Particle Accumulation Structure Research Articles

Influence of pulse-jet cleaning pressure on performance of compact dust collector with pleated filter operated in clean-on-time mode

• Accumulation structure of residual dust particles was studied for a filter medium. • Different pulse-jet pressures were considered, and a simple model was used. • Filter performance was studied by analyzing the dust accumulation structure. • The effective ratio of filtration area increased with pulse-jet pressure. • The dust penetration increased with pulse-jet pressure. To operate a bag filter continuously, pulse-jet cleaning of dust particles from the filter medium is commonly required, and the pulse-jet pressure significantly affects the filter performance. In this study, the accumulation structure of residual dust particles inside and on the surface of a filter medium at different pulse-jet pressures was investigated by constructing a simple model, and the influence of the dust structure on the filter performance was clarified. Using a simple model, we determined the effective ratio of filtration area β , which represents the ratio of the filterable area to the total filtration area, the true resistance coefficient due to the primary dust layer ζ p ’ thinly deposited on the filter surface, and the true resistance coefficient inside the filter media itself ζ f ’ . The effective ratio of filtration area β decreased with operation time for all pulse-jet pressures; however, it maintained a high value when the pulse-jet pressure was high. The validity of β analyzed by the model was verified using two different methods, and the results showed good agreement, indicating that the model is effective in identifying real conditions. The true resistance coefficient due to the primary dust layer ζ p ’ decreased as the pulse-jet pressure increased; however, the true resistance coefficient inside the filter media itself ζ f ’ was the highest at 0.5 MPa. In addition, the dust collection efficiency was different at each pulse-jet pressure, which was considered to be caused by the difference in the dust particle accumulation structure.

Preparation of hydrophilic polyvinylidene fluoride/polyvinyl alcohol ultrafiltration membrane via polymer/non-solvent co-induced phase separation method towards enhance anti-fouling performance

Membrane separation is a common water treatment technology, but the problem of membrane fouling should not be ignored. Hydrophilic modification is an effective method to reduce membrane fouling. Therefore, PVA/non-solvent co-induced phase separation method was proposed to achieve PVDF ultrafiltration membrane hydrophilic modification and structural control with high concentration polymer coagulation bath. PVA was uniformly distributed on the surface and inside of the hydrophilic modified membrane, which was stable and not easy to leach during filtration. With increasing PVA content in coagulant, the phase separation process changed from instantaneous to delayed, and the membrane surface changed from dense to spherulitic particle accumulation structure, while the connectivity of sponge pores was enhanced until it was completely transformed into a uniform spherical particle structure. The irreversible pollution rates of the modified membrane were 3.28% and 3.48%, respectively, which were significantly lower than those of the unmodified PVDF membranes (25% and 15.26%, respectively) when filtering simulate municipal wastewater with protein and humic acid. The flux recovery rate of the modified PVDF membrane was basically maintained above 90%. This study was a one-step method for membrane structure optimization and hydrophilic modification and contributed a theoretical basis for the role of high concentration polymer coagulant in the membrane forming process.

Ablation behavior of ZrC and ZrO2 coatings on SiC coated C/C composites under oxyacetylene torch with different heat fluxes

In this work, ZrC and ZrO2 coatings were prepared on SiC-coated carbon/carbon (C/C) composites by supersonic atmospheric plasma spraying. Their ablation behavior was investigated and compared under different heat fluxes to design multilayer anti-ablation structural coating. Results shown that ZrO2 coating exhibited denser oxide layer and lower mass consumption after ablation. According to their microstructure and thermal analysis, possible reasons can be ascribed to higher surface temperature and lower melting point of ZrO2 coating, which made the scale easier to be sintered during ablation. Moreover, the ablated ZrC coating presented particle accumulation structure at the initial ablation stage, hence causing the consumption from mechanical denudation to occur in these particles preferentially rather than sintering.

