Making Simple Refrigerators Residents living in African deserts can't use refrigerators to keep food fresh in summer because there is no electricity. The local people invented a simple "desert refrigerator". The refrigerator consists of an inner tank and an outer tank, and the gap between the two tanks is filled with wet sand. Put the food in the inner jar, cover the jar mouth with a wet cloth, and often sprinkle some water on the sand between the inner jar and the outer jar. When in use, it is placed in a dry and ventilated place to accelerate the evaporation of water in the sand between the inner tank and the outer tank, and use the evaporation of water to absorb heat to reduce the temperature of food, thus playing a certain role in keeping food fresh.