WETTABILITY EFFECT ON DROPLET GROWTH BEHAVIORS DURING DROPWISE CONDENSATION

초록

The present study examines the transient characteristics of droplet growth and heat transfer during dropwise condensation process on different hydrophobic surfaces. The self-assembled monolayer (SAM) of n-octadecyl mercaptan was coated on the surface to change the surface wettability with the contact angles of 148 degrees and 124 degrees. A Canon EOS 7D camera and an Infinity K2 lens were used to capture the spontaneous images during condensation. From the experiment, three regimes were observed: in the first regime where the droplets were formed with nearly homogenous pattern, the heat transfer coefficient increased rapidly. In the second regime, both the droplet size and the liquid area fraction increased. In the third regime, coalescence among larger droplets was dominant, causing the decrease in the liquid area fraction with time. Moreover, the measured fall-off time was faster in the case with higher contact angle because of relatively low surface energy.