Particle Collisions Research Articles

Numerical simulation of collision dynamics between a dry particle and a liquid-coated wet particle

A comprehensive understanding of wet particle collisions in the presence of a liquid film is essential for industrial processes. In this study, we conduct a numerical investigation into the dynamics of both normal and oblique collisions between a dry particle and a liquid-coated wet particle. In normal collisions, the gas flow velocity near the stretching liquid bridge increases significantly, while oblique collisions exhibit no such increase. The wetting area of particles reaches its maximum when solid particles come into contact, at which point the viscous and capillary forces acting on the particles also reach their peaks. The capillary force causes kinetic energy dissipation to be one magnitude greater than viscous energy dissipation. The normal wet restitution coefficient rises with the logarithm of the modified Stokes number, reflecting energy dissipation effects. As the collision angle increases, the normal wet restitution coefficient gradually increases and surpasses the tangential wet restitution coefficient.

Viscous overstability in dense planetary rings – effect of vertical motions and dense packing

ABSTRACT We investigate the linear axisymmetric viscous overstability in dense planetary rings with typical values of the dynamical optical depth τ ≳ 0.5. We develop a granular flow model which accounts for the particulate nature of a planetary ring subjected to dissipative particle collisions. The model captures the dynamical evolution of the disc’s vertical thickness, temperature, and effects related to a finite volume filling factor of the ring fluid. We compute equilibrium states of self-gravitating and non-self-gravitating rings, which compare well with existing results from kinetic models and N-body simulations. Subsequently, we conduct a linear stability analysis of our model. We briefly discuss the different linear eigenmodes of the system and compare with existing literature by applying corresponding limiting approximations. We then focus on the viscous overstability, analysing the effect of temperature variations, radial and vertical self-gravity, and for the first time the effects of vertical motions on the instability. In addition, we perform local N-body simulations incorporating radial and vertical self-gravity. Critical values for the optical depth and the filling factor for the onset of instability resulting from our N-body simulations compare well with our model predictions under the neglect of radial self-gravity. When radial self-gravity is included, agreement with N-body simulations can be achieved by adopting enhanced values of the bulk viscous stress.

Numerical study on the non-equilibrium characteristics of high-speed atmospheric re-entry flow and radiation of aircraft based on fully coupled model

The strong coupling interactions of non-equilibrium flow, microscopic particle collisions and radiative transitions within the shock layer of hypersonic atmospheric re-entry vehicles makes accurate prediction of the aerothermodynamics challenging. Therefore, in this study a self-consistent non-equilibrium flow, collisional–radiative reactions and radiative transfer fully coupled model are established to study the non-equilibrium characteristics of the flow field and radiation of vehicle atmospheric re-entry. The comparison of the present calculation results with flight data of FIRE II and previous results in the literature shows a reasonable agreement. The thermal, chemical and excited energy level non-equilibrium phenomena are obtained and analysed for the different FIRE II trajectory points, which form the critical basis for studying the heat transfer and radiation. The non-equilibrium distribution of excited energy levels significantly exists in the post-shock and near-wall regions due to the rapid vibrational dissociation and electronic under-excitation, as well as the wall catalytic reactions. The analysis of stagnation-point heating of FIRE II illustrates that the translational–rotational convection and the dissociation component diffusion play key roles in the aerodynamic heating of the wall region. The spectrally resolved radiative intensity in the entire flow field indicates that the vacuum ultraviolet radiation caused by the high-energy nitrogen atomic spectral lines makes the main contribution to the radiative transfer. Finally, it is found that the non-equilibrium flow–radiation coupling effect can exacerbate the excited energy level non-equilibrium, and further affect the gas radiative properties and radiative transfer. This fully coupled study provides an effective method for reasonable prediction of atmospheric re-entry flow and radiation fields.

Capacity, Collision Avoidance and Shopping Rate under a Social Distancing Regime.

Capacity restrictions in stores, maintained by mechanisms like spacing customer intake, became familiar features of retailing in the time of the pandemic. Shopping rates in a crowded store under a social distancing regime are prone to considerable slowdown. Inspired by the random particle collision concepts of statistical mechanics, we introduce a dynamical model of the evolution of the shopping rate as a function of a given customer intake rate. The slowdown of each individual customer is incorporated as an additive term to the baseline value of the shopping time, proportionally to the number of other customers in the store. We determine analytically and via simulation the trajectory of the model as it approaches a Little's law equilibrium and identify the point beyond which equilibrium cannot be achieved. By relating the customer shopping rate to the slowdown compared with the baseline, we can calculate the optimal intake rate leading to maximum equilibrium spending. This turns out to be the maximum rate compatible with equilibrium. The slowdown due to the largest possible number of shoppers is more than compensated for by the increased volume of shopping. This macroscopic model is validated by simulation experiments in which avoidance interactions between pairs of shoppers are responsible for shopping delays.

