Moist air may friz your hair, but science can now use it for green energy, as well.
image via (cc) flickr user booleansplit
As we prepare to enter the dog days of summer, it’s probably best to remind ourselves that when it comes to excessively uncomfortable seasonal climates, “it’s not,” as the cliché goes, “the heat. It’s the humidity.” As it happens, that same turn of phrase is also the key to an exciting development in green energy that might one day help power some of our smaller gadgets and gizmos, using nothing but airborne moisture. Yes, the same abundant, and entirely free, humidity that makes the summer so unbearable may someday help power the very air conditioning that saves us from the heat.
In “Scaling up nanoscale water-driven energy conversion into evaporation-driven engines and generators,” published this week in Nature Communications, researchers lead by Columbia University’s Ozgur Sahin describe how they were able to utilize humidity to generate power for a number of specially constructed small devices. The key isn’t, as one might expect, tapping into the flow of water vapor as it moves through the air. Rather, the process hinges on a key biological reaction which naturally occurs in certain forms of bacteria when they are exposed to humidity: They expand.
Sahin and his colleagues used the living but dormant spores from Bacillus subtilis, a species of bacteria commonly found in soil and in the human gastrointestinal tract. Each spore typically swells and then shrinks up to 6% when moved from dry air to extremely humid air and then back again,
By thinly layering these bacterial spores in tandem across curved sheets of polymer, researchers were able to harness their natural expansion to straighten the sheet’s curvature, which then returns to its normal shape after the spores contract. When the bacteria works in tandem with multiple spores, the unit created is capable of expanding to nearly four times its ordinary length, resulting in a more dramatic back-and-forth motion for the polymer strip. It’s that motion which the team was able to then translate into modest amounts of mechanical power. Enough to spin a small rotary wheel:
[youtube https://www.youtube.com/watch?t=26&v=VhPKI-FRmww expand=1]
Even (awkwardly) propel a lightweight vehicle:
That’s the good news. Unfortunately, Sahin and his team’s research is, for the time being, more significant as proof-of-concept than for any practical application. Still, it’s a promising development—even if it only works on a small scale—given the abundance of free humidity just waiting to be put to better use than simply frizzing our hair.