Electrohydrodynamic Flow Research Articles

Investigating the effects of Lorentz forces on electrohydrodynamic flow generated by corona discharge in a multi needle-to-cylinder configuration

Investigating the effects of Lorentz forces on electrohydrodynamic flow generated by corona discharge in a multi needle-to-cylinder configuration

Reconfigurable homochiral colloidal clusters assembled under orthogonally applied electric and magnetic fields

Chiral structures assembled from colloids are of great interest for applications in metamaterials and micromachines. However, similar to their molecular counterparts, these assemblies often result in racemic mixtures. Achieving homochirality by breaking the symmetry remains a significant challenge. Here, we report an approach to obtain single-handed clusters from colloidal dimers using orthogonal electric and magnetic fields. Applying an alternating-current electric field perpendicular to the substrate generates a mixture of chiral clusters with both handedness. However, symmetry is broken by superimposing a planar rotating magnetic field, favoring one chirality over the other. The cluster's chirality can be precisely controlled in situ by adjusting the magnetic field's direction and strength, as well as the electric field frequency. Remarkably, this method also induces uniform chirality in initially achiral clusters when exposed solely to the electric field. Both experimental and numerical analyses reveal that the stability of specific handedness depends on the competition between forces and torques generated by the magnetic field, electric field, and electrohydrodynamic flow. Furthermore, we propose a strategy for producing colloidal clusters with uniform sizes and single-handedness through dynamic tuning of the electric and magnetic fields. This work not only demonstrates the potential of integrating external fields but also provides a viable way to create reconfigurable chiral colloidal structures.

Transient colloidal crystals fueled by electrochemical reaction products

Conventional electric field directed colloidal assembly enables fabricating ordered structures but lacks temporal control over assembly state. Chemical reaction networks have been discovered that transiently assemble colloids; however, they have slow dynamics (hrs – days) and poor temporal tunability, utilize complex reagents, and produce kinetically trapped states. Here we demonstrate transient colloidal crystals that autonomously form, breakup, and reconstitute in response to an electrochemical reaction network driven by a time invariant electrical stimulus. Aqueous mixtures of micron sized colloids and para-benzoquinone (BQ) were subjected to superimposed oscillatory and steady electric potentials, i.e., multimode potentials, that induce electrokinetic flows around colloids and proton-coupled BQ redox reactions. Transient assembly states coincided with electrochemically generated pH spikes near the cathode. We demonstrate wide tunability of transient assembly state lifetimes over two orders of magnitude by modifying the electric potential and electrode separation. An electrochemical transport model showed that interaction of advancing acidic and alkaline pH fronts from anodic BQ oxidation and cathodic BQ reduction caused pH transients. We present theoretical and experimental evidence that indicates transient colloidal crystals were mediated by competition between opposing colloidal scale electrohydrodynamic and electroosmotic flows, the latter of which is pH dependent.

Lorenz Model for Chaos in Electrokinetic Instability.

We demonstrate that the Lorenz system of equationscan approximate the nonlinear flow dynamics of the electrokinetic instability (EKI) in a microchannel driven by an electric field applied parallel to the diffusive interfaces separating the co-flowing centre and sheath streams with mismatched electrical conductivity. Using Galerkin projection, we show that the electrohydrodynamic flow equationscan be approximated by the Lorenz equationsin the limit of small conductivity difference between the flow streams. The derived dynamical model qualitatively captures the characteristics of EKI in both linear and nonlinear regimes, including the neutral stability criterion and alternating transitions between periodic and aperiodic states with increasing electric Rayleigh numbers. While not quantitatively precise, this simplified dynamical model provides valuable insights into the essential nonlinearities responsible for chaotic behaviour observed in EKIexperiments.