Novel TiB2-reinforced 316L stainless steel nanocomposites with excellent room- and high-temperature yield strength developed by additive manufacturing

Selective laser melting (SLM) is an emerging additive manufacturing process for fabricating multifunctional parts by locally melting and consolidating powders in a layer-by-layer manner. Its flexibility enables the development of new alloys and metal matrix composites with unique, fine microstructures and complex-shaped components that are all difficult to realize with traditional manufacturing processes. This study investigates how TiB2 nanoparticle reinforcements affect the microstructure and high-temperature deformation behavior of a 316L stainless steel matrix. In SLM-processed pure stainless steel, fully directional columnar grains were observed, whereas TiB2 nanoparticles added to the steel matrix significantly reduced the sizes of the molten pools and grains and disrupted the directional structures. A chemical analysis revealed no compositional difference between the boundary and interior of the molten pool areas of the SLM-processed TiB2/316L nanocomposites, suggesting that elements did not segregate macroscopically. However, for higher TiB2 contents, alloying elements microsegregated at the boundaries of cellular structures due to the particle accumulation structure mechanism. Transmission electron microscopy confirmed the existence of mostly cube-like TiB2 nanoparticles both at the boundaries and in the interiors of the cellular structures. The nanocomposites exhibited high compressive yield strength and ductility at room and high temperatures, except at 600 °C, where embrittlement was observed. Observing the microstructure and flow stress of nanocomposites deformed at 700 and 800 °C shed light on the dynamic recovery and dynamic recrystallization phenomena. However, several conventional strengthening mechanisms could not predict the entire yield strength increase. Thus, a novel microsegregation strengthening mechanism was presented to explain the effect of TiB2 on the refined microstructure, and the novel microsegregation phenomenon and the enhanced mechanical properties were correlated. Hence, the SLM process shows high potential for fabricating new materials with outstanding properties.

Existence Conditions and Formation Process of Second Type of Spiral Loop Particle Accumulation Structure (SL-2 PAS) in Half-zone Liquid Bridge

We focus on unique phenomena known as particle accumulation structure (PAS), especially on the conditions of the existence for second-type spiral loop PAS (SL-2 PAS) and on their formation processes under normal gravity. We investigate the existence conditions as functions the aspect ratio of the liquid bridge and the Marangoni number, the intensity of the thermocapillary effect. We discuss the differences among SL-1 PAS, SL-2 PAS and the flow field without PAS through observation of the solid-like structures of the PAS in a rotating frame of reference with the hydrothermal wave, and through monitoring of the surface temperature by infrared camera. We evaluate the formation time of PAS by employing a modified accumulation measure by considering the effect of the particles’ size.

Evaluation of existence region and formation time of particle accumulation structure (PAS) in half-zone liquid bridge

We focused on the particle accumulation structure (PAS) produced by the thermocapillary effect in a half-zone liquid bridge. Although models of the formation of the PAS have been previously proposed, they have not been experimentally verified. An assessment of the region in which the PAS exists is very subjective and often dependent on the observer, and this has necessitated the development of an objective and quantitative evaluation method. We therefore conducted a series of experiments to verify the physical model of the particle path lines in a rotating frame of reference using the fundamental frequency of the hydrothermal wave. We evaluated the intensity of the particle accumulation based on a modification of the “accumulation measure” proposed by Kuhlmann and Muldoon (Phys. Rev. E, 2012) to objectively and quantitatively determine the existence region of the SL-1 PAS. The results of the quantitative experiment revealed that the best aspect ratio (ratio of the height to radius) of the liquid bridge for the SL-1 PAS was about 0.64, and that the PAS formation time was nearly the same as the thermal diffusion time under the considered conditions (184 words, within 200 words).

Assessment of the role of axial vorticity in the formation of particle accumulation structures in supercritical Marangoni and hybrid thermocapillary-rotation-driven flows

Evidence is provided that when the so-called phenomenon of particle accumulation structure (PAS) occurs, extended regions exist where ½ of the axial component of vorticity matches the angular frequency of the traveling wave produced by the instability of the Marangoni flow. Several cases are considered in which such axial component is varied by “injecting” vorticity into the system via rotation of one of its endwalls. The results show that both the resulting PAS lines and the trajectories of related solid particles undergo significant changes under the influence of imposed rotation. By analysis of such findings, a validation and a generalization/extension of the so-called “phase-locking” model are provided.

