Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E07: Microscale Flows: Interfaces |
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Chair: Thomas Cubaud, Stony Brook University Room: Georgia World Congress Center B212 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E07.00001: Geometric effects on retention capacity in liquid-infused surfaces Ian Jacobi, Lilach Mazor, Howard A Stone The shear-driven drainage of liquid-infused surfaces can be modified by longitudinal variation in the surface's underlying geometry. Because liquid-infused surfaces are playing an increasingly important role in a new generation of drag-reducing and omniphobic materials, the ability to manipulate and optimize their fluid retention capacity is crucial to improving material robustness. Theoretical and numerical calculations are performed on the steady-state fluid retention in streamwise-varying, open-capillary channels, with emphasis on the effect of interfacial deformation on resisting fluid drainage. Optimal substrate geometries and corresponding manufacturing tolerances for the production of efficient surfaces are developed as a function of the parameters accounting for interface deformation and channel geometry. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E07.00002: Metastable and Ultimate Stable States of Underwater Superhydrophobicity Huiling Duan Underwater superhydrophobic surface has many great performances, which are attributed to a gas cushion entrapped in the microstructures. However, many factors lead to the wetting transition and collapse of the gas cushion. In the current work, we explore the underlying mechanisms of wetting transition of underwater superhydrophobicity and demonstrate the existence of an ultimate stable state on underwater superhydrophobic surfaces. In situ observations are used to quantify the whole wetting transition process. The metastable state is obtained. A diffusion-based mode is developed to predict the evolution process and the longevity of the metastable states. We theoretically demonstrate a both mechanically and chemically equilibrated superhydrophobic state, which is denoted as an ultimate stable underwater superhydrophobic state. The long-term stable underwater superhydrophobic state is achieved experimentally under different liquid pressures and moderate flow rates. Moreover, with experiments on fresh lotus leaves, we prove that the ultimate stable state can also be realized on randomly rough superhydrophobic surfaces. The finding here contributes to a better understanding of the fundamental mechanism of wetting transition and long-term stability of underwater superhydrophobicity. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E07.00003: Thermocapillary flow over superhydrophobic surfaces Valeri Frumkin, Moran Bercovici We present an experimental realization of thermocapillary flow over a superhydrophobic surfaces subjected to controlled spatial temperature gradients. We demonstrate how a superhydrophobic surface can provide an interface for Marangoni stresses to drive fluid flow, thus allowing for thermocapillarity to be applied to closed fluidic systems lacking a continuous fluid-liquid interface. We show that hierarchical superhydrophobic structures are necessary in order to prevent the Cassie to Wenzel transition, enabling stable flows over long durations of time. Finally, using a Hele-Shaw chamber containing such superhydrophobic surface, we demonstrate the use of localized heating for obtaining desired flow patterns. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E07.00004: Continuum explanation of the cause of slip at an interface Joseph Thalakkottor, Kamran Mohseni Slip can be interpreted as the inability of an interface to transfer information across it. In the case of velocity and thermal slip this corresponds to the lack of transfer of momentum and energy across the interface, respectively. Here, we attempt to provide a continuum explanation of the cause of this lack of tangential transfer of information. Using the results from molecular dynamics simulations we demonstrate that slip is analogous to a shock in fluid dynamics. Mathematically, slip can be considered as a change in the characteristic nature of the governing equation as one approaches a slipped wall. In the case of a shock there is a jump in the component of velocity normal to its plane, while in the case of slip this jump is in the component of velocity tangential to the interface. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E07.00005: Integrable stress and viscous dissipation singularities of the Moving Contact Line Peter Zhang, Kamran Mohseni The classical hydrodynamic solution to the moving contact line (MCL) reported by Huh & Scriven (1971) is often associated with a singular force and viscous dissipation due to a diverging stress and viscous dissipation per unit volume. In our recent analysis, we find that these singular fields arise from the application of the divergence theorem to a volume cut by interfacial and line discontinuities. Furthermore, we find that the previously reported singular force and total viscous dissipation are a consequence of integral relations derived for interfacial surfaces. Unlike interfacial surfaces, contact lines are one-dimensional manifolds that have their own set of integral relations for quantities like force. In order to determine the total force and rate of work at the MCL, we integrate the stress and viscous dissipation per unit volume over an infinitely small cylindrical control volume that encloses the contact line only. Using the classical hydrodynamic solution, we find that the total integrated force and total rate of work is finite as this cylindrical volume captures the physical effects of the fluid-fluid interface, in addition to the fluid-solid interfaces. |
(Author Not Attending)
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E07.00006: Abstract Withdrawn |
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