From flow to jamming: Lattice Gas Automaton simulations in granular materials

We introduce the first extension of a Lattice Gas Automaton (LGA) model to accurately replicate observed emergent phenomena in granular materials with a special focus on previously unexplored jamming transitions by incorporating gravitational effects, energy dissipation in particle collisions, and wall friction. We successfully reproduce flow rate evolution, density wave formation, and jamming transition observed in experiments. We also explore the critical density at which jamming becomes probable. This research advances our understanding of granular dynamics and offers insights into the jamming behavior of granular materials.

Fine and ultrafine flotation with the Concorde CellTM – A journey

The Concorde Cell is a high-intensity pneumatic flotation cell dedicated to fines and ultrafines. Its development by Professor Graeme Jameson and later on by Metso was driven by two considerations: a reduction in bubble size and an increase in the shear rate and energy dissipation rate increases the particle–bubble collision and attachment efficiencies of fine particles. The Concorde Cell is a technology which produces fine air bubbles with high carrying capacity, thereby allowing increased capacity per unit; smaller footprint and a greater recovery of valuable fine particles which can be lost in other flotation cells. In addition, with a smaller number of flotation stages or less recycle required to achieve the desired recoveries, operational expenditures like power, water and reagents can be reduced.In this article, the potential of the Concorde Cell is explored through six cases, from base metals to metallurgical coal. Its main operating parameters, Air-to-Pulp Ratio, froth washing, froth depth and tailings recycle ratio, are investigated and show that the metallurgical performance of the Concorde Cell follows expectations based on the literature. Amongst others, higher APR leads to higher mass pulls and higher recoveries but lower grades, deeper froth depth increases selectivity… But the data also demonstrate the typical complexity of flotation, whereby the negative impact of increased APR can be compensated with froth washing to maintain high grades at high recoveries for example.About ten industrial scale flotation projects worldwide are deploying the Concorde CellTM. The examples of a metallurgical coal washing plant in Australia and of a copper plant in Zambia prove the capacity of the Concorde Cell to better recover the fines and ultrafines while providing high selectivity. In the two case studies, the Concorde Cell outperformed the previous technology specifically on the finest fractions of the processed streams.

Significant Progress in Improving Atorvastatin Dissolution Rate: Physicochemical Characterization and Stability Assessment of Self-Dispersible Atorvastatin/Tween 80® Nanocrystals Formulated through Wet Milling and Freeze-Drying

Atorvastatin (ATV) is a first-line drug for the treatment of hyperlipidemia. This drug presents biopharmaceutical problems, partly due to its low solubility and dissolution rate. In this work, nanocrystals of ATV stabilized with Tween 80® were designed by wet milling. A full factorial design was applied to optimize the process. Additionally, a cryoprotectant agent (maltodextrin, MTX) was identified, which allowed maintaining the properties of the nanocrystals after lyophilization. The storage stability of the nanocrystals was demonstrated for six months in different conditions. The obtained nanocrystal powder was characterized using SEM, EDXS, TEM, DSC, TGA, FT-IR, and XRD, showing the presence of irregular crystals with semi-amorphous characteristics, likely due to the particle collision process. Based on the reduction in particle size and the decrease in drug crystallinity, a significant increase in water and phosphate buffer (pH 6.8) solubility by 4 and 6 times, respectively, was observed. On the other hand, a noticeable increase in the dissolution rate was observed, with 90% of the drug dissolved within 60 minutes of study, compared to 30% of the drug dissolved within 12 hours in the case of the untreated drug or the physical mixture of components. Based on these results, it can be concluded that the nano-milling of Atorvastatin stabilized with Tween 80® is a promising strategy for developing new formulations with improved biopharmaceutical properties of this widely used drug.

