When a device like an enormous inverted funnel failed to capture the oil gushing into the Gulf of Mexico in 2010, mechanical engineer Kripa K. Varanasi saw it as an interface problem: crystals of natural gas forming on the sides of the funnel caused the oil, instead of whooshing up, to slide off.
To Varanasi, the Doherty Associate Professor of Mechanical Engineering, many engineering problems come down to interface problems: ice forming on airplane wings and wind turbine blades, the crystalline hydrates that inhibit deep sea oil recovery, water boiling or condensing in steam power plants or desalination plants or electronics cooling systems. “The interface between two forms of matter is most often what becomes a bottleneck. Altering those interactions in a positive way can have a huge impact on efficiency,” says Varanasi, whose work is supported by MITEI’s Energy Research Seed Fund Program, Shell International, and Masdar Institute of Science and Technology.
For instance, water droplets striking the surface of steam turbine blades flatten into mega-droplets and then into sheets that fly from one blade to the next, wearing them down and forcing the turbine to work harder. This can cause up to 40 percent of the efficiency losses in a steam power plant. To counter this, Varanasi’s tough new nanoengineered surfaces and coatings repel water the way duck feathers and lotus leaves shed water and debris.
Other materials repel ice or help transfer heat. A bonus is the new materials reveal thermal-fluid phenomena at the microscale. “Nucleation, such as carbon dioxide bubbles forming on the sides of a soda bottle, is a ubiquitous everyday experience, but spatial control of this phenomenon is extremely difficult,” Varanasi says. He and his colleagues accomplished this for the first time by creating a surface patterned with orderly rows of hydrophobic, or water-repelling, and hydrophilic, or water-attracting, regions. These rows control where droplets form so they can be shed more easily.
In the deep sea, hydrates — methane gas molecules trapped in an icy cage of water — form at very high pressures, plugging oil pipelines, causing flow disruptions, and forming on equipment such as the funnel employed in the Gulf spill. According to the U.S. Geological Survey, up to 300 million trillion cubic feet of methane exists globally in hydrate form — most of it in the ocean floor. Varanasi hopes to use nanoparticles to control where and how hydrates form, much like cloud seeding. This would prevent hydrates from plaguing pipelines and make it safer for engineers to safely extract their methane, potentially opening up access to 10 times more natural gas reserves than now available.
“We’re trying to come up with new materials, alter their structure at a molecular scale, and then scale them up to large-scale manufacturing with durable materials,” Varanasi says. “Applying those materials to technology on both the macroscale and the nanoscale is able to give us things we haven’t seen before.”