12th August 2006 - 10:24 AM
This looks like a nice sensible account of evaporation...http://daphne.palomar.edu/jthorngren/latent.htm
Water does not have to be at the boiling point to evaporate. ... In a given amount of water at a given temperature, some molecules of water will have more energy than others, so some molecules will be able to evaporate, while others remain in the liquid state. The lower the temperature of the water, the more energy is required for evaporation. If the water is liquid at a temperature of 0 degrees C, the latent heat of vaporization is 597 cal/g, compared to 540 cal/g at 100 degrees C. In between, at 50 degrees C, an input of 569 cal/g would be required for evaporation.
Sooo... very roughly it looks like the evaporation of 1 pound of water will cool about 200 pounds of water by 1 degree F.
Pictures of cooling towers and warning
Hope this helps,