Particles In Channel Research Articles

Numerical investigation of movement patterns of particles falling in a viscous fluid

To study the movement patterns of particles, the long-term sedimentation of multiple circular particles in a narrow channel filled with a viscous fluid is investigated numerically. The attention is focused firstly on the equilibrium movement pattern of particles at an intermediate terminal Reynolds number (Ret), and then on its connection with behaviors of multiple particles. For three particles released in a symmetric pattern, at the first stage, all particles tend to fall at the same speed, then after a dramatic interaction, particles split into two groups (1 + 2). The single particle moves steadily with a faster velocity along the central line, while the other two particles self-organize into a two-particle system, moving as a steady oblique doublet, periodic oscillation pair, or a steady symmetrical doublet. For the sedimentation of six particles, there are more separations after the first stage. The small groups owning 1, 2 and 3-particle move in their own typical equilibrium movement patterns. It seems that at intermediate Reynolds numbers multiple particles tend to break up into small groups that can maintain their own equilibrium movement patterns. It is shown that the study on the movement patterns of one/two particles can provide essential information for the self-organization behavior of multiple particles.

Numerical simulation of the effects of sandy water on regulator labyrinth channel in micro-sprinkler systems

Abstract The effects of sandy water on the W-shaped labyrinth channel of micro-sprinkler irrigation systems with large flowrate were investigated using Computational Fluid Dynamics (CFD). Using ANSYS FLUENT software and different inflow conditions (e.g., pressure, velocity, sediment concentration, and sand particle diameter), internal turbulent multiphase flow and sand deposition were simulated by the Eulerian multiphase flow model. Particle erosion in the labyrinth channel was calculated by the Discrete Phase Model (DPM). The results show that vortex movements and shear actions at the boundary layer cause self-flushing in the channel. The location of sand particle deposits and the turbulent dissipation rate are related to the operating pressure, which is optimal at 300 kPa. The erosion rate of the channel wall is proportional to the inflow sediment concentration but has no obvious relationship with inflow velocity. Based on the movement regulation of sand particles in the labyrinth channel, recommendations on filtration requirements and operating pressure of irrigation systems are proposed.

Experimental Study of Transport Behavior of Swellable Microgel Particles in Superpermeable Channels for Conformance Control

SummaryGel treatment is an effective way to attack excessive water production during oil development. The transport behavior of gel materials in reservoirs is of crucial importance to the effectiveness of gel treatments. The aim of this paper is investigating the transport behavior of swellable micrometer-sized preformed particle gels (PPGs, or microgels) through superpermeable (super-K) channels. Sandpacks with permeabilities ranging from 27 to 221 darcies were used to mimic the super-K channels. Multiple pressure sensors were applied along the sandpack models to monitor the propagation behavior of the microgels. The tested microgel particles could transport through the super-K channels, and a higher driving pressure gradient was required when the particle/pore size ratio was larger. The pressure gradient distribution along the super-K channels was relatively uniform when the particle/pore ratio was low (less than 1.3). However, the inlet section would show increasingly higher pressure gradients as the particle/pore ratio was increased, indicating increased difficulty in propagation. The propagation of the gel particles was significantly slower compared with the carrying fluid. The delayed propagation behavior was more pronounced when the particle/pore ratio was higher. The injection pressure was much less sensitive to the injection flow rate compared with a Newtonian fluid. The gel dispersion exhibited an apparent shear thinning (pseudoplastic) behavior when transporting through the porous channels. Breakage of the gel particles was observed especially at high superficial velocities. The particle breakage was partially responsible for the apparent shear thinning behavior. The breakage phenomenon was in favor of deep placement of the gel particles. The channel permeabilities were significantly reduced by the microgels, bringing sufficient resistance to subsequent waterflooding (more than 99.5%). At given matching size conditions, softer gels were more likely to establish in-depth placement and uniform water blocking capacity in the channels. The microgel particles exhibited salinity-responsive behavior to the post-brine flush. The gel particles could shrink and reswell according to the salinity of the injected water. Possibilities were discussed to use this salinity-responsive behavior. Also, the microgels exhibited a particular disproportionate permeability reduction (DPR) effect. After gel injection, the channel permeability to water flow was reduced by more than 20 to 92 times of the permeability to oil flow. This work provides important support to understand the transport behavior of gel particles in super-K channels. The achievements are helpful for gel product selection and gel treatment design.

