Behavior Of Particles Research Articles

Aggregation-Growth and Densification Behavior of Titanium Particles in Molten Mg-MgCl2 System.

In this work, the preparation of titanium sponge by magnesium thermal method is regarded as the liquid-phase sintering process of titanium, and powder-metallurgy sintering technology is utilized to simulate the aggregation-growth and densification behavior of titanium particles in a high-temperature liquid medium (the molten Mg-MgCl2 system). It was found that compared with MgCl2, Mg has better high-temperature wettability and reduction effect, which promotes titanium particles to form a sponge titanium skeleton at lower temperature. The aggregation degree of titanium particles and the densification degree of a sponge titanium skeleton can be improved by increasing the temperature and the relative content of Mg in the melting medium. The kinetics study shows that with the increase in temperature, the porosity of the titanium particle aggregates and the sponge titanium skeleton decreases, and their density growth rate increases. With the extension of time, the aggregation degree of titanium particles and the densification degree of sponge titanium gradually increase. This work provides a theoretical reference for controlling the density of titanium sponge in industry.

Numerical simulation and experimental investigation of the molten pool evolution and defects formation mechanism of Selective laser melted CuSn20/Diamond composites

Some defects such as small pores, thermal damage of diamond particle and micro-cracks between diamond and metal matrix existed in SLM-fabricated metal-bonded diamond tools. For further application, it is vital to understand the formation mechanism of such defects by SLM-fabricated parameters. In this work, a multiphysics field numerical simulation model based on computational fluid dynamics (CFD) was developed to investigate molten pool evolution and defects formation mechanism for SLM-fabricated CuSn20-bonded diamond composites. From simulation results, the metal particles melt and flow forward under the action of the laser. Also, the presence of diamond particles can obstruct the normal flow of melted CuSn20 fluid. Increasing the laser power can widen and stabilize the molten pool, however, exacerbate the thermal damage of diamond particles. Specially, the migration and marginalisation of the diamond particles during the formation of molten pool were found by simulation and experimental results. Unavoidably, there are obvious gaps in the interfacial bonding region of diamond and CuSn20 due to the comprehensive reasons of thermal gradient, differences in thermophysical properties of two materials and undergo continuous migration and rotational behavior of diamond particles. These findings have potential value for understanding and optimizing the process of SLM-fabricated metal-bonded diamond tools.

Transient behaviour analysis in silicon carbide alpha particle detector using TCAD and SRIM simulation

Time response characteristics of α particle detector are crucial for monitoring radiation fields varied with time and its characterization of pulse radiation field. Here, SRIM-informed TCAD simulation is utilized to visually investigate the transient behaviors of carriers and alpha particles in 4H-SiC Schottky barrier detectors for the time response characteristics. We identified external bias voltage and incident particle energy as key factors to influence transient current pulse broadening. Low-energy alpha particles result in low initial kinetic energy of the ionization-generated carriers, leading to transient current broadening and reduced time resolution characteristics. Conversely, high-energy alpha particles ionize carrier with high drift velocity, preventing the broadening effect. Our simulation provides a planform and valuable guidance for optimizing alpha particle detector, selecting appropriate bias voltages, and enhancing time resolution capabilities.

Inertial focusing of small particles in oscillatory channel flows

This study leverages the immersed boundary-lattice Boltzmann method to investigate the inertial focusing dynamics of a small neutrally buoyant particle in oscillatory channel flows driven by two distinct pressure gradient (PG) waveforms. Through an in-depth analysis of particle behavior, this research delineates the effects of PG waveforms, particle Reynolds number (Rep), and Womersley number (Wo) on the inertial focusing processes, and contrasts these findings with conventional Poiseuille flow-induced inertial focusing. Our results reveal that oscillatory flows induce more intricate focusing patterns than those observed in Poiseuille flow. The streamwise PG oscillation alters the particle focusing positions and introduces minor lateral oscillations in the post-focusing phase. The square PG waveform positions particles closer to the channel wall compared to Poiseuille flow, whereas the sine PG waveform positions particles closer to the channel center. Moreover, an increase in Rep nudges the focusing positions towards the channel center, while a higher Wo pushes them towards the walls. Notably, at Wo ≥ 5, the flow's oscillatory effect dominates over its inertial effect (i.e. Rep) on particle focusing. The study also underscores the capability of oscillatory flows to reduce the required channel length for particle focusing, albeit at the cost of increased focusing time. Contrary to Poiseuille flow, where the focusing length shortens with an increased Rep, oscillatory flow demonstrates an inverse correlation, with an increase in Rep extending the focusing length. Furthermore, while a higher Rep is beneficial in Poiseuille flow, it adversely affects the focusing effect in oscillatory flow. The focusing efficiency peaks at Wo = 3.5 for both waveforms, with the sine PG waveform offering superior efficiency due to the lower lift forces generated. Consequently, for optimal focusing in similar conditions, it is recommended to set Rep and Wo to 0.075 and 3.5, respectively.

