Numerical Analysis on the Stability Conditions of an Electrohydrodynamic Jet

2020 ◽  
Author(s):  
Sílvio Cândido ◽  
José C. Páscoa
Keyword(s):  
Numerical Model ◽  
Flow Rate ◽  
Applied Voltage ◽  
Taylor Cone ◽  
Fine Grid ◽  
Wide Range ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric ◽  
Multi Phase

Abstract The Taylor cone jet is a well-known electrohydrodynamic flow (EHD), usually produced by applying an external electric field to a capillary liquid. The generation of this kind of flow involves a multi-phase and a multi-physics process and its stability has a specific operation window. This operating window is intrinsically dependent on the flow rate and magnitude of the applied electric voltage. In case high voltages are applied to the jet it can atomize and produce an electrospray. Our work presents a numerical study of the process of atomization of a Taylor cone jet using computational fluid dynamics (CFD). The study intents to assess the limit conditions of operation and the applied voltage needed to stabilize an electrospray. The numerical model was implemented within OpenFOAM, where the multi-phase hydrodynamics equations are solved using a volume-of-fluid (VOF) approach. This method is coupled with the Maxwell equations governing an electrostatic field, in order to incorporate the electric body forces into the incompressible Navier-Stokes equations. The leaky-dielectric model is used and, therefore, the interface between the two phases is subject to the hydrodynamic surface tension and electric stress (Maxwell stress). This allows a leakage of charge though the phase due to ohmic conduction. Thus, the permittivity and conductivity of the phases are taken into consideration. A two-fluid system with relevant electric properties can be categorized as, dielectric-dielectric, dielectric-conducting, and conducting-conducting considering the electrical conductivity and permittivities of the participating phases. Due to the usage of the leaky-dielectric model, it is possible to simulate any of this physical situations. By increasing the applied voltage reaches a value where the cone instability is verified, allowing a discussion on this effect. It is demonstrated that to adequately model the process of atomization a fine grid refinement is needed. The validation of the numerical model is made by comparing against diverse experimental data, for the case of a stable jet. The diameter and velocity of the droplet and the electric current of the jet are the main variables that are compared with previous results. The tests were performed with Heptane. The cone and the jet are strongly affected by the flow rate. The dimensionless diameter, as a function of the dimensionless flow rate, agrees with the scaling laws. The model predicts accurate results over a wide range of flow rates with an accuracy of around 10%. The results are obtained using structured meshes.

scholarly journals Electrohydrodynamics of viscous drops in strong electric fields: numerical simulations

2017 ◽  
Vol 829 ◽  
pp. 127-152 ◽  
Author(s):  
Debasish Das ◽  
David Saintillan
Keyword(s):  
Numerical Simulations ◽  
Electric Fields ◽  
Small Deformation ◽  
Dielectric Liquid ◽  
Uniform Electric Field ◽  
Liquid Drops ◽  
Wide Range ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric

Weakly conducting dielectric liquid drops suspended in another dielectric liquid and subject to an applied uniform electric field exhibit a wide range of dynamical behaviours contingent on field strength and material properties. These phenomena are best described by the Melcher–Taylor leaky dielectric model, which hypothesizes charge accumulation on the drop–fluid interface and prescribes a balance between charge relaxation, the jump in ohmic currents from the bulk and charge convection by the interfacial fluid flow. Most previous numerical simulations based on this model have either neglected interfacial charge convection or restricted themselves to axisymmetric drops. In this work, we develop a three-dimensional boundary element method for the complete leaky dielectric model to systematically study the deformation and dynamics of liquid drops in electric fields. The inclusion of charge convection in our simulations permits us to investigate drops in the Quincke regime, in which experiments have demonstrated a symmetry-breaking bifurcation leading to steady electrorotation. Our simulation results show excellent agreement with existing experimental data and small-deformation theories.