Focusing of Brownian Particles in a Fluid Induced by the Temperature Difference

In this work the Brownian motion of particles in a two-dimensional channel was numerically studied through a fluctuating-lattice Boltzmann method. The effects of the fluid temperature difference on the biased Brownian motion of particles were examined. It is shown that the particles are likely to move towards and stay at the low temperature zone. More importantly, the focusing of Brownian particles may be realized if the temperature difference is large enough. This paper also provides a quantitative analysis on this issue.

Study on graphite particle motion and impact in the helium circulator of HTGR

The helium circulator is a key component in a high-temperature gas-cooled reactor. Here, the interactions between graphite dust and the circulator impellor are a matter requiring further investigations. In this paper, computational fluid dynamics is used to study the movement of particles in the vane channel, including the impact frequency, deposition fraction, and impact velocity of particles under the rated conditions. Then, based on the particle impact velocity, the finite element method is used to analyze the stress and strain during the impact of graphite particles on the FV520B vane wall. The results show that the deposition fraction for most of the graphite dust particle sizes is less than 1%. Large particles impact the wall with a higher velocity, which can reach 100 m/s. And the impact velocity in the vane is generally lower than that in the hub and shroud region. Finite element analysis results show that the maximum contact force increases, while the maximum stress decreases as particle diameter increases. Under the rated operating condition of the helium circulator, the wear of circulator wall due to the impact of graphite particles can be ignored.

Double-lens technique for efficient capture of short-lived particles by a crystal

For the experiment aiming to measure the dipole moments of short-lived particles via crystal channelling at LHC, we propose a beam-optics system of two crystal lenses that may increase the number of channeled short-lived particles per one incident proton on target of a factor up to 1000 at LHC.

Gravitational effect on particle deposition in narrow channels with porous walls

Convective transport of particles in a narrow horizontal channel with porous walls is analyzed by considering the gravitational effect. Particle concentration, penetration and deposition velocity in three different channels are obtained by using the theoretical solutions. The results show that the differences between the concentrations in the three channels become evident with the increase of the permeability coefficient and slip factor of porous materials, especially for fine particles. The wall structure of the channel has significant influences on particle deposition velocity. When both the upper and lower walls are porous, the deposition in the channel is weakened. In addition, particle deposition velocities on the porous walls are consistent with each other, and the velocities are higher than those on the solid walls.

Dual-Modality Imaging Microfluidic Cytometer for Onsite Detection of Phytoplankton

Phytoplankton monitoring is essential for better understanding and mitigation of phytoplankton bloom formation. We present a microfluidic cytometer with two imaging modalities for onsite detection and identification of phytoplankton: a lensless imaging mode for morphological features, and a fluorescence imaging mode for autofluorescence signal of phytoplankton. Both imaging modes are integrated in a microfluidic device with a field of view (FoV) of 3.7 mm × 2.4 mm and a depth of field (DoF) of 0.8 mm. The particles in the water flow channel can be detected and classified with automated image processing algorithms and machine learning models using their morphology and fluorescence features. The performance of the device was demonstrated by measuring Chlamydomonas, Euglena, and non-fluorescent beads in both separate and mixed flow samples. The recall rates for Chlamydomonas and Euglena ware 93.6% and 94.4%. The dual-modality imaging approach enabled observing both morphology and fluorescence features with a large DoF and FoV which contribute to high-throughput analysis. Moreover, this imaging flow cytometer platform is portable, low-cost, and shows potential in the onsite phytoplankton monitoring.

