Science Lesson: Making Ice in the Desert

Can someone make ice in the desert with no electricity, chemicals or gadgetry?  The answer is yes.   It's called evaporative cooling.

The idea of evaporative cooling is not new.  It takes place when liquid evaporates in the surrounding air which in turn cools any object or liquid that comes into contact with it.  Most people have experienced evaporative cooling effects after getting out of a swimming pool on a hot sunny day. 
 
The earliest recording of evaporative cooling comes from frescoes from about 2500 B.C. which show slaves fanning water filled jars to cool rooms for royalty.
 
In 2006, a Nigerian teacher named Mohammed Bah Abba took this simple, ancient concept and applied it to pots to help thousands of impoverished Nigerian farmers with inexpensive refrigeration.  By setting up a local production facility, his simple pot-in-pot system extended the shelf-life of perishable foods.
 
The pot-in-pot system is simply the application of two clay pots, one inside the other. Fill the space between the pots with moist sand and cover with a damp cloth.  The water in the sand will naturally migrate towards the outer pot which pulls the heat with it, making the inside pot very cold.  It's a cheap, easy-to-make refrigerator.
 
To create ice, fill the space between the pots with water (not sand).  Since hot water has higher kinetic energy than cold water it evaporates first.  This lowers the temperature in the reservoir by getting rid of the "hottest" molecules first.  Because it is extremely dry in a desert, the air sucks water into it and molecules with low kinetic energy (cooler water) is then able to evaporate.  This leaves only molecules with very low kinetic energy.  Eventually, the average kinetic energy will be so low that the temperature drops below 32 degrees and the remaining water freezes.   This is true even if the ambient air temperature is above freezing so long as the air's humidity level is dry enough.
 
In recognition of Abba's part in bringing this amazing technology to people in need at the very low cost of $1.20 per system, Abba was awarded numerous grants.  Having funded the first 7,000 systems from his own pocket, he used the award money to distribute over 100,000 additional pot-in-pot systems.
 
Which brings me to my point… Mohammed Bah Abba's story disproves the myth that one person cannot make a difference.  He took a simple scientific principle and applied it in such a way as to have an impact on millions of people.

 

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