Etching of subwavelength periodic stripes by using a nanosecond laser pulse

In this study, porous silica films, which have particle accumulation microstructure, were prepared using the sol-gel method. For comparison, compact silica films were deposited using the electron-beam-heating method. These films were then irradiated using nanosecond-pulsed laser beams with wavelengths of 1064 and 532 nm. Laser-induced damage thresholds were recorded and the film microstructures, as well as damage photographs, were observed using scanning electron microscopy. The experimental results show that different kinds of stripes formed on the surface of the silica films with particle accumulation structure. A kind of subwavelength periodic straight stripe was observed in the case of the 1064 nm wavelength, whereas another kind of annular stripe around the small damage pits was observed in the case of the 532 nm wavelength.

New damage behavior induced by nanosecond laser pulses on the surface of silica films

The discovery of subwavelength periodic stripes with similar grating structures is currently only associated with femto-/picosecond laser ablation experiments. A nanosecond laser is generally accepted as incapable of etching out subwavelength periodic stripes. While in this paper, the subwavelength periodic stripes on the surface of silica films induced by nanosecond laser pulses have been observed. The silica films have a particle accumulation structure. This laser damage behavior promotes the industrial production advancement of laser etching subwavelength periodic stripes. The microstructure and spatial period of the periodic stripes under different film structures and radiation energy densities were studied.

Formation of Particle Accumulation Structure (PAS) in Half-Zone Liquid Bridge under an Effect of Thermo-Fluid Flow of Ambient Gas

Formation of Particle Accumulation Structure (PAS) in Half-Zone Liquid Bridge under an Effect of Thermo-Fluid Flow of Ambient Gas

Accumulation of particles in time-dependent thermocapillary flow in a liquid bridge. Modeling of experiments

The study addresses the phenomenon of accumulation of rigid tracer particles suspended in a time-dependent thermocapillary flow in a liquid bridge. We report the results of the three-dimensional numerical modeling of recent experiments (1, 2) in a non-isothermal liquid column. Exact physical properties of both liquids and particles are used for the modeling. Two liquids are investigated: sodium nitrate (NaNO3 )a ndn-decane (C10H22). The particles are modeled as perfect spheres suspended in already well developed time-dependent thermo- capillary flow. The particle dynamics is described by the Maxey-Riley equation. The results of our simulations are in excellent agreement with the experimental observations. For the first time we reproduced numerically formation of the particle accumulation structure (PAS) both under gravity and under weightlessness conditions. Our analysis confirms the experimental observations that the existence of PAS depends on the strength of the flow field, on the ratio between liquid and particle density, and on the particle size.

Dynamic Particle Accumulation Structure due to Thermocapillary Effect in Noncylindrical Half‐Zone Liquid Bridge

We focus on the dynamic particle accumulation structure (PAS) due to the thermocapillary effect in a half-zone liquid bridge. In this study, by tracking particles in the liquid bridge and by measuring temperature on the free surface, we discuss the effects of a liquid bridge shape described by its volume ratio upon the shape of the PAS itself and motion of particle on the PAS. The variation of the liquid bridge volume ratio leads to a significant variation of the temperature gradient on the free surface, which results in difference of the shape of the PAS, especially width of the PAS blade. By considering the simply modeled particle motion, we explain that the width of the PAS blade is determined by several parameters, and we find that its variation is explained mainly by a drastic change of the axial velocity of the particle on the surface.

Effect of shape of HZ liquid bridge on particle accumulation structure (PAS)

We focus on the dynamic particle accumulation structure (PAS) due to thermocapillary effect in a half-zone liquid bridge. Effects of shape of liquid bridge upon shape of the PAS itself and motion of particle on the PAS are discussed in the present study by tracking particles in the liquid bridge and by measuring temperature over the free surface. It is found that the variation of the shape of the liquid bridge leads to a significant variation of the temperature gradient on the free surface, which results in difference of the shape of the PAS. The variation of the PAS shape is mainly explained by drastic change of the axial velocity of the particle and less change of its azimuthal velocity near the free surface.

Dynamic particle accumulation structure (PAS) in half-zone liquid bridge – Reconstruction of particle motion by 3-D PTV

Three-dimensional (3-D) velocity field reconstruction of oscillatory thermocapillary convections in a half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3-D particle tracking velocimetry (PTV). Simultaneous observation of the particles suspended in the bridge by two CCD cameras was carried out by placing a small cubic beam splitter above a transparent top rod. The reconstruction of the 3-D trajectories and the velocity fields of the particles in the several types of oscillatory-flow regimes were conducted successfully for sufficiently long period without losing particle tracking. With this application the present authors conducted a series of experiments focusing upon the collapse and re-formation process of the PAS by mechanically disturbing fully developed PAS.

