Scientists have found a way to harness the power of evaporating water to produce electricity that is powerful enough to light up a small LED and power a miniature car
Columbia University scientists developed two novel devices that derive power directly from evaporation - a floating, piston-driven engine that generates electricity causing a light to flash, and a rotary engine that drives a miniature car.
Ozgur Sahin, an associate professor of biological sciences and physics at Columbia University, had already found that when bacterial spores shrink and swell with changing humidity, they can exert force on other objects.
In a new study, to build a floating, piston-driven engine, researchers glued bacterial spores to both sides of a thin, double-sided plastic tape akin to that in cassette tapes, creating a dashed line of spores. They did the same on the opposite side of the tape, but offset the line so dashes on one side overlapped with gaps on the other.
When dry air shrinks the spores, the spore-covered dashes curve. This transforms the tape from straight to wavy, shortening the tape. If one or both ends of the tape are anchored, the tape tugs on whatever it's attached to.
Conversely, when the air is moist, the tape extends, releasing the force. The result is a new type of artificial muscle controlled by changing humidity.
Scientists then placed dozens of such tapes side by side inside a floating plastic case topped with shutters.
Inside the case, evaporating water made air humid. The humidity caused the muscle to elongate, opening the shutters and allowing the air to dry out.
When the humidity escaped, the spores shrunk and the tapes contracted, pulling the shutters closed and allowing humidity to build again. A self-sustaining cycle of motion was born.