Transient Electrohydrodynamic Manipulation of Particles on the Surface of a Drop

2016 ◽  
Author(s):  
Edison C. Amah ◽  
Ian S. Fischer ◽  
Pushpendra Singh
Keyword(s):  
Electric Field ◽  
Applied Electric Field ◽  
Control Parameter ◽  
Transient Behavior ◽  
Uniform Electric Field ◽  
Electrohydrodynamic Flow ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric

In our previous studies we have shown that particles adsorbed on the surface of a drop can be concentrated at its poles or equator by applying a uniform electric field. This happens even when the applied electric field is uniform; the electric field on the surface of the drop is nonuniform, and so particles adsorbed on the surface are subjected to dielectrophoretic (DEP) forces. In this study, we use leaky dielectric model to model the transient behavior of particles at low electric field frequencies. We show that the frequency of the electric field is an important control parameter that under certain conditions can be used to collect particles at the poles or the equator, and to move them from the poles to the equator. The speed with which particles move on the surface depends on the strength of the electrohydrodynamic flow which diminishes with increasing frequency.

scholarly journals “Leaky Dielectric” Model for the Suppression of Dynamic $R_{\mathrm{ON}}$ in Carbon-Doped AlGaN/GaN HEMTs

2017 ◽  
Vol 64 (7) ◽  
pp. 2826-2834 ◽  
Author(s):  
Michael J. Uren ◽  
Serge Karboyan ◽  
Indranil Chatterjee ◽  
Alexander Pooth ◽  
Peter Moens ◽  
...  
Keyword(s):  
Carbon Doped ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Gan Hemts ◽  
Leaky Dielectric

The electrostatically forced Faraday instability: theory and experiments

2019 ◽  
Vol 862 ◽  
pp. 696-731 ◽  
Author(s):  
Kevin Ward ◽  
Satoshi Matsumoto ◽  
Ranga Narayanan
Keyword(s):  
Interfacial Instability ◽  
Perfect Conductor ◽  
Dc Voltage ◽  
Fluid Systems ◽  
Instability Theory ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric ◽  
Rigorous Model ◽  
Parametric Frequency

The onset of interfacial instability in two-fluid systems using a viscous, leaky dielectric model is studied. The instability arises as a result of resonance between the parametric frequency of an imposed electric field and the system’s natural frequency. In addition to a rigorous model that uses Floquet instability analysis, where both viscous and charge effects are considered, this study also provides convincing validating experiments. In other results, it is shown that (a) the imposition of a periodic electrostatic potential acts to counter gravity and this countering effect becomes more effective if a DC voltage is also added, (b) a critical DC voltage exists at which the interface becomes unstable such that no parametric frequency is required to completely destabilize the interface and (c) the leaky dielectric model approaches a model for a perfect dielectric/perfect conductor pair as the conductivity ratio becomes large. It is also shown via experiments that parametric resonant instability using electrostatic forcing may be reliably used to estimate interfacial tension to sufficient accuracy.

scholarly journals TAYLOR CONE–JET MODE IN THE FABRICATION OF ELECTROSPRAYED MICROSPHERES

2018 ◽  
Vol 55 (1B) ◽  
pp. 216 ◽  
Author(s):  
Viet Linh Nguyen - Vu
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Polymer Solution ◽  
Flow Rate ◽  
Applied Voltage ◽  
Processing Parameters ◽  
Taylor Cone ◽  
Sem Micrographs ◽  
Scanning Electron

In this study, electrospray modes were investigated to clarify their effects on the morphology and size of polycaprolactone (PCL) particles. The result indicated that electrosprayed microspheres with homogeneous and stable morphology were fabricated by using cone–jet mode and suitable electrospray processing parameters. Besides, the PCL solution was created by dissolving in dichloromethane with different concentrations such as 3.5%, 4%, 4.5% and 5%. The scanning electron microscopy (SEM) micrographs pointed that electrosprayed PCL microspheres were formed by using 4.5 % polymer solution. In addition, the reproducible and homogeneous morphology of PCL microparticles were obtained at the following set of parameters: applied voltage of 18 kV, flow rate of 1.5 mL/h and distance tip to collector of 20 cm. Moreover, at the collecting distance of 15–25 cm, the flow rate of 1.2–1.8 mL/h and applied voltage of 18 kV the cone–jet mode was generated. It was an effective electrospray mode to create stable and homogeneous microspheres.

Linear Instability of Liquid Sheets Subjected to a Transverse Electric Field

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Xiao Cui ◽  
Qing-Fei Fu ◽  
Lijun Yang ◽  
Luo Xie ◽  
Bo-Qi Jia
Keyword(s):  
Growth Rate ◽  
Liquid Sheet ◽  
Linear Instability ◽  
Wave Number ◽  
Perfect Conductor ◽  
Liquid Density ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric ◽  
Gas To Liquid

