Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E36: Drops: Superhydrophobic: Icephobicity |
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Chair: Peichun Amy Tsai, University of Alberta Room: Portland Ballroom 251 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E36.00001: Universal wetting transition of an evaporating water droplet on superhydrophobic surfaces Peichun Amy Tsai, Adrien Bussonnière, Masoud Bigdeli, Di-Yen Chueh, Qingxia Liu, Peilin Chen An evaporating water droplet on a superhydrophobic surface undergoes a wetting transition from a heterogeneous wetting (Cassie-Baxter) to homogeneous wetting (Wenzel) state. The critical transition is manifested by a sudden decrease of contact angle, when ``Fakir” water drop permeates the minute hydrophobic cavities. This breakdown of superhydrophobicity would hinder various applications of self-cleaning, low-frictional, and potentially ice-phobic properties of superhydrophobic materials. In this work, we experimentally investigate such wetting transition using hydrophobic nanostructures. With a theoretical model, we find a universal criterion of the critical contact angle at the transition point. The prediction of critical contact angle, which solely depends on the geometrical parameters of the hydrophobic pillars, agree well with various data for both micro- and nano-structures. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E36.00002: Icephobicity of Leaves H. Pirouz Kavehpour, Elika T. Shirazi, Elaheh Alizadeh-Birjandi Ice adhesion and excessive accumulation on exposed structures and equipment are well known to cause serious problems in cold-climate regions; therefore, the development of coatings that can resist icing can solve many challenges in various areas of industry. This work was inspired by nature and ice-resistivity and superhydrophobicity of plants leaves. Kale is an example of a plant that can be harvested in winter. It shows superhydrophobic behavior, which is normally known as an advantage for cleaning the leaves, but we were able to show that its surface structure and high contact angle of water drops on kale leaves could delay the ice formation process making it a good candidate for an ice-repellent coating. We have performed in-depth experimental analyses on how different plants can prevent icing, and contact angle measurements and scanning electron microscopy (SEM) of the leaves were taken to further mimic their surface morphology. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E36.00003: Crystal deposition patterns from evaporating sessile drops on superhydrophobic and liquid impregnated surfaces Samantha McBride, Susmita Dash, Kripa Varanasi Accelerated corrosion and scale buildup near oceans is partially due to deposition of salty sea mist onto ships, cars, and building structures. Many corrosion preventative measures are expensive, time intensive, and/or have negative impacts on the environment. One solution is the use of specific surfaces that are engineered for scale resistance. In this work, we show that we can delay crystallization and reduce scale adhesion on specifically engineered liquid impregnated surfaces (LIS). The low contact angle hysteresis of the LIS results in a sliding contact line of the saline droplet during evaporation, and the elevated energy barrier of the smooth liquid interface delays crystallization. Experiments conducted on surfaces with different wettability also demonstrate the corresponding influence in controlling salt crystal polymorphism. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E36.00004: Designing icephobic surfaces by passively sustaining liquid film at ice-substrate interface Tom Zhao, Paul Jones, Neelesh Patankar Ice formation poses a significant barrier to transportation, energy generation and transport, gas extraction, etc. We propose to design icephobic surfaces that reduce ice formation and lower ice adhesion by sustaining a film of liquid water at the interface between bulk ice and the substrate. The liquid layer is in phase equilibrium with the surrounding bulk ice, and thus exists without constant energy input. Using molecular dynamic simulations, we show this liquid film can be maintained indefinitely by exploiting the phenomena of interfacial premelting and the freezing point depression of ice confined in surface texture due to the Gibbs Thomson effect. We demonstrate the reduction of both the work and strength of ice adhesion as a function of surface wettability and geometric parameters of the surface texture. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E36.00005: Dynamics of Defrosting on Hydrophobic and Superhydrophobic Surfaces Kevin Murphy, William McClintic, Kevin Lester, Patrick Collier, Jonathan Boreyko It has recently been demonstrated that frost can grow in a suspended Cassie state on nanostructured superhydrophobic surfaces, which has implications for enhanced defrosting rates. However, to date there have been no direct comparisons of the defrosting kinetics of Cassie frost versus frost on conventional surfaces. Here, we fabricate a hybrid aluminum plate where half of the top face exhibits a superhydrophobic nanostructure while the other half is smooth and hydrophobic. By growing frost to varying thicknesses and melting at several tilt angles, we reveal the advantages and disadvantages of each surface with regards to the extent and speed of the shedding of melt water. For sufficiently thick frost layers, the Cassie state of frost on the superhydrophobic surface uniquely enabled the rapid and effective shedding of melt water even at low tilt angles. On the other hand, the hydrophobic surface was more effective at removing very thin frost sheets, as the reduced contact angle of water on the surface facilitated the coalescence of droplets to grow the melt water beyond the capillary length for gravitational removal. Therefore, the utilization of superhydrophobic versus hydrophobic surfaces for defrosting applications depends upon the context of the system conditions. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E36.00006: An Experimental Investigation on Bio-inspired Icephobic Coatings for Aircraft Icing Mitigation Hui Hu, Haixing Li, Rye Waldman By leveraging the Icing Research Tunnel available at Iowa State University (ISU-IRT), a series of experimental investigations were conducted to elucidate the underlying physics pertinent to aircraft icing phenomena. A suite of advanced flow diagnostic techniques, which include high-speed photographic imaging, digital image projection (DIP), and infrared (IR) imaging thermometry, were developed and applied to quantify the transient behavior of water droplet impingement, wind-driven surface water runback, unsteady heat transfer and dynamic ice accreting process over the surfaces of airfoil/wing models. The icephobic performance of various bio-inspired superhydrophobic coatings were evaluated quantitatively at different icing conditions. The findings derived from the icing physics studies can be used to improve current icing accretion models for more accurate prediction of ice formation and accretion on aircraft wings and to develop effective anti-/de-icing strategies for safer and more efficient operation of aircraft in cold weather. [Preview Abstract] |
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