Particle Transport Research Articles

Osmotic and phoretic competition explains chemotaxic assembly and sorting

Microscale objects responding to chemical gradients by migrating toward or away from a preferred species is a simple yet constitutive mechanism by which transport occurs in biological organisms. Synthetic chemotaxis provides key physical descriptions of simplified systems that can be used in biological models, or in the creation of advanced responsive material systems. In this article, we provide a quantitative framework for understanding synthetic chemotaxis of microparticles which involves a competition between phoresis and osmosis. We present separate quantitative measurements of phoresis and osmosis acting on individual taxing particles, finding that phoresis follows the long-predicted [Formula: see text] scaling while the osmotic contribution depends on the geometry and details of the system, and must be solved on a case-by-case basis. Through this, we are able to develop a more accurate picture of particle transport at the single particle level. Equipped with this approach, we go on to describe how high concentrations of particles in a symmetric chemical gradient grow close-packed hives that reach a steady-state size tunable through light intensity or particle size. Last, we demonstrate that mixed particles experiencing the same chemical gradient will selectively migrate toward or away depending on the nature of the particle surface, thereby locally sorting out a particular species. We anticipate these results will be important in describing both biological and synthetic chemotaxis in phoretic systems and should bring a wealth of studies that take advantage of competing osmotic flows to illicit unexpected dynamic active behavior.

Acoustofluidic Tweezers Integrated with Droplet Sensing Enable Multifunctional Closed-Loop Droplet Manipulation.

Droplet manipulation technologies with surface acoustic waves attract significant attention for applications in fluid handling and bioanalysis. However, existing technologies face challenges in automation, precision, and functional integration, limiting broader applications. In this work, a highly integrated droplet-sensing acoustofluidic tweezer is developed, incorporating orthogonally arranged slanted finger interdigital transducers and a custom-designed control and detection circuit system. Using a single acoustic device, this tweezer enables switchable acoustic droplet manipulation and detection, providing multifunctional closed-loop manipulation of on-chip microliter-scale droplets. The platform takes advantage of the wideband frequency response characteristics of the transducers, along with an automated droplet detection algorithm, enabling high-precision detection of central positions, edge positions, contact diameters, and the number of droplets. With this feedback, automated closed-loop control of various droplet manipulation functions, including transportation, merging, mixing, splitting, and internal particle enrichment, is achieved for the first time on a single acoustic platform. This significantly enhances the precision, efficiency, and fault tolerance of the manipulation process. This droplet-sensing acoustofluidic tweezer provides an innovative acoustic solution for droplet manipulation technologies in fields such as fluid processing and biosensing, demonstrating significant application potential.

Particle transport and deposition in wall-sheared thermal turbulence

We studied the transport and deposition behaviour of point particles in Rayleigh–Bénard convection cells subjected to Couette-type wall shear. Direct numerical simulations (DNSs) are performed for Rayleigh number ( $Ra$ ) in the range $10^{7} \leq Ra \leq ~10^9$ with a fixed Prandtl number $Pr = 0.71$ , while the wall-shear Reynolds number ( $Re_w$ ) is in the range $0 \leq Re_w \leq ~12\,000$ . With the increase of $Re_w$ , the large-scale rolls expanded horizontally, evolving into zonal flow in two-dimensional simulations or streamwise-oriented rolls in three-dimensional simulations. We observed that, for particles with a small Stokes number ( $St$ ), they either circulated within the large-scale rolls when buoyancy dominated or drifted near the walls when shear dominated. For medium $St$ particles, pronounced spatial inhomogeneity and preferential concentration were observed regardless of the prevailing flow state. For large $St$ particles, the turbulent flow structure had a minor influence on the particles’ motion; although clustering still occurred, wall shear had a negligible influence compared with that for medium $St$ particles. We then presented the settling curves to quantify the particle deposition ratio on the walls. Our DNS results aligned well with previous theoretical predictions, which state that small $St$ particles settle with an exponential deposition ratio and large $St$ particles settle with a linear deposition ratio. For medium $St$ particles, where complex particle–turbulence interaction emerges, we developed a new model describing the settling process with an initial linear stage followed by a nonlinear stage. Unknown parameters in our model can be determined either by fitting the settling curves or using empirical relations. Compared with DNS results, our model also accurately predicts the average residence time across a wide range of $St$ for various $Re_w$ .

