KAIST coating boosts copper-tube condensation up to 5.5-fold

A copper tube covered in condensation usually ends up wearing a thin film of water—the thermal equivalent of an extra layer between the steam and the metal. A KAIST team led by Professors Youngsuk Nam and Sung Gap Im has now coated such tubes with an ultrathin polymer film that helped condensation transfer heat up to approximately 5.5 times better than conventional copper with a water film.

The team deposited the film using initiated chemical vapor deposition, or iCVD, a process that uses gas-phase precursors to build a thin coating. Its key move was to treat nanoscale polymer aggregates, previously regarded as defects, as useful landing sites for new droplets. On thinner films, approximately three times more droplets formed than on thicker ones.

That alone would not solve the problem. Rough surfaces can create more places for droplets to start, but can also trap them; smooth surfaces release droplets more easily, but offer fewer nucleation sites. The researchers used heat treatment to reduce the force holding droplets to the coating, separating the two jobs: film thickness encouraged formation, while thermal treatment encouraged removal.

On the coated copper tubes, the maximum condensation heat-transfer coefficient—a measure of how effectively heat moves—reached approximately 88 kW·m⁻²·K⁻¹. The result was also more than 50% better than a conventional hydrophobic coating surface. The work was published in Nature Communications.

So what changes in practice? If the coating works beyond the team’s evaluation, condensers in power plants and industrial heat exchangers could transfer heat more effectively; desalination and water-harvesting devices could collect water more efficiently; and electronic devices could shed heat faster. KAIST also says the process can produce extremely thin, uniform coatings on complex shapes. The evidence reported here is a research result on coated copper tubes.