Why evaporation can cool a wet surface
Liquid molecules have a range of energies, and molecules escaping into the air carry energy away. When that energy is not fully replaced, the remaining liquid and its surroundings cool. Evaporation is easier when moving, relatively dry air carries water vapour away from the wet surface.
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Escaping molecules carry energy
Evaporation occurs at a liquid's surface even when the liquid is not boiling. Some molecules have enough energy to escape the attractions holding them in the liquid.
Those departing molecules carry energy away. Energy needed for continued evaporation can come from the remaining liquid and nearby material, causing cooling if incoming heat does not replace it fully.
Drying and cooling are connected through energy transfer. Water does not need to reach its boiling point for this to happen.
- Drier air can accept more water vapour before approaching saturation.
- Moving air removes the humid layer near the surface.
- Very humid air reduces the opportunity for further evaporation.
This explains why the same damp cloth may dry quickly in a breeze but remain wet much longer in still, humid conditions.