Improvement of humid air condensate drainage through bi-philic patterned surfaces

•Complicate super-hydrophilic/hydrophobic bi-philic pattern surfaces are readily fabricated.•Condensation dynamics on super-hydrophilic, hydrophobic, and bi-philic surfaces are visualized.•Condensate discharge was greatly enhanced by the surface energy driving force of the bi-philic pattern.•Significant enhancement of condensation heat transfer is expected through the rapid discharge of condensate. This study investigates the condensation characteristics of humid air on a bi-philic patterned surface with alternating super-hydrophilic/hydrophobic zones. Surfaces with eight different bi-philic patterns are fabricated using the material inkjet printing technique. Condensation experiments are performed by supplying controlled humid air at a constant temperature and humidity in an open circuit wind tunnel to the fabricated surfaces. Condensate behavior on all surfaces is visualized with a CCD camera. It is observed that film condensation occurs on a completely super-hydrophilic surface, and dropwise condensation occurs on a hydrophobic surface. Surfaces with bi-philic patterning have condensation modes occurring at the same surface and can facilitate condensate drainage. Condensate movement occurs at the interface between the super-hydrophilic region and the hydrophobic region. This moving force is generated by surface energy discrepancy between two areas. The force causes discrete droplets formed on the hydrophobic region to be absorbed into the condensate film on the super-hydrophilic area. Thus, droplets can be expelled quickly through the liquid film stream before reaching the maximum droplet diameter, which can only be removed by gravity. In addition, the geometrical features of the bi-philic pattern influence droplet interaction, which plays a vital role in condensate discharge. In conclusion, the bi-philic patterned surface optimized in this study showed increased condensate discharge by 21.25% compared to the super-hydrophilic surface and 76.36% compared to the hydrophobic surface. Therefore, a significant enhancement effect of condensation heat transfer is expected through the rapid discharge of condensate.