Particles In Channel Research Articles

Fractional derivative modeling for sediment suspension in ice-covered channels.

Characterizing the anomalous diffusion behavior of sediment transport is a key factor in calculating sediment concentration. This study attempts to seek an equation that captures the nonlocal movement feature of the transport of an ensemble of sediment particles on ice-covered channels with a steady uniform flow field. Given that the fractional advection-dispersion equation with a noninteger order on the space term is nonlocal and able to describe the long-distance transport, a mathematical model with the Caputo fractional derivative is proposed to estimate the vertical diffusion of suspended sediment particles in the ice-covered channel. Results show that the fractional derivative model has a good predictive ability to the suspended sediment concentration as compared to the measurements. Especially in regions close to the undersurface of the ice cover, the proposed model matches better with experiments than the existing analytical model. Sensitivity analyses indicate that the strength of the turbulent diffusion effect dominates the uniformity of the sediment concentration profile. Besides, the sediment concentration is more sensitive to the variation of the boundary roughness than to the change of the sediment settling velocity. It should be noted that the sediment concentration reduces with the decrease of the order of the fractional derivative, which differs from the findings in previous studies.

Comparative study of pulsed breakdown processes and mechanisms in self-triggered four-electrode pre-ionized switches

This work investigates the pulsed breakdown processes and mechanisms of self-triggered pre-ionized switches with a four-electrode structure in nitrogen through intensified charge coupled device photographs. The diameter of the trigger plane hole mainly determines the switch’s electric field distribution. Two configurations with minimum and maximum trigger plane holes are adopted for comparison. In the switch with a minimum trigger plane hole, the maximum electric field distributes at the surfaces of the main electrodes. Although charged particles in the triggering spark channel cannot drift out, homogeneous discharges can be stimulated from both the cathode and anode surfaces through ultraviolet illumination. Two sub-gaps are likely to break down simultaneously. In the switch with a maximum trigger plane hole, the maximum electric field locates near the trigger electrodes. Discharges in both sub-gaps initiate from the trigger electrodes in the form of a positive or negative streamer. Due to the lower breakdown voltage and electric field threshold for discharge initiation, the cathode side sub-gap breaks down first. The analysis of two extreme examples can be referenced in the future design and improvement of self-triggered four-electrode switches with different trigger electrode structures.

Numerical Calculation of Solid-Liquid Two-Phase Flow in Open-Design Vortex Pump

This paper mainly based on the CFD platform, numerical simulation of the internal flow field in the open-design vortex pump under different solid particle concentration and particle size is carried out to explore the flow trajectory characteristics of solid particles in the impeller channel and the lateral cavity, as well as the distribution characteristics of solid particles, and calculate the sliding velocity of particles in the impeller channel. The results show that at different solid particle concentrations, the solid volume fraction f in the front and rear cover plate area of the blade is high and that in the middle area is low; The solid volume fraction f decreases gradually from the working face to the back, and the solid particles are widely distributed in the inlet area. Due to the asymmetry of the volute structure, the particle concentration in the inlet area corresponding to the casing tongue is significantly higher than that in other areas; Due to the existence of circulating flow and through flow, the solid particles are distributed in a circular direction in the lateral cavity, and the particle concentration in the middle region is large; In the impeller area corresponding to the casing tongue, the sliding velocity of solid particles decreases with the increase of particle size, and the sliding velocity values of 0.5mm and 1.0mm particle sizes are close.

Computational study of inertial migration of prolate particles in a straight rectangular channel

Inertial migration of spherical particles has been investigated extensively using experiments, theory, and computational modeling. Yet, a systematic investigation of the effect of particle shape on inertial migration is still lacking. Herein, we numerically mapped the migration dynamics of a prolate particle in a straight rectangular microchannel using smoothed particle hydrodynamics at moderate Reynolds number flows. After validation, we applied our model to 2:1 and 3:1 shape aspect ratio particles at multiple confinement ratios. Their effects on the final focusing position, rotational behavior, and transitional dynamics were studied. In addition to the commonly reported tumbling motion, for the first time, we identified a new logrolling behavior of a prolate ellipsoidal particle in the confined channel. This new behavior occurs when the confinement ratio is above an approximate threshold value of K = 0.72. Our microfluidic experiments using cell aggregates with similar shape aspect ratio and confinement ratio confirmed this new predicted logrolling motion. We also found that the same particle can undergo different rotational modes, including kayaking behavior, depending on its initial cross-sectional position and orientation. Furthermore, we examined the migration speed, angular velocity, and rotation period as well as their dependence on both particle shape aspect ratio and confinement ratio. Our findings are especially relevant to the applications where particle shape and alignment are used for sorting and analysis, such as the use of barcoded particles for biochemical assays through optical reading, or the shape-based enrichment of microalgae, bacteria, and chromosomes.

