Many parts of the world lack infrastructure, but there is plenty of sunlight, which makes buildings extremely hot. This is where a new system that uses a combination of sunlight and salt water for cooling, but operates without electricity, can help. The experimental facility, currently under development at King Abdullah University of Science and Technology in Saudi Arabia, takes advantage of the natural phenomenon of “phase change,” where energy is absorbed when salt crystals dissolve in water. This means that if salt is added to warm water, the water cools as quickly as the salt dissolves.
After several experiments with different types of salt, it was found that ammonium nitrate works best. Mainly because it is soluble in water and its cooling power is four times greater than the cooling power of the next best salt, ammonium chloride. In addition, it is relatively cheap. In addition to being used in the construction of refrigeration systems, this system can also be used to cool food.
In laboratory tests, water with added ammonium nitrate was placed in a metal beaker, and then placed in a sealed box of polystyrene foam. As the salt dissolves and the water cools, the cup’s temperature drops from room temperature (about 25°C) to 3.6°C in about 20 minutes. After all the salt had melted, the heat of the sun was used to vaporize the water. The salt remained in the form of crystals formed on the glass. It can then be collected and reused in the cooling system. An article on the research was published in the journal Energy and Environmental Sciences.
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