In silico formulation optimization and particle engineering of pharmaceutical products using a generative artificial intelligence structure synthesis method

Pharmaceutical drug dosage forms are critical for ensuring the effective and safe delivery of active pharmaceutical ingredients to patients. However, traditional formulation development often relies on extensive lab and animal experimentation, which can be time-consuming and costly. This manuscript presents a generative artificial intelligence method that creates digital versions of drug products from images of exemplar products. This approach employs an image generator guided by critical quality attributes, such as particle size and drug loading, to create realistic digital product variations that can be analyzed and optimized digitally. This paper shows how this method was validated through two case studies: one for the determination of the amount of material that will create a percolating network in an oral tablet product and another for the optimization of drug distribution in a long-acting HIV inhibitor implant. The results demonstrate that the generative AI method accurately predicts a percolation threshold of 4.2% weight of microcrystalline cellulose and generates implant formulations with controlled drug loading and particle size distributions. Comparisons with real samples reveal that the synthesized structures exhibit comparable particle size distributions and transport properties in release media.

The efficacy and safety of aerosol therapy in rhinology

Abstract Aerosol drug administration has a long history as an important part of the treatment for different respiratory disorders in both adult and paediatric patients. The nebulization process permits the drug delivery directly to the upper and lower airways tracts, allowing increased local effectiveness, and avoids systemic side effects. The aerosol therapy is mainly used in pneumology for lower respiratory tract disorders, a series of drugs having a proven efficacy. Few publications present the efficacy and safety of ENT nebulization, despite its worldwide utilization. Topical drug delivery to the nasal cavities and paranasal sinuses via aerosols appears to be an interesting, but also a challenging alternative. The transport and deposition of drugs and aerosol particles into the sinuses is debatable due to several factors: sinuses are poorly perfused and virtually non-ventilated cavities; they are protected by the efficient particle filtration function of the nasal cavities. The review evaluates the efficacy and safety of aerosol therapy in rhinologic pathology.

Particle transport and turbulence modification in unstably stratified mixed convection within a horizontal channel

Particle transport and turbulence modification in an unstably stratified, particle-laden turbulent flow within a horizontal channel is studied via direct numerical simulations combined with Lagrangian point‒particle tracking techniques. Two-way coupling in momentum and energy is considered in dilute gas‒solid flows under mixed convection (synergistic effects of shear and buoyancy). For comparison, simulations of neutral turbulence are also conducted with equivalent parameters. The study reveals that large-scale longitudinal vortical structures induce significant spatial heterogeneity in the spanwise distribution of inertial particles. This heterogeneity is characterized by an increase in the particle concentration on the side of the cold plume and a corresponding decrease on the side of the hot plume. In the context of unstably stratified turbulence, particles reduce the fluid streamwise velocity and promote its profile toward symmetry. This phenomenon contrasts with that observed in neutral flows, where particles induce velocity asymmetry by dragging the upper flow and accelerating the lower flow. A quantitative analysis of the heat flux indicates that particles absorb heat as they settle, thereby reducing the average temperature of the flow. Buoyancy effects slow the settling and reinjection of particles, which in turn diminishes thermal energy absorption. Particles with higher inertia preferentially settle on the cooler plume side, minimizing their participation in heat exchange due to prolonged durations of repeated wall collisions.

Statistical analysis of the association between El Niño and the biological carbon pump in the East Sea (Japan Sea)

Understanding the impacts of climate change on oceanic carbon cycling is important from a carbon sequestration perspective. A sediment trap study focused on the biological carbon pump system in the Ulleung Basin (UB) in the southwestern part of the East Sea (Japan Sea) was conducted from 2011 to 2017. Particulate organic carbon (POC) flux significantly increased by 37, 56, and 43% from 2014 to 2016 during the El Niño phase. We examined data related to water current variability, such as sea surface height, current velocity, and eddy frequency to understand their roles in particle transport. In addition, a Martin curve was employed to analyze the rate of vertical attenuation of POC flux in the UB. Current variability could be the most important factor influencing the increase in sinking-particle flux during the El Niño phase.

