Build-up Mechanism Research Articles

A Study of the Mechanisms of Particle Buildup on Single Rods in Dielectrophoretic Separation

A theoretical review of the particle buildup processes involved in dielectrophoretic capture of dielectric and conducting particles is presented. Trajectories are calculated, and the capture radius is plotted against the electric field and flow parameters. Photographic data of capture of barium titanate particulates are shown for the axial case, using a fine steel rod in laminar flow. A correlation for the radius of accumulation at saturation is obtained between the theoretical model and the experimental results.

Transient pulse buildup mechanisms in a synchronously-pumped mode-locked dye laser

Numerical calculations concerning transient pulse buildup processes are performed for a synchronously-pumped mode-locked dye laser system. Rate equations are used, including the amplified spontaneous emission (ASE) term. ASE is required to reach a stationary state. The calculated cavity length detuning characteristics are in good agreement with published observations. The observed large time-bandwidth product and spectral width of the pulse are explained by the shift of the gain spectrum peak with population change. Inhomogeneous broadening in the active medium causes the frequency shift in the pulse.

Mechanism of Charge Build-up on Polymer Powders after Passage through Metal Pipes

The electrification of polymer powders transported through numerous charging units (up to 12 units) was studied at a mean particle speed v=7 m/s∼26.4 m/s and a load ρ=0.006 kg/m3∼2.5 kg/m3. Each charging unit consisted of a combination of a U bend and a straight pipe. The charge/mass ratio of the powder passing through the units grew exponentially and tended to saturate as the number of units increased. The powder particles were found to be electrified mainly in the U-bend pipes. The electric field Es caused by the charged particle cloud has a considerable effect on the saturation tendency of nylon 12 powder, but no effect on that or HDPE powder.

Static Control in Film Transport Systems

The control of static charging of motion-picture films has become more important with the trend toward high-transport-speed systems. This article describes the mechanisms of static buildup and methods of static control. Problem areas in the lab operation - including processed film, high web speeds, low humidity, and unclean environment - and some possible solutions are discussed.

Mechanisms of Charge Build-up on a Polymer Particle by Repeated Impact

The dependence of the impact charge of a polymer particle on the charge previously deposited on it (pre-charge) was studied at impact speed v=9.04 m/s∼20.3 m/sandimpactangle θ=50^°∼60°. The impact charge of a particle decreased almost linearly with increase in the pre-charge. Observation of the optical density of the impact area made visible using electrophotographic liquid developer showed that this phenomenon was caused by the decrease in the charge density on the impact area. The electric field due to the pre-charge was thought to restrict the generation of new charge. This inference was confirmed by an experiment using a polyethylene sheet.

Mechanism of contamination build-up induced by fine electron probe irradiation

Abstract To clarify the transfer mechanism of contaminating molecules and the dominant source of them, carbon thin films were irradiated with a fine electron probe of 12 nm dia using three types of anti-contamination devices, individually. No contamination deposit was observed for a certain period or an incubation time after the specimen was pretreated by an electron beam shower. After the incubation time, the growth rate increased gradually with the elapsed time after the electron beam shower treatment and reached the saturated rate. The incubation time and the saturated growth rate depended largely on the type of the anti-contamination device used. It can be concluded that hydrocarbon molecules being adsorbed on the specimen surface are transferred to the irradiated area by surface diffusion. The dominant source of contaminating molecules is the residual gas molecules in the vicinity of the specimen even in a clean high vacuum.

A Mechanism of Radioactive Corrosion Product Buildup on the Stainless Steel Surface Used in the Primary Cooling Systems of Boiling Water Reactors

The mechanisms of radioactive corrosion product buildup on the stainless steel surface used for the primary cooling systems of boiling water reactors have been considered and the following conclusions obtained. Ionic species are taken into a spinel structure on the surface and the deposition rate is expressed as a function of exposure time and temperature of contact water. Crud is deposited on the oxide layers at a rate in proportion to the 0.82th power of the Reynolds number. Some ionic species are released from the crud on the oxide layers and are taken into a spinel structure as in item 1. Their contribution to the dose rate buildup is dominant at a dirty plant (which has a high iron content in the feedwater system). The spinel structure grows at the boundary between the oxide layers and the base metal as a result of dry corrosion of stainless steel, which involves ionic species diffusing through the oxide layers. The mechanism is supported by data from destructive measurements of the reactor water cleanup piping at Tsuruga Nuclear Power Plant.

