Nigerian inventor, Mohammed Bah Abba, of Mobah Rural Horizons, has received awards for his simple-to-implement invention of and evaporative cooler consisting of one pot inside another, with wet river sand in between and a damp cloth (or jute bag) on top. When kept in a dry, well-ventilated, and shady location, water evaporates, cooling the inner container.

The method is already starting to have widespread impact in the third world for food preservation in high-temperature, dry climates.

Eggplants can last 27 days rather than three. African spinach can be kept for 12 days instead of spoiling after one day. Tomatoes and peppers stay fresh for three weeks. Framers no longer need to sell their products in a hurry. Young girls are free to attend school, instead of hawking food every day.

The device owes its cooling powers to a simple law of thermodynamics. When moisture comes into contact with dry air, it evaporates, causing an immediate drop in temperature. When the water in the sand between the two pots evaporates, the inner pot is kept cool, preserving the goods inside.

This uses the heat of sublimation (120 calories per gram in reverse). Grandma Carrick used to have a similar refrigerator. It was on the north side of a big lilac bush by the door to her kitchen. It was a wooden box with a burlap sack hanging over the front. She had a water hose dripping on the top of the burlap. The water would wick down over the face of the shelves in the box, and as the water evaporated it would cool the air behind the burlap; i.e. the inside air where the milk and other things were kept cool.

The old canvas water bag works on the same principle. Dry, warm air over the face of the material causes the evaporation. In other words, it would not work in a high humidity situation; e.g. the humid jungle.

The eutectic salts we are using in our home use a similar idea -- the heat of fusion (80 calories per gram in Glauber's salts). I designed the addition to our farm home down the road to use this for heating in the winter and for cooling in the summer. These are called phase-change phenomena (liquid (water) to vapor; solid to liquid or liquid to solid. Most of the temperature control of the body is also the reverse of the heat of sublimation; you sweat and it evaporates. That is how a warm breeze can feel so cooling if you have water on you skin.

Mohammed Abba - Nigeria - Mohammed Abba runs Mobah Rural Horizons, which provides an electricity-free refrigeration system easy to operate by African villagers. He tells Global X why his simple technology, which better preserves local crops, is breaking the vicious cycle of poverty. The results: farmers sell their crops when demand is high, and more girls can go to school. (YouTube (http://youtube.com/watch?v=z9zKghNEu3M); December 19, 2007)

Originally published at:  http://peswiki.com/index.php/Directory:Abba_Pot-in-Pot_Cooling_System