Effect of finite conductivity on the nonlinear behaviour of an electrically charged viscoelastic liquid jet

2019 ◽  
Vol 874 ◽  
pp. 5-37 ◽  
Author(s):  
Fang Li ◽  
Shi-You Ke ◽  
Xie-Yuan Yin ◽  
Xie-Zhen Yin
Keyword(s):  
Numerical Study ◽  
Electrostatic Force ◽  
Complete Removal ◽  
Bond Number ◽  
Finite Conductivity ◽  
Nonlinear Behaviour ◽  
Secondary Importance ◽  
String Structure ◽  
Electrically Charged Jet ◽  
Electrically Charged

In this paper a one-dimensional numerical study on the nonlinear behaviour of an electrically charged jet of Oldroyd-B viscoelastic, Taylor–Melcher leaky dielectric liquid is carried out. The effect of surface charge level, axial wavenumber and finite conductivity on the nonlinear evolution of the jet is investigated. Different structures including beads-on-a-string with/without satellite droplets, quasi-spikes and spikes are detected, and their domains in the plane of the non-dimensional axial wavenumber and the electrical Bond number are illustrated. The underlying mechanisms in the formation of the structures are examined. It is found that tangential electrostatic force plays a key role in the formation of a quasi-spike structure. Decreasing liquid conductivity may lead to a decrease in the size of satellite droplets or even the complete removal of them from a beads-on-a-string structure, induce the transition from a beads-on-a-string to a quasi-spike structure or postpone the appearance of a spike. On the other hand, finite conductivity has little influence on filament thinning in a beads-on-a-string structure, owing to the fact that the electrostatic forces are of secondary importance compared with the capillary force. The difference between the finite conductivity, large conductivity and other cases is elucidated. An experiment is carried out to observe spike structures.

scholarly journals Drops bouncing off macro-textured superhydrophobic surfaces

2017 ◽  
Vol 824 ◽  
pp. 866-885 ◽  
Author(s):  
Ali Mazloomi Moqaddam ◽  
Shyam S. Chikatamarla ◽  
Iliya V. Karlin
Keyword(s):  
Contact Time ◽  
Numerical Study ◽  
Three Dimensional ◽  
Superhydrophobic Surfaces ◽  
Nonlinear Behaviour ◽  
Textured Surfaces ◽  
Texture Density ◽  
Wide Range ◽  
Quantitative Manner ◽  
The Impact

Recent experiments with droplets impacting macro-textured superhydrophobic surfaces revealed new regimes of bouncing with a remarkable reduction of the contact time. Here we present a comprehensive numerical study that reveals the physics behind these new bouncing regimes and quantifies the roles played by various external and internal forces. For the first time, accurate three-dimensional simulations involving realistic macro-textured surfaces are performed. After demonstrating that simulations reproduce experiments in a quantitative manner, the study is focused on analysing the flow situations beyond current experiments. We show that the experimentally observed reduction of contact time extends to higher Weber numbers, and analyse the role played by the texture density. Moreover, we report a nonlinear behaviour of the contact time with the increase of the Weber number for imperfectly coated textures, and study the impact on tilted surfaces in a wide range of Weber numbers. Finally, we present novel energy analysis techniques that elaborate and quantify the interplay between the kinetic and surface energy, and the role played by the dissipation for various Weber numbers.

Momentum equation for straight electrically charged jet

2011 ◽  
Vol 32 (12) ◽  
pp. 1515-1524 ◽  
Author(s):  
Ruo-jing Zhang ◽  
S. H. Hou ◽  
C. K. Chan
Keyword(s):  
Momentum Equation ◽  
Electrically Charged Jet ◽  
Electrically Charged

scholarly journals Charge Characterization of an Electrically Charged Fiber via Electrostatic Force Microscopy

2006 ◽  
Vol 1 (2) ◽  
pp. 155892500600100 ◽  
Author(s):  
Joyoun Kim ◽  
Warren J. Jasper ◽  
Juan P. Hinestroza
Keyword(s):  
Electrostatic Force ◽  
Mathematical Expression ◽  
Quantitative Agreement ◽  
Electrostatic Force Microscopy ◽  
Quantitative Interpretation ◽  
Polarization Effects ◽  
Force Microscopy ◽  
Sample Separation ◽  
Electrically Charged

