Abstract : In the past two decades numerous laboratories have microfabricated surfaces with the chemical and textural properties to mimic slippery surfaces found in nature, e.g. the superhydrophobic lotus leaf. This has been made possible by the continuing advances in nano/micro fabrication technology. This 3-part minisymposium will bring together engineers, physicists, and applied mathematicians in a multi-physics framework to discuss recent modelling and experimental applications.
Abstract : We present analytical models for the flow through tubes and annuli that possess slippery longitudinal slits along their surface. Firstly, these expressions can be employed with an arbitrary local slip length or shear stress being predefined at the slits, corresponding to an arbitrary Newtonian fluid. Secondly, the two solutions for tubes and annuli can be combined such that there is one fluid in the tube and another one in the annulus surrounding the tube.
[03964] Numerical study of longitudinal flow over liquid infused surfaces
Format : Talk at Waseda University
Author(s) :
Hiroyuki Miyoshi (Imperial College London)
Darren G. Crowdy (Imperial College London)
Abstract : A numerical method for the computation of two-phase pressure-driven longitudinal flow over liquid-infused surfaces is presented. These surfaces feature a periodic array of circular surface-embedded grooves filled with a subphase fluid that can enhance slip of an upper fluid, of different viscosity, flowing over it. A novelty of the numerical approach is that it deploys techniques from conformal geometry and complex analysis.
[02965] Viscoplastic Flows through Grooved Superhydrophobic Channels
Format : Talk at Waseda University
Author(s) :
Seyed Mohammad Taghavi (Université Laval)
Hossein Rahmani (Université Laval)
Abstract : We study the transport of viscoplastic fluids through channels with grooved superhydrophobic walls. To this end, we employ a comprehensive modeling approach and high-resolution numerical simulations and, in particular, consider longitudinal, transverse, and oblique orientations of the grooves. We use the perturbation theory to derive semi-analytical and closed-form solutions for the velocity fields, whose results are validated against our numerical simulations. Finally, we highlight the strong nonlinear effect of viscoplastic rheology and analyze the stabilizing/destabilizing effects of slip conditions on the flow.
[04260] Jeffery’s paradox for the rotation of a single ‘stick-slip’ cylinder
Format : Talk at Waseda University
Author(s) :
Michael S Siegel (New Jersey Institute of Technology)
Ehud Yariv (Technion)
Abstract : The two-dimensional fluid velocity due to the rotation of a superhydrophobic or `stick-slip’ cylinder in Stokes flow is
determined. We find that in the general case of an aperiodic distribution of stick and slip boundaries there is no
solution in which the fluid velocity vanishes at infinity. This is the first example of Jeffery’s paradox, typically
associated with the flow due to the counter-rotation of two rigid cylinders, for a single cylinder.
[03147] Experimental Applications of Slippery Liquid and Liquid-like-Solid Surfaces
Format : Talk at Waseda University
Author(s) :
Glen McHale (The University of Edinburgh)
Gary George Wells (The University of Edinburgh)
Rodrigo Ledesma-Aguilar (The University of Edinburgh)
Abstract : The liquid Amontons’ laws relate drop friction along a surface to the normal component of the capillary force. Here I outline work on low pinning surfaces which minimize the coefficient of static liquid friction. Using a liquid version of Young’s law, I show low friction uni-directional and bi-directional droplet motion on liquid-infused surfaces. I also show surfaces with liquid-like solid coatings which overcome the risk of lubricant depletion and provide excellent anti-biofilm properties.
[03590] Drop movement on lubricant-impregnated random textures
Format : Talk at Waseda University
Author(s) :
Ratan Bharat Ahuja (Indian Institute of Technology Bombay)
Amit Agrawal (Indian Institute of Technology Bombay)
Suhas S Joshi (Indian Institute of Technology Indore)
Abstract : Lubricant-impregnated surfaces (LIS), owing to their omniphobicity have shown remarkable success against Newtonian, non-Newtonian and yield stress fluids. These surfaces are, however, prone to failure due to lubricant drainage. In this work, we fabricate random textures using the micro-EDM process in an attempt to prolong lubricant retention within grooves. Drop motion and velocity against lubricant of three different viscosities are captured using digital imaging. The results would aid in designing a robust LIS system.