The Effect of Roughness Spacing and Size on the Lateral Deflection of Bedload Particles

Bedrock river lateral erosion plays a crucial role in landscape evolution, sediment transport and deposition, and the occurrence of geohazards. Fluvial erosion of massive rock is largely driven by impacts of bedload particles, which also drives crack propagation to prepare blocks for plucking. In straight channels, bedload particles generally move parallel to the channel walls and thus need to be deflected laterally to cause wall erosion. Sideward deflection of bedload particles occurs when they interact with roughness elements fixed on the riverbed. Here, we isolated the interaction of moving bedload particles with roughness elements in laboratory experiments. We conducted 21 sets of flume experiments to systematically investigate how spacing (5, 10, 20, 30, 40, 50, and 60 mm) and size (5, 10, and 20 mm) of roughness elements influence sideward deflection of bedload particles in straight channels with relatively low flow depth and a localized roughness zone covering half of the channel width. Velocity changes by the first impact increase with the size of roughness elements. The deflection length and velocity peak at intermediate values of the spacing of roughness elements. The likelihood for a bedload particle to leave the roughness zone decays with the bedload particle's distance to its edge. Our results suggest that lateral erosion rates in bedrock channels are dominantly controlled by the position of the roughness zone within the channel and its relation to the particle path.

Incoherent ultrarelativistic channeling particle scattering by electrons

The problem of high-energy charged particle motion in the field of atomic strings and planes of oriented crystals, widely applied to control large accelerator beams and generate intense gamma radiation, is addressed. Following the previously developed theory of channeled particles incoherent scattering by crystal atom nuclei, we consider here the same by crystal atom electrons. The theory developed takes into consideration all the effects of momentum transfer between fast particles and electrons of atoms in a crystal in the range from the nuclear radius up to the many inter-atomic distances. The theory also includes the temperature-dependent Debye – Waller factor, as well as both the atomic form factors and scattering function, evaluated with the detail consideration of atomic structure. All the modifications of electron scattering in crystals are reduced to the value of the effective minimum momentum transfer, which by an order of value exceeds that one, related with the Bethe – Bloch mean atomic energy. Substituting this quantity to the expression for the mean square of the scattering angle of a classically moving particle makes it possible to compare the scattering by electrons and nuclei, while its joint use with the Rutherford cross section allows for the correct simulations of the planar channeling of positively charged particles in the thickest crystals, supposed to be used for the beam extraction from high energy accelerators, measurement of electromagnetic characteristics of short-living particles and development of intense narrow-band X-ray and gamma radiation sources based on crystal undulators.

Platinum deposited on 2D and 3D mesoporous silica materials for the catalytic oxidation of volatile organic compounds: The oxidation of m-xylene and methanol

Pt particles deposited on 3D cage-type SBA-16 and 2D-hexagonal SBA-15 mesoporous silica are compared for the total oxidation of m-xylene and methanol. SBA-15 effectively controls the growth of Pt particles in hexagonal channels, producing a smaller particle size than the Pt particles in the cage-like SBA-16 mesopores. Pt particles deposited on SBA-15 provide a stronger ability to dissociate m-xylene and methanol molecules than those formed on SBA-16, thus leading to its high catalytic performance in both oxidation reactions. Regarding m-xylene oxidation, the Pt particles on SBA-15 induce the breakage of the CC bond between phenyl and methyl groups to form CO and carbonyl intermediates, thus enhancing catalytic activity. Methanol adsorbed on Pt catalysts undergoes competitive decomposition and dehydrogenation reactions to form CO and carbonyl species, respectively. SBA-15-supported Pt leads to notable CO formation while also exhibiting high activity for methanol oxidation.

Generalized Taylor dispersion for translationally invariant microfluidic systems

We consider Taylor dispersion for tracer particles in microfluidic planar channels with strong confinement. In this context, the channel walls modify the local diffusivity tensor and also interactions between the tracer particles and the walls become important. We provide a simple and general formula for the effective diffusion constant along the channel as well as the first non-trivial finite time correction for arbitrary flows along the channel, arbitrary interaction potentials with the walls, and arbitrary expressions for the diffusion tensor. The formulas are in particular amenable to a straightforward numerical implementation, rendering them extremely useful for comparison with experiments. We present a number of applications, notably for systems that have parabolically varying diffusivity profiles, to systems with attractive interactions with the walls as well as electro-osmotic flows between plates with differing surface charges within the Debye–Hückel approximation.

Determining particle depth positions and evaluating dispersion using astigmatism PTV with a neural network.

