We all know that water evaporates when temperatures rise, but researchers have just shown that there is another factor at play. This breakthrough could unlock long-standing atmospheric mysteries and lead to future technological advancements. The MIT team found that light in the visible spectrum is enough to loosen water molecules at the surface where they come into contact with the air and cause them to drift away.
In other words, although fluctuations in temperature cause evaporation, the water is constantly turning into water vapor due to the force of the beam alone. Scientists call this process the "photomolecular effect" and derive from Einstein's 1905 explanation of the photoelectric effect.
"The discovery that evaporation is caused by light rather than heat provides new and disruptive knowledge of the interaction between light and water," said Ruan Xiulin, a professor of mechanical engineering at Purdue University. Nguyen was not involved in the MIT study, which was published in the Proceedings of the National Academy of Sciences (PNAS).
"This can help us gain a new understanding of how sunlight interacts with clouds, fog, oceans and other natural water bodies to affect weather and climate," he added. There is significant potential practical application value, such as solar-driven, high-performance desalination. This study belongs to the rare truly revolutionary discoveries that will not be immediately widely accepted by society, but will take time, sometimes even a long time, to be confirmed. "
The difference between light-induced evaporation and heat-induced evaporation may not seem like much, but it would not only have a significant impact on how future evaporation projects are executed, but it would also explain a long-standing difference involving clouds, the researchers said.
For about eighty years, measurements of the way clouds absorb sunlight have often shown that clouds absorb more sunlight than physics thinks is possible. The photomolecular effect on these clouds – which causes additional, unexpected evaporation – may help solve this dilemma.
The team used lab equipment to shoot lasers into the water to observe the evaporation effect of light from Bryce-Vikmark
Because the discovery of light-based evaporation was so striking, MIT researchers conducted 14 different validation experiments, all of which supported the discovery. In the course of experiments using lasers, they found that the evaporation effect was strongest when a specific polarized light, known as transverse magnetic polarization, hit the surface of the water at a 45° angle. Green light also has the strongest evaporation effect, which surprised the team because green light is the color that makes water look the most transparent because it has the least interaction with water.
"The observations in the manuscript point to a new physical mechanism that fundamentally changes the way we think about evaporation dynamics," says Shannon Yee, associate professor of mechanical engineering at Georgia Tech, who was also not involved in the work. "Who would have thought that we were still learning something like water evaporation?"
Researchers have already been approached by a number of companies that believe the light-molecule effect could help their business, including one company that wants to use it for paper drying in paper mills and another company that wants to use the process to vaporize the syrup. While these applications may be feasible, the researchers believe that more work will benefit their research exponentially.
Gang Chen, a co-author of the study and a professor of power engineering at the Massachusetts Institute of Technology, said: "This phenomenon should be very common, and our experiment is really just the beginning. The experiments required to prove and quantify this effect are time-consuming. There are many variables that go from understanding water itself, to expanding to other materials, other liquids, and even solids. "