Identifying interrill, rill, and ephemeral gully erosion evolution by using rare earth elements as tracers

Understanding hillslope erosion processes is important for the development of physically-based erosion prediction models. However, quantitative information about the successive development of interrill–rill–ephemeral gully erosion on hillslopes is still rare. In this study, rare earth elements (REEs) were employed as tracers to monitor the successive development of different erosion processes on a hillslope. Ten different REE oxides were individually mixed with cultivated loessial soil from farmland on the Loess Plateau of China. The ten tagged soils were packed in ten layers into a flume (5 m in length, 1 m in width and 0.7 m in depth with a 20° gradient). Simulated rainfall events with natural rainstorm intensities of 60- and 90-mm h−1 were conducted, and each rainfall intensity event contained three subevents that lasted for 135 mm rainfall depth for each subevent. The runoff and sediments for each test were collected at the outlet of the flume at 4.5-minute and 3-minute intervals, respectively. The flow velocity, flow depth and width and depth of the main channel were also synchronously measured. The results showed that the hillslope erosion went through five evolutionary stages: interrill erosion, rill development, stabilized rill, ephemeral gully development, and stabilized ephemeral gully. These stages were quantitatively identified according to the changing contribution rates of the interrill, rill and ephemeral gully areas. The channel width always developed faster than the depth at both the 60 mm h−1 and 90 mm h−1 rainfall intensities. The hydrological parameters could greatly explain the channel evolution and particle size changes. A larger flow power of 90 mm h−1 intensified the channel morphology evolution in the early development stage. The friction coefficient finally remained steady and the W/D ratio eventually approached a stable value of approximately 2 in the stabilized ephemeral gully stage. Selective erosion occurred in the transportation processes were gradually weakened due to rapid increase of flow power and the overall detachment of the large clods in the channel, as manifested by particle size distribution in sediments approaching primary particle size distribution with time. This study is helpful for deeply understanding hillslope erosion processes, especially the successive evolution of interrill-rill-ephemeral gully.

Study on the Motion Characteristics of Solid Particles in Fine Flow Channels by Ultrasonic Cavitation.

Microjets caused by the cavitation effect in microchannels can affect the motion trajectory of solid particles in microchannels under ultrasonic conditions. The optimal parameters for an observation experiment were obtained through simulations, and an experiment was designed to verify these parameters. When the cavitation bubbles collapse in the near-wall area, the solid particles in the microchannel can be displaced along the expected motion trajectory. Using fluent software to simulate the bubble collapse process, it can be seen that, when an ultrasonic sound pressure acts on a bubble near the wall, the pressure causes the top of the bubble wall to sink inward and eventually penetrate the bottom of the bubble wall, forming a high-speed microjet. The maximum speed of the jet can reach nearly 28 m/s, and the liquid near the top of the bubble also moves at a high speed, driving the particles in the liquid towards the wall. A high-speed camera was used to observe the ultrasonic cavitation process of bubbles in the water to verify the simulation results. A comparison of particle motion with and without ultrasonic waves proved the feasibility of using the ultrasonic cavitation effect to guide small particles towards the wall. This method provides a novel experimental basis for changing the fluid layer state in the microchannel and improving precision machining.

Multiple scattering of channeled and non-channeled positively charged particles in bent monocrystalline silicon

We present the results of an experimental study of multiple scattering of positively charged high-energy particles in bent samples of monocrystalline silicon. This work confirms the recently discovered effect of a strong reduction in the rms multiple scattering angle of particles channeled in the silicon (111) plane. The effect is observed in the plane orthogonal to the bending plane. We show in detail the influence of angular constraints on the magnitude of the effect. Comparison of the multiple scattering process at different energies indicates a violation of the law of inverse proportionality of the rms angle of channeled particles with energy. By increasing the statistics, we have improved the results of multiple scattering measurements for particles moving, but not channeled, in silicon crystals.

