Motion Of Metallic Particles Research Articles

Induced-charge electrophoresis of a tilted metal nanowire near an insulating wall.

Electric fields are commonly used to control the orientation and motion of microscopic metal particles in aqueous suspensions. For example, metallodielectric Janus spheres are propelled by the induced-charge electro-osmotic flow occurring on their metallic side, the most common case in electrokinetics of exploiting symmetry breaking of surface properties for achieving net particle motion. In this work, we demonstrate that a homogeneous metal rod can translate parallel to a dielectric wall as a result of the hydrodynamic wall-particle interaction arising from the induced-charge electro-osmosis on the rod surface. The applied electric field could be either dc or low-frequency ac. The only requirement for a nonvanishing particle velocity is that the axis of the rod be inclined with respect to the wall, i.e., it cannot be neither parallel nor perpendicular. We show numerical results of the rod velocity as a function of rod orientation and distance to the wall. The maximum particle velocity is found for an orientation of between ∼30^{∘} and ∼50^{∘}, depending on the position and aspect ratio of the cylinder. Particle velocities of up to tens of µm/s are predicted for typical conditions in electrokinetic experiments.

Simulation Analysis of Metallic Particles Movement in Typical Structure of Oil-immersed Power Transformer

The insulation performance of oil-immersed power transformers is closely involved with the movement of metal particle impurities, and the movement characteristics of metal particles are not only influenced by the electric field, but also by the oil flow. In this paper, a solid-liquid two-phase flow simulation model was constructed, and the effect of electric field on the motion of metal particles was considered. Firstly, the validity of the simulation model was verified by using the experimentally observed motion of metal particles in the horizontal oil channel between parallel flat plate electrodes, based on which the motion of metal particles in the typical oil channels of a 500kV power transformer was studied. It was found that when the metal particles passed through the oil flow inlet, the number of metal particles settling increased with the increase of particle size. All the metal particles with 1mm particle size sank in the oil flow inlet during the oil migration process, it was almost impossible to enter the low, medium and high voltage winding parts. Through the middle or upper end of the high voltage winding, the smaller particles (50μm, 150μm) would easily migrate with the oil flow and move faster; the larger particles (500μm) would move slower or be more easily deposited. This research holds significant practical implications in the engineering study of metal particle motion distribution within transformers.

Motion characteristics and distribution of metal particles in insulating oil under DC voltage

Studying the dynamic behavior of metal particles in insulating oil in case of flow-electric field coupling is important to fully understand the insulation mechanism in transformers, such as partial discharge and insulation deterioration of contaminated insulating oil. In this paper, through experiments, the particle image velocimetry (PIV) technique is applied to study the motion of metal particles in the oil flow under direct current (DC) electric field. According to the observation results of flow field, the effects of voltage level, electric field non-uniformity, and oil flow velocity on the motion and distribution of particles are analyzed in detail. The obtained results show that the applied voltage has an obvious effect on the motion of metal particles in oil flow, and it causes the formation of wavy trajectories of particles, where such effect becomes more obvious as the voltage level increases. Moreover, it is observed that the increase of flow velocity can weaken the influence of electric field, and the electric field non-uniformity affects the trajectory of particles mainly by changing their velocity component in the vertical direction. In addition, the concentration of particles group in the oil flow is sensitive to the external electric field, where the concentration decreases with the increasing electric field. Certainly, the results reported herein are effective in further revealing the effect of impurity particles on the insulating oil.

Trap Parameters Optimization Based on Metal Particle Dynamic Simulation Method

Insulation failure usually occurs in AC gas-insulated transmission (AC GIL) in field operation, in which the primary cause is the charged motion of metal particles in the electric filed. At present, the particle inhibition method applied is to design particle traps on the inner wall of the GIL shell. However, due to the large randomness of the charged motion for metallic particles and the limitations of field test methods, a particle trap has not yet been designed from the perspective of particle trapping effectiveness. In this paper, firstly, referring to the size of a running 252 kV AC GIL, a 1:1 scaled 3-D similarity simulation model is established to obtain the dynamic characteristics of particles with different sizes under the operating voltage level. This model can form symmetry between the real equipment, and its simulated simulation trajectory can achieve symmetry with the actual one. Secondly, an experimental platform that can easily capture the motion of the particles is set up to experimentally verify the symmetry between the field operating equipment and the simulation model. Finally, the particle traps are set on both sides of the concave and convex surface of the basin insulator, and an optimization scheme for the design of the particle trap is proposed from three aspects: the electric field regulation of the trap, the captured probability of particles, and the trap location. The proposed research shows that, with respect to the motion characteristics of the particles, this paper selects circular hole-shaped trap and its thickness, slot spacing, and slot width are 10 mm, 6 mm, and 8 mm, respectively. When the traps are arranged, one at the bottom of the shell at 70 mm and 80 mm from each side of the concave and convex insulator, the capture probability of the traps on both sides can be as high as 78% and 70%, respectively. Therefore, the analysis and optimization method in this paper has important reference value according to similarity concepts for optimizing particle traps in AC GIL at a certain voltage level.