Numerical Simulation of Hydrodynamics and Heat Transfer in a Reactor with a Fluidized Bed of Catalyst Particles in a Three-Dimensional Formulation

The hydrodynamics and heat transfer in a reactor with a fluidized bed of catalyst particles and an inert material were simulated. The particle bed (the particle density was 2350 kg/m3, and the particle diameter was 1.5 to 4 mm) was located in a distribution device which was a grid of 90 × 90 × 60 mm vertical baffles. The behavior of the liquefying medium (air) was modeled using a realizable k-ε turbulence model. The behavior of particles was modeled using the discrete element method (DEM). In order to reduce the slugging effect, the particles were divided into four separate horizontal layers. It was determined that with the velocity of the liquefying medium close to the minimum fluidization velocity (1 m/s), slugging fluidization is observed. At a velocity of the liquefying medium of 3 m/s, turbulent fluidization in the lowest particle layer and bubbling fluidization on subsequent particle layers are observed. With an increase in the velocity of the liquefying medium over 3 m/s, entrainment of particles is observed. It was shown that a decrease in the density of the liquefying medium from 1.205 kg/m3 to 0.383 kg/m3 when it is heated from 298 K to 923 K would not significantly affect the hydraulic resistance of the bed. Based on the obtained results, it can be stated that the obtained model is optimal for such problems and is suitable for the further description of experimental data.

Responses of colonization and development of periphytic biofilms to three typical tire wear particles with or without incubation-aging in migrating aqueous phases

Understanding the behavior of tire wear particles (TWPs) and their impact on aquatic environments after aging is essential. This study explored the characteristics of TWPs generated using different methods (rolling friction, sliding friction, and cryogenic milling) and their transformation after exposure to environmental conditions mimicking runoff and sewage, focusing on their effects on river water and periphytic biofilms. Laboratory experiments indicate that at low exposure levels (0.1 mg/L), TWPs promoted biofilm growth, likely due to zinc release acting as a nutrient and the aggregation of particles serving as biofilm scaffolds. However, at higher concentrations (100 mg/L), TWPs inhibited biofilm development. This inhibition is linked to toxic byproducts like N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone and environmentally persistent free radicals, which reduce biofilm biomass, alter algal diversity, and decrease the production of essential biofilm components such as proteins and polysaccharides, consistent with the inhibitory behavior of TWPs on bis-(3′-5′)-cyclic diguanosine monophosphate and quorum sensing signals, including acyl-homoserine lactone and autoinducer-2. Aging processes, particularly after simulated sewage treatment, further affect ecological impacts of TWPs, reducing the benefits observed at low concentrations and intensifying the negative effects at high concentrations. Contribution of here lies in systematically revealing the impact of TWPs on the development of aquatic biofilms, emphasizing the logical relationship between their aging characteristics, environmental behavior, and ecological risks. It assesses not only the release effects of typical additives and conventional size effects but also highlights the emerging photochemical toxicity (persistent free radicals), thus providing valuable insights into the aquatic ecological risk assessment of TWPs.

Effect of vibration and airflow on separation of 6–1 mm fine coal in compound dry separation bed

The segregation behaviour of solid particles are affected by airflow and vibration in a compound dry separation bed. The distribution characteristics of airflow field on the bed surface have been systematically investigated by a novel method of regional air distribution, and the movement and segregation behavior of fine coal particles have been observed under different gas velocity. Meanwhile, the spatial distribution characteristics and ash variation of fine coal particles during the process of segregation and stratification were analyzed. The obtained results show that the airflow velocity of the bed showed a zonal air distribution characteristic of gradual decrease from the separation area to the clean coal section and the gangue section. The segregation and stratification of particles in the Y-axis and Z-axis directions of the bed surface can be enhanced by vibration. When the vibration frequency is 34 Hz, the probable error (E) is 0.08 g/cm3. The bed inclination and the bed grid height have a certain influence on the segregation behavior of fine coal.

