National Science Foundation-funded researchers showed this week they could boost the efficiency of their solar-powered desalination system by more than 50% simply by adding inexpensive plastic lenses to concentrate sunlight into "hot spots." In conventional membrane distillation, hot, salty water is flowed across one side of a sheet-like membrane while cool, filtered water flows across the other. The temperature difference creates a difference in vapor pressure that drives water vapor from the heated side through the membrane toward the cooler, lower-pressure side. Scaling up the technology is difficult because the temperature difference across the membrane -- and the resulting output of clean water -- decreases as the size of the membrane increases. The researchers' "nanophotonics-enabled solar membrane distillation" technology addresses this by using light-absorbing nanoparticles to turn the membrane itself into a solar-driven heating element.
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