Particle Travel Distance Research Articles

Particle-level insights into the powder flow behavior of the Fette 1200i tablet press feed frame using the discrete element method (DEM)

This study employs the DEM to simulate powder flow in the Fette-1200i tablet press three-chambered feed-frame system under varying operating conditions. It examines the influence of operational speeds on parameters like residence time, particle travel distance, shear work, paddle torque, tablet weight, and API concentration. Utilizing continuous spatial surface maps, the research comprehensively analyzes powder flow behavior. Results indicate that particle residence time increases with paddle speed but decreases with turret speed. Similar trends are observed for particle travel distance and shear work. Larger particle residence time can lead to overlubrication. The torque of the paddles is related to the volume of material in each chamber, with the distributing chamber having the largest volume. Tablet weight rises with paddle speed but drops with turret speed. The smallest particle (API) tends to collect near the paddle hub due to limited centrifugal force and on the chamber floor due to percolation. However, the tablet's API content eventually stabilizes at the target concentration.

On the influence of the natural shape of particles in multiphase fluid systems: Granular collapses

The collapse of natural granular particles is encountered in various scenarios, including landslides, tsunamis, avalanches, and industrial processes. However, our understanding of these phenomena is still limited due to the complex interactions and the wide range of parameters that influence such systems. Particle shape is one of the factors that can significantly impact granular collapse behavior. In this paper, we studied the role of particle morphology in the interaction between fluids and particles in collapse problems and wave generation in multiphase fluid systems. To achieve this, we employed an image-based Discrete Element Method coupled with the Volume-of-Fluid approach. Initially, the proposed method is validated using experimental data for spherical particles. Then, we increased the irregularity of the spherical particles in four incremental steps. Our study establishes a clear relationship between particle morphology and important characteristics such as displacement, velocity, inter-particle forces, and kinetic energy. We observed that as irregularity increases, interlocking between particles becomes more prominent, leading to reduced particle travel distances. Additionally, our findings demonstrate that interlocking also influences particle-fluid interactions, resulting in significant alterations in the formation of generated waves.

Coarse sediment mobility and fluxes in wide mountain streams: Insights using the virtual velocity approach

The investigation of coarse sediment transport in wide mountain streams is very challenging because of limitations that affect the adoption of direct and indirect field monitoring techniques. Such river type represents then a stream typology for which quantitative knowledge of coarse sediment mobility, dynamics and fluxes is poor. This study uses tracer particles and a virtual velocity approach to gain insights about sediment mobility and coarse bed material transport in a wide mountain stream. Monitoring at the study area was conducted by tagging two types of tracer clasts, installing scour chains, and collecting data on water levels, transport processes, particle travel distances, and active layers over a period of 19 months and five transporting floods in the Tegnas Torrent (the Dolomites, Italy). Bed sediment was mobilized during a limited number of hydrological events (i.e. 6 to 9 per year), taking place in 50 to 400 h and inducing a total coarse sediment flux of about 1200 to 1400 m3 yr−1. The mobilization of coarse particles forming the streambed begins in response to a dimensionless shear stress (τ*c = 0.018) that is lower than thresholds commonly reported in the literature for mountain rivers and the estimated unit bed material transport was remarkably higher compared with those obtained in other mountain streams or gravel-bed rivers. The high mobility of streambed material can be related to the availability of fresh and unstructured sediment transported and deposited in the active channel by a high-magnitude event that occurred a few months before monitoring was conducted in this work, suggesting that sediment fluxes in a stream recently affected by a large flood could be considerably higher than those normally expected in a specific context. Finally, despite the existence of some application constraints, the experiment generated satisfactory results as regards the applicability of the virtual velocity approach in investigations of this stream type. This new quantitative knowledge of sediment fluxes and dynamics is also crucial for management of wide mountain streams.

