[GlentoranMark (OP)]

I'm sure evapouration is the reason why clothes dry on the line but what has the biggest effect in drying clothes? Is it wind, the Sun, humidity or temperature? or something else?

[chiralSPO]

They all enter in to the equation. Which has the biggest effect will be determined by the contributions from the others.

Together the sunlight and air temperature determine how much available energy there is (which determines how quickly the water leaves the clothing).

The humidity (together with the atmospheric pressure) determines how quickly water goes back into the clothes (the process always goes both ways, with water constantly going from the clothes to the air and from the air to the clothes. If the water leaves the clothes faster than it comes in, then the clothes become drier, and if the water is coming in faster than it's leaving then it gets wetter (this second process is sometimes called "condensation" and is how the dew is formed. If the two processes are going at the same rate, then the moisture in the clothes stays the same).

Windspeed prevents the humidity from increasing due to evaporation of the water (in a closed room, the water evaporating from the clothes into the air increases the local humidity because the water has nowhere else to go, eventually reaching equilibrium where the water comes in just as fast as it leaves the clothes, and they do not dry any faster.) (If the humidity is sufficiently high for condensation to happen, wind will increase the amount of condensation by preventing the humidity from decreasing as the water leaves!)

So, if it's too humid, and not sunny enough no amount of wind will help the clothes dry. If the humidity drops a little, or the sun comes out and warms the clothes, then the wind will begin to help again.

[chris]

The discussion in this thread about washing drying will probably be of interest for you.