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 L17: Electrokinetic Transport I |
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Chair: Juan Santiago, Stanford University Room: 250 A |
Monday, November 25, 2024 8:00AM - 8:13AM |
L17.00001: Study of flow dynamics and gravity settling of slurry electrodes within an electrochemical cell using simultaneous current measurements and high-speed imaging Soumyadeep Paul, Yousif M Alkhulaifi, Tomek M Jaroslawski, Steven A Hawks, Juan G Santiago We study flowable carbon slurries as an electrode component for capacitive deionization and semi-solid flow batteries. A carbon particle slurry in 0.5 M NaCl solution was flowed into two horizontal, co-flowing channels of an electrochemical cell. The two channels were arranged one above another, and separated by a cation-exchange membrane. We performed simultaneous high-speed imaging and electrochemical measurements to investigate slurry dynamics and gravity-based settling on charge transport. Optical access enabled imaging in a plane parallel to gravity. The cell has four independently addressable electrodes, such that each channel has an electrode at the top and bottom (streamwise-spanwise) walls. Current responses for 1 V bias were measured across electrode pairs as a function of slurry flow rate. Based on the image and current data, two regimes can be identified. The first is characterized by low flow rates wherein dense particle beds promote charge percolation (electron transfer), and the electrodes which contact these beds yield the highest current. The second regime is characterized by thin particle beds and well mixed particle flows, and the electrodes in closest proximity achieve a current higher than the other electrode pairs. These observations provide insights into the design of flow cells and show that gravitational settling can yield a steady-state current enhancement. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L17.00002: Controlling particle dynamics in dead-end channels via tunable boundary effects Langqi Xing, Xiaoyu Tang This study examines chemically induced transport mechanisms for colloids in dead-end channels, specifically focusing on diffusiophoresis, which is driven by electrolyte concentration gradients. Within these channels, such gradients not only drive particle motion but also generate fluid flows along the channel walls (diffusioosmosis) in opposing directions. The wall slip velocity generates a parabolic bulk flow competing with the diffusiophoretic motion of the colloidal particles. Different particle delivery patterns can be generated and controlled. The particle velocities in these channels are influenced by the zeta potential of the particles, the contrasting diffusivities of electrolyte cations and anions, and the streaming potential of the walls. Variations in the materials at the dead-end boundaries significantly impact the streaming potential, thus affecting diffusioosmotic behavior. In this talk, I will demonstrate the manipulation of particle dynamics by modifying the wall streaming potential. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L17.00003: An immersed boundary method for simulating the electric potential in flows with active colloids Nils G Tilton, Kimmo Koponen, Ning wu, Brennan Sprinkle, Amneet Pal Bhalla This study is motivated by fluid flows with Janus particles actuated by an electric field. A Janus particle is a microparticle composed of two dielectric materials with different electric permittivities. This difference in permittivity generates an asymmetry in the electric field, which can be leveraged to control the particle’s motion. CFD simulations of Janus particles face the challenge of computing the electric potential in both the fluid and particle. This electric potential is coupled by a set of Dirichlet and Neumann conditions at both the fluid-particle interface and the interface between the two dielectrics in the particle. Applying these interface conditions using a conventional body-fitted grid is computationally expensive when the particle geometry is complex, particularly if the particle moves. We consequently develop a novel Immersed Boundary Method (IBM) for computing the electric potential to second-order spatial accuracy. The method places no constraints on the particle geometry, and permits general discontinuous Robin interface conditions if desired. To demonstrate our method, we solve for the electric potential and resulting force on a Janus particle adjacent to an electrode. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L17.00004: Minimum flow rate of Taylor cone-jets of highly viscous liquids Anupam Choubey, Abhishek K Singh, Supreet S Bahga Applying a high voltage to a liquid meniscus held at the exit of a metallic nozzle can deform the spherical meniscus to a conical shape, known as the Taylor cone, whose tip emits a fine jet. Steady cone-jetting is essential for applications such as electrospinning and electrohydrodynamic jet printing. However, steady jetting occurs only above a minimum imposed flow rate. It is well documented that this minimum flow rate for less viscous liquids is independent of the nozzle diameter and depends only on the properties of the liquid. In this work, using experiments and scaling analysis, we show that the minimum flow rate of highly viscous liquids, such as salt-doped glycerol, scales with the square of the nozzle diameter, besides depending on the liquid properties. We derive the scaling relations for the minimum flow rate and the corresponding jet diameter by balancing the viscous and the interfacial forces in the cone region and inertia and electrostatic suction forces in the cone-to-jet transition region. The derived scaling relations for the minimum flow rate and the corresponding jet diameter compare well with the experimental data without the need for any fitting parameter for highly viscous solutions with electrical conductivity varying over four orders of magnitude. