So, what happens when you put together biologists, physicists, and chemical engineers (of course, they’ll be part of the mix)? Well, if this group from Columbia University is any indication, you get a new kind of engine that may be the answer to our future power needs.
Drs. X. Chen, D. Goodnight, M. Delay, O. Sahin* (Biological Sciences), Z. Gao (Physics), A. Cavusoglu, N. Sabharwai (Chem E)- all from Columbia, along with Dr. A. Dirks from Loyola Microbiology collaborated on this research. Their developments were published in Nature Communications.
And, I’ve kept you in suspense long enough. What these folks developed was an engine that is powered by the process of evaporation. Yes- their research showed you can pull energy out of thin air (well, only to you non-techie types). Actually, they are harnessing the latent heat of evaporation, which is a thermodynamic element associated with water becoming vapor.
Dr. Sahin led this group (the * next to his above meant he had a joint appointment to the Physics department) in their creation of the first evaporation-driven engine. Right now, it doesn’t provide much usable power, but, this cheap (currently <$5) device, slightly less than 4 inches on a side, can power LED lights or a even miniature car. It produces power up to 60 microwatts (or at sustained levels of 1.8 microwatts)- but it is still in development.
The group called their material Sahin cells (after the leader, of course), that employs hygroscopy driven artificial muscles (HYDRAs). These thin, muscle-like bands respond to relatively small changes in humidity by expanding and contracting. Sahin et. al. claim the HYDRAs can withstand some million contractions with negligible deterioration in response- even though they can expand to four times their contractile shape.
The trick? The device, the HYDRA, is based upon microbial spores. Recall that some microbes form spores, when conditions are not ideal for their growth. The spores respond to changes in moisture; the outer shell of the spore absorbs and exudes water from the air- and expands and contracts when it does so.
So, Sahin et. al. “paint” the spores onto strips of plastic- on both sides, in alternating patches. When the humidity is right, the spores expand, causing the plastic to flex in a given direction (like a spring that expands), and contracts in the opposite fashion when the water level decreases.
The strips are then placed over ambient temperature water in an enclosure. When the surface water evaporates, the strips expand as they collect the humidity, pulling on a cord attached to an electromagnetic generator. (This coverts the movement of the cord into mechanical energy.) The HYDRAs also open shutters on the top of the enclosure, which releases the humidity from the enclosure; the HYDRA then shed their water, contracting in the process, and closing the shutters. Repeat the process and you have an engine cycle.
Sahin also developed a turbine sort of engine, using bending HYDRAs to spin a wheel. (This is how the miniature car mentioned above moves.)
The system works ay near ambient temperatures (60 to 90 F). However, one should note that hotter water works best, since water evaporates faster at higher temperatures. (This is why the engine cycles every 40 seconds at 60F, but every 10 at 90 F.)
Each cycle of the engine generates some 50 microwatts- but that is only 1% of the spore’s energy potential, so there’s plenty of room for additional development.
