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 T17: Magnetohydrodynamics II |
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Chair: Jonathan Cheng, US Naval Academy Room: 250 A |
Monday, November 25, 2024 4:45PM - 4:58PM |
T17.00001: Abstract Withdrawn
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Monday, November 25, 2024 4:58PM - 5:11PM |
T17.00002: Wide-field magnetic imaging the near-field of atmospheric microplasmas using spin resonance of nitrogen-vacancy ensembles Sean Mendoza, Morteza Gharib Nitrogen-vacancy (NV) centers in diamond have been leveraged as high-precision quantum sensors for detecting magnetic and electric fields, as well as for measuring temperature and strain. Traditionally, wide-field approaches using these NV centers have been demonstrated either through cumbersome scanning methods or by using scientific-grade phase-sensitive cameras to amplify the weak NV fluorescence signal. In this work, we develop a wide-field magnetometer based on a consumer-grade astrophotography camera to image planar ensembles of NV centers in low-cost diamond nanoparticles. By embedding planar NV ensembles within ultra-thin (<50 µm) quartz wafers, we achieve optical detection of magnetic signatures within magnetohydrodynamic (MHD) flows with a sensitivity of around 500 nT/√Hz. This proximity allows for the resolution of features in microfluidic MHD and electronic systems, such as operating circuit boards or microplasma structures, while also relaxing sensitivity requirements and eliminating the effect of magnetic far-field annihilation. We apply this system to spatially-resolve the DC component of the magnetic signature of toroidal microplasmas generated purely through hydrodynamic shear. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T17.00003: An anisotropic clustering instability due to inter-particle hydrodynamic and magnetic interactions in a sheared magnetorheological fluid subject to a magnetic field. Viswanathan Kumaran A magnetorheological fluid is made of magnetic particles, with permanent of induced dipole moments, suspended in a viscous liquid. These fluids exhibit a transition between a flowing state in the absence of a magnetic field and a jammed state with sample-spanning particle aggregates when a magnetic field is applied. The initiation of dynamical arrest of an initially well-dispersed sheared suspension is examined by considering the effect of inter-particle hydrodynamic and magnetic interactions. In a dilute suspension at low Reynolds number, there is a disturance due to the magnetic field around one particle due to the magnetic moment of neighbouring particles, and a velocity disturbance due to the hydrodynamic torque exerted by neighbouring particles on the fluid. There is a correction to the particle angular velocity due to the net torque resulting from the hydrodynamic and magnetic interactions. The total force and the drift velocity due to these interactions is zero in a uniform suspension. In the presence of concentration fluctuations, the collective effect of inter-particle interactions is shown to be equivalent to an anisotropic diffusion process. The diffusion coefficients in the directions perpendicular to the magnetic field are negative, indicating a strong clustering tendency in these directions. The diffusion coefficient in the magentic field direction is positive, and this results in the damping of concetration fluctuations in the direction fo the field. This instability could initiate the formation of sample-spanning clusters along the field direction, leading to dynamical arrest upon application of a magnetic field. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T17.00004: Magnetophoresis of Paramagnetic and Diamagnetic Metal Salts in Porous Media: Effects of Porous Media and Solutes Interactions Alwell Nwachukwu, Jamel Ali, Theo Siegrist, Munir Humayun, Hadi Mohammadigoushki We report experiments on magnetophoresis of a mixture of paramagnetic and diamagnetic metal solutes in porous media. Specifically, we focused on the magnetophoresis of individual paramagnetic (MnCl2) and diamagnetic (ZnCl2) metal salts, as well as their mixtures, at concentrations of 1, 10, and 100 mM. We find that compared to silica gel with a polydisperse size distribution, larger silica particles achieved moderately higher enrichment of paramagnetic ions. Additionally, diamagnetic metal salts (ZnCl₂) showed moderately stronger depletion at the surface of the magnet. When using smaller silica gel particles, no noticeable difference was observed in the concentration depletion of diamagnetic metal salts. However, for paramagnetic salts, the concentration enrichment was moderately lower in silica gel with smaller particle sizes compared to the polydisperse silica distribution. For binary mixtures of metal salts, we find enrichment in the region of highest magnetic field for both paramagnetic and diamagnetic metal salts. However, the overall enrichment for the mixture was lower compared to the enrichment levels observed for the individual metal salts. Our hypothesis is that in a mixture containing solvent, paramagnetic and diamagnetic ions, each individual ion experience magnetic forces in different directions. Presumably these opposing forces may induce competing convective flows that impact (lower) the overall magnetomigration of each ion in binary mixtures. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T17.00005: Magnetohydrodynamics and Fluid Structure Interaction Model for Flow in a Cantilever Microtube Yasser Aboelkassem Microtubes containing magnetic fluid have numerous applications in microfluidic and nanotechnology systems, including mixing, drug delivery, and microcantilever biosensors. The Lorentz force, induced by the interaction of flow velocity and magnetic field, can be used to guide or influence the flow within these microtubes. An important consideration and potential opportunity when using microtubes with magnetic fluid for biosensing applications is the vibration of the tube caused by fluid traction. In this work, we investigate the effect of a transverse magnetic field on the vibration and oscillations of cantilever microtubes conveying magnetic fluid, utilizing flow lubrication theory. We couple the Euler–Bernoulli beam model with the Navier-Stokes flow equations to derive a fluid-structure interaction (FSI) model for analyzing the vibrations of the cantilever microtube. The results indicate that a transverse magnetic field can significantly impact the flow motions and structural dynamics of the tube by increasing the system's natural frequencies and critical flow velocity, thereby contributing to the system's dynamic instability. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T17.00006: Transition in flows driven by converging currents Mohammad Y Abdelshafy, Bitong Wang, Ibrahim A Mohammad, Jonathan S Cheng, Douglas H Kelley The liquid metal battery is a promising technology especially suited to grid-scale storage. It comprises two liquid metal electrodes and a molten salt electrolyte that are stably stratified with density. We experimentally studied the flow in the positive electrode using a cylindrical apparatus with a layer of liquid gallium subject to converging current that interacts with the Earth's ambient magnetic field. At a Shercliff number S ≳ 123300, we observed electro-vortex flow (EVF) which is a poloidal flow generated by the interaction of the current with its own magnetic field, and a swirling flow which is generated by the interaction of the current with the ambient axial field, consistent with previous research. However, when we forced the flow at lower current S<123300, we observed a poloidal flow in the opposite direction to EVF. The mechanism of the latter flow is Ekman pumping, where a local fast swirl close to the thin electrode pushes fluid horizontally outward, falling along the side of the vessel and rising at the center. We also present a non-dimensional parameter, β, which is the ratio of the external field to induced field scaled by the ratio of wire radius to vessel radius, that captures the transition between these two motions. This non-dimensional number successfully predicts the transition in previous experiments in the literature. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T17.00007: Interaction of convective modes with current-driven flow in a liquid metal battery experiment Jonathan S Cheng, Mohammad Y Abdelshafy, Bitong Wang, Ibrahim A Mohammad, Douglas H Kelley Liquid metal batteries (LMBs) - a promising technology for grid-scale energy storage - are subject to a variety of flow forcings that may disrupt battery operation. In a typical model of the LMB anode, an adverse temperature gradient is established during operation due to Joule heating of the electrolyte layer. At the same time, the current tends to converge toward the negative current collector, inducing electrovortex flow (EVF). The specific interaction of these two forcings has seen little focus in laboratory studies. Here, we present a series of experiments in a cylindrical layer of gallium subject to the essential forcings of thermal convection and EVF. We scan through a range of temperature gradients and current strengths, using ultrasonic Doppler velocimetry to track the flow patterns. We find that at low currents, the jump-rope vortex (JRV) mode of convection tends to dominate. At the highest currents, the flow resembles canonical EVF. For a fairly broad range of intermediate currents, though, we observe flows that exhibit some properties of both EVF and JRVs, such as periodic oscillations resembling the JRV coinciding with a central jet descending from the electrode resembling EVF. Our results could have significant implications for the flows expected in industrial LMBs. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T17.00008: Magnetophoresis of Paramagnetic and Diamagnetic Particles in Suspensions under Nonuniform Magnetic Fields: Effects of Convection and Sedimentation Peter Rassolov, Jamel Ali, Theo Siegrist, Munir Humayun, Hadi Mohammadigoushki Magnetophoresis, or the magnetic field gradient driven movement of solutes or particles through a fluid medium, presents an efficient means of controlling the transport of suspended particles with various engineering, environmental, and medical applications. While magnetophoresis of ferromagnetic and superparamagnetic particles has been extensively studied, the movement of paramagnetic and diamagnetic particles under nonuniform magnetic fields remains poorly understood. In this work, we use a combination of experiments and numerical simulations to study the capture of paramagnetic manganese oxide and diamagnetic bismuth oxide particles in an aqueous suspension by nonuniform magnetic fields. We find that for magnetic Grashof numbers beyond the order of unity, the concentration gradients produced by magnetophoresis induce a bulk flow that accelerates the capture of paramagnetic particles. We also compare magnetophoresis with particle sedimentation and find that in cases where they act in opposite directions, the flow splits into two distinct regions: one where magnetophoresis drives particle capture, and one where particles settle due to gravity. The extent of this region can be predicted by comparing the magnetic Péclet number with the gravitational Péclet number. |
Monday, November 25, 2024 6:29PM - 6:42PM |
T17.00009: Electrodeless Magnetohydrodynamic Local Force Generator for Aerocapture Bernard Parent, Felipe Martin Rodriguez Fuentes, Spencer LaFoley We here present a novel magnetohydrodynamics (MHD) system for planetary entry aerocapture. The system is advantaged over previous approaches by having the following two characteristics: (i) it can be deployed locally to one or various flow regions, and (ii) it does not make use of electrodes. Previous MHD systems for planetary entry were either electrodeless global systems or two-electrode local systems. The proposed novel MHD system employs two magnets to establish a current loop resulting in a Faraday electromotive force (EMF). The first magnet is positioned to ensure the magnetic field faces outward from the shell, while the second magnet is oriented to ensure the magnetic field faces inward toward the shell. Preliminary findings demonstrate that when located on the surface of an Earth entry capsule at a flight Mach number of 35, the novel electrodeless MHD system can generate forces several times greater than a two-electrode system while utilizing the same magnetic field strength. The study is conducted entirely through numerical simulation using CFDWARP, a computational fluid dynamics (CFD) code that employs advanced numerical methods allowing for the full coupling between aerodynamics, magnetohydrodynamics, and non-neutral plasma sheaths. The physical model includes an 11-species finite-rate chemical solver including real gas effects, the drift-diffusion model for all charged species, along with an electric field potential equation that satisfies Gauss's law. |
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