Imaging Flow Cytometry for Sizing and Counting of Subvisible Particles in Biotherapeutics

Imaging flow cytometry (IFC), a technique originally designed for cellular imaging, is featured by the parallel acquisition in brightfield (BF), fluorescence (FL), and side scattering channels. Introduced to the field of subvisible particle analysis in biopharmaceuticals roughly ten years ago, it has the potential to yield additional information, e.g., on particle origin. Here, we present an extensive, systematic development of masks for IFC image analysis to optimize the accuracy of size determination of polystyrene beads and pharmaceutically relevant particles (protein, silicone oil) in BF and FL channels. Based on the developed masks, particle sizing and counting by IFC are compared to flow imaging microscopy (FIM). Mask verification based on fluorescent polystyrene particles revealed good agreement between sizes obtained from IFC and FIM. In the evaluation of counting accuracy, IFC reported lower concentrations for polystyrene particle standards than FIM. For the analysis of fluorescently stained silicone oil and protein particles however, IFC FL imaging reported higher particle concentrations in the low micrometer size range. Overall, we identified IFC as suitable tool to generate supportive data for particle characterization purposes or trouble shooting activities, but not as routine quantitative technique, e.g., for subvisible particle analysis during drug product development or quality control.

Effect of wall slip on the viscoelastic particle ordering in a microfluidic channel.

The formation of a line of equally spaced particles at the centerline of a microchannel, referred as "particle ordering," is desired in several microfluidic applications. Recent experiments and simulations highlighted the capability of viscoelastic fluids to form a row of particles characterized by a preferential spacing. When dealing with non-Newtonian fluids in microfluidics, the adherence condition of the liquid at the channel wall may be violated and the liquid can slip over the surface, possibly affecting the orderingefficiency. In this work, we investigate the effect of wall slip on the ordering of particles suspended in a viscoelastic liquid by numerical simulations. The dynamics of a triplet of particles in an infinite cylindrical channel is first addressed by solving the fluid and particle governing equations. The relative velocities computed for the three-particle system are used to predict the dynamics of a train of particles flowing in a long microchannel. The distributions of the interparticle spacing evaluated at different slip coefficients, linear particle concentrations, and distances from the channel inlet show that wall slip slows down the self-assembly mechanism. For strong slipping surfaces, no significant change of the initial microstructure is observed at low particle concentrations, whereas strings of particles in contact form at higher concentrations. The detrimental effect of wall slip on viscoelastic ordering suggests care when designing microdevices, especially in case of hydrophobic surfaces that may enhance the slippingphenomenon.

Improvements and validation of particle channeling model in GEANT4

In this work several modifications to the default GEANT4 channeling model are provided and the results are validated against experimental data. The channeling model in GEANT4 10.3 version comes with physical process wrapper classes instead of cross section biasing operations which are used in the version 11.0. Initial simulations have shown that inaccurate energy losses of channeled particles are simulated with the original GEANT4 11.0 channeling model. In order to correct this, the cross section biasing operations were changed with the wrapper classes and the energy loss of channeled particles was compared to experimental results. The energy loss of protons and deuterons was evaluated and validated along the 〈100〉, 〈110〉 and 〈111〉 directions of Si, Ge and GaAs in the energy region 1–20 MeV. The difference between the simulated and the experimental stopping powers was less than 10 % in most cases. Higher deviations (up to ∼ 20 %) were observed in the low energy region, below 4 MeV. The overall good agreement with the experimental results shows that the modified model is able to accurately predict stopping powers in channeling conditions for protons and deuterons. Another modification to the model was the inclusion of the condition of critical channeling angle. The simulations have shown that the simulated critical angle is in good agreement with the theoretical one. Also, the comparison of different particle step size limitations during the simulations has shown that the channeling process is particularly sensitive to simulation conditions such as beam spread, sample rotation, lattice quality etc. The modified model is being further developed and the possibility of RBS/C spectra simulation is investigated.

