Negative corona discharge from a water droplet under the pulsating DC field

Corona discharge from a fine water droplet always involves deformation of the droplet shape or Taylor-cone formation, emission of fine water jets or disruption of droplet. Therefore, corona discharge from a water droplet always manifests complicated aspects. In addition, disruption of Taylor cone simultaneously affects not only discharge current but also motion of water droplet. To confirm corona discharge phenomena from a water droplet protruded from a tip of a metal capillary tube with a diameter of 1 mm, negative corona discharge was investigated by using a water droplet located at a tip of grounded rod electrode facing a ring electrode with positive dc voltage superimposed by ac one. Since the droplet has inherent resonant vibrating frequency defined by the size or volume, the volume of water droplet was adjusted at 20 nL where the corresponding resonant frequency was 500 Hz. The period of the event of successive corona discharge is exactly consistent with resonant frequency defined by the size of the water droplet. As a result, corona pulse trains with a definite duration appeared intermittently corresponding to its resonant vibration. When dc voltage superimposed by ac voltage with resonant frequency of 500 Hz was applied to the water droplet, corona pulse trains appeared at the period corresponding to the frequency. The maximum value of corona current reasonably increased with the applied voltage. Even when the frequency of ac field superimposed on dc field was varied from the resonant frequency, corona pulse trains occur corresponding to not only the superimposed field frequency but also resonant frequency.     

Thin liquid films on a slightly inclined heated plate

The behavior of a thin liquid film on a uniformly heated substrate is considered. When the substrate is horizontal and the Marangoni number sufficiently large the film breaks up into a periodic array of drops. When the substrate is slightly inclined this drop-like state slides down the substrate. The relation between these states is discussed and their stability properties with respect to longitudinal perturbations are determined. The results shed light on the multiplicity of states accessible to systems of this type and on the possible transitions among them.     

Evidence for droplet reorientation and interfacial charges in a polymer-dispersed liquid-crystal cell

We observe a new feature ( plateau), sandwiched between two exponentially decaying components, in the switching response of a polymer-dispersed liquid-crystal (PDLC) cell. Upon application of square-wave electrical pulses, the cell response exhibits a complex decay whose characteristics are significantly different within and outside the applied field. We interpret these results in terms of reorientation dynamics of nonspherical droplets in the PDLC. Irradiation of the PDLC with gamma rays induces significant changes in the cell response in a manner that is consistent with redistribution of charges at the liquid-crystal-polymer interface in the PDLC.     

两平行接地大导体板间线电荷的电场

利用复数坐标系z上的保角变换,计算长直线电荷在两平行接地大导体板之间的电势和场强分布.     

Neutrino oscillations in the field of a rotating deformed mass

The neutrino oscillations in the field of a rotating deformed mass is investigated. The phase shift is evaluated in the case of weak field limit, slow rotation and small deformation. To this aim the Hartle–Thorne metric is used, which is an approximate solution of the vacuum Einstein equations accurate to second order in the rotation parameter a/M$a/M$ and to first order in the mass quadrupole moment q. Implications on atmospheric, solar and astrophysical neutrinos are discussed.     

Effect of a magnetic field on the damping of oscillations in deformed nickel and iron

A study was made of the effect of a magnetic field on the restoration of internal friction in polycrystalline nickel after brief plastic torsional deformation. The experimental results can be explained in terms of a redistribution of the ferromagnetic and nonferromagnetic internal-friction components in the magnetic field and in terms of a relaxation of the elastic stress which accompanies the inhomogeneous plastic deformation during the restoration of the domain structure.     

Analytical solution of the scalar wave equation for slightly deformed optical Bragg waveguide

Using a simple analytical method, we study the electromagnetic-wave propagation in an optical Bragg waveguide which is slightly deformed at one side. We show the results of computations in the form of dispersion curves and provide a comparison with standard circular Bragg waveguides and step-index circular waveguides. We show that the correspondence between the cutoff V values for the standard step-index fiber and the new Bragg waveguide, which is slightly flattened on one side, is quite close for the lowest mode under the weak guidance condition.     

液滴撞击孔口附近壁面运动过程的模拟研究

采用光滑粒子流体动力学(SPH)方法模拟了液滴撞击带孔壁面的问题, 提出了随计算区域变化的链表搜索法. 结合实验进一步研究了不同物理条件下黏性、重力和内部压应力波动对铺展过程中液滴在 孔口运动情况的影响, 详细分析了有限时间段内孔口断面处的压强变化. 结果表明: 液滴撞击表面后快速向两端铺展, 到达孔口上方时形成射流, 在极短暂时间内重力对射流的影响很小, 但是黏性会引起射流向孔内弯曲. 在内部压应力和惯性作用下射流下部产生有规律的波动, 使得孔口上方流体反复的膨胀和吸收将附近应力较高区域流体吸入孔内发生孔吸现象. 内部压应力是导致液滴被吸入孔内并撞击另一侧孔壁形成飞溅现象的主要原因, 模拟效果和实验结果符合良好. 关键词： 液滴 带孔壁面 光滑粒子流体动力学(SPH) 链表搜索法     