Transient Simulation of Absorption Machines

This paper presents a model for a water-cooled Lithium-Bromide/water absorption chiller and predicts its transient response both during the start-up phase and during the shutoff period. The simulation model incorporates such influencing factors as the thermodynamic properties of the working fluid, the absorbent, the heat-transfer configuration of different components of the chiller and related physical data. The time constants of different components are controlled by a set of key parameters that have been identified in this study. The results show a variable but at times significant amount of time delay before the chiller capacity gets close to its steady-state value. The model is intended to provide an insight into the mechanism of build-up to steady-state performance. By recognizing the significant factors contributing to transient degradation, steps can be taken to reduce such degradation. The evaluation of the residual capacity in the shut-off period will yield more realistic estimates of chiller COP for a chiller satisfying dynamic space cooling load.

A study of the mechanisms of particle buildup on single ferromagnetic wires and spheres

Particle buildup processes for paramagnetic, diamagnetic and ferromagnetic particles in HGMS are reviewed, and new data are presented. Previously published data are discussed using the local flow velocity in the vicinity of a collection wire instead of the average flow velocity.

Evaluation of magnetic filter performance

In recent years, in high gradient magnetic separation, two mainstream lines of basic investigation have evolved. The first of these has involved theoretical and experimental research on the basic mechanisms of particle build-up on individual fibres. The second deals with the overall performance of filters comprising random matrices in high magnetic fields and, in particular, with the phenomenon of breakthrough. This paper attempts to correlate information from these two major lines of effort.

SECONDARY SAND TRANSPORT MECHANISMS

The basic concept of coastal littoral drift consisting of a "river" of sand driven by the direct alongshore component of oblique waves has long been considered as a basis for littoral transport equations. This concept however is highly simplified since the actual littoral drift on real beaches represents only the final result of the inter-action of dozens or perhaps hundreds of secondary hydraulic processes which continuously occur in Nature. On many Coasts littoral transport is taken to represent the primary mechanism of beach recession or build-up but many of the secondary mechanisms themselves are only partially understood and their individual contributions to the primary process largely unexplored. This paper therefore discusses some of these secondary processes and since offshore- onshore sediment transport is probably the most important of these a mechanism for this transport mode is suggested based upon the interaction between wave energy and a work capacity parameter for the beach sediments.

熱サイクルによる回転機固定子巻線の破壊機構

The purpose of this study was to clarify the mechanism of the thermal deformation and stress build-up of stator windings as well as their failure mechanism under thermal cycling. In this study, the thermal elongation of stator windings was measured over a wide range of temperature variations. By comparing the experimental results with the theoretical ones, the mechanism of thermal deformation and stress build-up was discussed. Thermal cycling tests were also carried out on six kinds of stator windings to clarify the failure mechanism of the stator windings under thermal cycling. In this test, the failure was detected by measuring the flatwise thickness and the tangent delta characteristics of the stator windings. Moreover, the breakdown voltage characteristics were measured at the last stage of the test. The failure mechanism of the stator windings was discussed in conjunction with thermal stress.From this study, tape separation, mica slipping-out phenomena and bonding failure in mica splitting were revealed. Moreover, the relationship between the mechanical failures described above and the tangent delta and breakdown voltage characteristics was clarified.

The generation of picosecond pulses in actively mode-locked c.w. solid-state lasers. IV. The pulse formation†

This paper is the last in a series of four dealing with the problem of picosecond pulse generation in solid-state lasers. It is primarily concerned with active (as opposed to passive) modo-locking, and in particular with the early stages of the mode-locking process. The discussion is based on an aeousto-optic (loss) modulator and its interaction with the radiation present inside a laser cavity, from the moment the modulator is switched on until a fully modo-lockod pulso is formed. A brief discussion of the properties of loss modulators is alao included. The investigations have been carried out with the help of a computer model of the system, a typical Nd : YAG laser serving as an example. It is assumed that the laser radiation is composed initially of a large number of cavity modes (typically 30–100). their phases being distributed at random (narrow-bond noise). The mechanism of a gradual build-up of mode-locking under the influence of a loss modulator is carefully investigated using both the time-domain ...

Ionization waves (strata) in a bounded low-temperature plasma

Resonant properties of a positive column with excitation of induced strata are considered. The mechanism of steady-state amplitude buildup is established, and the conditions for the soft and hard modes of intrinsic strata excitation are obtained. The conditions under which strata are suppressed when the system is acted upon asynchronously by modulation of the discharge currents are investigated. The analysis is carried out for a bounded positive column using the generally accepted model [1, 3].

On friction and metal transfer of sliding surfaces undergoing subsurface plastic deformation

Results of sliding experiments under high normal pressure using a sapphire ball on a modified Brinell hardness testing machine and different work materials are reported. A rational approach to the mechanism of metal build-up on Al 2O 3 abrasive developed recently has been extended in the present sliding tests to verify the hypothesis, and good agreement was found. The results of this study show a wide range of behaviour relative to the equilibrium level of friction and the time required to reach equilibrium when different materials are rubbed against the sapphire ball.

