Dropwise steam condensation on various hydrophobic surfaces: Polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), and self-assembled micro/nano silver (SAMS)

Drop-wise condensation (DWC) phenomena are closely related to hydrophobic promoters. In this study, various hydrophobic coatings such as PPS, PTFE, and self-assembled micro/nano silver were fabricated using surface treatments, with plain copper as a reference. Fabricated surfaces were examined by scanning electron microscope, contact angle measurements, and condensation heat transfer experiments. Heat fluxes were measured, and DWC population densities were recorded and compared. Results showed that surface morphologies and wetting behaviors directly affected drop sizes and population densities. When steady-state was reached, superhydrophobic surfaces showed poor condensation heat transfer compared to the self-assembled micro/nano silver deposited surface. It is assumed that contact angle hysteresis induced strong pinning along condensate periphery, which hindered rolling-off motion and droplet renewal rates. Also, durability of performance of the self-assembled layer coating was demonstrated.