The Pot-in-Pot refrigerators we built at the workshop in Malaysia did not work. The inside of the pot was actually warmer than the air outside! At first we thought it might be because the sand we started with was hot since we got it from the beach, which was in the sun. So we dug below the surface and got cooler, wet sand. We also tried garden soil instead of sand. Still no luck.
We believe the problem was that the pots we used were glazed. The glaze forms a glass-like surface on the surface of the pot. This would seal the water inside the pot and prevent it from evaporating.
When we replicated the experiment we used unglazed clay flower pots. This time the inside of the Pot-in-Pot was definitely cooler than the air outside. Here is the record we kept:
| Time after setting up Pot-in-Pot Refrigerator |
Temperature inside pot
(degrees Celsius) |
Air temperature outside pot
(degrees Celsius) |
15 minutes |
23.7 |
23.8 |
20 minutes |
23.6 |
24.0 |
30 minutes |
23.2 |
23.8 |
40 minutes |
21.7 |
24.7 |
1 hour |
21.0 |
24.8 |
1 hour 15 minutes |
20.4 |
25.0 |
1 hour 30 minutes |
20.1 |
24.7 |
1 hour 40 minutes |
19.9 |
24.7 |
2 hours 30 minutes |
19.5 |
24.0 |
2 hours 40 minutes |
19.4 |
24.4 |
13 hours |
19.4 |
25.0 |
That may not be enough to keep your ice cream frozen, but it is cooler inside than outside.
- We want to try this with larger pots. In particular, a larger outside pot. We think the cooling effect will be greater if there is more outside surface from which water can evaporate.
- We think humidity may also be a factor. If humidity is low, evaporation should be greater. We want to try the experiment under different humidity conditions.
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