The charge of a corona charged electret fiber as well as an uncharged glass fiber was characterized via Electrostatic Force Microscopy (EFM). Electrostatic force gradient images were obtained by monitoring the shifts in phase between the oscillations of the biased EFM cantilever and those of a piezoelectric driver. EFM measurements were performed using noncontact scans at a constant tip-sample separation of 75 nm with varied bias voltages applied to the cantilever. A mathematical expression, based on the Coulombic and induced polarization effects, were used to model the EFM phase shifts as a function of the applied tip bias voltages. There was quantitative agreement between the experimental data and the mathematical expression, and the quantitative interpretation for charges on the fiber was made.

Bistability and hysteresis induced by form drag in nonlinear subcritical and supercritical double-diffusive Lapwood convection in shallow porous enclosures

2017 ◽  
Vol 812 ◽  
pp. 463-500 ◽  
Author(s):  
Redha Rebhi ◽  
Mahmoud Mamou ◽  
Patrick Vasseur
Keyword(s):  
Rayleigh Number ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Lewis Number ◽  
Linear Stability Theory ◽  
Nonlinear Behaviour ◽  
Form Drag ◽  
Solute Fluxes ◽  
Double Diffusive

This paper considers natural Lapwood convection in a shallow porous cavity filled with a binary fluid. The investigation is mainly focused on the nonlinear behaviour of subcritical convection and the bistability phenomenon caused by the combined effects of porous medium form drag and double-diffusive convection. The Dupuit–Darcy model, which includes the effect of the form drag at high Reynolds flow, is used to describe the convective flow in the porous matrix. The enclosure is subject to vertical temperature and concentration gradients. The governing parameters of the problem under study are the Rayleigh number, $R_{T}$, the buoyancy ratio, $\unicode[STIX]{x1D711}$, the Lewis number, $Le$, the form drag coefficient, ($1/P_{r}^{\ast }$), where $P_{r}^{\ast }$ is a modified Prandtl number, and the aspect ratio of the cavity, $A$. An analytical solution, valid for shallow enclosures ($A\gg 1$), is derived on the basis of the parallel flow approximation. Among other things, this work focuses on the effects of the form drag parameter on the convective flows that occur when the thermal and solutal buoyancy forces are opposing each other. For this situation, in the absence of the form drag effect, the onset of motion is known to occur at a subcritical Rayleigh number, $R_{TC}^{sub}$, which depends upon $\unicode[STIX]{x1D711}$ and $Le$ only. The effects of $P_{r}^{\ast }$ on $R_{TC}^{sub}$ and on the subsequent convective heat and mass transfer rates are found to be significant. A new bistability phenomenon arises when the onset of subcritical convection is shifted close to or beyond the threshold of supercritical convection, whether heating or cooling isothermally or upon applying constant heat and solute fluxes, regardless of the enclosure aspect ratio value. It is demonstrated, on the basis of linear stability theory, that the form drag parameter has a stabilizing effect and considerably affects the threshold for Hopf bifurcation, $R_{TC}^{Hopf}$, which characterizes the transition from steady to unsteady convection. In the range of governing parameters considered in this study, the heat, solute and flow characteristics predicted by the analytical model are found to agree well with the numerical study of the full governing equations.

Three-dimensional tomography of single charge inside dielectric materials using electrostatic force microscopy

2012 ◽  
Vol 1421 ◽  
Author(s):  
Clement Riedel ◽  
Richard Arinero ◽  
Angel Alegria ◽  
Juan Colmenero ◽  
Juan Jose Saenz
Keyword(s):  
Numerical Study ◽  
Electrostatic Force ◽  
Three Dimensional ◽  
Main Idea ◽  
Dielectric Materials ◽  
Electrostatic Force Microscopy ◽  
Reconstruction Algorithms ◽  
Force Microscopy ◽  
Atomic Force ◽  
Buried Object

