Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X14: Microfluidic Flow Applications II |
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Chair: Joseph Thalakkottor, South Dakota School of Mines & Technology Room: 155 D |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X14.00001: A Comparative Study of Wicking Flow on Micro-Engineered Surfaces Using Micro-PTV and Phase-Field Lattice Boltzmann Method ZEESHAN AHMAD KHAN, Arpan Ghimire Bohara, Nishagar Raventhiran, Abbas Fakhari, Yaofa Li Wicking in micro-engineered surfaces has gained significant attention owing to its broad applications in thermal management, bioengineering, microfluidics, textile industries, and oil recovery. The underlying advantages of these pillar structures lie in maximizing surface area to volume ratio and passive pumping mechanism. The passive pumping mechanism supplies fluid via capillary wicking which eliminates the need for external pumping. The wicking performance in these applications could be improved by understanding the flow dynamics and its variation with the pillar structure of these surfaces. This study explores the effect of pillar structure on wicking enhancement via a combination of numerical and experimental studies. The numerical approach is based on the phase-field Lattice Boltzmann method, whereas the experimental validation takes advantage of the microfabrication technique and 3D micro-PTV to track the wicking flow and 3D velocity profile. The results analyze the leading film flows with different pillar shapes and illustrate the importance of 3-phase contact lines to model the capillary wicking in micro-engineered structures accurately. In addition, the effects of pitch-to-diameter ratios of the micropillar are delineated, and analytical correlations based on the underlying physics are developed, which shows good agreement with the numerical and experimental study. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X14.00002: Navigation of a three-link microswimmer via deep reinforcement learning Yuyang Lai, Sina Heydari, On Shun Pak, Yi Man Swimming microorganisms employ effective gaits to navigate toward specific targets. Equipping artificial microswimmers with similar capabilities presents significant challenges in motion planning and gait design. In this study, we explore the use of deep reinforcement learning to enable a three-link microswimmer to navigate using AI-advised swimming gaits. We highlight how the swimming gaits that emerge during the learning process depend on specific choices of the reward function. We also compare these results with optimal swimming gaits reported in previous studies. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X14.00003: Understanding the non-isothermal fluid dynamics of the annular flow boiling regime inside a microchannel Darshan Mysore Basavaraja, Mirco Magnini, Omar K Matar Flow boiling inside microchannel heat sinks have been recognized as one of the efficient ways of cooling advanced electronic devices which generate high heat such as micro-electronic chips, micro-electro-mechanical systems (MEMS), fuel cells etc. Extensive research has been carried out in the past to understand the heat transfer characteristics inside a single microchannel using numerical simulations, however, the focus has been mainly on elongated slug/confined bubble regime. While such flow pattern does dominate near the upstream of the microchannel, film evaporation in annular flow becomes prominent at the downstream, but the flow dynamics in annular flow are relatively poorly understood. In the present work, three dimensional numerical simulations have been performed to understand the fluid flow dynamics and heat transfer associated with the annular flow regime inside microchannels. For this purpose, direct numerical simulations are carried out using the volume-of-fluid method with an additional model to handle liquid-vapour phase change. Furthermore, bubble nucleation is found to occur even in the thin annular film, hence an attempt will also be made to understand the dynamics of such bubbles nucleating in the thin annular film and its effect on flow boiling instabilities. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X14.00004: Ion-specific Activation and Inactivation of Ion Transport in 2D Subnanoporous Membrane Yechan Noh, Alex Smolyanitsky Ion transport at the nanoscale plays a crucial role in numerous biological functions, including neural signaling, muscle contraction, and auditory perception. One phenomenon critical in biology is mechanosensitive ion transport, serving as basis for transducing mechanical inputs (e.g., sounds and touch) into electrical signals. In artificial systems, such transport has been computationally demonstrated in the form of stretch-activated transport in sub-nanoporous 2D membranes. Here, we report an opposite behavior, wherein ion transport is inactivated upon stretching a 2D porous membrane. Using extensive molecular dynamics simulations, we demonstrate a reduction in aqueous K+ transport by a factor of 3-8 under ~3% stretching, depending on the material and pore structures. In striking contrast, the same porous membranes exhibit enhanced Na+ ion transport under tensile stretching of the same magnitude. This type of ion-specific activation and inactivation induced by membrane stress is, in fact, utilized by biological systems, except in a far more complex fashion. We explain in detail the physical mechanisms underlying the observed mechanosensitive behaviors to further enable biomimetic functionalities in artificial nanofluidic systems. