Effect of condensation on surface contact angle

Abstract

Understanding the effect of condensation on surface contact angle is important in many applications, e.g., waste-heat recovery systems. This work aims to fill the two knowledge gaps in the literature related to the effect of condensation on the contact angle: (1) how the drop contact angle varies over time during condensation process; and (2) whether the evaporation of the condensed drops can be the reason for the observed contact angle under condensation environment. In this study, three surfaces, polystyrene, Teflon AF, and superhydrophobic surfaces, were used in experiments. The experimental results show that the contact angle between water and all three surfaces decreases with the time when the surface was exposed to the condensation environment. Such change of contact angle over time is caused by the evaporation of the condensed drop, which prompts the formation of a film formed around the condensed drop. The film formed due to the adsorption of water vapor onto the surface, causes a decrease in the contact angle observed over time. A theoretical model which considers the evaporation effect was developed to help to understand the experimental observation. Finally, to demonstrate the importance of the change in contact angle in condensation environment over time, we show its effect on shedding of drops in the context of drop-wise condensation.