Tip Deflection and Blocking Force of Soft PZT-Based Cantilever RAINBOW Actuators

A piezoelectric/electrostrictive RAINBOW actuator is a monolithic bending device consisting of an electromechanically active layer and a reduced passive layer formed in a high-temperature reduction treatment. When the piezoelectric or electrostrictive layer is driven under an electric field or when the environmental temperature changes, bending deflection is produced because of the constraint of the reduced inactive layer or because of the thermal expansion coefficient difference of the two layers. In this study, general analytical expressions relating tip deflection, blocking force, and equivalent moment with an applied electric field and temperature change are derived for a cantilevered RAINBOW actuator. It is shown that optimal actuator performance can be achieved in the RAINBOW actuator by choosing a suitable thickness ratio of the reduced layer to the PZT layer. A series of RAINBOW cantilever actuators have been experimentally prepared from high-density, soft, lead zirconate titanate (PZT) ceramics. Different reduction layer thickness is obtained by adjusting the processing parameters, such as reduction temperature and time. The measured results on tip deflection and blocking force agree well with theoretical prediction under a weak electric field. However, when a high driving electric field is used, deviation is observed, which can be attributed to a nonlinear piezoelectric response and a nonlinear elastic behavior associated with soft PZT materials under high driving electric fields.     

非均匀电场作用下汽泡的行为

为进一步探索电场强化沸腾换热的机理,利用高速摄像仪对沸腾汽泡在非均匀电场作用下的生长过程进行了可视化实验研究,实验观察到非均匀电场作用下汽泡脱离壁面时的形态。当没有施加高压电场时,汽泡脱离壁面时基本上呈球形形状;而外加电场后,汽泡脱离壁面时呈椭球状,而且随着场强的升高,汽泡脱离壁面时汽泡沿场强方向的伸长更加明显。这是由于未加电场时,汽泡的长大主要受惯性力和表面张力的支配。外加电场后,汽泡的受力增加了电场力的作用,电应力在赤道方向压缩汽泡,在极轴方向拉伸汽泡。在电场作用下,汽泡由近似球形形状变成了椭球形形状。随着场强的增大,汽泡所受的电应力加大,使得汽泡脱离壁面时沿场强方向的伸长更加显著。施加电压后,汽泡脱离频率随着场强的增大而增大,当电场强度为1.4 kV/mm时,汽泡的脱离频率为不加电压时的1.85倍。研究结果表明,电场对汽泡的行为有显著的影响作用。     

Movement of dispersed droplets of W/O emulsion in a uniform DC electrostatic field:Simulation on droplet coalescence☆

Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as wel as its distribution, local concentration distribution and droplet size-velocity relation with the applied time of electric field. The sim-ulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence.     

Numerical Study of the Collision and Coalescence of Water Droplets in an Electric Field

The coalescence of binary water droplets in oil exposed to an external electric field is simulated using a model including both electrostatic and hydrodynamic sections. Available mathematical models for electric dipole‐dipole force are presented in the first part of the model. Volume of Fluid approach is applied in the second part of the model. The simulation results were in good agreement with the published experimental observations. The results indicated that an improvement in electrocoalescence speed could be achieved. It was also revealed that the skew angle of the electric field, the oil viscosity, and the initial drops distance influence the electrocoalescence. Moreover, a correlation was developed to predict electrocoalescence kinetic as a function of the participant parameters.     

Electrocoalescence of binary water droplets falling in oil: Experimental study

The approaching movement and consequent coalescence of binary water droplets falling in stagnant oil and exposed to an external electric field are investigated using a high speed camera. Different situation of the droplets and electric field intensities are applied in the experiments. The qualitative results of the experimental observations are exhibited through the scaled images of the binary droplets snapshots in milliseconds. Furthermore, different approaching trends of the droplets are presented as quantitative plots and discussed based on the theoretical electrostatic and hydrodynamic models. The effect of the applied voltage amplitude, initial distance of the drop pair, and skew angle of the electric field are investigated. The experimental results prove the electrostatic theories; as acceleration in electrocoalescence demonstrated using a stronger electric field as well as closer distance between the droplets. It was also revealed that the skew angle of the electric field decelerates the electrocoalescence until alignment of the droplets.     