Acoustic Drift: Generating Helicity and Transferring Energy

This article studies the general properties of the Stokes drift field. This name is commonly used for the correction addedto the mean Eulerian velocity for describing the averaged transport of the material particles by the oscillating fluid flows. Stokes drift is widely known mainly in connection with another feature of oscillating flows known as steady streaming, which has been and remains the focus of a multitude of studies. However, almost nothing is known about Stokes drift in general, e.g., about its energy or helicity (Hopf’s invariant). We address these quantities for acoustic drift driven by simple sound waves with finite discrete Fourier spectra. The results discover that the mean drift energy is partly localized on a certain resonant set, which we have described explicitly. Moreover, the mean drift helicity turns out to be completely localized on the same set. We also present several simple examples to reveal the effect of the power spectrum and positioning of the spectral atoms. It is revealed that tuning them can drastically change both resonant and non-resonant energies, zero the helicity, or even increase it unboundedly.

Pairwise interaction of in-line spheroids settling in a linearly stratified fluid

AbstractThis study investigates the transport of particles in density-stratified fluids, a prevalent natural phenomenon. In the ocean, particles and marine snow descend through fluids with significant density variations due to salinity and temperature gradients. Such heterogeneity in the background fluid affects the settling or rising rates of particles, often leading to accumulation at transitional density layers. Previous research has primarily focused on spherical particles, examining their isolated motion, pairwise interactions, and collective transport in stratified fluids. This work, however, extends the investigation to the interaction between two spheroidal particles settling in-line in a linearly stratified fluid. This study employs an immersed-boundary technique to perform particle-resolved numerical simulations in a three-dimensional Cartesian domain. The results showcase the effects of varying the stratification strength through the Froude number, the particles’ aspect ratios, and the initial separation distance between the particles on the interaction dynamics between the settling spheroids.

Sediment transport on rippled beds

We conduct an Euler-Lagrange, direct numerical simulation of a turbulent channel flow at a shear Reynolds number of Reτ=180 over an erodible particle bed. The particle bed consists of approximately 1.3 × 106 monodisperse particles, resulting in a bed thickness of around 12–13 particles. The particle density and size are chosen to achieve a ratio of 4 for the Shields stress to the critical Shields stress necessary for incipient motion such that particle transport occurs primarily as bedload. The simulation is run long enough for ripples to form. We track the temporal evolution of the particle flux and excess Shields stress for the entire bed as well as for the four regions of a ripple, namely, the crest, trough, lee side, and stoss side. We find that the particle flux and excess Shields stress closely match the Wong and Parker correlation when the particle bed is featureless at early time but diverge from the correlation when ripples form. This deviation primarily arises from particle transport in the trough and lee side regions. Conversely, particle transport in the crest and stoss side regions remains largely consistent with the Wong and Parker correlation. A root mean square-based correction for the bed is proposed to be used in conjunction with the Wong and Parker correlation. Additionally, ripples attain a self-similar profile in the shape and near-bed shear stress when they are sufficiently distant from their upstream neighbor. Any departure from self-similarity occurs when the upstream neighbor gets within close proximity.

Transport of particles in a model of 2D Rayleigh-Benard convection that conserves energy and vorticity

In contrast with the Lorenz model for 2-dimensional Rayleigh - Bénard system, the model proposed by Howard - Krishnamurti (HK) allows the possibility of a large scale horizontally shear flow making feasible the study of particles transport. However, this model lacks conservation of energy and vorticity in the absence of forcing and dissipation. A model that incorporates conservation of energy and vorticity was proposed by A. Gluhovsky et al (GTA). We perform the linear stability analysis of this later model and study the transport process on this velocity field background and make a comparison with the features of the former model. We found that the basic bifurcation structure is retained by the GTA model and discuss the differences that they indeed have. In regard to the transport processes, the basic features found using the HK velocity field background are also kept by the GTA model. We determine the size of the rather small gap in the Rayleigh number where the transport process shift from being shear flow dominated to a Brownian diffusion process.