The effect of natural and engineered hydraulic conditions on river-floodplain connectivity using hydrodynamic modeling and particle tracking analysis

Hydraulic conditions and water resources management projects can significantly alter river-floodplain connectivity, which in turn can alter hydrologic and biogeochemical processes in river corridors. In this study, the hydrodynamics of river-floodplain connectivity under different flood conditions and the effect of the Nanchang Water Resources Project Group (NWRPG) in the middle branch of the Ganjang River were investigated using a combination of two-dimensional hydrodynamic simulations and particle tracking. The hydrodynamic model was calibrated and validated using data from several gauging stations and field measurements. Floods in the Ganjang River can be limited to the river itself (“River Flood”, flood with normal lake level) or further extended to the Poyang Lake (“Lake Flood”, flood with high lake level). The results show that compared with “River Flood” scenarios, “Lake Flood” scenarios increased the water level flooding a larger area. The flow velocity decreased and the residence time (RT) of particles increased. The particle travel distance (PTD) of “River Flood” was larger than that of “Lake Flood”. The larger the flood, the greater the transboundary flux between the river and the floodplain, and the shorter the RT and PTD. The effect of NWRPG was the permanent flooding of part of the river floodplain, causing some habitat loss. Due to the increase in discharge, the implementation of the NWRPG results in a shorter RT with a smaller standard deviation, which has little effect on the PTD distribution. These findings can facilitate river connectivity restoration efforts in the Ganjang River and also provide a reference for assessing the impact of barrage projects.

Flow Strength and Bedload Sediment Travel Distance in Gravel Bed Rivers

AbstractThe quantification of bedload sediment transport in rivers is possible from statistics of individual particle displacements. However, there is a lack of empirical basis for a universal relation between particle displacement distance and hydraulic drivers. Previous work suggests that a simple linear relation exists between the energy of a flood and the mean travel distance of bedload particles. Such a relation would be advantageous, but a consistent model able to collapse the data from different rivers has not been developed. Here, we develop a predictive relation from a unique data set collected in three watersheds from a single region but contrasting hydrologic regimes due to urbanization and storm water management. Additional data from two rivers from outside the region are used to validate the model. We show that the mean of an exponential distribution of surface particle travel displacements can be reliably predicted from either the cumulative discharge or stream power exceeding the mobilization threshold, which is calibrated using field data. The strength of the relation decreases after large flood events that appear to cause tracer burial due to vertical mixing. This result indicates that the relation is most applicable for the entrainment phase of transport in which tracers are dispersing over the bed surface. Tracer movements become more challenging to predict over a long series of events due to burial and eventual tracer slowdown, but the relation remains valid for the particles located on the bed surface, making it suitable for analyzing the impact of climate and landscape changes over time.

Scaling up studies for mixing of granular materials in rotating drums

This study investigates the mixing of granular materials for rotating drums of different volumes which vary from 6.28 L to 402.12 L. Two groups of case studies are considered: Group I (constant particle diameter, d) and Group II (constant ratio of drum diameter to particle diameter, D/d). The results show that for Group I, the mixing performance deteriorates with drum size increasing. A correlation as a function of scale-up ratio and Froude number is proposed for mixing rate prediction. For Group II, at a constant Froude number, particle flow patterns and mixing performance are similar. The results also demonstrate that the scaled particle travel distances and displacements are affected by the ratio of D/d. For Group I, the scaled particle travel distances and displacements become more restricted as drums become larger, causing a delay in mixing. For Group II, similar particle travel distances and displacements are observed, hence the similar mixing performance.

Sensitivity of airborne transmission of enveloped viruses to seasonal variation in indoor relative humidity

In temperate climates, the peak in infection rates of enveloped viruses during the winter is likely heightened by seasonal variation in relative humidity within indoor spaces. While these seasonal trends are established in influenza and human coronaviruses, the mechanisms driving this seasonality remain poorly understood. Relative humidity impacts the evaporation rate and equilibrium size of airborne particles, which in turn may impact particle removal rates and virion viability. However, the relative importance of these two processes is not known. Here we use the Quadrature-based model of Respiratory Aerosol and Droplets to explore whether the seasonal variation in enveloped viruses is driven by differences in particle removal rates or by differences in virion inactivation rates. Through a large ensemble of simulations, we found that dry indoor conditions typical of winter lead to slower virion inactivation than humid indoor conditions typical of summer; in poorly ventilated spaces, this reduction in inactivation rates increases the airborne concentration of active virions, but this effect was important to virion exposure only when the susceptible person was farther than 2 m downwind of the infectious person. On the other hand, the impact of relative humidity on particle settling velocity did not significantly affect the removal or travel distance of virus-laden particles, suggesting that relative humidity is more likely to affect seasonal transmission via inactivation rates than via particle removal.

