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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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    $\begingroup$ Put water in Vacuum and it'll evaporate without even heat. $\endgroup$ – Schrödinger's Cat Jul 11 '14 at 6:58
  • $\begingroup$ 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) $\endgroup$ – Jim Jul 11 '14 at 12:58
  • $\begingroup$ 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. $\endgroup$ – Phil Frost Jul 11 '14 at 15:28
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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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  • $\begingroup$ 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? $\endgroup$ – Garet Claborn Sep 16 '12 at 23:13
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    $\begingroup$ @GaretClaborn The content and pressure will effect the equilibrium pressure, temperature and vapor pressure but will not fundamentally change the process at work. $\endgroup$ – dmckee --- ex-moderator kitten Sep 17 '12 at 0:27
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    $\begingroup$ @question - If the heating element raises the surface to the boiling point, that means the vapor pressure becomes greater than atmospheric pressure and the steam will just push away the air. Perhaps behind your comment is the idea that molecules will race off and not bump into anything. According to en.wikipedia.org/wiki/Mean_free_path, the mean free path at atmospheric pressure is 68 nanometers, so like smalls town girls in Hollywood they don't get far before colliding with reality. $\endgroup$ – jcohen79 Sep 17 '12 at 19:00
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    $\begingroup$ LOL, loved the last sentence! First of all, evaporation doean't raise the surface to boling temp, right? So is there going to be some other process with the heating lamp? Second, you said it yourself, that wtaer vapour is lighter than air, so shouldn't it rise like in a hot air baloon? thx! $\endgroup$ – question Sep 18 '12 at 17:45
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    $\begingroup$ 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. $\endgroup$ – Phil Perry May 29 '14 at 13:31
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As long as humidity is less than 100% there will be evaporation (even with no wind). Water at 70 F has a vapor pressure of 0.3631 atm. Other gas pressure does not matter. At 70 F as long as the partial pressure of water in air is less than 0.3631 psi there will be evaporation. Even ice has a vapor pressure - if you leave an ice tray in the freezer for a couple years it will evaporate.

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