Effects of fluid properties on coarse particles transport in vertical pipe

The mineral resources in deep-seabed are attracting extensive attention. A numerical simulation of particle transport in a vertical pipe for a deep-sea mining system is conducted using the CFD-DEM method. The effects of fluid density, fluid viscosity and rheological parameters of non-Newtonian fluids on the liquid-solid flow behavior in a vertical pipe are investigated. For Newtonian fluids, increasing the density or viscosity enhances the particles' performance in following the fluid and reduces the slip velocity, but also increases the pressure drop. The efficient lifting of particles can be facilitated by adjusting fluid density and viscosity, while considering factors such as energy consumption. For non-Newtonian fluids, an increase in either the flow behavior index n or the consistency coefficient k results in an increase in the fluid's apparent viscosity. This leads to an increase in the particle suspension capacity and local particle velocity, along with a decrease in local particle concentration.

Characteristics of Particle-Wet Wall Impact Damage: Effects of Liquid Film Parameters

Particle impact damage significantly affects the safe and stable operation of energy and chemical process equipment. During particle transportation, a liquid film may form on the wall, influencing the damage mechanism caused by particle effect. This study investigates the effects of liquid film parameters, specifically viscosity and thickness, on wall damage. Hydroxypropyl Methylcellulose (HPMC) solution was applied as a liquid film, and the effect of the liquid film's viscosity and thickness was examined through impact damage experiments using a particle (45 steel) and a wall (1060 aluminum alloy) with the liquid film. Results indicate that the presence of a liquid film can inhibit wall damage. Increased liquid film viscosity and thickness reduce wall damage, but they affect the turning points of damage characteristic parameters differently concerning impact angle and velocity. Finally, the study establishes correlation between dry and wet impact by introducing the effect coefficient of liquid film. This reveals the alteration rules of the influence coefficient and proposes a wet impact damage model, providing a reference for the damage prediction in process equipment.

Dry powder inhaler deposition in the larynx and the risk of steroid inhaler laryngitis: a computational fluid dynamics study

Dry Powder Inhalers (DPIs) are a mainstay in the treatment of obstructive respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). Deposition of inhaled corticosteroids in the larynx elicits local side effects, potentially leading to steroid inhaler laryngitis. The objective of this study was to estimate the dose of DPIs that are deposited in the larynx relative to other regions of the respiratory tract using computational fluid dynamics (CFD). An anatomically accurate model of the airways (mouth to main bronchi) was constructed based on medical imaging of a healthy adult. Respiratory airflow and particle transport were simulated for constant inhalation rates of 30, 45, and 60 L/min. Two turbulence models were compared, namely the large eddy simulation (LES) and the models. DPIs were assumed to generate an aerosol cloud with a log-normal particle size distribution characterized by the mass median aerodynamic diameter () and geometric standard deviation (). We compared two commercial DPIs, namely DPI 1 had a large particle size ( = 50 μm, ) and DPI 2 had a small particle size ( = 2 μm, ). The laryngeal dose was 1.6-to-3.8-fold higher than the bronchial dose for DPI 1, while the laryngeal and bronchial doses (units of mass per unit surface area) were similar for DPI 2 for both turbulence models and all inhalation rates. The choice of turbulence model had little impact on the total extrathoracic deposition, but a significant impact on regional doses, with the LES model predicting higher larynx-to-bronchi relative doses than the model. Our prediction that the larynx is a hotspot for DPI deposition is consistent with the observation of laryngeal side effects in DPI users. Importantly, our simulations suggest that DPIs with larger particles ( = 50 μm) may increase the risk of steroid inhaler laryngitis.

On the interplay between fluid flow characteristics and small particle deposition in turbulent wall bounded flows

This study investigates the transport and deposition of small particles (500 nm≤dp≤10 μm) in a fully developed turbulent channel flow, focusing on two fluid friction Reynolds numbers: Reτ=180 and Reτ=1000. Using the point particle–direct numerical simulation method under the assumption of one-way coupling, we study how fluid flow (carrier phase) characteristics influence particle deposition. Our findings suggest that changes in flow conditions can significantly alter the deposition behavior of particles with the same size and properties. Furthermore, we show for the first time that gravity has minimal impact on deposition dynamics only at high Reynolds numbers. This research enhances our understanding of small particle deposition and transport in turbulent flows at high Reynolds numbers, which is crucial for various industrial applications.