Metallic Particle Motion and Breakdown at AC Voltages in CO2/O2 and SF6

This study deals with gaseous insulation contaminated by free moving particles. Two gases were investigated: SF6 (0.45 MPa) and a CO2/O2 gas mixture (0.75 MPa). Video recordings were used to track a free particle moving between a plate and a Rogowski electrode for validation of a 1D particle motion model. The effect of fixed and free particles (4 or 8 mm, Ø 0.9 mm) on the breakdown voltage and the mean time between breakdowns was determined in a concentric set of electrodes. The value of the breakdown voltage for a free particle was between those of a particle fixed to the enclosure and the central electrode. The particle motion in the concentric case could not be observed in the experimental set-up and was therefore simulated using a 1D model. For the 4 mm free particle, the breakdown seemed to be initiated in the inter-electrode gap in CO2 and at the crossing in SF6, while for the 8 mm particle, breakdown occurred at lift-off in both gases. A parameter k describing the width of the time to breakdown distribution was introduced. A low value of k was associated with the breakdown from the particles at the electrodes, while k was larger than 10 when the breakdown was decided during particle flight.

Modeling the trajectory of motion of metallic and abrasive particles in a washing gutter

Thousands of tons of metal-containing sludge are produced every month at machine-building, especially bearing producing and metallurgy enterprises where is processed. In the production of bearings, up to 10.0 thousand tons of sludge containing up to 90 % of the metal fraction is produced annually. At present, the sludge is practically nonrecyclable and brought to landfills degrading the environment. To increase the uniformity of metal powder at the stage of sludge washing, it is necessary to separate the solid articles by their density. To solve this issue, a comprehensive system of environmentally friendly technology is used for reclaiming the grinding sludge where in the process of movement of the sludge particles in a flow of detergent solution, their washing and separation by density take place. The study of the trajectory of motion of solid sludge particles makes it possible to set the mode parameters of the gutter which provide effective separation of particles by density. This enables determining the height of separator installation in the solution flow and obtaining a larger percentage of homogeneous metal particles. The main parameters of the washing gutter which can ensure effective separation of metal and abrasive particles include length and width of the gutter, level of the solution flow, flow rate of the solution, flow rate of fluid through the sidewall of the gutter, flow rate of solution through nozzles, number of nozzles and distance between them. Based on theoretical studies and a mathematical model describing the motion of metallic and abrasive particles in a detergent solution, a program in the C++ language and in the C++ Builder 6 programming environment was developed. The developed program makes it possible to simulate trajectories of motion of metal and abrasive particles in the detergent solution flow in the gutter. In the mode of random particle parameters, diameter in a range of 18–500 μm for metal particles and in a range of 31–200 μm for abrasive particles is selected

Recycling of Dispersed Metal Wastes in Rotary Furnaces

The recycling of dispersed metal containing wastes is a considerable problem, as their accumulation in dumps today is commensurate with the volume of ore extraction. Several methods and technologies are developed to recycle metal containing wastes but almost all of them require the preliminary preparation of wastes resulting in an increased price of the recycled metals. Furthermore, it is especially difficult to recycle dispersed multicomponent wastes and, therefore, the problem of developing effective, flexible and reliable technology for recycling of dispersed metal containing wastes is still a pressing one. The article presents an alternative method of recycling dispersed iron-containing wastes based on a continuous solid-liquid process of iron oxides reduction in rotary tilting furnaces (RTF). The new method allows the processing of waste of almost any composition and state: from metal lumps to oxide and multicomponent (chips, scale, sludge, etc.) wastes, contaminated with moisture, oils, organic impurities without their preliminary preparation (cleaning, homogenization, pelletizing, etc.). The result of recycling is the production of cast iron or steel ingots or required casting alloys. Some features of technology are considered, including the gas flow and motion of charge metal particles within the RTF. Process parameters providing high metal output are established.

