71450.1773@compuserve.com (Steven B. Harris) (12/14/90)
>The only commercially competitive terrestrial application of >which I know for this heat sink is producing ice in 3rd-world >countries. (Place a shallow pan of water on top of a building or >hilltop so it only "sees" the night sky. Insulate the bottom. On >a calm, clear night, the water can radiate enough heat into >space to freeze solid even if the air temperature is above >freezing. Does that really work? Calculating with the Stefan-Boltzmann law and the heat of melting for water, I find that even with perfect insulation, water and air at 0 degrees C, and a com- pletely black sky, you would still only get about an inch thickness of ice in 8 hours. So you weren't kidding about needing a shallow pan if you want all your water to freeze. How close do you get to the theoretical thickness of ice in practice? I'm tempted to try it with a (wide mouth) thermos bottle. In fact, it strikes me that this would make a superior science fair project for some high school student. Steve Harris