Abstract
In the present work, an investigation of stagnation flow imposed on a supercooled water drop in cold environmental conditions was carried out at various air velocities ranging from 0 (i.e., still air) to 10 m/s along with temperature spanning from −10 to −30 °C. The net effect of air flow on the impacting water droplet was investigated by controlling the droplet impact velocity to make it similar with and without air flow. In cold atmospheric conditions with temperatures as low as −30 °C, due to the large increase of both internal and contact line viscosity combined with the presence of ice nucleation mechanisms, supercooled water droplet wetting behavior was systematically affected. Instantaneous pinning for hydrophilic and hydrophobic surfaces was observed when the spread drop reached the maximum spreading diameter (i.e., no recoiling phase). Nevertheless, superhydrophobic surfaces showed a great repellency (e.g., contact time reduction up to 30% where air velocity was increased up to 10 m/s) at temperatures above the critical temperature of heterogeneous ice nucleation (i.e., −24 °C). However, the freezing line of the impacting water droplet was extended up to 2-fold at air velocity up to 10 m/s where substrate temperature was maintained below the aforementioned critical temperature (e.g., −30 °C).
Highlights
Nano-micro topography of solid surfaces exhibits different characteristics when interaction of solid-liquid ranging from severe adhesion to strong repellency is taken into consideration [1].They have shown different outcomes when a hot [2] or cold surface [3] has been used for heat transfer and wetting dynamics evaluation
Wetting dynamics of an impacting supercooled water droplet on a cold substrate combined with cold stagnation flow is evaluated in the current study
In order to evaluate the net effect of airflow on an impacting supercooled water drop, the maximum air velocity was chosen based on the conception of no droplet deformation of a free falling drop exposed to gas flow
Summary
Nano-micro topography of solid surfaces exhibits different characteristics when interaction of solid-liquid ranging from severe adhesion to strong repellency is taken into consideration [1] They have shown different outcomes when a hot [2] or cold surface [3] has been used for heat transfer and wetting dynamics evaluation. An extremely low wettable surface, namely superhydrophobic surface, typically has a static and hysteresis contact angle larger than 150◦ and 10◦ , respectively [9,10] These surfaces exhibit a tremendous water repellency whether in room or low temperature conditions above the critical temperature of freezing (i.e., −24 ◦ C) [11].
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