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Q & A: freezing by evaporation

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Q:
Given near freezing temperatures of both air and water and under ideal conditions of high surface area, low humidity and wind, can the evaporational cooling of the water suffice to cause ice formation?
- Peter Patricelli (age 65)
Eugene, Oregon
A:
That's a great question.

You can definitely freeze water via vigorous evaporative cooling. It's pretty easy to do with a vacuum pump, so long as you start with enough water and have good thermal isolation.

It's not so easy if there's air around, since heat can flow back in from the air. However, if the temperature is just a tiny bit above 0C, that conduction becomes very small. So long as the water is insulated from any heat flow from the bottom, it sounds like this should be possible. One key fact is that the latent heat of vaporization is much bigger than the latent heat of melting, so each gram of water that evaporates should cool things enough to freeze more than a gram of water. That gives some room for heat leaks without stopping the process altogether.

Mike W.

(published on 01/20/11)

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