Experimental study on the unsteady evolution mechanism of centrifugal pump impeller wake under solid–liquid two-phase conditions: Impact of particle concentration

To study the spatiotemporal evolution process of particle wakes behind the impeller in the centrifugal pump, this paper utilized high-speed photography to capture the particle motion characteristics under different solid-phase particle concentrations (1%, 1.5%, and 2%). First, this paper studies the changes in hydraulic performance of the centrifugal pump under solid–liquid two-phase flow conditions. It then introduces the evolution process of the impeller particle wake, comparing the differences in particle wake evolution under varying solid-phase concentrations. Finally, the impact of the solid-phase concentration on the wear of the volute's partitions is investigated. This study found that as the solid-phase particle concentration increases, the hydraulic performance of the pump gradually declines. Under the design conditions, when the solid-phase concentration increases by 0.5%, the efficiency of the centrifugal pump decreases by 0.56% and 0.35%. There is mutual transport of particles between adjacent wakes, and the movement of particle wakes within the volute passage is not equidistant over time. As the solid-phase particle concentration increases, wake cutting occurs at the volute partitions, and there is a significant solid–liquid separation between the particle wakes. The spatial evolution of the particle wakes is significantly influenced by the solid-phase concentration. Wear at the volute partitions intensifies with increasing solid-phase concentration and is also affected by changes in the particle wakes. The research results provide a basis for further exploration of the solid–liquid two-phase flow dynamics within centrifugal pumps.

Experimental research on nonlinear vibration characteristics of double-layer mining string for deep-sea hydrate extraction under internal and external flow excitation

The vibration mechanism of the deep-sea hydrate mining string is extremely complex due to the combined effects of internal gas–liquid solid multiphase flow, structural contact collision, soil creep effect, and external ocean random load. Based on this, using the principle of similarity, a simulation experimental platform for the vibration of double-layer mining riser in deep-sea hydrate wells under internal and external flow excitation is developed, considering the vortex-induced effect of external flow field on the mining riser in the ocean section (which can simulate a maximum ocean flow velocity of 0.5 m/s), the three-phase flow-induced effect of gas–liquid–solid inside (which can simulate a maximum flow velocity of 2.0 m/s), and the coupling effect of mining string–conductor anchor node (CAN)–seabed. The influence of particle size, phase ratio, three-phase flow, and external flow velocity on the vibration response characteristics and nonlinear behavior of mining string are investigated. It is found that the vibration of vertical string is significantly affected by external ocean currents and internal three-phase currents. The vibration displacement amplitude of the horizontal section (average 0.08 mm) is significantly smaller than those of the vertical section (average 70 mm). The strong vibration positions of the vertical and horizontal sections of the mining string are different, in that the vertical section is mostly located below the middle section (just at 1800–2400 mm), while the horizontal section is mostly located at the three-phase inlet (just at 500 mm). The vertical section of the mining string presents a motion trajectory of oblique straight line, wide oblique straight line, or approximately wide oblique straight line, while the horizontal section is mostly a chaotic trajectory or an “8”-shaped chaotic trajectory. The decrease in particle mesh size and the increase in solid-phase proportion are reflected in the difficulty and accumulation of particle transport, leading to an increase in vibration displacement, as well as a decrease in vibration displacement amplitude and vibration energy. When the particle size set as 50 mesh, the displacement of mining string is largest, just for 110 mm of vertical section and 0.08 mm of horizontal section. The increase in the proportion of gas phase will lead to changes in the flow state of multiphase flow, which will affect the vibration displacement amplitude of the mining string to varying degrees. The increase in three-phase flow velocity further induces vibration of the mining string, and when the flow velocity is between 1.5 and 1.75 m/s, it will resonate with the string system, resulting in a sudden increase in the amplitude of vibration displacement. The research results can effectively guide operations and improve the service life of deep-sea hydrate mining riser.