ABSTRACTIn this contribution, we report on a numerical study demonstrating how to realize Electrostatic Force Microscopy (EFM) tomography. Based on the Equivalent Charge Method, both force and force gradient between a buried object (or trapped charges) and the Atomic Force Microscope tip are calculated. The main idea is to scan the sample at different tip sample distances and obtain the position and charge value of the object using reconstruction algorithms. The quantitative analysis here presented is a first step toward tomography for samples presenting “dilute” point charges creating non correlated signals by the interpretation of EFM signals. Lateral resolution, sensitivity (i.e. ability to detect an object), performance and limitations of EFM are also discussed in the paper.

scholarly journals Numerical simulations and experiments on droplet coalescence dynamics over a liquid–air interface: mechanism and effect of droplet-size/surface-tension

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Javed Shaikh ◽  
Nagesh D. Patil ◽  
Atul Sharma ◽  
Rajneesh Bhardwaj
Keyword(s):  
Surface Tension ◽  
Excellent Agreement ◽  
Numerical Study ◽  
Droplet Diameter ◽  
Bond Number ◽  
Liquid System ◽  
Critical Values ◽  
Surface Tension Coefficient ◽  
Droplet Coalescence ◽  
Partial Coalescence

AbstractPresent study is on partial/complete coalescence dynamics of a droplet (surrounded by air) over a horizontal pool of the same liquid. Experimental and numerical studies are presented for both isopropanol and glycerol droplet of a constant diameter. Numerical study is presented in more detail for the isopropanol droplet to study the effect of diameter ($$D=0.035-6.7 mm$$ D = 0.035 - 6.7 m m ) and surface tension coefficient ($$\gamma =2-200 mN/m$$ γ = 2 - 200 m N / m ) on the coalescence dynamics. For partial coalescence of an isopropanol droplet and complete coalescence of a glycerol droplet, excellent agreement is demonstrated between our numerically and experimentally obtained interface dynamics; and a qualitative discussion on the mechanism of the partial and complete coalescence is presented. Three regimes of partial coalescence − viscous, inertio-capillary and gravity − proposed in the literature for a liquid-liquid system are presented here for the present liquid-air system while studying the effect of diameter of the isopropanol droplet. Probably for the first time in the literature, our numerical study presents a flow and vorticity dynamics based quantitativeevidence of the coalescence-mechanism, analogy with a freely vibrating Spring-Mass-Damper System, the gravity regime for a liquid-gas system, and the effect of surface tension coefficient $$\gamma$$ γ based coalescence dynamics study. The associated novel $$\gamma$$ γ based droplet coalescence regime map presents a critical Ohnesorge number $$Oh_{c}$$ O h c and critical Bond number $$Bo_{c}$$ B o c for a transition from partial to full coalescence; and such critical values are also presented for the transition under effect of the droplet diameter. The critical values based transition boundaries, obtained separately for the varying D and varying $$\gamma$$ γ , are demonstrated to be in excellent agreement with a correlation reported in the literature.

Preparation and Characterization of Nanometer-scale Polycarbonate Fibers: Bead Formation

2002 ◽  
Vol 736 ◽  
Author(s):  
Jamila Shawon ◽  
Changmo Sung
Keyword(s):  
Surface Tension ◽  
Electron Microscope ◽  
Liquid Droplet ◽  
Electrostatic Force ◽  
Research Work ◽  
Nanometer Scale ◽  
Solvent Mixtures ◽  
Bead Formation ◽  
Small Pore ◽  
Electrically Charged

ABSTRACTElectrospinning is a superior process compared to other conventional spinning methods for the production of fibers in the sub-micron to nanometer scales. Such fiber membranes have exceptionally large surface areas and small pore sizes. The process requires an electrostatic force, which induces charges on the liquid droplet of the polymer solution or melts and therefore overcomes the surface tension and viscoelasticity forces to create an electrically charged jet. When the jet dries or solidifies, an electrically charged fiber remains, which can be directed or accelerated by the electrical forces and then collected in non-woven fiber membrane or other useful shapes. The present research work demonstrates the electrospinning of polycarbonate solution with solvent mixtures THF (Tetrahydrofuran) and DMF (Di-methyl formamide) to produce nanometer scale polycarbonate fibers. The solvent mixture of THF and DMF was the major parameter for producing nano-polycarbonate fibers along with the formation of byproducts beads. The electrostatic voltage, viscosity and surface tension also showed significant effect on bead formation and bead density. The microstructures of the polycarbonate beads were quantitvely investigated by Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM).

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