[05601] Asymptotic solutions for convection in longitudinal-fin heat sinks
Format : Talk at Waseda University
Author(s) :
Toby Kirk (Imperial College London)
Marc Hodes (Tufts University)
Abstract : We consider forced convection in a longitudinal-fin heat sink, i.e. a periodic array of thin, thermally conducting fins aligned with the direction of air flow. Sparrow, Baliga and Patankar (1978) solved this problem numerically, investigating the effect of the gap between the fin tips and the shroud. We solve the same problem in the realistic asymptotic limit of small fin spacing, and make connections to similar mathematical problems for liquid flow over superhydrophobic grooved surfaces.
[02837] Inertial effects on the flow resistance of axial-groove heat pipes
Format : Talk at Waseda University
Author(s) :
Haotian Jia (Tufts Univeristy)
Marc Hodes (Tufts University)
Toby Kirk (Imperial College London)
Abstract : We captured the effects of slowly-varying meniscus curvature on the flow resistance of the adiabatic section of an axial-groove heat pipe in the presence of inertial effects due to the changes in the cross-sectional areas of the liquid and vapor phases along the adiabatic section. This was by done by extending a hybrid analytical-numerical method for a single-phase problem with slowly-varying meniscus curvature to two-phase.
[04287] Laminar drag reduction in surfactant-contaminated superhydrophobic channels
Format : Talk at Waseda University
Author(s) :
Samuel Tomlinson (University of Manchester)
Frédéric Gibou (University of California, Santa Barbara)
Paolo Luzzatto-Fegiz (University of California, Santa Barbara)
Fernando Temprano-Coleto (Princeton University)
Oliver Jensen (University of Manchester)
Julien Landel (University of Manchester)
Abstract : Although superhydrophobic surfaces (SHSs) show promise for drag reduction (DR) applications, their performance can be compromised by traces of surfactant. This question is addressed for a three-dimensional laminar flow in a periodic channel with SHSs along both walls, in the presence of soluble surfactant. The system exhibits multiple regimes where asymptotic solutions can be constructed, which compare favourably with numerics. This analysis provides a guide for designing surfactant-contaminated SHSs to maximise the DR for applications.
[04901] Hypermobilization of superhydrophobic microchannels using light
Format : Talk at Waseda University
Author(s) :
Michael Mayer (Imperial College London)
Marc Hodes (Tufts University)
Xiaozhe Hu (Tufts University)
James Adler (Tufts University)
Abstract : This talk seeks to reframe the role of superhydrophobic surfaces, transforming them from passive lubricants to sources of active flow control. Utilizing a new model for the transport of photosurfactants, chemicals that can reversibly switch between two different states under differing light wavelengths, we show that it is possible to use light to generate surface tension gradients across menisci on superhydrophobic surfaces large enough to pump stationary fluid or even “hypermobilize” pressure driven flow.
[04001] Analysis of surface diffusion on steady "stagnant caps'' of surfactant
Format : Talk at Waseda University
Author(s) :
Anna Elizabeth Curran (Imperial College London)
Darren Crowdy (Imperial College London)
Abstract : We present a detailed analytical study, based on complex variable methods, which examines the remobilizing effects of surface diffusion on the structure of steady "stagnant caps'' on a surfactant-loaded interface between a viscous fluid and a constant pressure region. Both insoluble and soluble surfactants are considered. We demonstrate mathematically how, in the presence of a convergent flow, stagnant caps can immobilize interfaces leading to sharp edges which can then be smoothed out by surface diffusion.
[04344] Slip flow enhanced by Marangoni Stresses at a superhydrophobic air-water interface
Format : Online Talk on Zoom
Author(s) :
dong song (Northwestern Polytechnical University)
Baowei Song (Northwestern Polytechnical University)
guang pan (Northwestern Polytechnical University)
Abstract : Surfactant-induced Marangoni stress at an air-water interface would balance the shearing stress which causes the collapse of drag reduction of superhydrophobic surfaces, whereas few solutions have been proposed to overcome the adverse influence due to the difficulty in removing surfactant from water. In this work, we demonstrate that, by changing the orientation or shape of the air-water interface with respect to the bulk flow, the balance between Marangoni stress and shear stress can serve as a driving force of an apparent slip flow without the external input of surfactant. The theoretical model agrees well with the experiments.
