Condensation on CICNT Structured Superhydrophobic Surfaces

This study investigates subcooling, surface feature size (CNT diameter), and time duration on dropwise condensation and condensate removal on superhydrophobic surfaces. Experiments were conducted in a low-pressure chamber with a vertically oriented test CNT surface. The CNT diameter was varied between 20-120 nm, and the surface subcooling ranged from 0.5-9 C. Three types of condensation were observed: drop jumping, complete wetting of the CNTs, and surface flooding. The results reveal that drops retain their mobility at CNT diameters smaller than ~60 nm and at subcooling temperatures less than ~7C. Here drops are mobile and self-remove from the surface by the mechanism of jumping. The results also show that as the CNT diameter is increased to 70-75 nm, the drops lose mobility and begin to be more pinned. Condensation transitions from droplet jumping to surface flooding over this region. The same transition occurs with an increase in subcooling magnitude to 9-10 C. The amount of time the condensate resides on the surface also impacts mobility and the transition from jumping to wetting occurs at a smaller CNT diameters or lower surface subcooling.