Using some of the more basic principles of physics, a grassroots inventor in Nigeria named Mohammed Bah Abba developed a way to refrigerate items simply by using two different sized clay pots. Malapati Sekhar on the Rural Development of India blog explains how this invention, called the Zeer, works:
The pot-in-pot consists of two earthenware pots of different diameters, one placed inside the other. The space between the two pots is filled with wet sand that is kept constantly moist, thereby keeping both pots damp (slightly wet). Fruit, vegetables and other items such as soft drinks are put in the smaller inner pot, which is covered with a damp cloth. The phenomenon that occurs is based on a simple principle of physics: the water contained in the sand between the two pots evaporates towards the outer surface of the larger pot where the drier outside air is circulating. By virtue of the laws of thermodynamics, the evaporation process automatically causes a drop in temperature of several degrees, cooling the inner container, destroying harmful micro-organisms and preserving the perishable foods inside.
Sekhar continues on to highlight how such a simple innovation like this could have a significant impact on farmers’ current behaviors, as it would enable them to preserve their produce long enough to sell at urban markets where prices are much more amenable to them. Utilizing this simple refrigeration mechanism would mean that such food could be stored and sold in areas with the greatest demand.