Numerical investigation of condensation on microstructured surface with wettability patterns

A numerical investigation of condensation on microstructured surfaces with wettability patterns is reported in this paper. Detailed droplet dynamics and heat transfer performance of four different wettability patterns are discussed: a hydrophilic case, a superhydrophobic case, a hybrid wettability case, and a dynamic wettability case. Several interesting droplet dynamic phenomena such as droplet coalescence jump, pillar squeezing droplet jump, and droplet dragging up by wettability gradient were observed. Through comparison of droplet distribution on the microstructured surface with the corresponding wall heat flux contour, a previously unknown impact is revealed: the regions where droplets sit have higher heat transfer rate due to the large heat transfer area of the droplet surface. The hybrid wettability case shows the highest heat transfer rate compared to the hydrophilic and superhydrophobic cases, because it not only increases droplet nucleation density but also sustains large liquid-vapor interfacial areas. Dynamic control of wettability is finally suggested to detach large droplets to avoid the flooded state of the hybrid wettability case. The detachment of droplets from the surface decreases the condensation heat transfer rate sharply because of the loss of effective liquid-vapor interfacial area, but it cleans the surface for fast re-nucleation. This paper provides promising insights to improve heat and mass transfer of condensation on microstructured surfaces of heat exchangers. (C) 2017 Elsevier Ltd. All rights reserved.