A NIGERIAN teacher has invented a remarkably simple and cheap cooler for
storing fruit and other perishable foods. Mohammed Bah Abba’s award-winning
“pot-in-pot” system needs no external energy source and is already improving
life in semi-arid northern Nigeria.
One earthenware pot sits inside the other, with wet sand filling the space
between them. You put food in the smaller pot, and cover it with a damp cloth.
Warm air outside draws moisture to the surface of the outer pot, where it
evaporates. The water vapour carries heat away with it, so this drying action
creates a constant heat flow from…