The effect of van der Waals and charge induced forces on bed modulus of elasticity in ac/dc electrofluidized beds of fine powders—a unified theory

Perturbation theory is applied to an ac electrofluidzed bed of fine powder (glass and FCC) using electric field bubble control to infer the relation between interparticle forces (microscale) and the bulk bed modulus of elasticity (macroscale). Electrostatically induced and permanent van der Waals forces are modeled in a unified theory with bulk fluidized bed behavior. The extrapolation of the electric field to zero strength gives the permanent bed force and bulk bed modulus of elasticity as limiting cases. The resulting equations involve atomic as well as macros-scale parameters. The charge induced forces are identified through the bed modulus of elasticity as a function of the applied electric field strength. The semi-empirical approach is based on the principle that the conservation equations for the perturbed fluidized bed become unstable at the onset of bubbling giving characteristic eigenvalues for the bed modulus, a condition that is readily identifiable experimentally. Eigenvalues from the one-dimensional linearized conservation equations for the fluidized state are examined for growth, neutrality, or decay from the perturbation, which together with bed data are evaluated at bubbling conditions to give the bed modulus of elasticity. Both Richardson-Zaki and Carman-Kozeny bed expansion models of fluidization are examined. The former approach is found to give self-consistent results in which the bed modulus varies linearly with the electric field strength. The results are extended to dc beds as a limiting case of zero field frequency.The modulus of elasticity (a macroscopic bed property) is finally related to particle charge separation at the particle level through an interparticle force model applicable to ac-dc electric fields.     

Nonvolatile-memory current characteristics of BiFeO3 nanodots switched by applying external bias and force

In the domain structure of ferroelectric materials, the directions of polarization are diverse and uniformly separated, and the current flows along the domain wall due to the domain wall's relatively low bandgap. To control the ferroelectric domain structure of ferroelectric materials, it is possible to apply not only an external electric field but also a flexoelectric field, which is externally applied by an external force. In this study, we controlled the domain structure of BiFeO₃ nanodots using an external electric field as well as a flexoelectric field, and these BiFeO₃ nanodots showed changes in resistance depending on the domain structure and domain wall. The formation of domain walls in BiFeO₃ nanodots caused relatively low-resistance states, whereas when domain walls were removed, BiFeO₃ nanodots showed high-resistance states. The experimental results show that nonvolatile memory devices can be applied by controlling the domain wall in BiFeO₃ nanodots.     

脉冲电场强度及频率对乳化液脱水的影响

为提高油田原油脱水处理效率,保证脱水电场的稳定性,满足陆上及海上石油处理设备紧凑、高效的技术要求,开展了脉冲电场下电场强度和频率对乳化液脱水效果影响的研究;通过水滴伸缩模型的建立,分析了水滴在电场作用下的受力情况,推导得出水滴形变量与电场强度的关系式;建立水滴振动动力学模型,分析水滴振动时的受力情况,得出水滴共振时外施电场频率的表达式,从理论上给出了最佳脱水频率的选择方法.研究结果表明,乳化液脱水过程中存在最佳脱水电场强度和最佳脱水频率.随着外施电场强度增加,脱水率逐渐升高,当外施电场强度超过水滴临界破裂电场强度时,脱水率有所下降,且脱水电场不稳定;当外施电场频率使水滴达到共振时,水滴振幅最大、脱水效果最好.     

Some theoretical aspects of the electrophoretic sedimentation of particles

This paper concerns the theoretical interpretation of the results of a previous experimental study of the sedimentation of oxidized fine aluminum and iron particles in waste kerosene under the influence of an electric field. Following the Kynch analysis of the mode of gravity sedimentation, a modified particle volume flux is introduced to compensate for the effect of the electric field strength. It is shown that if the local electric field strength at the settling interface is used as the true driving force for electrophoretic sedimentation, the settling curves can be predicted with reasonable accuracy, provided that electrical heating effects and consequent temperature changes in the system are taken into account.Some theoretical aspects of the effects of dielectric polarization on settling are also discussed and illustrated qualitatively by the experimental data. Finally, some of the factors which might be expected to affect the energy efficiency of a particle separator operating by electrophoretic sedimentation are considered.     

低电导率工质中气泡的极化运动实验研究

为探讨电场作用下气泡在低电导率工质中的极化运动特性,采用高速数码摄像技术对气泡在正庚烷溶液中的生长和分散过程进行了可视化研究,并结合无量纲数分析了不同气体流量和施加电压下的气泡演变特征以及极化力主导的气泡运动规律。结果表明,增大电场强度可导致气泡生长周期缩短,气泡尺寸显著减小,产生频率加快。在低电场强度下,气泡运动主要表现为流体动力学特性;而在强电场作用下,气泡首先受极化力主导而表现为电流体动力学特性,其直线轨迹高度随Bo_E增大而增大。但随着电场强度在竖直方向上的衰减以及液相阻力影响,气泡运动速度不断减小;当气泡脱离极化力主导区域后,其运动再次表现为流体动力学特性,受尾迹诱导和气泡间相互作用影响,气泡在竖直方向上沿毛细管轴向四周扩散。     