Particle energy partitioning and transverse diffusion during rarefied travel on an experimental hillslope

Abstract. Rarefied particle motions on rough hillslope surfaces are controlled by the balance between gravitational heating of particles due to conversion of potential to kinetic energy and frictional cooling of the particles due to collisions with the surface. Here we elaborate on how particle energy is partitioned between kinetic, rotational, and frictional forms during downslope travel using measurements of particle travel distances on a laboratory-scale hillslope, supplemented with high-speed imaging of drop–impact–rebound experiments. The drop–impact–rebound experiments indicate that particle shape has a dominant role in energy conversion during impact with a surface. Relative to spherical and natural rounded particles, angular particles give greater variability in rebound behavior, resulting in more effective conversion of translational to rotational energy. The effects of particle shape on energy conversion are especially pronounced on a sloping sand-roughened surface. Angular particles travel shorter distances downslope than rounded particles, though travel distance data for both groups are well fit by generalized Pareto distributions. Moreover, particle–surface collisions during downslope motion lead to a transverse random-walk behavior and transverse particle diffusion. Transverse spreading increases with surface slope as there is more available energy to be partitioned into the downslope or transverse directions during collision due to increased gravitational heating. Rounded particles exhibit greater transverse diffusion than angular particles, as less energy is lost during collision with the surface. Because the experimental surface is relatively smooth, this random-walk behavior represents a top-down control on the randomization of particle trajectories due to particle shape, which is in contrast to a bottom-up control on randomization of particle trajectories associated with motions over rough surfaces. Importantly, transverse particle diffusion during downslope motion may contribute to a cross-slope particle flux and likely contributes to topographic smoothing of irregular hillslope surfaces such as scree slopes.

Rarefied particle motions on hillslopes – Part 2: Analysis

Abstract. We examine a theoretical formulation of the probabilistic physics of rarefied particle motions and deposition on rough hillslope surfaces using measurements of particle travel distances obtained from laboratory and field-based experiments, supplemented with high-speed imaging and audio recordings that highlight effects of particle–surface collisions. The formulation, presented in a companion paper (Furbish et al., 2021a), is based on a description of the kinetic energy balance of a cohort of particles treated as a rarefied granular gas, as well as a description of particle deposition that depends on the energy state of the particles. Both laboratory and field-based measurements are consistent with a generalized Pareto distribution of travel distances and predicted variations in behavior associated with the balance between gravitational heating due to conversion of potential to kinetic energy and frictional cooling due to particle–surface collisions. For a given particle size and shape these behaviors vary from a bounded distribution representing rapid thermal collapse with small slopes or large surface roughness, to an exponential distribution representing approximately isothermal conditions, to a heavy-tailed distribution representing net heating of particles with large slopes. The transition to a heavy-tailed distribution likely involves an increasing conversion of translational to rotational kinetic energy leading to larger travel distances with decreasing effectiveness of collisional friction. This energy conversion is strongly influenced by particle shape, although the analysis points to the need for further clarity concerning how particle size and shape in concert with surface roughness influence the extraction of particle energy and the likelihood of deposition.

Rarefied particle motions on hillslopes – Part 1: Theory

Abstract. We describe the probabilistic physics of rarefied particle motions and deposition on rough hillslope surfaces. The particle energy balance involves gravitational heating with conversion of potential to kinetic energy, frictional cooling associated with particle–surface collisions, and an apparent heating associated with preferential deposition of low-energy particles. Deposition probabilistically occurs with frictional cooling in relation to the distribution of particle energy states whose spatial evolution is described by a Fokker–Planck equation. The Kirkby number Ki – defined as the ratio of gravitational heating to frictional cooling – sets the basic deposition behavior and the form of the probability distribution fr(r) of particle travel distances r, a generalized Pareto distribution. The shape and scale parameters of the distribution are well-defined mechanically. For isothermal conditions where frictional cooling matches gravitational heating plus the apparent heating due to deposition, the distribution fr(r) is exponential. With non-isothermal conditions and small Ki this distribution is bounded and represents rapid thermal collapse. With increasing Ki the distribution fr(r) becomes heavy-tailed and represents net particle heating. It may possess a finite mean and finite variance, or the mean and variance may be undefined with sufficiently large Ki. The formulation provides key elements of the entrainment forms of the particle flux and the Exner equation, and it clarifies the mechanisms of particle-size sorting on large talus and scree slopes. Namely, with conversion of translational to rotational kinetic energy, large spinning particles are less likely to be stopped by collisional friction than are small or angular particles for the same surface roughness.