Fluctuational Features of Diffusive Passage of Particles in Narrow Channels with Obstacles

Fluctuational Features of Diffusive Passage of Particles in Narrow Channels with Obstacles

Reliability-based vulnerability analysis of bridge pier subjected to debris flow impact

In this paper, a finite element model of a highway bridge pier subjected to debris flow is established, which comprises a double-column pier, a gully channel, moving fluid and solid particles. By using the arbitrary Lagrangian-Eulerian (ALE) algorithm to calculate the fluid-solid coupling effect, the process of debris flow impacting on the pier is simulated. Based on the ‘two-phase flow’ theory, a simplified equation to calculate the impact force of debris flow containing both fluid and solid phases is proposed, and the variable parameters in the equation are determined through numerical simulation using the established FE model and the field-measured data. By comparing with the historical records of actual debris flows, the effectiveness of the numerical model and the proposed equation is verified. A reliability model of the pier subjected to debris flow is established, and the structural vulnerability is estimated by the MCS method. Using the site-observed data, the failure mode of a highway double-column pier subjected to impact of two-phase debris flow is studied. The critical velocities of debris flow causing the structure to have different modes of damage, and the critical impact height of debris flow on the pier suffering bending and shear failures are determined.

Motion of submicrometer particles in micrometer-size channel measured by defocusing nano-particle image velocimetry

Understanding the motion of colloidal particles flowing in small spaces is a general issue in various fields such as thermal engineering and micro/nanofluidics. In the present study, we investigated the motion of fluorescent submicrometer particles in a 3-μm microchannel by defocusing nanoparticle image velocimetry. An optical measurement system with controlled spherical aberration and an algorithm for processing defocused particle images with multiple diffraction rings were developed. By detecting the centroid position and the diameter of the outermost diffraction ring, which is proportional to the distance between the focal plane and the particle, the position of particles was determined with the spatial resolutions of 154–204 nm in the streamwise direction and 76–311 nm in the depthwise direction, which are comparable to or smaller than the optical diffraction limit. A reusable microfluidic device containing a size-regulated microchannel made of glass was developed, which is suitable for optical measurements and precise flow control. By controlling the strength of low-temperature glass bonding, detachment of the bonded glass substrates, washing, and reuse were achieved. Based on this method and technology, the velocity of particles with diameters of 199, 457, and 1114 nm was successfully measured in pressure-driven laminar flow. Results suggested that for larger particles comparable to the channel size, the particle velocity is slowed from the flow velocity by particle–wall hydrodynamic interactions. Therefore, the motion of colloidal particles in 100-μm spaces is considered to be affected by particle–wall hydrodynamic interactions, as well as 102-μm spaces reported previously.

Capturing of particles in suspension flow through a micro cross-shaped channel

Capturing of microscale particles through microfluidics has been a flourishing research area in chemical and biological engineering applications. This work follows our previous report (Zhang et al., AIChE J., vol. 66, 2019, e16822) by using micro plane laser-induced fluorescence (μPLIF) and high-speed photography technology to study the flow of a diluted suspension of buoyant particles in a micro cross-shaped channel at 30≤Re≤350. Particular attention is paid to particle accumulation behaviors caused by vortex breakdown within the steady engulfment flow and vortex shedding flow. Three particle capture modes are identified in accumulation regions including the particle chain mode, the steady and unsteady particle cluster mode at 100≤Re≤300. Multiple stable equilibrium orbits formed by captured particles in accumulation regions are attributed to the axial force balance. In addition, perturbations in particle trajectories induced by the vortex shedding flow or particle-particle interactions contribute to the particle release.

Particle Dynamics-Based Stochastic Modeling of Carbon Particle Charging in the Flow Capacitor Systems

Aqueous electrochemical flow capacitors (EFCs) have demonstrated high-power capabilities and safety at low cost, making them promising energy storage devices for grid applications. A primary performance metric of an EFC is the steady-state electrical current density it can accept or deliver. Performance prediction, design improvements, and up-scaling are areas in which modeling can be useful. In this paper, a novel stochastic superparticle (SP) modeling approach was developed and applied to study the charging of carbon electrodes in the EFC system, using computational superparticles representing real carbon particles. The model estimated the exact values of significant operating parameters of an EFC, such as the number of particles in the flow channel and the number of electrolytic ions per carbon particle. Optimized model parameters were applied to three geometrical designs of an EFC to estimate their performance. The modeling approach allowed study of the charge per carbon particle to form the electric double-layer structure. The linear relationship between the concentration of SPs and the ionic charge was observed when optimized at a constant voltage of 0.75 V. The simulation results are in excellent agreement with experimental data, providing a deep insight into the performance of an EFC and identifying limiting parameters for both engineers and material scientists to consider.

