Boiling water in a cold air

We had fun to throw several times boiling water into freezing air in front of our house.  Yesterday and today was really low temperature, less than -22F/-30C. So it was an opportunity do experiment with boiling water thrown into the air. It morphs immediately into white vapor cloud, and almost no liquid water hits the ground.

But why?

Let’s say we have cup of boiling water. As soon as we throw that water in the air, it will disperse into many smaller or bigger droplets, which fly through  air. Cold air is very dry, is has low relative humidity, and very low absolute humidity. Flying droplet is warming boundary layer of the air. Warmer air is able to absorb much more  water, and vapor from droplet surface is evaporating quickly into very dry air. Only big drops don’t evaporate completely, and hit the ground. Soon after air cools off and water vapor condense into little droplets and ice crystals. And we see it as a white cloud.

Links: Phase diagram of water, Psychrometrics diagram, Psychrometrics, Relative humidity.

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