Phase-field-based regularized lattice Boltzmann method for axisymmetric two-phase electrohydrodynamic flow

In this study, a phase-field-based regularized lattice Boltzmann method is proposed to solve axisymmetric two-phase electrohydrodynamic (EHD) flow problems. Three regularized lattice Boltzmann equations are formulated to solve the axisymmetric electric scalar potential equation, the axisymmetric conservation form of the Allen–Cahn phase field equation, and the axisymmetric velocity-based Navier–Stokes equation, respectively. Both the perfect dielectric model and the leaky dielectric model are considered. The accuracy and stability of the proposed regularized lattice Boltzmann model are evaluated through several numerical examples in axisymmetric geometries, including static droplet tests, EHD droplet deformation, EHD Rayleigh–Taylor instability, EHD Rayleigh–Plateau instability, and ionic liquid ferrofluid droplet spreading. The numerical results are in good agreement with existing analytical, experimental, and numerical data. The findings indicate that the presence of the electric field significantly influences the two-phase flow dynamics. For the leaky dielectric model when the conductivity ratio is less than the permittivity ratio, the EHD flow deforms perpendicular to the direction of the electric field. In contrast, in other cases, the EHD flow deforms along the direction of the electric field. In most scenarios, the electric field intensifies the evolution of the two-phase interface and induces complex interfacial hydrodynamic behaviors.

ON CONTACT WETTING ANGLES IN THE LATTICE BOLTZMANN METHOD AND THEIR MEASUREMENT

Lattice Boltzmann method is applied for the computer simulation of liquid droplets that are in contact with a solid surface. In such problems, the value of contact angle at the three-phase contact line needs to be set. To achieve this, interaction forces between fluid and solid are introduced. The simulation of the equilibrium shapes of droplets is performed. We show that the use of commonly accepted forms of the interaction between fluid and solid in LBM leads to a non-physical change of the density near the solid surface. This hinders the correct calculation of heat fluxes. A new method is proposed to control the contact angles where only the tangential components of forces acting on fluid from solid nodes are taken into account (tangential force method, TFM). Use of this method does not change the fluid density in layers adjacent to the boundary. This is important in the simulation of flows with heat transfer and electrohydrodynamic flows. The dependence of the contact angle on the parameter of fluid-solid interaction is obtained.

Controlling the heating wall temperature during melting via electric field

Controlling the heating wall temperature during melting via electric field

Electrohydrodynamic flow about a colloidal particle suspended in a non-polar fluid

Nonlinear electrokinetic phenomena, where electrically driven fluid flows depend nonlinearly on the applied voltage, are commonly encountered in aqueous suspensions of colloidal particles. A prime example is the induced-charge electro-osmosis, driven by an electric field acting on diffuse charge induced near a polarizable surface. Nonlinear electrohydrodynamic flows also occur in non-polar fluids, driven by the electric field acting on space charge induced by conductivity gradients. Here, we analyse the flows about a charge-neutral spherical solid particle in an applied uniform electric field that arise from conductivity dependence on local field intensity. The flow pattern varies with particle conductivity: while the flow about a conducting particle has a quadrupolar pattern similar to induced-charge electro-osmosis, albeit with opposite direction, the flow about an insulating particle has a more complex structure. We find that this flow induces a force on a particle near an electrode that varies non-trivially with particle conductivity: while it is repulsive for perfectly insulating particles and particles more conductive than the suspending medium, there exists a range of particle conductivities where the force is attractive. The force decays as the inverse square of the distance to the electrode and thus can dominate the dielectrophoretic attraction due to the image dipole, which falls off with the fourth power with the distance. This electrohydrodynamic lift opens new possibilities for colloidal manipulation and driven assembly by electric fields.

Numerical study on characteristics of spiked electrode electrostatic precipitator

The characteristic of the spiked electrode electrostatic precipitator was numerically studied. The spiked electrode had significant effects on the distribution of electric field and charge density. The electric field and charge density were quite high in the area around the spiked electrode tips while decreased rapidly in other area far from the tips. Complicated electrohydrodynamic flow was observed and strong vortices were formed in the upstream and side areas of the spiked electrode. The gas velocity at the tip of the spiked electrode was as high as 28.1 m/s at the working potential of 45 kV. The working potential was more effective for the removal of large particle. The removal efficiency increased 42.4% for 10 µm particle and 15.2% for 0.25 µm particle as working potential increased from 22.5 kV to 45 kV. Low gas velocity was beneficial to the removal of all size particles. The removal efficiency increased by 10% to 15% for all size particles when the gas velocity decreased from 1.0 m/s to 0.6 m/s.

