Analysis of the electrostatic force on a dielectric particle with partial charge distribution

This paper presents the analysis of the electrostatic force acting on a charged dielectric particle on a grounded plane. The force has been determined by a numerical field calculation method to make clear the effect of particle dielectric constant and charge distribution on the particle surface. The charge is treated to be distributed in three ways: (a) uniformly over entire surface, (b) partially on the upper, or (c) on the lower part of a particle. The calculation results show that, if a particle with dielectric constant ?_p = 3 is partially charged on the lower part by a zenith angle π/2, π/4 and π/8, the force shall be higher by 0.7, 4.3 and 20 times, respectively, than that for a uniform charging with the same charge amount. On the other hand, the force becomes weaker when charge is on the upper part. The effect of the particle dielectric constant is found to be dependent on the charge distribution. With charge uniform on the entire surface or on the upper part, the force always increases with the dielectric constant. However, when surface charge is restricted to a small area at the lower part of the particle (θ_q < π/4), the force may decrease with increasing the dielectric constant.     

A full 3D numerical model of the industrial electrostatic coating process for moving targets

In this paper, a full three dimensional FLUENT numerical model of the electrostatic coating process as used in the automotive industry is presented and selected parametric studies on the numerical model have been conducted. The model incorporates a moving mesh capability in order to simulate movements of the target. The target follows piecewise linear motion and the entire area of the target has been coated in multiple passes. All the dominant mechanical and electrical phenomena were taken into account and cases with both neutral and charged particles were examined. It was confirmed that the transfer efficiency increases when the electrical forces are present in the model and that the coating uniformity improves with the movement of the target. The deposition pattern corresponds to the motion of the target and gradually builds up in a cumulative manner. Due to the aggregation effect associated with the target movement, the deposition uniformity is dramatically improved.     

3D numerical model of the electrostatic coating process with moving objects using a moving mesh

In this paper, a full three dimensional FLUENT numerical model of the electrostatic coating process with the embedded moving mesh capability and piecewise linear type target motion is presented. The model includes target geometries that do not exhibit symmetry. All the dominant mechanical and electrical phenomena are taken into account. Mechanical phenomena include shaping air effects, downdraft effects and the motion of the polydispersed particles. Electrical phenomena include the particle space charge distribution, corona discharge and the electrohydrodynamic flow effects. It was demonstrated that the numerical model can accurately mimic the type of the motion used in real world applications.     

Numerical simulation of the electrostatic powder coating process with a corona spray gun

In this paper results of investigations are described aiming to numerically simulate the electrostatic powder coating process using an extended commercial computational fluid dynamics (CFD) code. The fully three-dimensional turbulent flow was calculated. Based on the Lagrangian approach the trajectories of the powder particles were modelled considering electric and aerodynamic forces. In the calculations of the particle propagation both the particle size distribution and the particle charge distribution obtained through experiments have been applied. The model accounts for the space charge effect of the charged particles and the turbulence dispersion on the particle trajectories. It was found that the space charge plays an important role for the final spray pattern shape, also increasing the transfer efficiency. The numerical results, such as velocity profiles, static and dynamic film thickness on the target were in good agreement with experiment.     

The influence of particle size on separation and dustiness in powder mixtures during nonelectrostatic and electrostatic coating

Common food powders and their mixtures, consisting of two powders with the same composition but different in particle size: fine (51–95 μm) and coarse (244–401 μm) NaCl, KCl, sucrose, rice starch, maltodextrin, whey protein, casein and soy protein, were coated on a target at 0 and −25 kV. Over half of the mixtures showed separation due to a difference in particle size. Separation was caused by the difference in individual transfer efficiency of the powders and interactions during coating. Both composition and differences in size were found to be important. Being in a mixture did not change the amount of dust formed.     

Density ratio effect on particle sedimentation in a vertical channel

A circular particle settling in a confined vertical channel with static fluid is investigated by lattice Boltzmann method, the effect of density ratio on the particle motion and flow pattern is discussed. It shows that the particle starting from an initial position off-center displays various moving modes accompanied by different flow patterns for 1.003 ≤ γ ≤ 5.0: when γ < 1.1, the particle is finally in a stable equilibrium near the centerline and settles uniformly with a symmetrical flow, but there are different modes before reaching the centerline at different density ratios, a monotonic approach appears at γ ≤ 1.005 and an transient overshoot appears at 1.005 < γ < 1.1; When γ = 1.1, a weak oscillation appears in the particle moving but the flow is almost symmetrical, it is in a critical state of the particle moving from stable equilibrium with a transient overshoot to oscillation; When 1.1 < γ ≤ 3.0, the particle oscillates regularly around the centerline with the uniform amplitude and frequency, and it turns into irregularity for γ > 3.0. Meanwhile the rotation of the particle depends on the distance from a wall; it rolls up the closer wall and stops at centerline.     