An implicit unified gas-kinetic particle method with large time steps for gray radiation transport

For a long time, efficient algorithms for high-dimensional equations, represented by photon radiation transport, have been one important topic in the development of computational methods for particle transport processes. In this paper, we present an implicit unified gas-kinetic particle (IUGKP) method for multiscale gray radiative transfer. Based on the integral solution of the radiative transfer equation, the photon transport processes are categorized into non-equilibrium transport processes with a large photon free path and equilibrium transport processes with a small photon free path. The long-path processes are solved by an implicit Monte Carlo (IMC) method, and the short-path processes are solved by an implicit diffusion system. The closure formulation of photon distribution is derived from the local integral solution of the radiative transfer equation to couple the IMC and diffusion system. The improvement of the proposed IUGKP method over UGKP method is that particles can be tracked continuously instead of just until the first collision, making simulation with large time steps possible. The IUGKP method has the properties of asymptotic-preserving (AP) and regime-adaptive (RA). The AP property states that the IUGKP method converges to the consistent numerical methods for the asymptotic limiting equations of RTE in the limiting regimes. The RA property states that the computational accuracy of the IUGKP method adapts to the regimes. In this paper, the mathematical proof of the AP and RA properties is presented, and the multiscale numerical tests are performed to demonstrate the accuracy and efficiency of the IUGKP method.

Numerical Simulation of Solid Diverting Particles Transport and Plugging in Large-Scale Hydraulic Fracture

Diversion technology, also known as temporary plugging technology, has become an integral part of hydraulic fracturing in unconventional reservoirs. The solid diverting particles are a common type of chemical diverting agents used in horizontal well multistage fracturing. The transport and plugging of solid diverting particles within the fractures are crucial physical processes in the far-field diversion technology. In this study, in order to clarify the formation of the plugging layer by solid diverting particles in large-scale hydraulic fracture and to offer insights for the quantitative optimization of far-field diversion technology (FFD), an enhanced simplified two-fluid model within the Euler-Euler framework is employed to simulate the transport and plugging process of solid diverting particles within the fracture. And the numerical schemes of the front settlement region, the plugging layer formation region and the rear settlement region are also optimized. The proposed model is verified through comparison with experimental results from visual fracture test device. Based on the numerical results across various particle, pumping and fracture parameters, our findings indicate that: (1) The duration required to form a complete plugging layer can be reduced to 3% to 20% by increasing injection concentration, injection rate, and fracturing fluid viscosity; (2) Increasing the injection concentration (from 10kg/m3 to 30kg/m3) significantly enhances the length of the plugging layer by about 1 to 16 times, compensating for the inability to achieve a complete plugging layer with smaller particle sizes. Merely increasing the injection rate alone (from 0.35m3/min to 0.80m3/min) does not remedy the inability of small particles to form a complete plugging layer under identical plugging conditions. Excessive fracturing fluid viscosity (higher than 6mPa·s) impedes the formation of a complete plugging layer with smaller particles. High fracturing fluid leak-off rate (higher than 2.5×10-7m/s) markedly reduces the length of the plugging layer by about 37% to 44%; (3) Achieving a high close packing degree of particles within the plugging layer is facilitated by increasing injection concentration, increasing injection rate, and reducing fluid viscosity; (4) The abrupt variation in fracture width or height along the fracture length affects up to about 18% of the length of the plugging layer at the top of fracture. To ensure large length of the plugging layer at the top of fracture and high close packing degree of particles within the plugging layer, we recommend injection concentration above 10kg/m3, fracturing fluid viscosity below 6mPa·s, and injection rate exceeding 0.35m3/min. For particle size less than 1.8mm, we suggest injection concentration above 20kg/m3, and fracturing fluid viscosity not exceeding 3mPa·s.

On the 3D Transport of Low-energy Galactic Cosmic-ray and Jovian Electrons in the Inner Heliosphere in the Presence of a Fisk-type Heliospheric Magnetic Field

Modeling the transport of low-energy (1−10 MeV) cosmic-ray electrons can lead to valuable insights as to the behavior of the heliospheric magnetic field (HMF), due to the fact that the mean free path (MFP) of these particles parallel to the HMF is significantly larger than their perpendicular MFP, and that these particles experience little in the way of drift due to gradients/curvatures in the HMF and along the heliospheric current sheet. Jovian electrons are particularly suitable for such an endeavour, as they originate from a decentral source in the inner heliosphere. To this end, the transport of these electrons is studied using a 3D, ab initio particle transport code that incorporates theoretical expressions for electron diffusion coefficients, and utilizes as inputs for these transport coefficients turbulence quantities calculated using a two-component turbulence transport model. The effects of a novel Fisk-type field on the transport of these Jovian electrons are investigated and compared with the effects of a standard Parker field.