Quantum-mechanical four-body versus semi-classical three-body theories for double charge exchange in collisions of fast alpha particles with helium targets

AbstractWithin the two-channel distorted wave second-order perturbative theoretical formalism, we study capture of both electrons from helium-like targets by heavy nuclei as projectiles at intermediate and high impact energies. The emphasis is on the four-body single-double scattering (SDS-4B) method and the three-body continuum distorted wave impact parameter method (CDW-3B-IPM). The SDS-4B method deals with the full quantum-mechanical correlative dynamics of all the four interactively participating particles (two electrons, two nuclei). The CDW-3B-IPM is a semi-classical three-body independent particle model (one electron, two nuclei), using a combinatorial calculus to describe double capture by a product of two uncorrelated probabilities, integrated over impact parameters. Both theories share a common feature in having altogether two electronic full Coulomb continuum wave functions. One such function is centered on the projectile nucleus in the entrance channel, whereas the other is centered on the target nucleus in the exit channel. These two methods satisfy the correct initial and final Coulomb boundary conditions in the asymptotic region of scattering, at infinitely large inter-particle separations. Yet, it is presently demonstrated that most of the available experimental data on total cross sections for the double capture from helium by alpha particles distinctly favor the SDS-4B method. This is especially true at intermediate energies. Such energies are critically important in versatile applications under the general umbrella of ion transport in matter, including thermonuclear fusion (plasma physics) and ion therapy (medicine).

Application of the Euler–Lagrange Approach and Immersed Boundary Method to Investigate the Behavior of Rigid Particles in a Confined Flow

The presence of particles with a small but finite size, suspended in viscous fluids with low volumetric concentrations, is observed in many applications. The present study focuses on the tridimensional and incompressible lid-driven flow of Newtonian fluids through the application of the immersed boundary method and the Euler–Lagrange approach. These methods are used to numerically predict three-dimensional particle motion by considering nearly neutrally buoyant conditions as well as all relevant elementary processes (drag and lift forces, particle rotation, particle–wall interactions, and coupling between phases). Considering the current stage of the numerical platform, two coupling approaches between phases are considered: one-way and two-way coupling. A single particle is inserted in the cavity after steady-state conditions are achieved. Its three-dimensional motion is obtained from numerical simulations and compared with research data, considering the same conditions, evidently showing that the particle trajectory follows the experimental data until the first collision with a solid surface. After this first contact, there is a deviation between the results, with the two-way coupling results better representing the experimental data than the one-way coupling results. The dimensionless forces’ peaks acting on the particles are associated with the relative velocity of the particle near the wall–particle collision position. In terms of magnitude, in general, the drag force has shown greater influence on the particle’s motion, followed by the rotation-induced and shear-induced lift forces. Finally, a special application is presented, in which 4225 particles are released into the domain and their dynamic is evaluated throughout dimensionless time, showing similar behavior for both couplings between phases, with variations in local concentrations observed in certain regions. The mean square displacement used to quantify the dispersion evolution of the particles showed that the particulate flow reaches an approximately homogeneous distribution from the moment of dimensionless time tU/S = 130.

Experimental and numerical study of an alternative technique for fruit processing: Rotary drum with inert bed for acerola pulp dehydration

Acerola is renowned as a potent natural source of vitamin C. However, its high perishability presents challenges for harnessing its health benefits. In this study, we explored an alternative method, the Rotary Dryer with Inert Bed (RDIB), to transform acerola pulp into a powdered form. Through both experimental and numerical investigations, we quantified how various operational variables affect RDIB's performance in acerola pulp dehydration. In numerical simulations using the Discrete Element Method (DEM), we analyzed the number and forces of particle collisions. We combined DEM results into a single response using a desirability function, pinpointing the optimal configuration: a drum with three continuous flights, each 25 mm long. Subsequently, experimental tests with this optimal setup considered temperature (T), inert fraction (FI), and maltodextrin concentration (M) effects on drying yield and bioactive compound levels. Multi-response optimization aimed to maximize both yield and bioactive compounds, yielding the optimal conditions: M = 6.25%, FI = 46.19%, and T = 77.2 °C. Thus, the results of this study show that RDIB efficiently dehydrates acerola pulp and has promising potential for industrial applications, facilitating the production of high-quality fruit powder.

Numerical and Experimental Investigations of Particle Dampers Attached to a Pipeline System

The structure of pipeline systems is complex, and the working environment is harsh. Under the excitation of the engine equipment foundation and pump fluid, it is easy to generate excessive vibration, which seriously affects the safe operation of the equipment. Particle damping achieves structural vibration suppression through the principle of particle collision dissipation. Due to the drawbacks of traditional pipeline vibration reduction methods, this article introduces a particle damping technology for pipeline system vibration suppression and designs particle dampers based on the structural characteristics of pipelines. We analyzed the energy dissipation mechanism of particle damping, revealed the influence of the materials, structure, external excitation, and other parameters of the pipeline particle dampers on the energy dissipation characteristics of the particle damping, established a pipeline vibration reduction test system with particle damping, and verified its effectiveness in pipeline system vibration reduction. This study can provide a technical reference for vibration reduction in pipeline systems.