An Apparatus to Determine the Pull-Off Force of a Conducting Microparticle from a Charged Surface

A unique experimental apparatus has been developed to determine the pull-off force of a conducting microparticle resting on a conducting surface in the presence of a DC electric field. The apparatus precisely measures the applied electric-field strength at which an individual microparticle of known diameter, which is measured in situ, is removed from the surface. This information is used to determine the adhesion pull-off force required to remove the microparticle from the surface to within an uncertainty of approximately 12% at 95% confidence. In the experiment, the electric field strength between a conducting-surface electrode and a grounded electrode is increased in time using a microcontroller-driven digital-to-analog converter. Both electrodes are semi-transparent, which permits the surface-resident microparticles to be viewed from underneath the surface using microphotography. The microphotography system is operated in conjunction with pixel-intensity, gradient-search software to determine the diameter of each surface-resident microparticle. The apparatus is designed to explore a wide range of operating conditions, including microparticles of diverse composition and sizes, surfaces of differing roughness, and environments of various relative humidity including vacuum. The theory of operation and instrument design are presented in detail. Preliminary results also are given as a proof of concept.     

Non-coalescence behavior of neutral droplets suspended in oil under a direct current electric field

The excessive electric field gives rise to droplet non-coalescence and droplet chains in the electric dehydrator, which severely deteriorates oil–water separation efficiency and even leads to short circuit. To reveal the underlying mechanism of droplet non-coalescence, dynamic behavior of two neutral droplets in silicone oil under a direct current electric field is investigated by using high-speed photography. The experimental results show that there exists a critical electric field strength above which two droplets will bounce off after the contact. The critical electric field strength of droplet non-coalescence is affected by the initial separation distance between droplets, the radius of droplet, and the surfactant concentration. Whether the non-coalescence behavior occurs in the electric field is determined by the competition of electric force and capillary force, which dominates the evolution of tiny connection channel.     

协同场作用下钒离子在质子交换膜中的传质过程

研究了VO²⁺在Nafion117质子交换膜中的传质过程, 重点考察了不同操作工况下浓度场和电场的协同作用。定量了电场对钒离子透膜传质过程的影响大小, 并根据实验数据拟合出了VO²⁺在Nafion117膜中的表观电迁移率。结果表明:电场对高浓度电解液的离子透膜过程影响较大, 升高温度和增加电解液对流均强化了电场作用在钒离子透膜传质的影响, 加入的正向电场越强, 跨膜渗透越剧烈, 且电场因子随着时间的增加而增加。反向电场有利于缓解钒离子透膜传递过程。     

磁电复合场下正极钒离子的跨膜传质

探究了全钒液流电池在外加磁场、电场、磁电复合场下正极电解液中的钒离子在Nafion117膜上的跨膜传质过程,以及在磁电复合场下硫酸浓度和电解液添加剂对传质过程的影响。根据达西定律拟合得出相应的扩散传质系数。实验结果表明正向电场会加剧钒离子渗透,且当电场强度达到30 V·m^-1时渗透情况严重可达到无电场时的2.53倍。非匀强磁场的加入可明显降低钒离子的跨膜渗透性。且当外加磁场和电场复合场时,磁场对降低钒离子跨膜渗透的作用更加显著。实验还得出在不同的外加复合场中较高浓度硫酸有利于降低钒离子的跨膜渗透。此外丙三醇、木质素磺酸钠正极电解液添加剂的加入也降低了VO₂⁺的跨膜渗透性。     

Numerical simulation of microscopic motion and deposition of nanoparticles via electrodynamic focusing

A computational model was developed to simulate microscopic motion and deposition of charged aerosols during the nanoparticle patterning process utilizing electrodynamic focusing concept (Kim et al., 2006). Our computational model includes Brownian random force, Coulomb and image forces, fluid drag and van der Waals force for determining Lagrangian particle trajectories after solving electrostatic fields in the deposition chamber. Our results are in agreement with the previous experimental findings. The effects of operation parameters such as surface charge density, applied voltage and particle charges were investigated. It was found that the electric field-induced motion of particles dominated over Brownian random motion of 10 nm nanoparticles near the surface and the inertial motion of charged nanoparticles under high electric field would be important to determine the precise deposition pattern within submicrometer scale structures.     