Effects of external field and potential on non-relativistic quantum particles in disclinations background

In this work, we investigate the behavior of non-relativistic quantum particles immersed in a cosmic string space-time background. Our study involves the examination of these particles as they interact with a range of influences, including potential, magnetic, and quantum flux fields. We employ analytical methods to solve the associated wave equation, leading to the derivation of eigenvalue solutions for this quantum system. Subsequently, we leverage these eigenvalue solutions to scrutinize several potential models. For each model, we present and engage in a thorough discussion of the corresponding eigenvalue solutions. In an extension of our investigation, we explore the thermodynamic and magnetic properties of the quantum system when it is exposed to non-zero temperature conditions, denoted by [Formula: see text]. Our analysis encompasses the calculation of essential parameters such as the partition function for the system and other pertinent functions. Following these calculations, we meticulously examine and interpret the outcomes, shedding light on the system’s behavior and characteristics in the presence of temperature variations. Furthermore, we calculate entropic information to investigate the location of particles in the system.

Achieving fully equiaxed grains with minor Sc addition of a novel Al-Li alloy fabricated by laser direct energy deposition

In this study, a novel Al-Li alloy with minor Sc addition was fabricated by laser directed energy deposition (LDED), resulting in a fully equiaxed grain structure. The precipitation behavior of primary Al3Sc particles was studied based on transient nucleation theory, and the results showed that sufficient heterogeneous nuclei by primary Al3Sc particles could preferentially form at initial solidification stage and induce into equiaxed grains. Besides, a large number of acicular T1 (Al2CuLi) phases and spherical Al3Sc phases, as well as rod-shaped TB (Al7Cu4Li) phases and quasicrystalline T2 (Al6CuLi3) phases, were distributed in as-built alloy that served as primary strengthening phases by thermal cycling. However, the specific nucleation behavior of α-Al grains on primary Al3Sc particles and subsequent growth behavior during rapid solidification need to be further investigated.

Influence of Coherent Vortex Rolls on Particle Dynamics in Unstably Stratified Turbulent Channel Flows

This work investigates the dynamics of heavy particles dispersed in turbulent channel flows under unstable thermal stratification conditions using point-particle direct numerical simulations (PP-DNS), to quantify the influence of large-scale coherent vortex rolls, arising from the combined effects of shear and buoyancy, on the spatial distribution and preferential sampling behavior of inertial particles. We examined three particle Stokes numbers (St+=0.6,60,120) and two friction Richardson numbers, Riτ=0.272 and Riτ=27.2, which exemplify the regimes below and above the critical condition for vortex roll formation, respectively. The results indicate that the flow reorganization into large-scale longitudinal vortices significantly alters the topological features of small scales in the near-wall region impinged by the thermal plumes, resulting in a prevalence of vorticity-dominated topologies. The interplay between this phenomenon and the tendency of particles to preferentially sample strain-dominated topologies leads to a distinctive asymmetric particle distribution in the near-wall planes. Inertial particles markedly accumulate in the strain-dominated regions where the coherent thermal plumes emerge from the walls, while avoiding the vorticity-dominated impingement zones. This peculiar particle response to the vortex rolls is most pronounced when the particle response time matches the characteristic timescale of the large-scale coherent motions in the cross-stream planes.

Hydrodynamic behavior of Janus particles in a finite inertial flow

Hydrodynamic behavior of Janus particles in a finite inertial flow is studied numerically using the lattice Boltzmann method (LBM) in the range of Reynolds number 0.05 ⩽ Re⩽ 10 and swimming parameter −3 ⩽ β ⩽ 3. Some results are validated by comparing with the existing results. The effects of Re, β on the hydrodynamic behavior of Janus particles are analyzed. The results show that the velocity of a pusher (a type of Janus particles) monotonically increases with the increase of Re, while the velocity of a puller (another type of Janus particles) exhibits a non-monotonic change. At high Re, the puller is unstable and presents a lateral displacement, while the pusher remains stable. The power consumption for the pusher and puller, the hydrodynamic efficiency for the pusher increase monotonically with increasing Re, while the hydrodynamic efficiency for the puller exhibits a non-monotonic change. At low Re, the power consumption and hydrodynamic efficiency of Janus particles exhibit symmetry with the variation of surface velocity distribution. This symmetry is disrupted with the increase of Re, similar to the velocity changing with the surface angle.