Diffraction enhancement effect and new possibilities of measuring the electric charge of the neutron and its inertial-to-gravitational mass ratio

Diffraction enhancement of small effects affecting a neutron undergoing Laue diffraction at Bragg angles θ _B close to 90° is predicted and experimentally observed. The enhancement is due to the delay of the neutron inside the crystal during diffraction and is proportional to tan² θ _B. As a result, the diffraction enhancement factor may be as large as ～10⁸–10⁹. On this basis, a new method is proposed for searching for the electric charge of the neutron and for measuring the ratio of its inertial mass m _i to the gravitational mass m _G . It is shown that the accuracy of the neutron charge measurement can be improved by more than two orders of magnitude in relation to the present-day accuracy and that the ratio m _i /m _G can be measured to an precision of σ(m _i /m _G ) ～ 10^?6.     

热对流条件下固液密度比对颗粒沉降运动影响的直接数值模拟

本文应用任意拉格朗日-欧拉(ALE)算法对固液两相流流场中考虑热对流的非等温颗粒在竖直通道中的沉降运动进行了数值模拟.在牛顿流体中通过积分黏性应力和压力获得颗粒的受力跟踪颗粒运动,使用有限元方法数值求解流场的N-S方程和能量方程,模型不需经验假设.通过模拟来研究颗粒沉降的运动规律和热对流下固液密度比对固液两相流的影响作用.结果表明随着固液密度比的增加,颗粒经历了稳定沉降、周期性摆动,不规则摆动等过程;热对流使颗粒的摆动幅度和沉降速度发生变化;热对流对颗粒的影响作用随着固液密度比的增加而减小.     

光学材料亚表面缺陷处强激光电磁场分布的3维模拟

利用时域有限差分法求解麦克斯韦旋度方程,研究了光学材料表面缺陷对入射激光场的调制作用,建立了亚表面缺陷的3维模型。以长方体表面缺陷为例,对缺陷附近的光场分布进行了3维数值计算,给出了电场强度3维分布图和缺陷不同尺寸时的最大电场强度。研究表明,相对于2维简化情况,3维表面缺陷对强激光电磁场的调制作用更加明显。     

Probability distribution of the ratio of consecutive level spacings in interacting particle systems

We study the probability distribution of the ratio of consecutive level spacings for embedded one- plus two-body random matrix ensembles with and without spin degree of freedom and for both fermion and boson systems. The agreement between the numerical results and the recently derived analytic form for the distribution and other related quantities is found to be close. This establishes that the statistics of quotients of successive spacings, which do not depend on unfolding, is useful tool in the analysis of local level fluctuations in many-particle systems.     

光学材料亚表面缺陷处强激光电磁场分布的3维模拟

 利用时域有限差分法求解麦克斯韦旋度方程,研究了光学材料表面缺陷对入射激光场的调制作用,建立了亚表面缺陷的3维模型。以长方体表面缺陷为例,对缺陷附近的光场分布进行了3维数值计算,给出了电场强度3维分布图和缺陷不同尺寸时的最大电场强度。研究表明,相对于2维简化情况,3维表面缺陷对强激光电磁场的调制作用更加明显。     

Systematics of charge distribution studies in low-energy fission of actinides

Charge distribution studies were carried out in the thermal neutron-induced fission of ²²⁹Th, ²⁴¹Pu and ²⁴⁵Cm as well as in the spontaneous fission of ²⁵²Cf. The width parameter (σ_z/σ_A), the most probable charge/mass (Z_p/A_p) and the charge polarization (ΔZ) as a function of fragment mass were deduced. The slope of charge polarization as a function of fragment mass [δ(ΔZ)/δA′], average charge dispersion parameter (〈σ_z〉) and proton odd-even effect (δ_p) were also obtained for these fissioning systems. These data along with the literature data for even-Z fissioning systems such as ²³³Th¹, ²³³U¹, ²³⁴U¹, ²³⁶U¹, ²³⁹U¹, ²³⁹Pu¹, ²⁴⁰Pu¹ and ²⁵⁰Cf¹ are discussed in terms of nuclear-structure effects and dynamics of descent from saddle point to the point of neck formation and from the formation of the neck to the scission point.     

Analytical method for computing the electrostatic field distribution in the reflector of the time-of-flight mass spectrometer

The method of analytical calculation of a nonlinear electrostatic mirror of the time-of-flight mass spectrometer and the numerical method of computation of a nonlinear mirror are analyzed. We present the results of simulating of the devices with nonlinear focusing mirrors, which are calculated analytically and by the numerical method, and of the device with a linear reflectron. It is concluded on the basis of the results of simulation that the proposed analytical method for calculating a nonlinear electrostatic mirror of the time-of-flight mass spectrometer is much better than the existing numerical method.     

