Image: © Romolo Tavani/Stock.adobe.com
The team believes this phenomenon may be happening ‘widely in nature’ and could explain more about the Earth’s water cycle and its climate.
A new study from the Massachusetts Institute of Technology (MIT) suggests that – under certain conditions – light can evaporate water without the assistance of heat.
The study also claims that in some cases, light can evaporate water more efficiently than heat. The results may help scientists learn more about how evaporation works.
The researchers said water evaporation under sunlight is a “pervasive phenomenon” that has been shown to exceed the “theoretical thermal evaporation limit” in some experiments.
The team claims that in previous experiments with a sponge-like material called hydrogel, water has been shown to evaporate at double or triple the expected speed based on the amount of heat or thermal energy present.
To verify these claims, the team monitored the surface of a hydrogel as they subjected it to different colours of light, while measuring the evaporation rate.
“First we evaporate the water into vapor and then we need to condense the vapor to liquify it into fresh water,” said Yaodong Tu, MIT postdoc student and one of the co-authors of the study. He adds that with this discovery, they can potentially “achieve high efficiency on the evaporation side”.
The researchers found that the evaporation varied with the light colour and peaked at a particular wavelength of green light. The team said this has no relation to heat, which suggests that the light itself is causing at least some of the evaporation.
The extra confusing part of this result is the fact that neither water or hydrogel absorbs light to any significant degree. The study suggests that when both are combined, they become strong absorbers, which may contribute to the evaporation phenomenon.
The team now aims to replicate this phenomenon – dubbed the photomolecular effect – to apply it to real-world scenarios. The researchers believe this process could be happening “widely in nature” and could explain more about the Earth’s water cycle and climate, while presenting certain “clean water and energy technology applications”.
The discovery could also improve desalination processes by improving the evaporation efficiency, which has various potential benefits such as efficient solar cooling systems.
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