The Pot-in-Pot Cooler—used in Burkina Faso, Cameroon, Chad, Eritrea, Ethiopia, and Niger—keeps food from spoiling. The simple system consists of two clay pots, sand, and water. A smaller clay pot is nested inside a larger pot, and the space between them is packed with sand. Produce is placed inside the smaller pot, and water is poured into the packed sand. The evaporating water pulls heat out of the interior of the small pot, keeping the food cool and prolonging its storage capacity. Tomatoes, for instance, can last up to three weeks using the Pot-in-Pot, compared with two or three days without it. Source: http://www.spectrum.ieee.org/jul07/5405