Abstract A temporal linear instability analysis was performed for a liquid sheet moving around the inviscid gas in transverse electrical field. The fluid was described by the leaky-dielectric model, which is more complex and more comparable to the liquid electrical properties than existing models. As a result, the sinuous and the varicose modes exist, in which the dimensionless dispersion relation between wave number and temporal growth rate can be derived as a 3 × 3 matrix. According to this relationship, the effects of liquid properties on sheet instability were performed. It was concluded that, as the electrical Euler number (Eu), the ratio of gas-to-liquid density (ρ), Weber number (We), Reynolds number (Re), and the relative relaxation time (τ) increased, the instability of the sheet was enhanced. This work also compared the leaky-dielectric model with the perfect conductor model and found that the unstable growth rate in the leaky-dielectric model was higher than the one in the perfect conductor model. Moreover, as the ratio of gas-to-liquid improved, this difference decreased. Finally, an energy approach was adopted to investigate the instability mechanism for the two models.

scholarly journals LATTICE BOLTZMANN STUDY OF ELECTROHYDRODYNAMIC DROP DEFORMATION WITH LARGE DENSITY RATIO

2011 ◽  
Vol 22 (07) ◽  
pp. 729-744 ◽  
Author(s):  
ZHI-TAO LI ◽  
GAO-JIN LI ◽  
HAI-BO HUANG ◽  
XI-YUN LU
Keyword(s):  
Electric Field ◽  
External Electric Field ◽  
Lattice Boltzmann ◽  
Density Ratio ◽  
Droplet Deformation ◽  
Large Density ◽  
Dielectric Model ◽  
Large Density Ratio ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric

The lattice Boltzmann method (LBM) has been applied to electrohydrodynamics (EHD) in recent years. In this paper, Shan–Chen (SC) single-component multiphase LBM is developed to study large-density-ratio EHD problems. The deformation/motion of a droplet suspended in a viscous liquid under an applied external electric field is studied with three different electric field models. The three models are leaky dielectric model, perfect dielectric model and constant surface charge model. They are used to investigate the effects of the electric field, electric properties of liquids and electric charges. The leaky dielectric model and the perfect dielectric model are validated by the comparison of LBM results with theoretical analysis and available numerical data. It shows that the SC LBM coupled with these electric field models is able to predict the droplet deformation under an external electric field. When net charges are present on the droplet surface and an electric field is applied, both droplet deformation and motion are reasonably predicted. The current numerical method may be an effective approach to analyze more complex EHD problems.

scholarly journals Influence of Salts on Electrospinning of Aqueous and Nonaqueous Polymer Solutions

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Fatma Yalcinkaya ◽  
Baturalp Yalcinkaya ◽  
Oldrich Jirsak
Keyword(s):  
Lithium Chloride ◽  
Polyethylene Oxide ◽  
Polymer Solutions ◽  
Fibre Diameter ◽  
Tetraethylammonium Bromide ◽  
Web Structure ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric ◽  
Spinning Behaviour

A roller electrospinning system was used to produce nanofibres by using different solution systems. Although the process of electrospinning has been known for over half a century, knowledge about spinning behaviour is still lacking. In this work, we investigated the effects of salt for two solution systems on spinning performance, fibre diameter, and web structure. Polyurethane (PU) and polyethylene oxide (PEO) were used as polymer, and tetraethylammonium bromide and lithium chloride were used as salt. Both polymer and salt concentrations had a noteworthy influence on the spinning performance, morphology, and diameter of the nanofibres. Results indicated that adding salt increased the spinnability of PU. Salt created complex bonding with dimethylformamide solvent and PU polymer. Salt added to PEO solution decreased the spinning performance of fibres while creating thin nanofibres, as explained by the leaky dielectric model.

Electrohydrodynamic deformation and interaction of drop pairs

1998 ◽  
Vol 368 ◽  
pp. 359-375 ◽  
Author(s):  
J. C. BAYGENTS ◽  
N. J. RIVETTE ◽  
H. A. STONE
Keyword(s):  
Electric Field ◽  
Local Electric Field ◽  
Uniform Electric Field ◽  
Dielectric Model ◽  
Leaky Dielectric Model ◽  
Leaky Dielectric

The motion of two drops in a uniform electric field is considered using the leaky dielectric model. The drops are assumed to have no native charge and a dielectrophoretic effect favours translation of the drops toward one another. However, circulatory flows that stem from electrohydrodynamic stresses may either act with or against this dielectrophoretic effect. Consequently, both prolate and oblate drop deformations may be generated and significant deformation occurs near drop contact owing to enhancement of the local electric field. For sufficiently widely spaced drops, electrohydrodynamic flows dominate direct electrical interactions so drops may be pushed apart, though closely spaced drops almost always move together as a result of the electrical interaction or deformation.

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