Fragmentation behavior of diamond particles with different particle size and ratio under high pressure compaction

The fragmentation behavior of mixed diamond particles with different grain sizes under high pressure is important to guide the design of raw material diamond powder ratios and obtain high performance polycrystalline diamond compact (PDC). In this study, five different grain size diamond powders commonly used for the preparation of PDCs were selected, and the single and mixed diamond particles were cold pressed at 7.7 GPa for 60s. The particle size variations of diamond powders with different principal particle sizes and ratios after cold pressing were analyzed by a laser particle size scanner, and the crushing behavior was observed by scanning electron microscopy. The results showed that the larger the initial grain size, the more significant the degree of fragmentation under high pressure. The crushing morphology of fine-grained diamond showed that the majority of grains were locally fractured at the edge, and the peak of the grain size distribution curve was shifted to the left after high pressure. In comparison, the coarse-grained diamond produced a large number of cracks and fractures along the weak grain boundaries under high pressure, which generated a large number of fine grains, and multiple secondary peaks in the particle size distribution curve. The addition of fine-grained diamond as filler particles to coarse-grained diamond could inhibit the crushing phenomenon to some extent. As the proportion of filler particles increased, the crushing of coarse-grained diamond was inhibited more significantly. When the proportion of filler particles was 30 wt%, the crushing under high pressure was greatly limited, especially when the size difference between filler particles and main particles was large. The results of the cold pressing experiments provided preliminary evidence that 30 wt% of filler particles were too high, and that a better ratio should be between 10 wt% and 20 wt%.

Dissolution behaviour of WC particles and evolution of precipitated phases in the plasma transfer arc Ni-based composite coating reinforced by 30 wt% WC particles

Ni-WC composite coating was prepared on Q235 steel substrate by plasma transfer arc (PTA) with welding current ranging from 70 A to 85 A. The results show that the dissolution behaviour of WC particles and the elemental diffusion at the interface promoted by the increased welding current promote the formation and evolution of precipitates, including M7(B, C)3 and M6C. The increased current reduced the volume fraction of WC particles in the coating, but increased that of the precipitates. At welding currents of 75 A and 80 A, dendritic-like M7(B, C)3 presented a regular distribution at the bottom of the coating. At a welding current of 80 A, M6C phase began to form at the bottom of the coating. When the welding current reached 85 A, the dendritic structure was broken, and the M6C phase aggregated and grew. The Ni-WC coating had visible delamination. WC particles at the upper part of the coating dissolved more severely compared to those at the middle and bottom of the coating. Ni3Si compound was formed at the upper and middle of the coating, and it had a crystal orientation relationship of [011]Ni3Si∥[011]γ-Ni, (11-1)Ni3Si∥(11-1)γ-Ni, (−200)Ni3Si∥(-200)γ-Ni, (-11-1)Ni3Si 1.3° from (-11-1)γ-Ni with γ-Ni. The average hardness of the coating decreased slightly due to the dissolution of WC, but the hardness at the interface increased, showing an improved bonding of the interface. The newly formed high hardness precipitates can share the load coming from the friction paired ball, thus reducing CoF and wear loss of the coating.

