Climate change affects the poorest countries the most, where air conditioning is a luxury, this passive cooling solution can cool environments and food using only water, salt and solar radiation.
There are many parts of the world that lack infrastructure but receive a lot of sunlight. This turns buildings into furnaces that need large amounts of electrical energy for cooling, precisely where the energy is out of reach for the population.
A new passive cooling system uses a combination of sunlight and salt water, but no electricity, to produce a cooling effect. The experimental system, which is being developed at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, takes advantage of a natural phenomenon of phase change, in which energy is absorbed when salt crystals dissolve in water. This means that if you add salt to hot water, it cools quickly as the salt dissolves. An article about this research, led by Professor Peng Wang, was recently published in Energy and Environmental Science magazine.
After experimenting with different types of salts, it was found that ammonium nitrate provided the best results. It is a very water-soluble salt, so its cooling power is four times that of the next candidate salt, ammonium chloride. Furthermore, ammonium nitrate is already widely used as a fertilizer and is quite cheap.
Ammonium nitrate has a cooling power four times greater than the next candidate salt
In addition to its use in building refrigeration systems, the system can also be used to refrigerate food. In laboratory tests, the water with added ammonium nitrate was placed in a metal beaker, which in turn was placed in a sealed Styrofoam box. As the salt dissolved and the water cooled, the cup temperature dropped from room temperature, about 25°C to 3.6°C, in about 20 minutes. The chamber was kept below 15ºC for more than 15 hours.
Also, once all the salt was dissolved, solar heat was used to evaporate the water. The salt remained in the form of crystals that formed in the glass, and these crystals could be collected and reused in the refrigeration system. While letting water evaporate in dry, dry environments may seem like a waste, most of that water can be recovered and reused using a solar still.
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