Shedding of Water Drops from a Surface under Icing Conditions

Abstract

A sessile water drop exposed to an air flow will shed if the adhesion is overcome by the external aerodynamic forces on the drop. In this study, shedding of water drops were investigated under icing conditions, on surfaces with different wettabilities, from hydrophilic to superhydrophobic. A wind tunnel was used for experiments in a temperature range between -8 and 24.5 °C. Results indicate that the temperature has a major influence on the incipient motion of drop shedding. The critical air velocity (U(c)) at which a drop first starts to shed generally increases under icing conditions, indicating an increase in the adhesion force. The contact angle hysteresis (CAH) and the drop base length (L(b)) are found to be the controlling factors for adhesion. A correlation was also developed to deduce the drag coefficient, C(D) for the drop. It was found that C(D) can decrease under icing conditions. In general, a lower C(D) and higher adhesion together lead to a higher critical air velocity. However, there are systems such as water on Teflon for which the critical air velocity remains practically unaffected by temperature because of similar adhesion and C(D) values, at all temperatures tested.

Nearly Perfect Durable Superhydrophobic Surfaces Fabricated by a Simple One-Step Plasma Treatment

“…The force analysis on droplet detachment supports our experimental results showing that at the same wind speed, smaller water droplets move easily on the surface. The increasing trend of the critical wind velocity with decreasing the volume of liquid droplets is also matched with other previous studies 41, 42 .…”

On Modulating Interfacial Structure towards Improved Anti-Icing Performance

“…Figure 11 shows changes of up to two orders of magnitude with differentials in interfacial area. The extreme effect of substrate temperature shown in Figure 11 is further exhibited in experimental measurements of droplet shedding for different wettabilities at a higher temperature range [150]. From these observations, one can infer that control in interfacial area of droplet-substrate through surface modification is a relevant factor in the technological design of anti-icing surfaces.…”

A Review on Applications of Superhydrophobic Materials in Civil Engineering

“…The commonly used active method for anti-icing and deicing consumed a lot of energy, and freezing point inhibitors used in the passive method were not good for the environment. [79][80][81][82] Although not all SHPB surfaces are anti-icing, the roughness and free energy required for SHPB surfaces may affect the anti-icing property. [83,84] At present, SHPB materials have been applied in the anti-icing field of architecture engineering.…”