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| Pedal-Powered (Vacuum) Zeolite Refrigerator |
The continued pedaling (which drives the vacuum pump down to 10^-2 atm) will ensure that the water freezes as it continues to boil. After only about 10 min of pedaling, the valve to the vacuum pump can be shut off, and the zeolite container line opened.
Zeolite are common absorbers based on aluminum silicates and will swell up to 30% its mass with water.
The zeolite then absorbs the vapor produced by the boiling of the water, and, in order for the liquid water to remain in equilibrium with the vapor phase, it must continue to boil (for up to a day).
In general, one can achieve constant temperatures of 0-6 Celsius for 1 day with only 10min of pedaling. Now this is a real way to cool for cheap.
Even ice cubes can be made, and one cool advantage of this system is that the hotter it is outside, the more cold you can generate!