Herein, a calibration procedure to determine the depth positions of particles in a microfluidic channel via astigmatism particle tracking velocimetry (APTV) has been described. A neural network model focusing on the geometrical parameters of distorted particle images was developed to calibrate APTV. To demonstrate the efficiency of this procedure, the Poiseuille flow and depth of the particles, and dispersions in the microchannel were studied. The depth positions were determined with an uncertainty of ±1µm. The present results suggest that the particle position dispersion could be a result of the degree of particle image deformation and its deviation.

Study of the characteristic differences of positive and negative half-cycles from atmospheric pressure glow discharge driven by resonant AC voltage

There are many advantages in obtaining low-temperature plasmas that are rich in active particles by atmospheric pressure glow discharge, so there has been a lot of research on the acquisition method and application of it. However, there is a lack of knowledge about the mechanism of atmospheric pressure glow discharge driven by an AC resonant power supply. In this paper, we describe our study of the characteristic differences between half-cycle positive and negative atmospheric pressure glow discharges driven in open air by an AC resonant power supply, and we describe our analysis of the associated physical mechanism. The comparison and analysis of experimental results indicate that both positive-cycle and negative-cycle discharges led to typical glow discharge and no streamer discharge appeared in the discharge process. There were still charged particles in the discharge channel when the discharge current was zero. With increasing amplitude of the output voltage of the power supply, the glow area near the electrode surface and the plasma distribution area in the discharge channel increased. When the output voltage of the power supply was low, the negative polarity discharge was more likely to form in the gap of the pin-to-plate electrode. In the AC discharge process, the α-mode discharge was dominant, and the developing speed of the positive-cycle discharge was faster than that of the negative-cycle discharge. The polarity effect became less obvious with the increase in the output voltage amplitude of the power supply.

A discrete scheme of the fluid motion equation based on the pore-scale SPH method

To study the phenomenon of convection diffusion and solute migration in porous media, the smoothed particle hydrodynamics method is used to solve the N–S equation describing pore water flow and the linear homogeneous second-order differential equation describing the solute diffusion process. The accuracy of the simulation method is verified by solving the one-dimensional definite solution of the convection diffusion equation at a low Peclet (Pe) number. Under the condition of a high Pe number, the simulation experiment of solute breakthrough porous media at the pore scale is simulated. Through the analysis of the velocity distribution of fluid particles in pore channels of porous media and the mechanical dispersion process of solutes in porous media, it is found that the flow velocity presents a parabolic distribution in the pore channel, and the particles with high velocity are mainly concentrated in the middle of the pore channel between the solid particles. The solute dispersion is obvious in porous media, and some fluid particles containing solutes penetrate porous media earlier along fast-flowing pore channels. Finally, the solute breakthrough curve and the motion path length of the particle are obtained through the simulation experiment. The calculation methods of the dispersion degree and tortuosity of porous media are further given, and the dispersion degree of porous media in this paper is 0.000 95 m.

Numerical study of acoustophoretic manipulation of particles in microfluidic channels.

The microfluidic technology based on surface acoustic waves (SAW) has been developing rapidly, as it can precisely manipulate fluid flow and particle motion at microscales. We hereby present a numerical study of the transient motion of suspended particles in a microchannel. In conventional studies, only the microchannel's bottom surface generates SAW and only the final positions of the particles are analyzed. In our study, the microchannel is sandwiched by two identical SAW transducers at both the bottom and top surfaces while the channel's sidewalls are made of poly-dimethylsiloxane (PDMS). Based on the perturbation theory, the suspended particles are subject to two types of forces, namely the Acoustic Radiation Force (ARF) and the Stokes Drag Force (SDF), which correspond to the first-order acoustic field and the second-order streaming field, respectively. We use the Finite Element Method (FEM) to compute the fluid responses and particle trajectories. Our numerical model is shown to be accurate by verifying against previous experimental and numerical results. We have determined the threshold particle size that divides the SDF-dominated regime and the ARF-dominated regime. By examining the time scale of the particle movement, we provide guidelines on the device design and operation.