Comparison of laser induced breakdown spectroscopy and fast ICCD imaging for spatial and time resolved measurements of atmospheric pressure helium plasma jet

In this paper we compared the fast Intensified Charge Coupled Device (ICCD) imaging with the newly developed diagnostic method that utilizes laser induced breakdown in plasma jet. Our helium plasma jet was powered by an 80 kHz high-voltage sine wave and propagated into the ambient air. Pulsed laser beam 1064 nm (4 ns pulse duration and 5 Hz repetition rate) was focused with the lens into the plasma jet at energy below breakdown threshold in helium. Laser pulses and the jet powering signal were synchronized. Laser induced plasma is highly dependent on the concentration of seed electrons and other charged particles in the plasma jet channel. We compared the radial profiles of the plasma jet obtained with these two methods. For laser induced breakdown it was ±0.5 mm and for ICCD measurement it was ±1.75 mm, while the ionization wave velocities obtained with these two methods were 15 km s−1 and 20 km s−1 respectively. Electrical characteristics of the plasma jet were also presented and one can see a large hysteresis effect when the applied power to the plasma jet was reducing. We show that the laser induced breakdown spectroscopy can be used as a complementary diagnostics technique with ICCD measurements.

A Ferromagnetic Particle Sensor Based on a Honeycomb Permanent Magnet for High Precision and High Throughput

A multi-channel passive ferromagnetic particle inductive sensor is proposed, which is mainly composed of a honeycomb permanent magnet and a set of coils. The honeycomb magnet generates the same high gradient static magnetic field in each channel (a total of 7 channels, 6 surrounding and 1 center), which helps improve the sensor’s throughput while maintain high precision. An induced voltage model that includes most of the structural design parameters is proposed, which provides theoretical support for sensor optimization. The correctness of this model is verified by finite element simulation and experiments. The experimental results show that the detection performance of each channel is almost the same, which is expected to be further improved by setting a reference channel. Moreover, the sensor can detect 70 μm iron particles in a single channel of diameter 4 mm. The proposed sensor can reduce the influence of magnetic field radial uniformity on the induced signals, improve the detection precision, and achieve high throughput (about a 14-fold increase in throughput compared to our previous work). Its high precision and high throughput favor lots of lube oil detection.

Drag coefficient modification for proppant transport in fractures considering wall retardation

Proppant transport is crucial in hydraulic fracturing, which determines fracture conductivity and well productivity. Proppant transport in hydraulic fractures is essentially the dense solid−liquid flow. Unlike the widely studied fluid-solid flow in chemical engineering and fluvial sediment transport, the motion of proppants (particles) will be significantly affected by walls of narrow channels such as fractures and slots, because the drag force is changed. This paper studies the wall-retardation effect on particle movement, and modified the drag coefficient for simulating liquid−solid flow in narrow-width fractures. Both experiments and simulations on proppant transport are conducted. The drag coefficient considering wall-retardation effect is modified by the Lattice Boltzmann method (LBM), and is integrated into OpenFOAM for two fluid method (TFM) numerical simulation. Experiment and simulation results show a good agreement, and the improved drag model is more advanced than the Gidaspow model in reproducing the movement characteristics of suspended particles in narrow channels. Compared to previous research outcomes about this topic, this work can efficiently improve the accuracy on proppant transport simulation and be widely applied in industrial numerical simulations.

Research on a Critical Hydraulic Gradient of Piping in Noncohesive Soils

The critical hydraulic gradient of cohesive soil is an important condition for judging soil piping. For force analysis of movable particles in pore channels of soil, this study proposes to consider the influence of surrounding particles on the drag force of movable particles by water flow. According to the principle of relative motion, considering the interaction force between moving objects in still water, the value of the drag force of water flow that is affected by surrounding particles is calculated, to derive the method of the critical hydraulic gradient. This calculation method is suitable for the results of previous piping tests, and the method is accurate and concise.

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.