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L17.00005: Electroconvective and compositional instabilities during electrodeposition of alloys Arvil Dasgupta, Ankush Mukherjee, Lynden Archer, Donald Lyle Koch Electrodeposition of a single metal cation can occur by electromigration and diffusion in a quiescent electrolyte solution at low applied voltages. Increasing the applied potential leads to strong concentration polarization, the formation of an extended space charge layer near the electrode surface, and subsequently an electroconvective flow that degrades the quality of the metal film. In this study, we determine the conditions under which two metal species can be simultaneously deposited by electromigration and diffusion through a quiescent solution to form a solid-solution metal alloy film. The conditions leading to formation of a space charge layer due to depletion of one of the metal cations will be examined. Linear stability analysis will reveal the nature and growth rate of electroconvective instabilities that would lead to compositional as well as morphological variations of the metal film. An interesting question is whether the formation of a space charge layer is a prerequisite for electroconvection during deposition of an alloy as it is for a single metal species. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L17.00006: Electrokinetic flow of non-Newtonian fluid through a micro-channel with deformable surfaces: An analytical approach Subhajyoti Sahoo, Ameeya K Nayak The study of the electroosmotic flow in deformable microchannels is crucial for developing a deep insight into the hydrodynamics of physiological flows. The effectiveness of these microchannels is determined by their load-carrying capacity, which specifies the highest load the deformable wall can handle. In this study, the intricate coupling between fluid flow and wall deformation is analyzed under the influence of an externally applied electric field. The microchannel walls are assumed to be elastic in response to the deformation, and the non-Newtonian behavior of the fluid is governed by the simplified Phan-Thein-Tanner model. The hydrodynamics of ion and fluid transport are studied through the Poisson-Nernst-Planck-based Navier-Stokes model, coupled with the system of forces endured by both induced and external electric potential. The resulting coupled nonlinear equations are solved to capture the dynamics of wall deformations using continuum mean-field theories in the solid-liquid coupled system following the conservation principle. The electroosmotic flow deals with the lubrication approximation theory in the limit of the small channel aspect ratio. The result is validated with the pure electroosmotic flow of viscoelastic fluid for undeformed channels and also for the Newtonian fluid with deformable channels. Additionally, the coupling effect between wall deformation and electrokinetic transport modifies the quantitative response of wall relaxation dynamics and flow within the channel, which can provide a significant contribution to comprehending electrokinetic flow through charged viscoelastic media for microfluidic fabrications. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L17.00007: Propulsion mechanism of miniature diodes in aqueous solution under AC or light stimuli Minh-Thang Hoang, Rebecca K Banner, Leonard C Feldman, Michael A Filler, Jerry W Shan Semiconductor nanowires in suspension have been shown to be controllable under electric or light stimuli thanks to their asymmetrical response to these fields, making them excellent candidates for nanomotors that could be deployed in biomedical applications. However, their propulsion mechanism is not very well understood. Here, we study the propulsion of miniature diodes floating in aqueous solution under AC or light activation. These diodes share similar rectifying behavior with nanowire diodes but are much larger, thus allowing us to readily visualize their motion as well as perform direct-contact electrical measurements. We observe that the propulsion of the diode is driven by the forward current in an AC field, and by photocurrent under illumination. This is because the current creates an imbalance of ions at the two ends of the diode, which induces an electric field and drives an electrokinetic flow around the diode. In both cases, we find that the propelling velocities scale linearly with the current. Moreover, we measure the propelling velocity of diodes that are intentionally damaged by very high reverse biases. Our measurements show the velocity is substantially reduced for the damaged diodes, which have a smaller difference between forward and reverse currents. Our findings reveal potential applications in manipulating, characterizing, and separating nanowire diodes based on a key device property, their reverse-saturation current. This method may also be applicable to other electronic devices, such as transistors and logic gates. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L17.00008: Abstract Withdrawn
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Monday, November 25, 2024 9:44AM - 9:57AM |
L17.00009: Instability of a biomimetic membrane in a DC electric field Zongxin Yu, Shuozhen Zhao, Michael John Miksis, Petia M. Vlahovska The linear instability of a zero-thickness lipid membrane, separating electrolytes with different conductivities, subjected to a uniform electric field, is investigated within the electrokinetic framework. The Poisson-Nernst-Planck equations are solved and the flow driven by the charge in the Debye layers formed near the membrane are studied. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L17.00010: Effects of electrohydrodynamic charge transport on surface motion and deformation at a plasma-liquid interface Zhe Feng, Evert Klaseboer, Hongying Li, Wai Hong Ronald Chan We study the two-dimensional interactions between a weakly ionised single-fluid plasma and an incompressible liquid layer below it through high-fidelity numerical simulations based on the Navier–Stokes and Poisson–Nernst–Planck equations, where the conservative phase-field method has been incorporated to explore the effects of plasma-induced flow on a plasma-liquid interface. An electric potential difference is imposed across a nozzle-plate set-up, where a downward-pointing nozzle orifice serves as a source of positive ions into the overhanging plasma and a plate placed on the bottom domain boundary supports a pool of liquid above it. Consistent with experimental results, an ascending flow of liquid takes place along the vertical symmetry axis normal to the nozzle orifice, and circulation vortices emerge surrounding this liquid motion. By controlling the injection strength of ions and the magnitude of the externally applied voltage difference, unsteady undulations of the liquid surface can be clearly observed. The extent of interfacial deformation is closely related to the magnitude of the Coulomb force, which can also enhance the stabilisation of the phase interface and suppress corrugations. |
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