The fate of volcanic ash: premature or delayed sedimentation?

A large amount of volcanic ash produced during explosive volcanic eruptions has been found to sediment as aggregates of various types that typically reduce the associated residence time in the atmosphere (i.e., premature sedimentation). Nonetheless, speculations exist in the literature that aggregation has the potential to also delay particle sedimentation (rafting effect) even though it has been considered unlikely so far. Here, we present the first theoretical description of rafting that demonstrates how delayed sedimentation may not only occur but is probably more common than previously thought. The fate of volcanic ash is here quantified for all kind of observed aggregates. As an application to the case study of the 2010 eruption of Eyjafjallajökull volcano (Iceland), we also show how rafting can theoretically increase the travel distances of particles between 138–710 μm. These findings have fundamental implications for hazard assessment of volcanic ash dispersal as well as for weather modeling.

The active layer in gravel‐bed rivers: An empirical appraisal

AbstractThe vertical position of the streambed–water boundary fluctuates during the course of sediment transport episodes, due to particle entrainment/deposition and bedform migration, amongst other hydraulic and bedload mechanisms. These vertical oscillations define a topmost stratum of the streambed (i.e. the ‘active layer or active depth’), which usually represents the main source of particles entrained during long and high‐magnitude bedload transport episodes. The vertical extent of this layer is hence a capital parameter for the quantification of bedload volumes and a major driver of stream ecology in gravel‐bed rivers. However, knowledge on how the active depth scales to flow strength and the nature of the different controls on the relation between the flow strength and the active depth is still scarce. In this paper we present a meta‐analysis over active depth data coming from ~130 transport episodes extracted from a series of published field studies. We also incorporate our own field data for the rivers Ebro and Muga (unpublished), both in the Iberian Peninsula. We explore the database searching for the influence of flow strength, grain size, streambed mobility and channel morphology on the vertical extent of the active layer. A multivariate statistical analysis (stepwise multiple regression) confirms that the set of selected variables explains a significant amount of variance in the compiled variables. The analysis shows a positive scaling between active depth and flow strength. We have also identified some links between the active depth and particle travel distances. However, these relations are also largely modulated by other fluvial drivers, such as the grain size of the bed surface and the dominant channel macro‐bedforms, with remarkable differences between plane‐bed, step‐pool and riffle‐pool channels. © 2020 John Wiley & Sons, Ltd.

Linear Transport in Porous Media

The linear transport theory is developed to describe the time dependence of the number density of tracer particles in porous media. The advection is taken into account. The transport equation is numerically solved by the analytical discrete ordinates method. For the inverse Laplace transform, the double-exponential formula is employed. In this paper, we consider the travel distance of tracer particles whereas the half-space geometry was assumed in our previous paper [Amagai et al. (2020). Trans. Porous Media 132:311–331].

The problem of underpowered rivers

AbstractThis study has hypothesized that for many rivers the trade‐off between flow accumulation and the decrease in slope along channel length means that stream power increases downstream and, moreover, that given the low slope angles in headwater and low‐order streams, they would have insufficient stream power to erode let alone transport sediment. The study considered the stream power profile, the particle travel distances and the application of the Hjulström curve based on the velocity profile of nine, large UK catchments. The study showed that: Some rivers never showed a maximum in their longitudinal stream power profile, implying that some rivers never develop a deposition zone before they discharge at the tidal limit. Particle travel distances during a bankfull discharge event showed that for some rivers 91% of the upper main channel would not be cleared of sediment. Furthermore, while some rivers could transport a 2 mm particle their entire length in one bankfull event, for another river it would take 89 such events. The Hjulström curve shows that for three of the study rivers the upper 20 km of the river was not capable of eroding a 2 μm particle. The study has shown that for all rivers studied, erosion is focused downstream and deposition upstream. Many UK rivers have a dead zone where, on time scales of the order of centuries, no erosion or transport occurs and erosion only occurs in the lower courses of the channel where discharge rather than slope dominates – we propose these as underpowered rivers. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Particle motion on burned and vegetated hillslopes