Unitarity violation in field theories of Lee–Wick’s complex ghost

Abstract Theories with fourth-order derivatives, including the Lee–Wick finite QED model and quadratic gravity, have a better UV behavior, but the presence of negative metric ghost modes endangers unitarity. Noticing that the ghost acquires a complex mass by radiative corrections, Lee and Wick, in particular, claimed that such complex ghosts would never be created by collisions of physical particles because of energy conservation, so that the physical S-matrix unitarity must hold. We investigate the unitarity problem faithfully, working in the operator formalism of quantum field theory. When complex ghosts participate, a complex delta function (a generalization of the Dirac delta function) appears at each interaction vertex, which enforces a specific conservation law of complex energy. Its particular property implies that the naive Feynman rule is wrong if the four-momenta are assigned to the internal lines after taking account of the conservation law in advance. We show that complex ghosts are actually created and unitarity is violated in such fourth-order derivative theories. We also find a definite energy threshold below which ghosts cannot be created: The theories are unitary and renormalizable below the threshold.

Commissioning of Pixel Sensor Telescope for Monolithic Active Pixel Sensor Characterization

The Monolithic Active Pixel Sensors (MAPS) have been promisingly demonstrated as a core part of tracking detectors used in many experiments. In order to obtain decent particle tracks generated after high-energy particle collision, it is especially important that the detector must consist of high-performance MAPS. A pixel sensor telescope is a tool employed to investigate the properties of MAPS using high-energy particle test beams. At the Synchrotron Light Research Institute (SLRI), the pixel sensor telescope assembled with five layers of 50-µm thick pixel sensors has been commissioned and tested both in the laboratory with a radioactive source and by a high-energy electron test beam produced at the SLRI Beam Test Facility. With sensor signal threshold ranging from 9.73 to 10.15 DAC and noises between 0.62 and 0.87 DAC, each plane of the pixel sensor telescope can detect particles decaying from the radioactive source. Moreover, the test beam profiles have been measured to be 4.00 - 4.56 mm and 1.15 - 2.29 mm in horizontal and vertical axes, respectively. Correlations between each plane have been observed and confirm the proper operation of the pixel sensor telescope. Consequently, the pixel sensor telescope can be used to characterize the pixel sensor prototype.

Effect of nuclei particle shape and baffle setting on the drum granulation in iron ore sintering process

Discrete element method is used in this work to investigate the sintering granulation process of different-shaped nuclei iron ore particles and different drum baffle settings in rotating drums. The results show that the nuclei particle shape does not affect the flow pattern much, and the baffle setting can affect the time needed for particle flow to stabilize and the fluctuation intensity of particle collisions. The shape of iron ore nuclei significantly affects the number of attached small particles (per unit area), with the order of sphere > schistose > sphero-polyhedron > ellipsoid > polyhedron. Drums with the inclined baffles and ring baffles have faster water exchange rate. The 4-baffle drum has the highest number of adhered particles on the nuclei particle surface, showing a better granulation performance. The drum baffle setting does not affect the proportion of adhered iron ore, coke, and flux particles much.

Scale-Up Investigation of a Pilot and Industrial Scale Semi-Autogenous Mill Using a Particle Scale Model

A particle scale model based on a full two-way coupling of the Discrete Element Method (DEM) and Smoothed Particle Hydrodynamics (SPHs) methods is applied to SAG mills. Motion and collisions of resolved coarser particles within an SAG mill are performed by the DEM component. Fine particles in the feed combine with the water to form a slurry, which is represented by the SPH component of the model. Slurry rheology is controlled by solid loading and fine particle size distribution for each volume of slurry. Transport, dispersion, and grinding of the slurry phase particle size distribution are predicted by solving additional coupled advection–diffusion equations in the SPH component of the model. Grinding of the finer particles in the slurry due to collisions and shear of the coarser particles (rocks and grinding media) is achieved via the inclusion of population balance terms in these equations for each SPH particle. This allows prediction of the transport of both coarser and finer material within the grinding and pulp chambers of an SAG mill, including the discharge performance of the mill. This particle-scale model is used to investigate the relative performance (throughput, product size distribution, resident particle size distribution, net power draw, wear) for an SAG mill at a pilot scale and a 36 ft industrial scale. The 36′ SAG mill considered is a geometrically scaled-up version of the 1.8 m Hardinge pilot scale mill but with a longer belly length, reflecting current SAG mill design preferences. The belly lifters are scaled to a lesser degree with a larger number of lifters used (but still many fewer liners than would typically be used in a large SAG mill based on conventional liner selection rules). The model shows that despite reasonable qualitative similarities, many aspects of the charge structure, slurry transport, coarse particle and slurry discharge through the grates, and the collision energy spectra vary in important ways. This demonstrates that a near purely geometric scale-up of an SAG mill is not sufficient to produce a comparable performance at the two physical mill scales.