Data-driven prediction of flow fields in a needle-ring-net electrohydrodynamic pump system

In this paper, a data-mechanism hybrid modeling method for efficiently obtaining an electrohydrodynamic flow field is proposed. First, a backpropagation (BP) model with high accuracy is trained to get the value of essential parameter q0 for the mechanism simulation of flow fields. Subsequently, the mechanism model is used to generate a database for flow field reconstruction. Three machine learning algorithms, namely, BP neural network, random forest regression (RFR), and convolutional neural network (CNN), are employed to predict and reconstruct the flow behaviors of a needle-ring-net electrohydrodynamic pump. The RFR model demonstrates higher accuracy and precision in predicting velocity and pressure in the flow field compared to the BP and CNN models. The use of machine learning models for flow field prediction can significantly reduce the computational time while maintaining the computational accuracy. Additionally, an analysis assessing the impact of varying dataset sizes on the prediction accuracy of the model is conducted. The results indicate that the size of the dataset significantly influences the model predictive performance. Specifically, larger datasets are suggested to enhance both the accuracy and the generalization capabilities of the model. This observation highlights the critical role of dataset size in optimizing the performance of machine learning models for predictive tasks in engineering applications. These results offer important references for improving the design and optimization of electrohydrodynamic pumps.

A two-dimensional numerical characterization on the droplet dynamics in the electric field by VOSET method

A two-dimensional numerical characterization on the droplet dynamics in the electric field by VOSET method

Melting kinetics of PCM under synergistic effects of passive nanoparticle addition and active electric field exposure

Melting kinetics of PCM under synergistic effects of passive nanoparticle addition and active electric field exposure

A smoothed particle hydrodynamics method for two-phase electrohydrodynamics modeling with Nernst–Planck equations

The widely used leaky dielectric model often overlooks the rate of change in electric charges, leaving the impact of the charge conservation mechanism on two-phase electro-hydrodynamics (EHD) flows inadequately explored. In this study, we address this gap by introducing a charge-conservative model (CCM) for simulating such EHD systems within the framework of the smoothed particle hydrodynamics (SPH) method. Our methodology employs a fully explicit incompressible SPH (EISPH) approach to discretize the pressure Poisson, the electric potential Poisson, and the Nernst–Planck (N–P) equations. This work presents two notable contributions: (i) the introduction of the charge-conservative model into the incompressible SPH framework and (ii) the achievement of its discretization through a fully explicit methodology. To validate the proposed CCM, we conduct a comprehensive comparison with analytical solutions, as well as existing numerical and experimental results. The results affirm that the CCM consistently produces accurate outcomes across various test cases.

Role of surface charge convection on oblate droplets in different conductivity regimes

This paper presents a robust numerical model to simulate the electro-hydrodynamic flows of a neutrally buoyant liquid droplet suspending in another liquid for varying electrical conductivities ranging from near-dielectric to highly conductive fluids. The effect of such conductivity on the interfacial charge transport in the droplets has been investigated. The model is first validated with the theory of electro-rotation corresponding to the strong electric field. The results are compared with the theoretical predictions from the Quincke theory. The angular velocities at different electric field ratios agree well with theoretical predictions. Furthermore, droplet investigations are performed in distinct conductivity regimes with the electric Reynolds number ranging from 10−2 to 104. The findings reveal that conductivity influences the evolution of diverse droplet shapes in the corresponding regimes through surface charge convection. We observe prolate shapes at very low electric conductivities, while larger conductivities of droplets and suspending media lead to oblate drop shapes. With increasing electrical conductivity of the droplet and the medium, we observe the onset of distinct droplet shapes similar to the existing literature. The mechanism for the onset of different regimes is adequately explained by quantifying surface properties like tangential stress and velocity.

