Korea Advanced Institute of Science and Technology (KAIST) has developed a condensation coating technology that boosts heat transfer performance by up to 5.5 times. It is expected to be applicable to power plants, desalination facilities, and electronic device cooling.
KAIST said on the 23rd that a joint research team led by Professor Nam Young-seok of the Department of Mechanical Engineering and Professor Lim Seong-gap of the Department of Chemical and Biomolecular Engineering has introduced a technology that optimizes both droplet formation and removal by controlling the thickness and structure of an ultrathin polymer coating film. The study was published on Aug. 16 in the international journal Nature Communications.
Condensation, in which water vapor turns into liquid water, is widely used in power plant steam cycles, desalination and moisture harvesting, and thermal management of electronic devices. On ordinary metal surfaces, condensed water forms a film that hinders heat transfer, whereas dropwise condensation, in which water forms droplets, exposes a new surface each time a droplet falls, improving efficiency. However, there has been a dilemma in which roughening the surface makes it hard for droplets to detach, while smoothing it reduces nucleation sites.
The research team addressed this issue through the nanostructure of an ultrathin polymer film and a heat treatment process. Using initiated chemical vapor deposition (iCVD), they coated a fluorinated polymer, pPFDMA, to thicknesses of 25, 100, and 500 nanometers (nm). In films thinner than 100 nanometers, tightly packed semicrystalline polymer agglomerates formed, yielding a nucleation density about three times higher than that of the 500-nanometer film. They flipped the script by using the nanostructures, once considered defects, as elements to promote droplet formation. They then heat-treated the polymer film at 80 degrees for 1 hour to reduce adhesion, enabling droplets to detach quickly even at small sizes and allowing new droplets to form again.
When the optimized polymer film was applied to copper tubes for actual condensers, heat transfer performance was about 4.5 to 5.5 times higher than that of a bare copper surface, and coatings 100 nanometers or thinner maintained stable dropwise condensation for 4 weeks under pure steam conditions.
Professor Nam Young-seok said, "We used nanostructures once considered defects as elements that help generate droplets," adding, "By jointly controlling the formation and removal of droplets to improve heat transfer efficiency, we expect these results to be used across various energy and environmental fields."