Cardstock and plastic above cold water





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Uploaded on Feb 8, 2012

A piece of cardstock, half of which was covered by a sheet of plastic film, was placed on top of a cup of cold water. Interestingly, the cardstock and plastic film above the water quickly cooled off. Between the cardstock/plastic and the water there is only air and we know air is an extremely poor heat conductor. So what is responsible for this rapid cooling in the area of the cardstock/plastic above the cold water?

This video shows that there was no similar degree of condensation heating that was observed with overnight water (http://www.youtube.com/watch?v=WzGNLy...). Water molecules probably still evaporated from the surface of cold water. But the air above the cold water was cool. When a piece of cardstock or plastic film was placed on top of the cold water, it was immediately cooled down by the cold air. This heat transfer process has little to do with the material, paper, cardstock, or plastic, because it is the result of countless collisions between the surface and air molecules.

Another contribution comes from radiation heat transfer. The cardstock or paper radiated more energy than the cold water.

Visit http://energy.concord.org/ir for more.

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