Scientists have developed two new devices that are directly powered by evaporation.
A research team created a floating, piston-driven engine that generates electricity to power a flashing light and a rotary engine that drives a miniature car, Columbia University reported. The researchers believe this technology could lead to devices such as giant floating power generators and wind turbines.
"Evaporation is a fundamental force of nature," said Ozgur Sahin, an associate professor of biological sciences and physics at Columbia University and the paper's lead author.
When bacterial spores shrink and swell with changes in humidity, the can move other objects. The new devices are powered by this type of technology. To create the piston-driven engine, the researchers glued spores to both sides of a thin, double-sided plastic tape; the dashes they created on one side filled overlapped the gaps on the other. When dry air shrinks the spores it causes the dashes to curve, transforming the tape from straight to wavy and shortening it. If both ends of the tape are anchored, it will tug on whatever it is attached to. When the air is moist, the tape extends and releases the force.
Dozens of these tapes were placed side by side to create a strong artificial muscle that was placed inside a floating case topped with shutters. Evaporating water caused the air in the case to become humid, triggering the muscle to expand, opening the shutters and drying out the air. When the moisture was removed the tape contracted and pulled the shutters closed to allow the air to become humid once again.
"When we placed water beneath the device, it suddenly came to life, moving on its own," said Xi Chen, a postdoctoral fellow who worked on the project.
The device acted as an evaporation-driven piston that generated enough electricity to power a small flashing light.
"We turned evaporation from a pool of water into light," Sahin said.
The team's other invention, dubbed the Moisture Mill, consists of a plastic wheel with protruding tabs of tape covered with spores on one side. The wheel sits half in dry air (causing the tabs to curve) and half in moist air (causing the tabs to straighten). The result is a rotating wheel that acts as a rotary engine.
Using these novel devices, the researchers built a small toy car that can roll on its own and is powered solely by evaporation. The researchers hope in the future this technology could be used to create full-sized engines that could propel vehicles and to power wind turbines to generate power.
The findings were published in a recent edition of the journal Nature Communications.
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