Climate change is causing increasingly widespread, frequent, and intense wildfires across the western United States. Many geomorphic effects of wildfire are relatively well studied, yet sediment transport models remain unable to account for the rapid transport of sediment released from behind incinerated vegetation, which can fuel catastrophic debris flows. This oversight reflects the fundamental inability of local, continuum-based models to capture the long-distance particle motions characteristic of steeplands. Probabilistic, particle-based nonlocal models may address this deficiency, but empirical data are needed to constrain their representation of particle motion in real landscapes. Here we present data from field experiments validating a generalized Lomax model for particle travel distance distributions. The model parameters provide a physically intuitive mathematical framework for describing the transition from light- to heavy-tailed distributions along a continuum of behavior as particle size increases and slopes get steeper and/or smoother. We show that burned slopes are measurably smoother than vegetated slopes, leading to 1) lower rates of experimental particle disentrainment and 2) runaway motion that produces the heavy-tailed travel distances often associated with nonlocal transport. Our results reveal that surface roughness is a key control on steepland sediment transport, particularly after wildfire when smoother surfaces may result in the preferential delivery of coarse material to channel networks that initiate debris flows. By providing a first-order framework relating the statistics of particle motion to measurable surface characteristics, the Lomax model both advances the development of nonlocal sediment transport theory and reveals insights on hillslope transport mechanics.

The influence of channel morphology on bedload path lengths: Insights from a survival process model

SummaryTracer studies are a commonly used tool to develop and test Einstein‐type stochastic bedload transport models. The movements of these tracers are controlled by many factors including grain characteristics, hydrologic forcing, and channel morphology. Although the influence of these sediment storage zones related to morphological features (e.g., bars, pools, riffles) have long been observed to “trap” bedload particles in transport, this influence has not been adequately quantified. In this paper we explore the influence of channel morphology on particle travel distances through the development of a Bayesian survival process model. This model simulates particle path length distributions using a location‐specific “trapping probability” parameter (pi), which is estimated using the starting and ending locations of bedload tracers. We test this model using a field tracer study from Halfmoon Creek, Colorado. We find that (1) the model is able to adequately recreate the observed multi‐modal path length distributions, (2) particles tend to accumulate in trapping zones, especially during large floods, and (3) particles entrained near a trapping zone will travel a shorter distance than one that is further away. Particle starting positions can affect path lengths by as much as a factor of two, which we confirm by modelling “starting‐location‐specific” path length probability distributions. This study highlights the importance of considering both tracer locations and channel topography in examinations of field tracer studies. © 2020 John Wiley & Sons, Ltd.

Experimental Study on Uniform and Mixed Bed-Load Sediment Transport under Unsteady Flow

The scouring and deposition of sediment caused by unsteady flows (e.g., storm waves and floods) produces many secondary disasters. The resultant bed-load movement exhibits different transport laws compared with that by steady flow. In this study, the flume experiments were performed to study the bed-load movement under unsteady flow with different velocity skewness. The movement of uniform and non-uniform non-cohesive sediment under unsteady flow as well as the influence of the steady and unsteady flow on sediment transport rate are compared. Additionally, the non-uniform sediment transport formula of fine-to-coarse particle diameter ratio was investigated. The results showed that the sediment transport rate between uniform and non-uniform sand under the same median diameter is different. The non-uniform sediment transport rate is 1.27-, 3.19-, and 0.68-times as large as that in uniform sediment under d50 = 0.664, 1.333, and 2.639 mm under unsteady flow, respectively. For non-uniform sand, the transport rate of non-uniform sand with a larger adjacent particle size ratio (δ = 0.29) was 1.31-times greater than that of the non-uniform sand with a smaller adjacent particle size ratio (δ = 0.50). Moreover, theoretical deduction was carried out and the incipient sediment motion was analyzed from the force mechanism. A new unsteadiness parameter based on the acceleration concept was proposed. The relationship between the travel distance and velocity skewness of sediment particles was set up. The experimental results and theoretical analysis showed that sediment under unsteady flow were easier to start and transport than those under steady flow in the same flow effect. The travel distance of sediment particles was longer under unsteady flow than that under steady flow.