Motion and discharge characteristics of metal particles existing in GIS under DC voltage

Free particles formed in the discharge process or equipment aging severely threaten the operation security of GIS, which draws great attention of researchers. However, seldom research focuses on disc-type particle, which is the majority of shaped particles in practical GIS. In this paper, an elliptic coordination system is built for obtaining the theoretical lift-off electric field of disc-type particles, and experimental system and observation system are established for studying motion behavior and discharge characteristics of metal particles. Results show that for spherical particles, while the distance between two particles d<9rs, the downward force caused by impurities on electrodes can be neglected; for wire-type particles, as lengths of particles increase, lift-off electric fields and probabilities of Firefly tend to be larger. Besides, lift-off electric fields grow exponentially with the increases of radius. When length of particle exceeds 3 mm, the gap between practical values and theoretical values becomes larger with the decrease of radiuses; for disc-type particles, with the increase of radiuses, dispersions of lift-off electric field becomes larger; the difference between practical and theoretical values broadens with the fall of radiuses. Besides, lift-off electric fields of disc-type particles are higher than that of wire-type particles with same qualities and with the increase of radius, probabilities of Firefly increase in an unapparent speed in comparison to wire-type particles; in the end, discharge processes in SF6 gap are illustrated. When particles are close to the bottom electrode, the lower end of particles will breakdown first. Then the top end of particles will form streamer discharge. With the continuous development of streamer, the gap will eventually breakdown.

Study on insulation characteristics of GIS under combined voltage of DC and lightning impulse

Operating experience shows that residual DC voltage remains in GIS bus bar for a long time after opening of disconnectors. This DC voltage will not only cause accumulation of charges and contaminants on the insulator surface, but will also easily lead to motion of free metallic particles in SF6 gas gap, weakening the insulation ability of GIS. At the time of disconnectors reclosing, impulse voltage could be generated in the bus bar and superimpose on the pre-existing DC voltage. As a result, GIS will be under combined voltage of DC and impulse. This paper experimentally studies the insulation characteristics of GIS under combined voltage of DC and lightning impulse. It is found that, for non-contaminated insulators, when DC and LI voltage are of the same polarity, flashover voltage under combined voltage is nearly the same as the flashover voltage under LI alone. However, when they are of the opposite polarity, flashover voltage decreases with increasing DC voltage. In cases there are metallic particle or powder around insulator, pre-stressed DC voltage will cause adhesion of contaminants on the insulator surface and lead to decrease of flashover voltage. Specially, for the particle-contaminated insulator, it is found that the surface charge accumulation caused by DC voltage will have big influence on the flashover voltage, and the most critical condition is when DC and LI voltage are of the opposite polarity. In addition, the breakdown characteristics of SF6 gas gap with free metallic particle are investigated. It is found that under pre-stressed DC voltage, particle will do standing motion or bouncing motion. And breakdown voltage becomes lowest when particle is doing standing motion. The results of the experiments show that residual DC voltage in GIS could deteriorate its insulation ability and the combined voltage of DC and impulse is found to be a critical condition for GIS insulation. Moreover, the combined voltage is shown to be more sensitive to detect some insulation defects in GIS than applying impulse voltage alone, especially for free metallic particles, which are commonly found in GIS but up to now no effective detection method is proposed. Therefore combined voltage of DC and impulse could be considered to serve as a supplement of field test for GIS.

Motion of metallic microparticles in superfluid helium in the presence of space charge

We report an experimental and theoretical study of the motion of metallic micro- and nanoparticles in cryogenic superfluid helium in the presence of a static electric field. Depending on the polarity of the applied field, the system is charged with a large number of positive ions or free electrons. For the electrons, we observe the formation of a negative charge layer above the free surface of liquid He and a shuttle-like motion of metallic particles between this layer and the positively charged bottom electrode. For the positive ions, the positive space charge is created in the liquid and the particle motion resembles bouncing off the (negatively charged) bottom electrode. The observations are explained by a theoretical model based on classical electrostatics and hydrodynamics.

Exponential difference schemes for solving boundary-value problems for convection-diffusion type equations

The paper considers the numerical solution of boundary-value problems for multidimensional convection-diffusion type equations (CDEs). Such equations are useful for various physical processes in solids, liquids and gases. A new approach to the spatial approximation for such equations is proposed. This approach is based on an integral transformation of second-order one-dimensional differential operators. A linear version of CDE was chosen for simplicity of the analysis. In this setting, exponential difference schemes were constructed, algorithms for their implementation were developed, a brief analysis of the stability and convergence was made. This approach was numerically tested for a two-dimensional problem of motion of metallic particles in water flow subject to a constant magnetic field.

