How does water evaporate at cold temperatures?

Question

I put a dust sheet over my car windows recently,to keep them frost free overnight.In the morning (it worked) the sheet was wet through and frosty.I left it in the drive,draped over an old barbeque.,and a couple of days later ,with the temperatures staying near zero, it was virtually dry.How could this happen?

Answer 1

Water does not need to be hot to evaporate. Water can (and does) evaporate at any temperature, as long as the air adjacent to the water is not saturated with water vapor (e.g., 100% RH). It is true, though, that heat increases evaporation rate. In general, any substance with a non-negligible vapor pressure is going to evaporate at some rate.

Answer 2

A temperature is an average.

At a given temperature, there will be some molecules at higher energy.

Water is just about always both evaporating and condensing.

If there isn't a lot of water vapor in the air, there won't be much condensation. So more water will evaporate than condense.

Also, some of the water is probably dripping off the bottom of the sheet.

(That thing about warmer air "being able to hold more water vapor" is a myth, BTW. If you type "Bad Science" into a search engine, you'll hit a site by someone who teaches (taught? It's an old site, by Web standards) meteorology who debunks that idea.)

Answer 3

Even at low temperatures, there is always a certain amount of water that is evaporating and condensing. Were it a closed system, you would not see a volume difference because you would reach a steady state where the same amount of water is evaporating as is condensing, and you will have reach a saturation point for water in the air.

In a open system, the air above the water is always being replaced, so as long as the air above the water is not at 100% humidity (which will depend on temperature for the exact amount of water the air can hold), all the water will eventually evaporate.

Answer 4

At any given temperature, no matter how low, the water molecules have a range of velocities. Even near freezing, a few of the molecules are moving fast enough to escape; in other words, to evaporate.

Answer 5

Water will evaporate at 4 degrees centigrade or above. Must assume it reached that temp over those days. I don't know how quick water evaporates at 4 dgrees though.

Answer 6

It is called sublimation...when a substance goes from a solid to a gas without passing through the liquid state.

Answer 7

Cold air is typically very dry. Any water is sucked into the air.

Answer 8

weird