Cooling with salt, water and solar heat

Wenbin Wang and his doctoral advisor Peng Wang of King Abdullah University of Science and Technology (cf. http://kaust.edu.sa) in Saudi Arabia use this cooling effect, which occurs when certain salts are dissolved in water. After each cooling cycle, the now highly saline water is heated by solar heat so that it evaporates and the salt remains. Then the cycle can start all over again.

Ammonium nitrate as a key

"In sunny regions without electricity, it is attractive to use the sun's heat for cooling," says Wenbin Wang. Together with Professor Wang, he has developed a two-step cooling and regeneration system. The first step involves dissolving ammonium nitrate in water, a salt used in large quantities to make fertilizer and explosives. Comparing 20 different salts, ammonium nitrate had the best cooling effect, but must be handled with care because it is explosive.

"The salt's exceptional cooling power is due to its high solubility," Wenbin Wang points out. It is 208 grams per 100 grams of water, while other salts are generally below 100 grams. The fact that it is very cheap is less important because it can be used again and again. It is, in a sense, a storehouse for climate cooling.

Cooling effect for up to 15 hours

The Wang team tested the process by gradually dissolving the salt in a metal beaker embedded in an insulating shell of polystyrene foam, better known as Styrofoam. Within 20 minutes, the temperature of the cup dropped from 25 to 3.6 degrees Celsius. For 15 hours, the temperature remained below 15 degrees. Then the researchers poured the salty water into another container designed to absorb as much solar heat as possible. They collected the evaporating water to reuse in the next cycle. This is important for regions where water is scarce. Since the researchers deliberately avoided using electrical energy, all processes have to be done by hand.

Source: pressetext.redaktion, Wolfgang Kempkens