Initiation of the Adiabatic Wave of Combustion for Obtaining the Substances with the Free Valence

According to the task of obtaining substances with the free valence for the linkage of the nano-powders, the procedure of the synthesis of materials under the extreme nonequilibrium conditions is presented. The combustion of multilayer aluminothermic systems in the revolving reactor was investigated. Experiments were carried out in the reactor of high-temperature centrifuge. The initiation of process realizes by electric pulse in the effective layer. Further the wave of combustion was propagated along the axis of the reactor. The particles of the restored metal penetrated the underlayers of fresh mixture under the action of centrifugal acceleration and created the additional centers of ignition. The higher the density of metal, the higher speed and depth of penetration. An increase in the centrifugal acceleration strengthens the activity of process also. The speed of the motion of metallic particles grows. According the theoretical calculations it reaches 90 m/s in the case of tungsten.

Initiating Potential of Centrifugally Accelerated Metal Particles in the Inorganic Synthesis Reactions

The method of producing clusters of various metals by using self-propagating high-temperature synthesis (SHS) in the conditions of high-speed rotation is presented. The purpose of a study is development of the technology of the acceleration of strong- endothermic reactions and synthesis of ceramic materials and products. The task of a experimental study consists of the observation of the wave of combustion in the effective layer, the determination of the coordinate of its passage in the adiabatic regime and the arrangement here of less effective layer for the purpose of obtaining gradient and composite materials. The possibility of the output of the process of the combustion of oxide system to the adiabatic regime is shown. The limits of inflammability in the centrifugal-force field come down by the attack of the adiabatic wave of combustion by accelerating the front of combustion with the molten particles of metal, returned into the zone of reaction by centrifugal acceleration. The potential possibility of using the centrifugal efforts for the production of ceramic materials was demonstrated for the multilayer aluminothermic systems. The speed of motion of metal particles under the influence of centrifugal acceleration is calculated. In the reactor of 30 cm long the speed of particles of tungsten reaches 94 m/s with a frequency of rotation of 3 000 rev/min received accelerated clusters of metals that are considered as possible sources of initiation of the chemical processes having about MJ/mol of activation energy. This method was allowed to produce gradient materials.

Factors dominating dielectric performance of real-size gas insulated system and their measures by dielectric coatings in SF6and potential gases

The paper focuses on the factors that lower the dielectric performances of real-size gas insulated systems, and show the examples of the measures by using dielectric coatings. The factors studied in this paper are area effects of electrodes and metallic particle motion which are now dominant to determine the size of gas insulated switchgear (GIS). The gases for the systems are basically SF6 but potential gases like N2/SF6 gas mixtures, CO2, dry air and N2 are also included. Area effects of electrodes are studied by reviewing the minimum breakdown data at lightning impulse (LI) of large effective electrode area over about 5 × 104 mm2 under high gas pressures up to 1.9 MPa. The breakdown electric field strength (BDE) or breakdown voltage (BDV) is normalized by the theoretical value and evaluated in terms of effective electrode area and gas pressure. Under the same gas pressure in the range between 0.2 and 0.7 MPa at negative LI, the normalized values of SF6 are lower than those of the potential gases which show similar values. However, the normalized BDVs of N2 at positive LI are further lower than those of SF6 at negative LI. The advanced dielectric coatings enable high dielectric performances over 80% of the theoretical values in SF6 and CO2. Concerning the second factor, metallic particle motion, the experimental data of metallic particle levitation and crossing to high voltage electrode are gathered for dielectric coated and bare enclosures in SF6, N2/SF6 and dry air. The data are classified into two cases of with and without mechanical impulsive force to the enclosure, which simulates the force by the operation of circuit breakers, disconnecting switches and earthing switches. The particle lift-off/levitation electric field strength on the inner surface of dielectric coated enclosure is about 2 to 11 times higher than that on bare enclosure without a mechanical vibration. With a mechanical vibration, the particle lift-off/levitation and crossing electric field strength on dielectric coated enclosure decrease but still about 2 to 3.5 times and 1.3 to 1.6 times higher than those on bare enclosure, respectively.

