By Caleb Sooknanan ‘20

Over 1 billion people lack access to safe drinking water worldwide, and for many coastal regions with little or no rain and expensive water transportation measures, water only appears in dense fog layers. Fog collection or fog harvesting techniques have become useful for extracting water from these regions, with some systems mimicking natural collection mechanisms within animals and plants. Most fog collectors utilize meshes that capture water droplets, allow these droplets to coalesce, and gather the droplets in containers. However, the coalescing of water droplets can clog and decrease the efficiency of the meshes, so more research is needed to determine a more effective collection approach. Doctor Kripa K. Varanasi and researchers from the Massachusetts Institute of Technology designed a new droplet collector that would use ion emitters and electric fields to direct droplets into containers. The generated electric forces, the researchers suggested, would allow newer fog collectors to maintain higher efficiencies.

To design their system, the researchers introduced a space charge into a fog cloud and distributed a net charge across incoming water droplets using a cylindrical wire system. A cylindrical wire system, according to the researchers, involved a collector being electrically grounded and a separate electrode being exposed to a high voltage to generate an electric field. The field would increase electron movement and energy levels to ionize atoms within the air; these electrons would then collide with water droplets. The researchers used the resulting electric field to direct droplets towards specific containers, and they verified the resulting system by experimentally comparing the droplet collection efficiencies of single-wire systems to those of two-wire systems and meshes, with all three systems using electric fields.

The researchers suggested that single-wire electric field systems would be effective at collecting water droplets within a certain volume range; as the system’s voltage increased, the electric force increased to collect more droplets. However, increased droplet collection would lower the system’s efficiency. The researchers also suggested that two-wire systems could have electric field lines that affect water droplet trajectories between wires, thereby decreasing system’s ability to collect droplets in a uniform direction. Aside from this, the mesh systems were observed to be effective and capable of being modified to collect droplets at different voltages. More work is needed to commercialize these fog collection systems, but as the researchers suggested, such systems could be used to collect water for purposes such as drinking and irrigation.

References

1. M. Damak, K. Varanasi. Electrostatically driven fog collection using space charge injection. Science Advances 4, 1-8 (2018). doi: 10.1126/sciadv.aao5323  
2. Image retrieved from: https://c1.staticflickr.com/8/7316/16466809032_07bda6dfa3_b.jpg