The Mechanism of Roll-Coating Buildup During Hot Rolling of Aluminum

An important limitation to the quality of rolled aluminum is the transference of metal from the slab to the roll and back to the surface of the slab during hot rolling, producing defects known as pickup. The way in which the buildup of roll-coating controls pickup has been studied using a small laboratory mill. The top roll of the mill was modified to take inserts which were ground in place to the same finish as the roll. The inserts could be removed between the rolling of one strip and the next so that the process of coating buildup could be followed in the scanning electron microscope. The distribution of aluminum on the surface of the roll-was mapped using the energy dispersive X-ray spectrometer attachment to the microscope. Additional chemical analysis of the coating was obtained by X-ray photo-electron spectroscopy. The coating built up initially as large isolated lumps streaked out in the rolling direction, which become overlaid with an accumulation of much smaller particles. The coaling was found ...

Qualitative observations on the diffusion of copper and gold through a nickel barrier

To retard failure of gold plated copper parts by diffusion of copper to the gold surface, a layer of nickel is frequently used between the copper and gold as a diffusion barrier. To evaluate the mechanisms whereby the nickel retards the motion of copper atoms to the gold surface, planar tri-couples of Cu/Ni/Au were prepared by electroplating nickel and gold layers on OFHC copper coupons. Diffusion anneals were carried out at temperatures from 150 to 750°C. A qualitative evaluation of diffusion behavior was provided by an electron microprobe utilizing X-ray wavelength dispersive analysis on polished cross sections. Results demonstrate that the nickel layer retards but does not block the transport of copper to the gold surface. Possible mechanisms for the anomalous buildup of copper at the gold/nickel interface and gold at the copper/nickel interface are discussed.

Energy build-up and release mechanisms in solar and auroral flares

Flare phenomena in the solar atmosphere and in the terrestrial magnetosphere exhibit many similarities. The mechanical energy of enhanced photospheric motion is converted and stored in the form of magnetic potential energy in sunspot fields, which is analogous to the case of the growth phase of magnetospheric substorms. The energy release during the explosive phase is initiated by a sudden collapse in the magnetic field topology and the X-type magnetic neutral point is created in the corona. Subsequent electrical discharge takes place in the form of an intense electrojet current flowing in the base of the chromosphere at the altitude where the Cowling conductivity is a maximum. It is suggested that the field-aligned precipitation of hot electrons and the Ohmic heating in the chromosphere result in major features of solar flares.

Energy build-up and release mechanisms in solar and auroral flares

Flare phenomena in the solar atmosphere and in the terrestrial magnetosphere exhibit many similarities. The mechanical energy of enhanced photospheric motion is converted and stored in the form of magnetic potential energy in sunspot fields, which is analogous to the case of the growth phase of magnetospheric substorms. The energy release during the explosive phase is initiated by a sudden collapse in the magnetic field topology and the X-type magnetic neutral point is created in the corona. Subsequent electrical discharge takes place in the form of an intense electrojet current flowing in the base of the chromosphere at the altitude where the Cowling conductivity is a maximum. It is suggested that the acceleration of particles by field-aligned electric fields and the Ohmic heating in the chromosphere result in major features of solar flares.

Mechanism of alumina buildup in tundish nozzles during continuous casting of aluminum-killed steels

During continuous casting of aluminum-killed steels, the pouring rate through the tundish nozzle often diminishes, posing serious operating problems. This happens because a buildup of microscopic alumina particles at the nozzle orifice effectively decreases the nozzle orifice diameter and causes constriction of the liquid-steel pouring stream. There are two major aspects of the constriction problem: (1) the source of the depositing particles, and (2) the mechanism by which the particles deposit at the nozzle orifice. Detailed microscopic examination of the buildup of alumina particles in nozzles from various casting trials and petrographic examination of the nozzle refractory indicated that the particles depositing at the nozzle orifice were already present in the melt because of deoxidation and reoxidation processes. A model proposed herein explains why and how the alumina particles deposit and stay at the nozzle orifice. The model considers a microscopically thin boundary layer at the nozzle bore where the velocity of the liquid steel approaches zero. Particles passing close to the refractory surface and in the slow-moving boundary layer attach to the wall and to each other. The presence of eddy currents in and close to the turbulent boundary layer increase the particle to particle collision. Such collisions of the particles thrown from outer region of boundary layers with the already attached particles keep on dumping the particles toward the refractory surface. The high interfacial energy of alumina inclusions in steel is a driving force for particles to attach to the refractory wall and to each other, and high-temperature sintering then occurs to form a network of alumina particles.