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 X06: Drops: Electric Field Effects |
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Chair: Yang Liu, City College of New York Room: Ballroom F |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X06.00001: In-Flight Interaction of Water, Glycol, and Alcohol Droplets with a Dielectric Barrier Discharge Plasma Jorge Ahumada Lazo, Haipeng Zhang, Yang Liu The use of non-thermal plasmas is becoming ubiquitous for many processes such as disinfection of medical equipment, treatment of surfaces, waste-water treatment, and airplane wing de-icing. It is noted that in most of the aforementioned uses of plasmas there is interaction with droplets of water or other liquids commonly used in these processes, namely alcohols and glycols. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X06.00002: Hydrodynamics of a Water Droplet Impact on a Surface Dielectric Barrier Discharge Plasma Jorge Ahumada Lazo, Petr Lelikov, MD Sohaib Bin Sarwar, Yang Liu Dielectric discharge barrier (DBD) actuators generate a non-thermal plasma discharge over a dielectric surface. This can be exploited for flow control, de-icing of aircraft wings, disinfection of surfaces, among other applications. An actuator consists of at least one pair of electrodes, where one is exposed to air and the other one is encapsulated by a dielectric material. When voltage is applied between the electrodes, the air surrounding the exposed electrode and the dielectric material becomes ionized, and a sheet of plasma is formed along the edge of the exposed electrode. In most flow control and de-icing applications, wing surfaces, turbine, and compressor blades on which DBD actuators operate are constantly exposed to humid environments. In particular, water droplets can impact the actuators during typical operations. It is thus needed to understand the dynamics as well as the multi-phase, multi-physics processes during droplet impact on an actuator. Our experimental work yielded consistent results on the spreading of the droplet, formation of glow and streamer plasma discharges within the droplet, and disruption on the otherwise smooth induced flow. These results are believed to be fundamental for flow control, de-icing applications, as well as other industrial processes. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X06.00003: Real-time control of textile waterproof performance upon droplet impact Georgia Ioannou, Corinne Stone, Michael Dennis, Jose Rafael Castrejón-Pita Droplet impact on permeable surfaces such as sieves, metallic meshes and textiles has attracted research interest as it is a process ubiquitous in many applications, from preventing stains and entrainment of rain drops in clothes to entrapment of aerosols through filters. Here, we aim to investigate whether textile wettability can be varied on demand by employing the dielectrowetting effect. Dielectrowetting occurs when a dielectric liquid is present within an electric field. By varying the strength of the electric field, we can control the dielectrophoretic force acting on the liquid. This dielectrophoretic force alters the energy balance, affecting the droplet spreading and penetration dynamics upon impact. Employing high-speed imaging, we study the behaviour of droplets during the first milliseconds after impact. A parametric analysis enables us to construct a regime map that identifies the conditions for penetration or no penetration of the droplet through the textile. Noteworthy is the observation that a droplet that would normally penetrate the textile, and disintegrate, can be captured on the textile in the presence of the dielectrophoretic force at a sufficient potential strength. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X06.00004: Finite-time singularity formation in drop electrohydrodynamics Gunnar G Peng, Ory Schnitzer In the Taylor-Melcher leaky-dielectric model, a suspended drop with an imposed external electric field may attain a singular steady state, in which the surface-charge density blows up (anti-symmetrically) near the equator as q ~ x^(-1/3), where x is the distance to the equator [Peng, Brandão, Yariv and Schnitzer, Phys. Rev. Fluids 9, 083701 (2024)]. This is associated with an anti-parallel surface-charge polarization driving a surface flow v ~ x^(1/3) which advects opposite charges towards the equator where they "annihilate" at a rate qv, which is non-zero despite both q and v being odd functions of x. We use finite-difference numerical simulations of a symmetric two-dimensional circular drop to study how an initially smooth state evolves towards the singular steady state, and find that a singularity develops in finite time, but with q ~ x^(-0.28). The singularity formation can be described with a local similarity solution, in which the universal exponent emerges from the condition that the solution approaches x=0 linearly rather than with a non-integer power. By introducing an extremely small amount of artificial surface-charge diffusion, we simulate the evolution beyond the finite-time singularity, which is described by another similarity solution, and the approach to the ultimate profile with q ~ x^(-1/3). *This work was funded by the Leverhulme Trust Research Project Grant RPG-2021-161. