KAIST coating boosts condensation heat transfer 5.5×

KAIST researchers announced on August 23 that a new ultrathin polymer coating can increase condensation heat transfer up to 5.5 times over conventional copper surfaces. The coating, created by Professor Youngsuk Nam and Professor Sung Gap Im, uses nanoscale polymer aggregates that were previously considered defects.

Condensation and Heat Transfer

Condensation occurs when water vapor turns into liquid water. In many industrial systems, such as power plants and desalination units, efficient removal of condensed water is essential. When water forms a continuous film on a metal surface, the film acts as a barrier that slows heat flow, much like extra layers of clothing reduce body heat loss. In contrast, dropwise condensation-where individual droplets repeatedly form and detach-keeps fresh surface area exposed and allows heat to pass more readily.

Designing the Coating

Previous surface designs struggled with a trade-off: rough surfaces provide many nucleation sites but trap droplets, while smooth surfaces allow easy droplet removal but offer few nucleation sites. The KAIST team turned this challenge into an advantage by deliberately creating thin polymer films that contain many small aggregates. These aggregates serve as nucleation sites, increasing droplet formation by roughly three times compared to thicker films.

Enhancing Droplet Detachment

After establishing more nucleation sites, the researchers applied a heat treatment that weakened the adhesion between droplets and the coated surface. This treatment allows droplets to leave the surface before they grow too large, ensuring that fresh areas are quickly exposed for new droplets to form. By controlling nucleation and detachment separately, the team overcame the usual conflict between droplet density and mobility.

Performance Results

The coating was tested on copper tubes commonly used in condensers. The maximum condensation heat transfer coefficient reached approximately 88 kW·m-2·K-1. This value represents a performance increase of about 5.5 times compared with a conventional copper surface covered by a water film, and more than 50% better than a standard hydrophobic coating.

Applications and Future Work

If adopted in power plants or industrial heat exchangers, the coating could improve energy efficiency by allowing heat to move more effectively. It could also enhance water collection in desalination and water-harvesting devices, and provide better cooling for electronic equipment. The researchers noted that the coating can be applied even to surfaces with complex shapes, making it suitable for a wide range of energy and environmental applications.

The study, led by Jun Soo Kim and Minjeong Kang as first authors, was published online in the international journal Nature Communications on July 16. The results were supported by several Korean research programs, including the Mid-Career Researcher Program and the SME Technology Innovation Development Program. The technology could soon be integrated into fixtures in power plants and other high-heat-transfer systems.