Why/How do clothes dry?

Question

I have a pair of trousers, which are damp because I rinsed some coffee off them. Eventually they will dry, but why?

Because they're in a room thats only about 20-25 degrees and thats no way near enough to make water evaporate? Is it to do with water potential or something?

I am very confused.

Answer 1

Ah - you're confusing evaporation with boiling....

At room temperature, the molecules in the water are in a liquid state.

At any given time, they are bouncing around - some of them, near the surface, will have enough energy to break the bonds holding them to the rest of the water, and bounce off, into the surrounding air. As more of them do so, the volume of water left in the trousers will decrease - aka the trousers will dry.

As the temperature increases, the average speed at which the molecules bounce around goes up, so more start taking off... and the trousers dry faster.

At the same time, there are water molecules in the air, and some of them, as the whiz around, hit the trousers, making them wetter again! The more water molecules there are in the air, the more carry out this reverse process... (The air is more humid), and the trousers dry more slowly.

At 100 degrees C, however, an odd thing happens - the molecules are, on average, moving around SO FAST that even those hitting the existing water in the trousers don't "join up" with them - and ALL the water remains in the gaseous form. At this temperature, any water that's still a liquid has an average speed so high that little pockets of gas appear in the MIDDLE of the liquid, and bubble to the surface - hence the "boiling" effect.

Answer 2

So long as the Water Vapour Pressure of the water in the trousers is higher than the WVP of the atmosphere water will evaporate from them. This requires an energy input - the energy of vapourisation. When clothes are 'aired' they are effectively deprived of water in excess to the WVP of the atmosphere. When they become moist when worn the energy is given back when the material becomes wet.

That's why dry clothes are warm and pleasant to put on and those exposed to the atmosphere not so warm!

RoyS

Answer 3

Is the important thing not that they will dry rather than how ?

Answer 4

The water does, in fact, evaporate at cold temperatures. The evaporation process does slow considerably the colder it is, but it does evaporate. Your local humidity percentage has a lot to do with the rate of evaporation.  

Try this experiment: Put a tray of water in the freezer and leave it alone for a number of weeks. If it is left long enough, the ice cubes will "shrink". If your freezer has a fan, causing air flow within the box, it will be a bit quicker. Where does the ice go? It evaporates.

Answer 5

on the washing line

Answer 6

Even in a seemingly calm ambient air there is circulation of air molecules which are brushing against surfaces(including the water). The water is either absorbed by the air or by your skin or by the adjacent clothing materials.