Theoretical and Numerical Study of Electrohydrodynamic Flow in a Planar, Cylindrical, and Spherical Conduit

This paper analyzes the mathematical model of electrohydrodynamic (EHD) fluid flow in a general conduit (planar, cylindrical and spherical) with an ion drag configuration. The phenomenon is modelled using a nonlinear differential equation. The velocity field is obtained by solving this nonlinear equation using two analytical methods. The effects of the Hartmann electric number and nonlinearity strength are discussed and presented graphically. Additionally, we compare this method with a numerical solution obtained using MATLAB, demonstrating that the proposed approaches are less computational intensive and more efficient for solving the underlined problem.

Flow structure beneath periodic waves with constant vorticity under strong horizontal electric fields

Flow structure beneath periodic waves with constant vorticity under strong horizontal electric fields

Consistent and conservative lattice Boltzmann method for axisymmetric multiphase electrohydrodynamic flows

Consistent and conservative lattice Boltzmann method for axisymmetric multiphase electrohydrodynamic flows

Simulation Analysis of Charge and Flow Features in a Needle-to-Ring Electrohydrodynamic Actuator

Three-dimensional (3D) numerical studies closer to real physical scenarios have received increasing academic attention for providing a better design reference for electrohydrodynamic (EHD) pumping technology. A 3D computational model of a cylindrical EHD cascade actuator based on needle-to-ring electrodes is established in this paper, in which the effects of injection, field-enhanced dissociation, and surface charge accumulation are jointly involved. We explore the strongly coupling behavior of the EHD flow pattern with charge motion in an isothermal incompressible dielectric liquid, analyzing the flow rate, dynamic pressure, and current. It is found that an asymmetrical 3D vortex structure appears within the 2D axisymmetric actuator body, which is attributed to the motion of opposite charges.

Exploring Electrohydrodynamic Flows Inside Leaky Dielectric Drops: A Laser Velocimetry Approach

A novel experimental methodology based on laser velocimetry for the investigation of electrohydrodynamic (EHD) flows inside a neutrally buoyant leaky dielectric drop of 2.25 mm of radius is proposed. Utilizing fluorescent particles, 2D and 3D Lagrangian Particle Tracking (LPT) measurements of the EHD flows inside an initially spherical drop under a constant electric field are reported. Two leaky dielectric fluids, namely Silicone and Castor oils, were used as either the drop or the medium phases, depending on the case investigated, thus covering oblate and prolate drops both with small and larger deformations. 2D measurements of the trajectories and velocities of the tracer particles in a Lagrangian referential enabled a direct comparison with the leaky dielectric model (LDM), a well-stablished theory covering drops with smaller deformations, showing a good agreement with our measurements. The symmetry inside a drop with increased deformation is investigated from an analysis of the mean 3D velocity field, whose measurements converge to the two-dimensional analysis at the plane of symmetry of the drop, suggesting symmetrical flow structures inside the drop.

Analytical model and flow velocity control of electrohydrodynamics system with multi-needle corona discharge

For the flow field distribution and control mechanism generated by the electrohydrodynamics (EHD) system with multi-needle corona discharge, this paper takes the multi-needle EHD pump as the research object, establishes different types of physical models through regional division, constructs multi-physical field coupling relationship, and derives a simplified EHD flow velocity equation suitable for the EHD system with multi-needle corona discharge. Combined with the intelligent optimization method of population evolution, a novel and effective intelligent algorithm is designed for the numerical analysis of the velocity profile distribution of a multi-needle EHD pump, and the flow velocity control law of the multi-needle EHD pump is analyzed by quantitative calculation. The validity of the model and analysis is verified by the electric field and flow field simulation of the multi-needle EHD pump system. The calculation results show that the voltage parameter is more dominant than the electrode spacing parameter in the steady-state flow velocity control of the multi-needle EHD pump, and both the maximum flow velocity and the average flow velocity are superlinearly controlled by voltage. In the design of multi-needle EHD pump with an electrode spacing of 1 cm, the simulation results show that the maximum gas flow velocity of 0.82 m/s can be obtained by providing 5000 V voltage, which verifies the design of a miniaturized multi-needle EHD pump and its feasibility in gas lasers and other application scenarios.