Shedding of Water Drops from a Surface under Icing Conditions.
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.
Department of Mechanical Engineering, York University , Toronto, ON M3J 1P3, Canada.
Deepak Kumar
DK
Mandal
New Devices Engineering EMEA, Takata Corporation , D-63743 Aschaffenburg, Germany.
Antonio
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Criscione
Institute for Fluid Mechanics and Aerodynamics, Center of Smart Interfaces, Technische Universität Darmstadt , D-64287 Darmstadt, Germany.
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C
Tropea
Department of Mechanical Engineering, York University , Toronto, ON M3J 1P3, Canada.
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A
Amirfazli