Structure and properties of metal-free conductive tracks on polyethylene/multiwalled carbon nanotube composites as obtained by laser stimulated percolation

The fabrication and characterization of conductive tracks by laser irradiation on non-conductive multiwalled carbon nanotube/polyethylene (MWCNT/HDPE) composites is reported. Along the irradiated paths the percolation of MWCNTs is occurring, as demonstrated by field emission scanning electron and atomic force microscopies. An increment of the track conductivity of several orders of magnitude is documented by single pass Kelvin probe force and current sensing atomic force microscopies, together with electrical measurements. The structure of conductive paths has been estimated by secondary electron charge contrast imaging.The investigation has been developed from basic characterization up to industrial scale manufacturing. The method is fast, flexible and innovative, because: (i) highly adherent tracks of any selected pattern on a low cost material can be obtained, (ii) the tracks are metal-free, a fact rendering the composite fully recyclable and (iii) the irradiated materials have application for electrical signals transport; (iv) the tracks are also characterized by piezoresistive properties so allowing their employment as pressure sensors.     

Effects of an external electric field on the collection efficiency of air filters: Filtration mechanisms with an external e-field

An external electric field was applied on the filter to improve its collection efficiency, and the collection efficiencies of the different filters under various conditions were evaluated. Dominant electrical filtration mechanisms for each condition were investigated using experimental and theoretical approaches. Four types of air filters were used as test filters: a charged fiber filter, a low-grade filter with 50% collection efficiency in the most penetration particle size (MPPS) zone, and two high-grade filters with more than 95% collection efficiency in the MPPS zone. Three different particle charge states—neutralized, single-charged and uncharged—were considered. For neutralized particles, the external electric field led to a 14.5%p. and 2.5%p. increase in the collection efficiencies of the low-grade filter and charged fiber filter, respectively. With the electric field, the collection efficiency of the low-grade filter increased by 30%p. for single-charged particles. The electric field also affected the collection efficiencies of the charged filter and high-grade filters, but the effect was not significant. For uncharged particles, the electric field did not lead to a remarkable increase in the collection efficiencies of any of the filters. Through experimental and theoretical analysis, it was found that the polarization force imposed on the charged fiber was the dominant factor for the charged fiber filter regardless of application of the external electric field. The Coulombic force imposed on the electric field was the dominant factor for the low-grade filter, while both the Coulombic and the polarization forces affected the collection efficiency of the high-grade filter.

Copyright © 2017 American Association for Aerosol Research     

Separation of solid particles in liquid dielectrics

The basic stages of deriving the equations for the ponderomotive electric force in a non-uniform electric field are given. The electrical properties of liquid dielectrics and the calculated distribution of ponderomotive forces in hyperbolic and wedge-shaped electric fields are described. The results of measuring the ponderomotive forces in a quadrupole wedge-shaped field are presented. The permittivity of dielectric suspensions is computed and experimental results reviewed. Investigations of the permittivity of suspensions of ultrafine semi-conducting particles in a non-polar liquid are described and the results of measurements of the ponderomotive forces are analysed. Two numerical examples of DS are given; the permittivities and electric strengths of commercial separating dielectrics are estimated.     

电场强化乙酸乙酯自然对流和沸腾换热的实验研究

对沉浸于强极性有机液体工质乙酸乙酯中的平板表面上的自然对流和沸腾换热的外加电场强化进行了实验,得出了自然对流和沸腾换热的表面传热系数、强化效果与电场电压、热通量的关系.实验数据表明,外加电场对平板表面自然对流换热的强化效果好于对沸腾换热的强化效果.实验条件下,当施加外电场时,平板表面的自然对流换热的传热系数最大可达到无外电场时的6～7倍,沸腾换热的传热系数最大可达到无外电场时的4～5倍.     

A REVIEW OF THEORY AND EXPERIMENTS ON DIFFUSION FROM SUBMICROSCOPIC PARTICLES

Diffusion-controlled evaporation or growth of submicroscopic particles is considered theoretically and experimentally. The conditions for which Fick's law apply are elucidated for Knudsen aerosols, and Fick's law together with the Chapman-Enskog molecular theory of gases are applied to determine diffusivities and Lennard-Jones intermolecular force parameters from experimental data on single submicron aerosol evaporation. The experimental method involving light scattering from a single droplet suspended in an electric field is reviewed, and the results for diffusion-controlled and noncontinuum evaporation are presented. For Knudsen numbers greater than 0.05, where diffusion theory does not apply, evaporation rate data are compared with available theoretical and semi-theoretical equations. A recently published solution of the stationary Boltzmann equation, modified to include the collision integral, is shown to be in excellent agreement with our experimental data for dibutyl sebacate evaporating into nitrogen.