2023-11-03 12:46:53
MADRID, 3 Nov. (EUROPA PRESS) –
Under certain conditions, at the interface where water meets air, light can directly cause evaporation without the need for heat, even more efficiently.
After carrying out a series of new experiments and simulations, and re-examining some of the results from several groups that claimed to have exceeded the thermal limit, A team of researchers from MIT has reached this surprising conclusion.
In these tests, water was held in a hydrogel material, but the researchers suggest that the phenomenon can also occur under other conditions.
The phenomenon could play a role in the formation and evolution of fog and clouds and, therefore, it would be important to incorporate it into climate models to improve their accuracy, the researchers say. And it could play an important role in many industrial processes, such as water desalination with solar energy, perhaps allowing alternatives to the step of first converting sunlight into heat, according to a statement from MIT.
The researchers subjected the water surface to different colors of light in sequence and measured the evaporation rate. They did this by placing a container of hydrogel loaded with water on a scale and directly measuring the amount of mass lost through evaporation, as well as monitoring the temperature on the surface of the hydrogel. The lights were shielded to prevent them from introducing additional heat. The researchers found that the effect varied with color and peaked at a particular wavelength of green light. This color dependence has no relation to heat and therefore supports the idea that it is light itself that causes at least some of the evaporation.
The researchers attempted to double the observed evaporation rate with the same setup but using electricity to heat the material and without light. Although the thermal input was the same as in the other test, the amount of water that evaporated never exceeded the thermal limit. However, it did so when the simulated sunlight was on, confirming that light was the cause of the additional evaporation.
Although water itself doesn’t absorb much light, and neither does the hydrogel material, when the two are combined they become strong absorbers, says mechanical engineering professor and first author Gang Chen. This allows the material to harness the energy of solar photons efficiently and exceed the thermal limit, no need for dark dyes for absorption.
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