My first assumption was based on "evaporation causes cooling" but I realized that it is not the case as it is cooler even if I am submerged under it. Are all liquids generally cooler than air ? Just curious.
Answer
Firstly, to make a valid comparison between how water and air 'feels' on your skin, two conditions would need to be met:
- Both water and air would have to be at exactly the same temperature.
- That temperature would have to be lower than human body temperature (strictly speaking skin temperature).
If those conditions are met then water would certainly feel cooler than air. Several factors are responsible for this.
- Water has a much higher Specific Heat Capacity than air, making it a far better coolant than air.
- More intimate contact between water and skin, compared to air and skin, results in a higher Heat Transfer Coefficient which makes water again a better coolant.
- In the case of fairly thin layers of water evaporative cooling also takes place in the case of water on skin. As Latent Heat of Vaporisation is carried off the water will cool down and eventually skin will cool too due to heat transfer.
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