Formation of dynamic particle accumulation structures in oscillatory thermocapillary flow in liquid bridges

We report on the behavior of small particles of dilute concentration in time-dependent (oscillatory) thermocapillary flow in cylindrical liquid bridges. The particles accumulate in a dynamic string for certain aspect ratios of the liquid bridge and at, typically, two times the critical Marangoni number for the onset of time dependence. This was observed for particles with a density larger and smaller than that of the fluid and for the isodense case. If looked at in a snapshot, this string would be wound m times around the thermocapillary vortex as a deformed spiral. If one looked at the full dynamics, it would be seen that the spiral string is rotating around its ring-shaped axis. The phenomenon is called a dynamical particle accumulation structure (dynamical PAS). The mode m is the mode number of the oscillatory flow field with m wavetrains of the hydrothermal wave (HTW) traveling in the azimuthal direction. We visualize and describe the different modes m in detail. We give direct experimental evidence for the gathering of liquid with particles during the cold phases of the HTW and the injection of liquid with particles into the return flow in azimuthally traveling “cold spots.” We varied the particle diameter at constant density and the ratio of the particle density to fluid density at constant particle diameter to measure the time of the formation of PAS and discuss and explain the experimental results in comparison with possible mechanisms underlying the formation process. We describe the results of an experiment under microgravity to exclude gravity as a PAS-forming mechanism. We conclude by describing a possible mechanism that could account for the observed particle accumulation in certain regions of the flow. This mechanism involves the observed gathering and injection of liquid during the cold phases of the HTW and the particle enrichment of the injected fluid due to particle migration in sheared flow. PAS occurs at a resonance between the azimuthally traveling wave and the “turnover time” of the PAS-string in the thermocapillary vortex.

Particle accumulation structures in time-dependent thermocapillary flow in a liquid bridge under microgravity

The formation of a dynamic spiral string of particles with larger density than the fluid was investigated for time-dependent thermocapillary flow in liquid bridges under various gravity conditions including microgravity. The dynamic spiral string forms after approximately 20–60 oscillation periods from the homogeneous dilute particle suspension. It was found that the action of gravity is not decisive in the process of the particle accumulation structure (PAS) but gravity influences the flow field for PAS-formation. We could realize and observe PAS with modal structure m=3 under μ-g but modal structure m=2 occurred only during a transient of the operating parameters in an aspect ratio-range different from that under normal gravity. The correlation of the optically observed PAS structure with the temperature structure of the azimuthally rotating hydrothermal wave on the free surface is the same under microgravity as under normal gravity indicating that PAS is a pure Marangoni effect.

4025 液柱内マランゴニ対流場における粒子集合現象と数値シミュレーション(F-3 フォーラム「界面流体力学の新展開」)

4025 液柱内マランゴニ対流場における粒子集合現象と数値シミュレーション(F-3 フォーラム「界面流体力学の新展開」)

D153 液柱内マランゴニ対流場における粒子集合現象の数値解析(一般セッション 対流)

D153 液柱内マランゴニ対流場における粒子集合現象の数値解析(一般セッション 対流)

A233 液柱内マランゴニ対流における動的粒子集合 : 1. 実験的研究

Thermocapillary convection is induced by the temperature difference ΔT between two cylindrical rods sustaining a liquid bridge. The induced flow is usually visualized by using fine particles as tracers. Under certain flow conditions, the tracer particles were found to exhibit so called particle accumulation structure (PAS), after Schwabe et al. On the previous study by authors revealed that the particles gathered along a closed single path, which was named Twisted-loop PAS (TL-PAS). The TL-PAS exhibited several types of closed path lines. In the present study the relation between the position of the TL-PAS and the shape of particle-free zone was detected. It was found that the particle size has a lager influence than the density upon the formation time of the TL-PAS.

A234 液柱内マランゴニ対流における動的粒子集合 : 2. 数値シミュレーション

A234 液柱内マランゴニ対流における動的粒子集合 : 2. 数値シミュレーション