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Researchers at the Massachusetts Institute of Technology (MIT) have developed a solar desalinator with high water production, using a multistage system of evaporators and condensers. It offers cost-effective solar desalination, making solar-powered drinking water cheaper than tap water for the first time.
Researchers from MIT and Shanghai Jiao Tong University have demonstrated solar-powered multistage membrane distillation. They claim that it can significantly reduce the cost of water production.
“The configuration of the device allows water to circulate in eddies, similar to the thermohaline circulation of the ocean,” the scientists explain. “This circulation, combined with the heat of the sun, causes the water to evaporate and leave behind salt. The resulting water vapor can be condensed and collected as pure, drinkable water. Meanwhile, excess salt continues to circulate through and out of the device, instead of accumulating and clogging the system.”
Thermohaline circulation describes how fluid movement occurs due to the difference in buoyancy between hot, less dense material that rises and cold, denser material that sinks due to gravity, resulting in a transfer of heat.
Researchers say that if the system is scaled up to the size of a small suitcase, it could generate 4 to 6 liters of drinking water per hour and last several years before needing replacement components. At this scale and with this performance, the system could produce drinking water at a more affordable price than tap water.
The device consists of a series of compartments with heat exchangers and condensate collectors. The central component is a single-stage unit resembling a thin box covered in dark, heat-absorbing material. Inside, the box is divided into upper and lower sections.
Water flows through the top half, which has an evaporator layer on its surface that uses solar heat to evaporate the water directly. The resulting water vapor is directed to the bottom half of the box, where a condensation layer cools it, transforming it into a salt-free drinkable liquid. The researchers placed the entire tilted box inside a larger empty container, connecting a tube from the top half of the box to the bottom of the container and allowing it to float in salt water.
“In this configuration, the water can naturally push up through the tube and into the box, where the tilt of the box, combined with the thermal energy of the sun, induces the water to swirl as it flows through.” of it,” the researchers explained. “The small eddies help bring the water into contact with the top evaporation layer, while keeping the salt circulating, rather than settling and getting stuck.”
The team built several prototypes, with one, three and 10 stages, and tested their performance in water of different salinities, including natural seawater and water seven times saltier.
“With a 10-stage device, we achieved a record solar water efficiency of 322%-121% in a salinity range of 0 to 20% by weight, under the illumination of a single sun. In addition, we demonstrate extreme resistance to salt accumulation with a 180-hour continuous desalination of seawater concentrated at 20% by weight,” they conclude. |
