# Hygiene thermodynamics 2

Two kinda related questions here:

1. Is evaporation rate and temperature difference related? There is an experiment of pouring cup of hot water out the window during winter. The water evaporates almost instantly forming a vapor cloud.

2. I was showering during winter (outside: ~15 degrees Celsius below the Celsius' zero). I opened the window and as the cold air came in the room filled with vapor. It seemed almost like the vapor was coming in through the window. What happened there? My guesses:

a. It's the question 1 thing.
b. I got in a lot of dry air which allowed more water to evaporate.
c. I lowered the air temperature which caused the air humidity to condense forming this fog.
d. or something else did happen?

• Regarding your second question, i would say it's the same thing that happens when you breath out into the air. The vapour in the shower room (where there's a lot of vapour) crystallizes. But I'm not sure of this.. It may also be because whatever reason causes ice cream to smoke(iirc it has to do with the triple point of water). Not sure of that either :/ – Manishearth Mar 18 '12 at 13:16
• @Manishearth I'm afraid there's no crystalization going on here… or at least it's not needed. You can observe this phenomenon with strictly positive temperatures! (Of course, if it's really cold, then some droplets of condensed water might turn into ice, but that's not needed for you to see you breath.) – F'x Mar 18 '12 at 14:03
• @f'x sorry, meant condensation. Since we usually have crystallization(atleast in New England, where I used to live, I guess I subconciously wrote it :/ – Manishearth Mar 18 '12 at 14:30

$$\frac{\mathrm dM}{\mathrm dt}=(p_\mathrm v-p_\mathrm p)\sqrt{\frac m{2\pi kT}}.$$