Dielectrophoretic motion of a red blood cell in a microfluidic environment: Insights from numerical simulations

This research delves into the dielectrophoresis (DEP) behavior of a biological cell within a sinusoidal-shaped microchannel utilizing the Maxwell stress tensor (MST) theory. A red blood cell (RBC), immersed in a viscoelastic fluid, is studied considering the Oldroyd-B model. The study aims to fill a gap in the literature by examining the DEP characteristics of RBC in a realistic geometric configuration and fluid environment, bridging the divide between theoretical modeling and practical application. This work uniquely explores the DEP behavior of an RBC within a sinusoidal microchannel in the presence of a viscoelastic flow regime, which simulates plasma properties, marking a novel contribution to the field. The two-dimensional numerical model incorporates the finite element method to accurately simulate the DEP effect and describe the behavior of the viscoelastic fluid. Validation results confirm the accuracy of the MST model. Crucially, numerical findings highlight the strong dependence of DEP force on electric potential and fluid permittivity. As a consequence of their heightened levels, there is an associated increase in both the DEP force and velocity. While the augmentation of fluid viscosity merely results in a deceleration of DEP velocity. The study provides valuable insights into the interplay between physical parameters and particle behavior, paving the way for advancements in microfluidic particle manipulation techniques.

Error analysis of asymptotic solution of a heavy particle motion equation in fluid flows

For weakly inertial particles subjected to volumetric forces and Stokes drag force in fluid flows, we can solve the simplified particle motion equation using the perturbation method. This method allows us to obtain a recursive formula for the nth-order correction of the asymptotic solution of particle velocity. We verified the error of the asymptotic solution under two typical flow fields: a time-varying uniform flow field with a volumetric force field and a two-dimensional non-uniform cellular flow field. In the former, the relative error of the asymptotic solution of particle velocity and position increases with the Stokes number, and we provided a quantitative analysis of the results. In the latter, we verify and analyze the asymptotic solution from two perspectives: the behavior of a single particle and the collective behaviors of many particles. For asymptotic solutions with maximum velocity and position errors of less than 5%, we select the solution with the lowest order correction and designate it as the optimal asymptotic solution. The order of the optimal asymptotic solution increases with increasing Stokes numbers and motion durations. However, in most cases, for weakly inertial particles [St ∼ O(10−3)], and the time t* ∼ O(10), the first-order asymptotic solution can achieve accuracy, where both St and t* are defined using the flow field characteristic time, Tf = 4π s. The results validate the rationale behind utilizing first-order asymptotic solutions in the fast Eulerian method for turbulent dispersion of weakly inertial particles.

Emergent dynamics: Collective motions of polar active particles on surfaces

In this study, we focus on the collective dynamics of polar active particles navigating across three distinct surfaces, each characterized by its own unique blend of topological and geometrical properties. The behavior of these active particles is influenced by a multitude of factors, including self-propulsion, inter-particle interactions, surface constraints, and under-damped stochastic forces simulated via Ornstein–Uhlenbeck processes. Our exploration unveils the prevailing collective patterns observed within these systems across three surface types: a sphere, a torus, and a landscape featuring hills and valleys, each distinguished by its specific topological and geometrical attributes. We underscore the profound impact of surface curvature and symmetry on the sustainable spatial-temporal dynamics witnessed. Our findings illuminate how the interplay between substantial surface curvature and particular symmetrical characteristics gives rise to a diverse spectrum of spatial-temporal patterns. Notably, we discern that high curvature tends to drive collective motion toward cyclic rotation on spheres and tori, or spatial-temporal periodic traveling ring patterns on landscapes with hills and valleys. Additionally, we observe that rough surfaces and the incorporation of excluded volume effects can disrupt the complexity of these collective spatial-temporal patterns. Through this investigation, we provide invaluable insight into the intricate interplay of curvature and symmetry, profoundly shaping collective behaviors among active particles across varied surfaces.

Evolution of some flow-related properties of diffusive aerosols along a tube

This is the third of a series of papers dealing with the behavior of Brownian aerosol particles immersed in a laminar fluid flow. The evolution along the tube of the distributions of particle radial positions (RPD), particle residence time (RTD), and particle mean axial velocity (MAVD) were determined by Monte Carlo (MC) simulation of particles trajectories. The RPD and particle penetration was also determined by numerical solution of the advection-diffusion equation (ADE) with negligible particle axial diffusion. The fairly good agreement shown between the results obtained by these two methods justifies our confidence on the use of the MC technique to determine other particle properties, as MAVD and RTD, for which the corresponding differential equation is yet unknown. Flow-related properties of the aerosol, such as penetration and residence time, are mainly determined by its MAVD. The MAVD is intimately related to the RPD; the latter evolves in such a manner that the surviving particles tend to accumulate nearer the tube axis and farther from the wall. When the fluid local velocity depends on the spatial location, the mean particle axial velocity increases as the aerosol flows downstream the tube, and its value can be considerably larger than the mean fluid velocity, in spite that no external force is acting on the particle. A direct consequence of this counterintuitive fact is that the mean aerosol residence time in the tube can be much smaller, by a factor of ∼0.65, than that of the fluid for even moderate values of the particle diffusion coefficient. This asymptotic value of the aerosol mean residence time can be predicted using the ADE in conjunction with a simple estimation model proposed here. If the fluid velocity is constant within the tube (uniform or plug flow), the mean particle axial velocity is everywhere equal to the fluid velocity, and particles and fluid spend the same time to traverse the tube. The larger the departure of the fluid velocity profile from uniformity, the larger the difference of mean axial velocity and mean residence time between particles and fluid.