Effect of relaxation and retardation times on dusty Jeffrey fluid in a curved channel with peristalsis

In recent work, the Jeffrey liquid with uniform dust particles in a symmetric channel is studied. Moving sinusoidal wave is executed on the walls of the channel, which generates peristaltic transport in the fluid. The governing equations for fluid and dust particles have been formulated using stream function. Perturbation method is used to get analytical solution of the problem by using small wave number. Graphical analysis has been carried out for stream function and velocity of fluid and dust particles. Effects of different parameters such as curvature k, relaxation time [Formula: see text], wave number [Formula: see text] and retardation time [Formula: see text] are debated through graphs for both dust particles and fluid. The noteworthy outcomes are fluid velocity, pressure gradient in the region [Formula: see text] and bolus size increases by increasing [Formula: see text]

Hydrological controls on oviposition habitat are associated with egg‐laying phenology of some caddisflies

Abstract Seasonal variation in resource availability can have strong effects on life histories and population densities. Emergent rocks (ERs) are an essential oviposition resource for multiple species of stream insects. The availability of ERs depends upon water depth and clast size, which vary with discharge and river geomorphology, respectively. Recruitment success for populations may depend on whether peak egg‐laying periods occur at times when ERs are also abundant. For multiple species that oviposit on ERs, we tested whether seasonal fluctuations in ER abundance were concurrent with oviposition phenology. We also tested whether high discharge drowned ERs for sufficiently long periods to preclude egg laying, and whether this problem varied between rivers differing in channel morphology and particle size distribution. We obtained a continuous timeseries of water level (WL) measured every 30 min for 2 years at sites on three rivers in south‐eastern Australia with similar hydrology but different geomorphology. A relationship between WL and ER numbers was determined empirically at each site and these relationships were used to predict ER availability over the 2 years. Egg masses of 10 species of caddisflies were enumerated each month for a year in one river to establish oviposition phenology. Abundance of ERs was inversely related to discharge in all three rivers. ERs were most abundant during autumn and scarce during spring. Site‐specific geomorphology resulted in skewed or multimodal distributions of ER abundance each year. Between years, catchment‐scale hydrometeorology mediated patterns of ER availability, despite the close proximity of sites. Temporal variance in ER availability was not consistently correlated with mean WL or WL variance. ER variance increased with WL variance, when WL was below a threshold equivalent to mean annual WL. Above this threshold, most ERs were likely to be submerged. Oviposition phenology varied strongly among the 10 species of caddisflies, with egg‐laying ranging from 1–2 months to year‐round. Temporal variations in ER and egg mass abundance were not correlated for most species. Below a threshold minimum number of ERs, egg masses were highly crowded onto the few available ERs, which is evidence that ERs were in short supply. For five species, high egg mass abundance was positively associated with periods of the year when the time above the threshold number of ERs was high. Unusually, two species laid most egg masses during winter and when the time above this threshold was short. Three species showed no association between egg mass abundance and time above this threshold; two of these species laid eggs year‐round. Regional hydrometeorology controlled the availability of ERs, but between‐river differences were sufficient to deliver different outcomes in the availability of oviposition sites between years and seasons. Caddisflies were rarely prevented from laying eggs but periods when ERs were in short supply created crowding, which may be associated with negative fitness effects on hatching larvae. Geomorphological controls on availability of oviposition resources may have strong implications for the coexistence of species that overlap in egg‐laying phenology. ​

Progress towards the first measurement of charm baryon dipole moments

Electromagnetic dipole moments of short-lived particles are sensitive to physics within and beyond the Standard Model of particle physics but have not been accessible experimentally to date. To perform such measurements it has been proposed to exploit the spin precession of channeled particles in bent crystals at the LHC. Progress that enables the first measurement of charm baryon dipole moments is reported. In particular, the design and characterization on beam of silicon and germanium bent crystal prototypes, the optimization of the experimental setup, and advanced analysis techniques are discussed. Sensitivity studies show that first measurements of $\Lambda_c^+$ and $\Xi_c^+$ baryon dipole moments can be performed in two years of data taking with an experimental setup positioned upstream of the LHCb detector.

Simulation of cuttings removal processes in the horizontal well

The paper presents the results of a numerical simulation of the process of cleaning the annulus of a horizontal well. The effect of the cuttings particle size on the efficiency of cuttings removal from the annulus of the well was studied. The geometry of a real well was used as the calculation model. Cutting particles with sizes from 2 to 5 mm were considered in the numerical study. Velocity profiles of the solid phase (cuttings particles) in annular channels were obtained in the course of conducted numerical simulation.