Controlling the Motion and Placement of Micrometer-Sized Metal Particles Using Patterned Polymer Brush Surfaces

In this paper, we show that silicon surfaces patterned with poly(methacrylic acid) brushes are able to control the Brownian motion of 2-3 μm iron particles, which sediment onto the surface in aqueous solution and experience differences in repulsive force depending upon their position. Differences in repulsion lead to different gravitational potential energies across the surface, which gives bias to the Brownian motion taking place. Three regimes have been identified depending upon the brush height: (i) no control of Brownian motion when the brush height is small, (ii) Brownian motion that is influenced by the polymer brush when the brush 17 height is intermediate, (iii) Brownian motion that is confined by polymer brush barriers when the brush height is greatest. The height of brush found necessary to significantly influence iron particle motion was small at 39 nm or 2% of the particle diameter.

On the lumped lorentz force approximation for modeling the motion of free metallic particles

The force acting upon a free metallic particle in an alternating electric field will determine its motion and ultimately allow for the estimation of the risk imposed due to dielectric failure of the high voltage equipment. Existing models approximate the force with Lorentz' law and consider the charge resting upon the surface as being lumped into a point charge at the center of the particle during its motion. The model proposed in this paper demonstrates a time stepped electrostatic Finite Element Method to calculate these forces, therefore taking into account the charge distribution upon the surface of the particle. The use of this model is seen to have a significant effect upon the motion of the particle under certain conditions.

Motility of Metal Nanoparticles in Silicon and Induced Anisotropic Silicon Etching

AbstractThe autonomous motion behavior of metal particles in Si, and the consequential anisotropic etching of silicon and production of Si nanostructures, in particular, Si nanowire arrays in oxidizing hydrofluoric acid solution, has been systematically investigated. It is found that the autonomous motion of metal particles (Ag and Au) in Si is highly uniform, yet directional and preferential along the [100] crystallographic orientation of Si, rather than always being normal to the silicon surface. An electrokinetic model has been formulated, which, for the first time, satisfactorily explains the microscopic dynamic origin of motility of metal particles in Si. According to this model, the power generated in the bipolar electrochemical reaction at a metal particle's surface can be directly converted into mechanical work to propel the tunneling motion of metal particles in Si. The mechanism of pore and wire formation and their dependence on the crystal orientation are discussed. These models not only provide fundamental interpretation of metal‐induced formation of pits, porous silicon, and silicon nanowires and nanopores, they also reveal that metal particles in the metal/Si system could work as a self‐propelled nanomotor. Significantly, it provides a facile approach to produce various Si nanostructures, especially ordered Si nanowire arrays from Si wafers of desired properties.

Polarization and particle size dependence of radiative forces on small metallic particles in evanescent optical fields Evidences for either repulsive or attractive gradient forces

We have observed the motion of metallic particles above various optical waveguides injected by 1064nm radiation. Small gold particles (250nm diameter) are attracted towards the waveguide where the intensity of the optical field is maximum, and are propelled at high velocity (up to 350mum/s) along the waveguide due to radiation pressure. The behaviour of larger metallic particles (diameter >600nm) depends on the polarization of the evanescent field: for TM polarization they are attracted above the waveguide and propelled by the radiation pressure; for TE polarization they are expelled on the side of the waveguide and propelled at much smaller velocity. This is consistent with calculations of radiative forces on metallic particles by Nieto-Vesperinas et al. 3D-finite element method calculations carried out for our experimental situations confirm the observed dependence with the polarization of the field and the size of the particles. These observations open the way to the development of new microsystems for particles manipulations and sorting applications.

高電界SF&lt;sub&gt;6&lt;/sub&gt;ガス中における部分放電を考慮した金属異物挙動解析技術の開発

高電界SF&lt;sub&gt;6&lt;/sub&gt;ガス中における部分放電を考慮した金属異物挙動解析技術の開発

Study on Metallic Particle Motion and Partial Discharge Characteristics in a GIS Tank Filled with CO2 and SF6

We investigate the insulation properties of CO2 gas in the presence of a metallic particle. CO2 gas attracts attention as an alternative gas to SF6 gas because of its relatively very small global warming coefficient gas and relatively good dielectric strength. To design CO2 gas-insulated apparatus, the influence of a metallic particle on insulation properties has to be clarified. In this paper, we investigate the motion of a metallic particle and partial discharges in CO2 and SF6 gases by measuring acoustic and electromagnetic signals. As a result, it was found that a free metallic particle motion differs in CO2 gas and SF6 gas because of differences in partial discharge characteristics.