The Desert Refrigerator
The desert refrigerator is made up of two earthenware (i.e. porous) pots, one placed inside the other. The gap between the two different diameter pots is filled with wet sand in order to keep both pots damp. A damp cloth is then used to cover the top, and the finished assembly placed in a shaded, dry, and well-ventilated location.
The water in the sand evaporates out through the outer pot and into the dry air outside. This simple evaporative process reduces the temperature of the pots and the perishable contents (e.g. fruits and vegetables) kept in the inner pot.
The drier and windier the location, the better the desert fridge works as evaporation happens more quickly. Rather than using electrical power, small amounts of water need to be added to the sand to keep it moist, and the cloth cover must also be kept damp.
This is a great way to keep your drinks cool at a barbecue!