Electrochemical behavior and microstructural characterization of nano-SiC particles reinforced aluminum matrix composites prepared via friction stir processing

The present work aims to elucidate the mechanism of microstructural evolution in different regions of nano-SiC particles reinforced aluminum matrix composites prepared by friction stir processing (FSP) on its electrochemical behavior. Electron backscatter diffraction technique (EBSD) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution of stir zone (SZ), advancing side thermomechanically affected zone (AS-TMAZ), retreating side thermomechanically affected zone (RS-TMAZ) and base metal (BM). The electrochemical behaviors of the above zones were investigated using electrochemical tests. A homogeneous and fine microstructure is formed in SZ, not only the nano-SiC is homogeneously distributed within the grains with an average grain size of 3.5 μm, but also the recrystallized grains account for the highest percentage of 85 %. The potentiodynamic polarization curve indicates that the corrosion current densities of the BM, RS-TMAZ, AS-TMAZ and SZ are 0.89, 0.39, 0.85 and 0.36 μA/cm2, respectively, while the polarization impedances are 33.40, 51.42, 48.72 and 73.79 kΩ cm2, respectively. Combining the Nyquist and Bode plots analysis, the optimal electrochemical corrosion resistance is in SZ. The fine and homogeneous recrystallized grains in SZ significantly improve its electrochemical corrosion resistance. This is mainly ascribed to the increase in crystal defects as a result of the increase in grain boundaries, elevating the electron scattering. Simultaneously, the increase in high-energy state grain boundaries is beneficial to the rapid formation of a thicker passivation film.

Numerical analysis of the sand hydro-abrasion of a Pelton turbine injector

Abstract Pelton turbines have great application prospects in the exploitation of high-head hydraulic resources. However, sediment abrasion within its components is the major challenge. In this paper, Euler-Lagrangian method is used to simulate the flow process of the sediment particles in Pelton turbines injector numerically. The hydraulic characteristics of the three-phase flow, the behaviour of the sediment particles and the abrasion distribution are also analysed in detail. Calculation result shows that the predicted motion characteristics of the particles are in good agreement with theoretical model, and the predicted abrasion distribution also matches well with the measured results.

Hot deformation behavior and processing map of vanadium particles reinforced AZ31 composite

The vanadium particles reinforced AZ31 matrix composite (VP/AZ31) was prepared using the powder metallurgy method. Subsequently, hot deformation behavior of VP/AZ31 composite was studied through hot compression trials. The experimental parameters were set in a temperature range of 250–400 °C and a strain rate range of 0.001–1 s−1. Based on the experimental results, a strain-compensated Arrhenius constitutive model was developed to accurately forecast the flow behavior of VP/AZ31 composite. Moreover, the thermal activation energy was calculated to be 138.605 kJ/mol and the processing map was delineated according to the dynamic material model theory. The processing map revealed that the optimal processing area existed under 363–400 °C/0.001–0.004 s−1, where the efficiency of power dissipation exceeded 23 %. Notably, the highest efficiency of power dissipation occurred at 400 °C/1 s−1, which exceeded 30 %. Under these conditions, dynamic recrystallization (DRX) was sufficiently developed, indicating the enhancement of workability. It is estimated that the instability region for VP/AZ31 composites occurred within the conditions of 250–325 °C/0.16–1 s−1, characterized by crack formation. The DRX of VP/AZ31 composite is predominantly governed through the mechanism of discontinuous DRX (DDRX).