We all know by now that evaporation is usually thought of as a process driven by heat. However, researchers were baffled in recent years by the discovery that water evaporated during experiments at a higher rate, up to three to four times faster than the theoretical maximum limit based on thermal energy alone. MIT researchers then discovered that under certain conditions, light could be used to initiate evaporation without any input of heat.
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In a surprising discovery, MIT researchers discovered that light can cause water to evaporate without heating it. The findings were published this week in a research paper* in PNAS, by a team of MIT researchers who conducted a series of experiments and simulations using water in hydrogel, a soft JELL-O-type material that can hold a lot of water.
The discoveries came as a surprise to the researchers because water itself does not absorb light. However, they began to support the idea that light alone causes water to evaporate, without any source of heat energy. They called this effect the photomolecular effect.
Q: What is the photomolecular effect?
The photomolecular effect is a newly discovered light-induced evaporation process in which photons of light can displace clumps of water molecules from the surface of water without the need for heat. This process differs from traditional evaporation, which requires heat to break the bonds between water molecules.’
Q: How did researchers make this discovery?
The researchers placed a container of hydrogel filled with water on a scale and directly measured the amount of mass lost through evaporation. They also monitored the temperature above the surface of the hydrogel and ensured that no heat was introduced from the light source.
According to MIT’s official website, “In the lab, they monitored the surface of a hydrogel, a JELL-O-like matrix composed mostly of water bound by a spongy lattice of thin membranes. They measured its responses to simulated sunlight with precisely controlled wavelengths.”
The researchers found that the rate of evaporation increased as the light intensity increased. They also found that the effect was strongest for green light.
Evaporation of water from hydrogel using green light, without heating. Image: MIT News
Q: What are the potential applications of this new photomolecular effect?
It’s a relatively new discovery, but MIT researchers have found that their new evaporation process is more efficient than traditional evaporation processes that use heat. Potential applications of this new evaporation process include desalination, food processing and pharmaceutical manufacturing. It can also be used to develop new cooling and heating technologies.
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The researchers also believe that the photomolecular effect may play a role in the formation and evolution of fog and clouds, and that its inclusion in climate models could improve their accuracy. They also believe it could play an important role in many industrial processes, such as solar-powered water desalination, potentially providing alternatives to the step of converting sunlight into heat.
* Paper: “Probable photomolecular effect leading to evaporation of water exceeding the temperature limit.”
Categories: Trends
Source: HIS Education