to time, one of these vapor molecules comes flying down to the water and gets stuck again. So we see that what looks like a dead, uninteresting thing—a glass of water with a cover, that has been sitting there for perhaps twenty years—really contains a dynamic and interesting phenomenon which is going on all the time. To our eyes, our crude eyes, nothing is changing, but if we could see it a billion times magni- fied, we would see that from its own point of view it is always changing: molecules are leaving the surface, molecules are coming back. Because just as many molecules are leaving as are coming back! In the long run "nothing happens." If we then take the top of the vessel off and blow the moist air away, replacing it with dry air, then the number of molecules leaving is just the same as it was before, because this depends on the jiggling of the water, but the number coming back is greatly reduced be- cause there are so many fewer water molecules above the water. Therefore there are more going out than coming in, and the water evaporates. Hence, if you wish to evaporate water turn on the fan!

So you can't vaporize water without reducing the number of vapor water molecules above its surface. But that doesn't happen only due to wind. For example if the container is significantly big compered to the quantity of water the vapor water molecules will take over the whole volume of the container, thus reducing the number o vapor close to the surface of the liquid body. Therefore if the container was the "whole nature" i believe you could manage to vaporize water without wind!

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