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X06.00005: Forces on Drops due to Slide Electrification Chirag Hinduja, Benjamin Leibauer, Aaron D Ratschow, Shalini Singh, Rüdiger Berger, Hans-Jürgen Butt A drop sliding on a water repellent surface acquires a net electrical charge and the counter charges are deposited at the solid surface. This phenomena is known as slide electrification. Slide electrification results in electro-capillarity and hence, alters the solid-liquid and solid-air interfacial energies [1]. The resulting effects contribute to forces on the drop and influence the drop motion [2]. However, the exact mechanisms by which slide electrification affect the drop motion are unclear. In this talk, we quantitatively disentangle the mechanisms by sliding the drop at a defined and constant velocity. We omit the influence of viscous dissipation in the drop and quantify two phenomena: electrowetting due to drop charge and change in solid surface energy due to deposited charges. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X06.00006: On the mechanism of jet splitting in electrospinning Krishna Raja Dharmarajan, Muhammad Faheem Afzaal, Yuan Si Tian, Er Qiang Li, Sigurdur T Thoroddsen
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Tuesday, November 26, 2024 9:18AM - 9:31AM |
X06.00007: Numerical and asymptotic analysis of the three-dimensional electrohydrodynamic interactions of a drop and a nearby planar boundary Mohammadhossein Firouznia, Diptendu Sen, Petia M. Vlahovska, David Saintillan We study the interaction of a drop with a planar wall under an applied uniform DC electric field using the leaky dielectric model framework. We develop three-dimensional numerical simulations using the boundary integral method and an analytical theory assuming small drop deformations. By integrating numerical simulations with theoretical analysis, we examine the electrohydrodynamic interactions as a function of separation distance and fluid properties. Specifically, we focus on a drop near an insulating wall, where the electric field is tangential to the wall surface. Our results show that the drop migrates away or towards the wall, depending on the relative conductivities and permittivities of the drop and the suspending fluid. For instance, a drop that is more conducting than the suspending fluid experiences electrohydrodynamic attraction but electrostatic repulsion—due to the interaction with the image dipole—by the insulating wall, leading to a stable hovering state. We compare our simulations with experiments, particularly in cases where the drop is less conducting than the suspending fluid, resulting in electrohydrodynamic and electrostatic repulsion. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X06.00008: Transient Electrohydrodynamic Behaviour of a Non-Newtonian Droplet in Another Non-Newtonian Medium: A Mathematical Exploration Pulak Gupta, PURBARUN DHAR, Devranjan Samanta Due to the encapsulated structure, small volume, and large surface area, droplets are ideally suited for use as specialized material carriers and reactors. Extensive studies of deformation and flow fields within droplets under an external electric field, among other fields such as magnetic, pressure, micropump, or combinations thereof, are well-known in the scientific community, particularly in microfluidic applications where deformation, manipulation, breakup, and coalescence are crucial. Many experimental, mathematical, and analytical work has been done on Newtonian droplets, considering both steady-state and transient conditions. However, in practical applications, the fluid often exhibits non-Newtonian behaviour, yet very few studies have addressed the non-Newtonian nature of droplets under transient conditions. This gap motivates the present study, which involves the mathematical analysis of an immiscible, leaky dielectric non-Newtonian droplet confined in a different surrounding medium under the small deformation regime, in the presence of an external, low-intensity DC electric field of irrotational nature. The study focuses on examining the transient deformation and flow fields within the droplet and the surrounding medium, considering various interfacial stresses. The investigation is constrained by a critical value of the Weissenberg number, set to 1, ensuring that the elastic nature remains less than or equal to the viscous nature without exceeding it. The mathematical analysis incorporates electrical phenomena via Laplace's equation and the charge conservation equation, hydrodynamic phenomena through the continuity equation and Cauchy momentum equation, and addresses the non-Newtonian behaviour using the upper convected Maxwell model. These equations are non-dimensionalized using appropriate characteristic scales and non-dimensional numbers, and solved with suitable non-dimensional forms of boundary and interfacial conditions. Validation of our mathematical model is conducted against existing experimental and mathematical literature. In addition to deformation, flow field patterns are analyzed by generating streamline patterns, suggesting deeper exploration in non-Newtonian fluids holds promise for advancing in the development of microfluidic devices. