Researchers have discovered how chemical micro-patterns can beused to control frost formation due to condensation with inspiration from the shell of a beetle.
Crawling in one of the hottest climates, the Namib Desert Beetle collects airborne water molecules at the top of each bump of its shell. The beetle can drink from this water using flat paths which direct collected water to the beetle’s mouth."The main takeaway from the Desert Beetle is we can control where dew drops grow," said Jonathan Boreyko, assistant professor of Biomedical Engineering and Mechanics at Virginia Tech.
Controlling Frost via Photolithography
By means of photolithography – a process using light to transfer patterns from a photomask to a light-sensitive chemical on a substrate – scientists can persuade chemical arrays to attract water onto a surface that would normally repel water. With this technique, frost can be controlled or altogether prevented.
This chemical pattern was used by researchers from Virginia Tech on a thin film of about one centimeter to control frost.
Although photolithography is used for micro-scale fabrication, researchers believe upscaling is possible using hydrophilic patterns overtop of hydrophobic surfaces."We made a single dry zone around a piece of ice," Boreyko said. "Dew drops preferentially grow on the array of hydrophilic dots. When the dots are spaced far enough apart and one of the drops freezes into ice, the ice is no longer able to spread frost to the neighboring drops because they are too far away. Instead, the drops actually evaporate completely, creating a dry zone around the ice.”
The following video shows frost spreading faster when droplets are closer together. By adjusting condensation spacing, the rate at which frost spreads is reduced or completely eliminated.
(Video courtesy of Saurabh Nath/Virginia Tech.)
"Fluids go from high pressure to low pressure," Boreyko said. "Ice serves as a humidity sink because the vapor pressure of ice is lower than the vapor pressure of water. The pressure difference causes ice to grow, but designed properly with this beetle-inspired pattern, this same effect creates a dry zone rather than frost."
Cost Savings in Staying Dry using Less Energy
With a frost-free zone application, expensive de-frosting such as using harsh deicing chemicals for wind turbines or airplane wings as well as maintaining heat coil pumps can be eradicated.
“Keeping things dry requires huge energy expenditures,” said C. Patrick Collier, a research scientist at the Oak Ridge National Laboratory and co-author of the study. “That’s why we are paying more attention to ways to control water condensation and freezing. It could result in huge cost savings.”
The results of Boreyko and Collier’s report can be read in detail in the online journal Scientific Reports.