Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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!!!!

share|cite|improve this question
Put water in Vacuum and it'll evaporate without even heat. – SS-3 Jul 11 '14 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 '14 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 '14 at 15:28

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.

share|cite|improve this answer
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 '14 at 13:31

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.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.