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X06.00009: Experimental study on hybrid multi-emitter gallium FEEP thruster Kyung Heon Kim, Dong Kee Sohn, Kyun Ho Lee, Jung Won Kuk, Han Seo Ko Field emission electric propulsion (FEEP) thrusters are CubeSat-compatible electric thrusters characterized by high specific impulse and micronewton scale thrust. Since the thrust of a single-emitter FEEP thruster ranges from 1 to 10 μN, a multi-emitter configuration is required to satisfy various thrust demands for CubeSats. In this study, a multi-emitter with a 2x2 array of needle-capillary hybrid emitters with various extractor shapes was tested to derive an optimal design for uniform emission and high emitter packing density. For an extractor with a single hole, non-uniform emission with a tilted Taylor cone caused by a radially biased electric field was observed. Conversely, for an extractor with a 2x2 array of holes, uniform and axis-aligned ion emission from all four emitters was confirmed. Although the grid array of extractor holes demonstrated stable and uniform emission, further improvement in the emitter packing density is still required. To enhance packing density, a linear array of emitters with slit-shaped extractor holes is planned for future investigation. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X06.00010: Actuating a Selectively Metallized Plate with Electrowetting Force Behzad (David) Parsi, Max Gunn, Daniel Maynes, Nathan b Crane Electrowetting on dielectric (EWOD) driven micropump actuators can be integrated into microfluidic reconfigurable radio frequency (RF) devices. In this research, a technique will be introduced to actuate an RF metallized plate using EWOD forces. In the proposed configuration, the plate is supported by four droplets. The top plate is coated with a hydrophilic material and the bottom plate is coated with a hydrophobic material. The actuation velocity determines the tuning speed of the device the velocity increases by maximizing the actuation force, minimizing the moving mass (droplets and metallized plate), and reducing all resistances (contact line drag, fluid drag). To achieve this goal, first, we build an analytical model of EWOD actuation that can calculate the relation between the physical dimensions and velocity of the EWOD-actuated system as a function of input voltage so we can evaluate whether EWOD can overcome the drawbacks that are expected with piezoelectric actuation, such as low accuracy, large size, and difficulty in reliable actuation to multiple positions. In addition, the experiments are employed to verify the proposed model. The model is validated with an EWOD experiment, and the data demonstrates less than a 5.6% error between the measured and predicted maximum plate velocity for different voltage inputs. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X06.00011: ABSTRACT WITHDRAWN
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Tuesday, November 26, 2024 10:23AM - 10:36AM |
X06.00012: Electronic cleaning glass for object detection in autonomous driving Jungwoo Yoon, Lin Chai, Sanghyun Park, Sang Kug Chung, Kang Yong Lee This study proposes an electronic cleaning glass based on liquid dielectrophoresis for reliable operation of object detection systems in autonomous driving. The glass is capable of simultaneously removing both conductive and non-conductive droplets, as well as selectively removing specific types of droplets. The glass comprises a glass substrate and an array of transparent interdigitated electrodes coated with a dielectric layer. The contact angle of droplets with various dielectric constants is quantified in dependence on the amplitude and frequency of the applied voltage. The minimum switching time of the voltage for each interdigitated electrode is measured using a digital I/O board. Based on the aforementioned results, experiment is performed to remove multiple droplets with various dielectric constants simultaneously, and the cleaning rate is quantified over time. Furthermore, it is experimentally verified that the glass is capable of cleaning only certain types of droplets. Finally, the effect of the glass's operation on object detection performance is evaluated by measuring mean average precision (mAP) in images captured by the camera equipped with the glass. It is observed that mAP decreased by the contaminant but returned to its original value upon operating the glass. |
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