Numerical simulation of conductive particle behaviour at the surface of a plate electrode affected by a DC corona field

The electric field in certain electrostatic devices can be modeled by a grounded plate electrode affected by a corona discharge generated by a series of parallel wires connected to a DC high-voltage supply. The system of differential equations that describe the behaviour (i.e., charging and motion) of the conductive particle in such an electric field has been numerically solved, using several simplifying assumptions. Thus, it was possible to investigate the effect of various electrical and mechanical factors on the trajectories of conductive particles. This model has been employed to study the behaviour of coal particles in fly-ash corona separators.     

Investigation on dynamics of double emulsion droplet in a uniform electric field

Phase field method based on Cahn–Hilliard free energy formulation is adopted for predicting the behavior of double emulsion droplet suspended in a continuous phase under the influence of a uniform electric field. The role played by the inner droplet on the electric-field-driven fluid flow, and also on deformation of the outer droplet is predicted by present numerical simulation. Three different kind of deformation type of outer and inner droplet (prolate–oblate, prolate–prolate and oblate–prolate) has been observed. With increase in the volume fraction of inner drop, transition in the deformation of outer drop from prolate to oblate occurs at lower value of fluid permittivity ratio.     

平衡接触角对受热液滴在水平壁面上铺展特性的影响

壁面温度是影响壁面润湿性的重要外部条件. 为解决液滴铺展中三相接触线处应力集中问题, 已有研究多采用预置液膜假设, 但无法探究壁面温度对润湿性的影响. 本文针对受热液滴在固体壁面上的铺展过程, 基于润滑理论建立了演化模型, 通过数值模拟, 从平衡接触角角度分析了温度影响壁面润湿性及铺展过程的内部机理. 研究表明: 随温度梯度增大, 液滴所受Marangoni效应增强, 致使液滴向低温区的铺展速率加快; 铺展过程中, 位于高温区的接触线与液滴主体部分间形成一层薄液膜, 重力与热毛细力先后主导该区域的铺展; 当液-固或气-液界面张力对温度的敏感度高于另两个界面时, 低温区方向的平衡接触角不断增大, 使壁面润湿性恶化, 导致液滴铺展减慢; 而当气-固界面张力对温度的敏感度高于其他两个界面时, 低温区方向上的平衡接触角将减小, 由此改善壁面润湿性, 加快液滴铺展; 在温度影响壁面润湿性和液滴铺展过程中, 平衡接触角起关键作用.     

二维导体微粗糙面与其上方金属平板的复合电磁散射研究

研究了二维导体微粗糙面与其上方金属平板复合电磁散射特征.应用互易性原理使求解二次散射场简化为求解包含平板上的极化电流和微粗糙面散射场的积分方程，从而降低了求解难度.应用物理光学近似和微扰法分别求解了平板上的极化电流和粗糙面的电磁散射场，得到了复合散射截面计算公式并进行了数值计算.尤其对该复合模型后向耦合电磁散射结果进行了详细分析和讨论. 关键词： 互易性原理 复合电磁散射 微粗糙面 平板     

Bifurcations of the shape of a magnetic fluid droplet in a rotating magnetic field

An analysis is made of the behavior of a magnetic droplet suspended in a liquid in a high-frequency uniform, rotating magnetic field. In weak fields the droplet is spheroidal while in strong fields it is disk-shaped. The observed change in the shape of the droplet as the amplitude of the field increases depends on the magnetic permeability μ of the liquid and takes place according to three scenarios: (a) for small μ the spheroidal droplet is continuously converted into a disk; (b) for intermediate μ there is a range of fields in which the droplet becomes a triaxial ellipsoid with its major axis lying in the plane of the field, and spheroid-triaxial ellipsoid-disk transitions take place as a result of a soft bifurcation; (c) at high μ both transitions are hard. Theoretical calculations are made of the stability curve for the various droplet shapes. It is predicted that a change in the types of droplet shape bifurcations will occur in strong fields. A comparison is made with the experimental data.     

Numerical study on transient response of droplet deformation in a steady electric field

The transient response of droplet deformation in a steady electric field is investigated by the numerical simulation and the motion of interface is captured by level-set method. The numerical scheme is validated and found to be in good agreement with classic analytical solutions. The effects of electric field intensity, interfacial tension, oil viscosity and droplet size on the transient deformation process are systematically discussed. The numerical results show that electric field intensity can accelerate the deformation of the droplet, while interfacial tension and oil viscosity damp it. Furthermore, the relation between electric capillary number and dimensionless deformation time is obtained.