Stochastic motion of the untrapped particle in electrostatic mode

The stochastic energy diffusion of the untrapped particle in the electrostatic mode is investigated analytically. We find that the equilibrium electrostatic field of periodical structure plays the same role as the usual focusing magnetic field to lead the test particle to stochastic motion. The resonance overlapping criterion for the random state is given, and also the Fokker-Planek-Kohnogorov approach to diffusion is considered for our system.     

Stochastic motion of the untrapped particle in electrostatic mode

The stochastic energy diffusion of the untrapped particle in the electrostatic mode is investigated analytically.We find that the equilibrium electrostatic field of periodical structure plays the same role as the usual focusing magnetic field to lead the test particle to stochastic motion.The resonance overlapping criterion for the random state is given,and also the Fokker-Planck-Kolmogorov approach to diffusion is considered for our system.     

Numerical research on effect of overlap ratio on thermal-stress behaviors of the high-speed laser cladding coating

High-speed laser cladding technology, a kind of surface technology to improve the wear-resistance and corrosion-resistance of mechanical parts, has the characterizations of fast scan speed, high powder utilization rate, and high cladding efficiency. However, its thermal-stress evolution process is very complex, which has a great influence on the residual stress and deformation. In the paper, the numerical models for the high-speed laser cladding coatings with overlap ratios of 10%,30%, and 50% are developed to investigate the influence rules of overlap ratio on the thermal-stress evolution, as well as the residual stresses and deformations. Results show that the heat accumulation can reheat and preheat the adjacent track coating and substrate, resulting in stress release of the previous track coating and decreased longitudinal stress peak of the next track coating. With the overlap ratio increasing, the heat accumulation and the corresponding maximum residual stress position tend to locate in the center of the cladding coating, where the coating has a high crack susceptibility. For a small overlap ratio of 10%, there are abrupt stress changes from tensile stress to compressive stress at the lap joint, due to insufficient input energy in the position. Increasing the overlap ratio can alleviate the abrupt stress change and reduce the residual deformation but increase the average residual stress and enlarge the hardening depth. This study reveals the mechanism of thermal-stress evolution, and provides a theoretical basis for improving the coating quality.     

An experimental study on the characterization of electric charge in electrostatic dust removal

Automatic dust removal using the electrostatic forces of electrodynamic screen (EDS) is an emerging method for mitigation of energy yield losses caused by dust accumulation on solar collectors. Both electric field distribution and dust particles' charge acquired during the removal process play pivotal roles in thorough evaluation of EDS performance. Previous studies have comprehensively analyzed the electric field distribution in EDS. In this paper we have conducted a number of experiments to examine how two EDS design parameters, electrode width and inter-electrode spacing, and two operational parameters, applied voltage and relative humidity, affect dust particles' charge. Sixteen EDS prototypes in two sets were developed and tested in a laboratory environment to study the acquired charge by dust particles via charge-to-mass ratio measurements. It has been shown that the charge-to-mass ratio is directly affected by the electric field intensity on an EDS surface. Furthermore, we have shown the detrimental impact of relative humidity on EDS performance. The results are advantageous in the evaluation of EDS design and its optimization to attain maximum dust removal efficiency.     

Electric ignition energy evaluation and the energy distribution structure of energy released in electrostatic discharge process

Ignition energy is one of the important parameters of flammable materials, and evaluating ignition energy precisely is essential to the safety of process industry and combustion science and technology. By using electric spark discharge test system, a series of electric spark discharge experiments were conducted with the capacitor-stored energy in the range of 10 J, 100 J, and 1000 J, respectively. The evaluation method for energy consumed by electric spark, wire, and switch during capacitor discharge process has been studied respectively. The resistance of wire, switch, and plasma between electrodes has been evaluated by different methods and an optimized evaluation method has been obtained. The electric energy consumed by wire, electric switch, and electric spark-induced plasma between electrodes were obtained and the energy structure of capacitor-released energy was analyzed. The dynamic process and the characteristic parameters(the maximum power, duration of discharge process) of electric spark discharge process have been analyzed. Experimental results showed that, electric spark-consumed energy only accounts for 8%–14% of the capacitor-released energy. With the increase of capacitor-released energy, the duration of discharge process becomes longer, and the energy of plasma accounts for more in the capacitor-released energy. The power of electric spark varies with time as a damped sinusoids function and the period and the maximum value increase with the capacitor-released energy.