Old Technology Passed Off as New
I'm always amazed about how people forget about ancient technologies.
I read this on an industry e-newsletter:
Sudanese Farmers Use New Means of Refrigeration
DARFUR, Sudan—Farmers who sell their crops at an outdoor market often lose much of their inventory due to hot weather. A simple refrigerating device invented last year by a local teacher is helping to alleviate the problem. The zeer is a large pot containing a smaller pot with a clay lid. The space between the two pots is filled with sand, creating an insulating layer around the inner pot. The sand is then kept damp by adding water at regular intervals, which reduces the temperature within the inner pot. Each zeer can contain 4.7 lbs. (12 kg) of vegetables, and costs less than $2 to produce.
The clay pot with wet sand is a very old device.....not something just "invented" by a local school teacher. The evaporation of the water in the sand cools down the air in the pot; its called evaporative cooling (or for those science people out there adiabatic cooling).
I think tommorrow I'll go out and invent a round stone structure that can be used to move things with......
posted by Dern @ 8:26:00 AM
3 Comments:
I was watching a science show last year (way back when I lived in rural California and could get every station imaginable) and they had a desert island science challenge. They had to make maps of the island that were true to scale, formulate sunscreen, and make ice -- all using naturally occuring tools and ingredients found on the island. They ended up making wood alcohol to use as the evaporation solution. The rest of the tools used included the sand, a lot of bamboo for tubing, and some kind of suction sytem they created. In the end, the water got really cold, but it never froze.
Reminds me of the Coolgardie Safe.
Great post, I've got a few Sudanese students, they'll like this.
Thanks for the link to the Coolguardie Safe. Definitely the same principle.
They used wood alcohol as the evaporation media? Makes sense, lower freezing point than water, but evaporative cooling works by transferring the state of water from liquid to gas. In this case alcohol, but still its the water in the air that cools down right?? I really don't know that much about low temperature air and the psychrometric chart....anyone else out there that might know, please chime in.
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