A barrier method for contact avoiding particles in Stokes flow

Rigid particles in a Stokesian fluid experience an increasingly strong lubrication resistance as particle gaps narrow. Numerically, resolving these lubrication forces comes at an intractably large cost, even for moderate system sizes. Hence, it can typically not be guaranteed that artificial particle collisions and overlaps do not occur in a dynamic simulation, independently of the choice of method to solve the Stokes equations. In this work, the potentially large set of non-overlap constraints, in terms of the Euclidean distance between boundary points on disjoint particles, are efficiently represented via a barrier energy. We solve for the minimum magnitudes of repelling contact forces and torques between any particle pair in contact to correct for overlaps by enforcing a zero barrier energy at the next time level, given a contact-free configuration at a previous instance in time. Robustness for the method is illustrated using a multiblob method to solve the mobility problem in Stokes flow, applied to suspensions of spheres, rods and boomerang shaped particles. Collision free configurations are obtained at all instances in time, and considerably larger time-steps can be taken than without the technique. The effect of the contact forces on the collective order of a set of rods in a background flow that naturally promote particle interactions is also illustrated.

Experimental study of particle collision and rebound with moving walls

Particle–wall collision always occurs in transportation systems with multi-phase flows containing particles in pneumatic conveying, coal liquefaction production, and wastewater treatment. Especially within rotating fluid machinery, collision and rebound between particles and moving walls occur frequently. It is necessary to conduct research, as it can provide theoretical support for controlling particle trajectories and reducing particle erosion. In this study, experimental investigations are carried out to analyze the trajectories and restitution coefficients of particle collision and rebound at different velocities of the moving wall, wall roughnesses, and collision angles. Particle trajectories and the influence of particle rotation on restitution coefficients in normal collisions are investigated, and particle motion behavior, tangential and normal restitution coefficients of the particle collision and rebound, and effective rebound angles in oblique collisions are analyzed and discussed at different operating conditions. The differences in collision and rebound characteristics between normal and oblique particle impacts are identified.

Collisions of particles near Kerr-MOG black holes

Collisions of particles near Kerr-MOG black holes

Multiphase turbulent flow explains lightning rings in volcanic plumes

Hunga Tonga-Hunga Ha’apai (HTHH), a submarine caldera volcano of the Tonga archipelago, erupted explosively on January 15, 2022. The eruption generated the highest concentration of lightning events ever recorded, producing characteristic ring patterns of electrical discharges concentric to the vent. Here we reproduce the key features of the observations using three-dimensional simulations of buoyant plumes in a stably stratified atmosphere. Our idealized minimal model based on the Boussinesq approximation and heavy particles reveals that the essential mechanism underlying the formation of lightning rings is turbulence-induced particle clustering, which generates structures, favorable conditions for charge concentration by particle collision. We propose that the location, size, and persistence of lightning ring structures can reveal pulsatory activity at the vent that the opaque ash cloud hides from the satellite observation and can be used as a proxy for eruption parameters regulating the generation of hazardous impacts on the environment.

Modelling deformation effects in multiple collisions using Collisional-SPH

Multiple collisions of granules on a substrate are encountered in a wide range of applications. In this work, such multiple collisions are analysed using Collisional Smooth Particle Hydrodynamics (CSPH) to understand how deformation caused by an impact influences the collision dynamics of subsequent impacts. It is found that the collision dynamics depends on the location of the impact and the deformation of the substrate caused by the preceding impacts. The predictions of three theoretical models are also compared with CSPH to assess the accuracy of the assumptions made by the models. The theoretical model predictions are only found to be useful when the granule repeatedly impacts the same location. Since these models do not simulate the shape change during the substrate deformation they fail to accurately model the cases where multiple impacts occur at different locations.