Characterizing the Influence of Fracture Density on Network Scale Transport

AbstractThe topology of natural fracture networks is inherently linked to the structure of the fluid velocity field and transport therein. Here we study the impact of network density on flow and transport behaviors. We stochastically generate fracture networks of varying density and simulate flow and transport with a discrete fracture network model, which fully resolves network topology at the fracture scale. We study conservative solute trajectories with Lagrangian particle tracking and find that as fracture density decreases, solute channelization to large local fractures increases, thereby reducing plume spreading. Furthermore, in sparse networks mean particle travel distance increases and local network features, such as velocity zones where flow is counter to the primary pressure gradient, become increasingly important for transport. As the network density increases, network statistics homogenize and such local features have a reduced impact. We quantify local topological influence on transport behavior with an effective tortuosity parameter, which measures the ratio of total advective distance to linear distance at the fracture scale; large tortuosity values are correlated to slow‐velocity regions. These large tortuosity, slow‐velocity regions delay downstream transport and enhance tailing on particle breakthrough curves. Finally, we predict transport with an upscaled, Bernoulli spatial Markov random walk model and parameterize local topological influences with a novel tortuosity parameter. Bernoulli model predictions improve when sampling from a tortuosity distribution, as opposed to a fixed value as has previously been done, suggesting that local network topological features must be carefully considered in upscaled modeling efforts of fracture network systems.

Advective Transport Phenomena to Better Understand Dispersion in Field and Modeling Practice.

The absence of recent research on dispersion in engineering applications indicates the need for a description that is more focused on field and modeling practice. Engineers may benefit from simple calculation tools allowing them to understand the processes encountered in the field. Based on a conceptual model for advective transport through an elongated conductivity zone, for example, in fluvial sediments, explicit expressions are presented for macro‐scale phenomena: (1) the different travel distances of water particles traveling in laminar flow through and adjacent to a single zone with conductivity higher or lower than that of the aquifer; (2) the affected thickness of the bundle of flowlines; (3) the distinction of inflow, outflow, and through‐flow sections; (4) the development of a plume front vs. that of a tail; (5) conservation of mass causing water particles to travel both slower and faster than the aquifer average velocity while passing a single zone. The spread derived from a spatial distribution in a field experiment relates to the geometric mean of the spreads of the plume front and tail. The results obtained for a single conductivity zone are expanded for a general aquifer that is characterized by stochastic parameters. A fundamental new expression describes the dispersive mass flux as the product of the advective volume shift and the related local concentration difference. Contrary to Fickian theory, the dispersive mass flux in both the front and tail of a plume in highly heterogeneous aquifers is limited. In modeling, the advective volume shift is proportional to the cell size.

A review on frontiers in plasmonic nano-photocatalysts for hydrogen production

Nanoparticles have plenty of active sites in each particle and short travel distance for photoexcitons proved to be beneficial characteristics for photocatalytic hydrogen generation. Noble metal (Au, Ag, Pt, Pd, Ru, and Rh) attached with semiconductor photocatalyst displayed plasmonic oscillations results in localized surface plasmon resonance (LSPR) effect and schottky junction formed to pump the photoelectrons to surface for reactions. Literature reports evidenced that the choice of synthesis method and experimental conditions directly affects the catalytic and optical properties. Hence, this review discusses comprehensive information on chemical methods reported for the preparation of plasmonic photocatalyst that resulted in co-catalyst and visible light sensitizer properties. Recent developments and achievements on plasmonic photocatalyst for hydrogen production in pure water and sacrificial agent containing water are discussed and highlighted.