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X14.00005: A comparative numerical evaluation of the cooling performance in microchannel heat sinks for low and high Reynolds number laminar flows. Lekwetje Maureen M Ramaube, Marcel M Louis, Howard A Stone, Sonya T Smith The aim of this research is to use numerical simulations combined with analytical approximations to investigate the cooling performance of low and high Reynolds Number (Re) laminar flow conditions in microchannel heat sinks (MCHSs). A comparative analysis is performed for Re in the ranges of 10 to 800, on a single-phase flow in a rectangular channel with a given aspect ratio categorized into two cases of low and high Re laminar flows. The two cases were conducted with constant thermophysical properties and further evaluated with a temperature-dependent viscosity condition. Subsequently this study further investigates the impact on performance by the addition of hydrophobic nanostructures within the walls of MCHSs inducing slip flow; essentially evaluating how boundary conditions such as slip affect heat exchange for a given pressure drop. The numerical results will be compared with analytical results based on boundary layer theory. The findings indicate that the model's heat transfer predictions are improved by accounting for variable viscosity. The results also show that heat transfer is significantly affected by wall slip as it decreases the thickness of the boundary layers further enhancing the performance. The outcomes of this study are expected to provide useful and valuable insights for MCHSs and contribute to the design progression of advanced cooling technologies |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X14.00006: Isobaric molecular simulation of boiling Avik Saha, Omar K. Matar Despite widespread applications of boiling, its nanoscale features e.g., nucleation, microfilm boiling, adjoint pressure, non-evaporative layer etc. are not yet well explored. In past decades, molecular dynamics evolved out to be a reliable tool to investigate these nanoscale features. However, most of these studies are carried out in isochoric condition, which fails to mimic the actual scenario. In the present study, a moving piston-based system is prepared using LAMMPS, and a constant force is applied to it to maintain a constant pressure. Further, a viscous force is added against the piston motion proportional to its velocity to avoid piston oscillations. The interaction force between the piston and water is critical for a piston-based system because a traditional Lenard-Jones force will impart an additional adjoint pressure to the fluid. As the attractive part of the Lenard-Jones force field is responsible for the adjoint pressure, a repulsive-only force field is implemented in this study by chopping off the attractive part of the force field. To validate the system, water in liquid and vapor form is placed underneath the piston. The density of the system is studied at different temperatures and was found to be close to the ideal density values. The measured pressure of the vapor system also seems stable with small-amplitude oscillations over the time range (10 ns) of the simulation. However, for the liquid phase, measurement of the exact pressure is not possible because of high fluctuations. Further, the system is validated in terms of the saturation temperature for two different pressures (1 and 10 bar). To understand the effect of the piston-fluid force interaction, a liquid water pool is equilibrated at 125˚ C and 1 bar pressure with both traditional and repulsive-only force field. Using the latter, the piston rises monotonously, however, with the former, the piston stays stable over the liquid pool without any sign of phase-change. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X14.00007: Structure and Collective Transport Dynamics of Ln3+ Ions Under an External Field: Insights from Non-Equilibrium Molecular Simulations Pauline Simonnin, Bruce Palmer, Christopher Mundy, Gregory K Schenter, Venkateshkumar Prabhakaran, Jaehun Chun Enabling future separation technologies that reduce energy consumption and chemical waste requires accessing "beyond equilibrium diffusion" to achieve higher selectivity and efficiency. This is crucial for separating rare earth elements (REEs) from unconventional feedstocks (e.g., mine tailings) where targeted ion concentrations are <10-2 ppm. Existing separation processes relying on equilibrium conditions are energy and chemically intensive at low concentrations for large-scale implementation. Therefore, accessing non-equilibrium processes is imperative to accelerate the separation and concentration of REEs, making them adaptable to existing industries. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X14.00008: Coupling state-based peridynamics and lubrication theory to understand flow-induced deformation and damage of microchannels Ziyu Wang, Ivan C. Christov The purpose of this study is to deepen our understanding of the interaction between a fluid flow and the soft walls of a microchannel, a multiphysics problem that arises in applications ranging from microfluidics to biomedical engineering and chemical synthesis. A one-dimensional model is developed to analyze the coupled fluid-structure interaction (FSI) between a 2D soft-walled microchannel and the viscous fluid flow within it. Unlike previous works on the subject, this study employs a peridynamic state-based formulation of the Euler-Bernoulli beam theory to model the bending and damage of the soft wall of the microchannel. The fluid dynamics problem is simplified by cross-sectionally averaging the 2D Navier-Stokes equations, under the lubrication approximation, to yield a one-dimensional description. Notably, the peridynamic theory employed in this study is capable of simulating the onset and progression of damage to the elastic wall, specifically the incipience of fracture. We demonstrate how our approach offers an understanding of the timing and location of the failure of the soft wall. Specifically, we examine how these outcomes are influenced by the key dimensionless numbers of the problem: the Reynolds number of the flow, a Strouhal number associated with the wall inertia, a compliance number capturing the FSI, and a nonlocality number arising from peridynamics. These parameters are systematically varied to study the conditions under which a 2D soft-walled channel can fail under both static and dynamic loading conditions, showing that the potential failure location shifts when the beam is two-way coupled to the flow. Thus, our modeling approach provides new insights into the mechanical resilience of microfluidic devices under various conditions, which can aid in the design and optimization of devices made of soft polymeric materials. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X14.00009: Flow around an anchored soft hair. Abhineet S Rajput, Amir A Pahlavan The deformation dynamics of flexible microfibers are critical to many industrial and biological processes. The complex interaction between fluid and solid physics can create diverse non-linear behaviors. Such behaviors are at the heart of understanding plant and animal vasculatures characterized by deformable microchannels. Unraveling the poroelasticity of these structures is vital in designing bioinspired active and passive flow control devices. Inspired by these, in this talk, we explore the deformation mechanics of such microfibers in anchored configuration for flow-controlled systems at low Reynolds numbers. Our experiments highlight that confinement induces a strong coupling between fluid and solid physics. Further, such deformation response can be classified into regimes based on the Elastoviscous number for the system, which is obtained by developing a theoretical model based on the coupling of Euler-Bernoulli and Stokes equations. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X14.00010: An effective diffusion model for particle-laden interfaces Timo van Overveld, Valeria Garbin Nanoparticles can stabilize the interface of emulsion droplets, forming so-called Pickering emulsions. Their long-term stability makes them promising candidates for sustainable chemical conversion processes. However, the step towards industry-scale applications is currently hampered by our limited fundamental understanding of diffusive transport in multi-phase systems with particle-laden interfaces. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X14.00011: Probing the relationship between wall misalignment and water transport properties in sub-nm hexagonal boron nitride slit channels Enrique Wagemann, Elton Oyarzua, Diego Becerra, Harvey A Zambrano Recent advances in nanofabrication techniques are enabling the assembly of van der Walls (vdW) heterostructure-based artificial conduits of molecular sizes (with slit channel heights below 1 nm). As the characteristic length of a nanoconduit is decreased and becomes comparable to the atomic size of a confined fluid, surface effects dominate. In conduits with characteristic lengths smaller than 1 nm, interfacial effects become even more pronounced as a regime is reached wherein the bulk condition is no longer present, and the fluid becomes purely interfacial. Accordingly, the hydrodynamic properties of water in sub-nm confinement are highly influenced by the solid's crystallographic features and atomic nature. In this study, we probe the liquid-solid interfacial properties of water confined in sub-nm hexagonal boron nitride slit channels. Particularly, we conduct molecular dynamics to investigate how the lattice mismatch between the different layers comprising the nanochannel walls affects the resistance to water transport exerted by said channel. Simulation results show a significant relationship between wall misalignment and interfacial friction, which can be traced down to the morphology of the free energy landscape felt by a single water molecule at the solid surface. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X14.00012: Theoretical, numerical and experimental study of capillary wetting rates on smooth vertical surfaces for liquids of varying Kapitsa numbers Shiyu Zhang, Jiahui Guo, Yanxiu Ge, Dion S Antao When the surface of a liquid encounters a solid surface, a dynamic meniscus forms that traverses along the surface. This dynamic capillary wetting process plays a role in a wide range of technical applications and natural phenomena, such as liquid interaction with coatings on industrial materials, power generation system and atmospheric water harvesting technology. While wetting dynamics on flat horizontal surfaces and vertical curved surfaces are well studied, the precise mechanism of a wetting front advancing on a flat vertical surface remains partially understood. Predictive models for wetting dynamics in existing literature rely on specific empirical coefficients or simplified scaling laws, both of which reduce their applicability. In this presentation, the distinct wetting behavior of liquids with varying viscosity and surface tension is presented using a threshold based on the Kapitza number (Ka). For low Ka liquids, a semi-analytical framework is developed to account for key factors such as dynamic contact angle, and associated viscous friction related to the moving contact line. For high Ka liquids the semi-analytical framework does not provide a closed form solution and numerical simulations (using an interface tracking model, VOF) are required. The theoretical and numerical predictions are compared with our transient experimental measurements for both contact angle and wetting distance, with good agreement. |
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