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A mesh-free dynamic physics simulation framework built on the Reproducing Kernel Particle Method (RKPM) is developed for explicit dynamic computational solid mechanics with large strains and high strain rates. Potential applications include simulation of armor and shielding, soft body impacts, and projectile behavior. A quasi-static variation of the patch test is used for numerical validation and a selected Taylor bar impact experiment is used as a benchmark problem for verification.

In an atmospheric plasma spray (APS) process, in-flight powder particle characteristics, such as the particle velocity and temperature, have significant influence on the coating formation. The nonlinear relationship between the input process parameters and in-flight particle characteristics is thus of paramount importance for coating properties design and quality control. It is also known that the ageing of torch electrodes affects this relationship. In recent years, machine learning algorithms have proven to be able to take into account such complex nonlinear interactions. This work illustrates the application of ensemble methods based on decision tree algorithms to evaluate and to predict in-flight particle temperature and velocity during an APS process considering torch electrodes ageing. Experiments were performed to record simultaneously the input process parameters, the in-flight powder particle characteristics and the electrodes usage time. Various spray durations were considered to emulate industrial coating spray production settings. Random forest and gradient boosting algorithms were used to rank and select the features for the APS process data recorded as the electrodes aged and the corresponding predictive models were compared. The time series aspect of the data will be examined., International Thermal Spray Conference 2021, May 24-28, 2021, Virtual Event

Acoustophoresis is an emerging method for tuning the microstructure in composites as a way to improve their functional properties. This method uses standing sound waves to push functional particles in a fluid to the pressure nodes of that field. That patterned arrangement is then transformed into a material with microstructure determined by the pattern of the acoustic field. Controlling the pattern of particles can enables a wide range of functional materials, including patterned energy storage electrodes, flexible electronics, and sensor arrays. Particle patterning via acoustics offers an attractive path to generate a wide variety of 2D periodic patterns that introduce tailorable hierarchical porosity, useful for controlling surface area, transport distances, and other properties. This work explores a variety of improvements to the technique and develops models to allow for informed adjustment and improvement of these processes and patterns. In this work multiple new scalable processing methods are developed. Acoustophoretic direct ink writing is extended from single line printing to simultaneous deposition of many patterned microstructural features. This technique is developed on test materials mimicking the properties of Lithium ion battery electrodes and then successfully demonstrated with actual battery materials to generate large samples of cathodes with controlled microstructure enabling faster charging. This technique is then extended into a new approach which is used to rapidly form 2,400 cm2 of patterned particles. This represents an orders of magnitude increase in the scale of acoustics experiments which has previously been limited to several cm2. To better enable improvements in these systems,the motion of particles in non-newtonian fluids like the battery slurries are modeled using several classic rheological models. Both of these printing approaches generated linear micro-structures. To enable a wider range of microstructural features patterning of particles in multi-wave fields is also explored. A simple energy minimization model is proposed for predicting the patterns that form from high loadings of particles in arbitrary acoustic fields. This model is validated both with more complex discrete particle modeling and with experiments. Development of this model enabled the demonstration of new multi-scale hierarchical microstructures. To further increase microstructural control, systems utilizing fibers are investigated. Acoustic fields can control not only the position of fibers, but also their orientation. Patterning fibers in 2D fields is shown to form grid-like microstructures which span 2D space at very low loadings. Models were developed to describe the motion of fibers in 2D fields and predict what microstructures would form as a function of the applied field and fiber characteristics such as length. Understanding of microstructure gained from this modeling is used to design flexible conductive composites. Finally this work takes a broad look at all of the other existing approaches for manufacturing composites using acoustophoresis, and then proposes new motifs for enabling finer control of more aspects of microstructure in diverse materials systems.

Particle Impact Drilling (PID) is a new technology to effectively improve the rate of penetration (ROP) for oil and gas drilling in hard and strongly abrasive formations. In this paper, numerical simulation method is used to analyse the motion characteristics and the modulation method of particle swarm in high-pressure tank for the particle injection system based on differential pressure ejection in PID. The numerical simulation results show that: when there is no modulation elements, the motion of particle swarm in the high-pressure tank follows an asymmetric funnel flow with pulsating state, which could be divided into vertical flow domain, fast flow domain, slow flow domain and stagnation domain. The unstable dynamic arching effect of the funnel flow, the viscous effect of the liquid bridge force and the collapsing effect of the particle swarm could probably lead to the blockage of the discharge port of the high-pressure tank. When the semiapex angles of the high-pressure tank decreases, the volume flow rate of particles increases and the stagnation domain becomes smaller, but it becomes easier to form arching and blockage. The modelling results indicate that the pulsation of the funnel flow is minimum when the semiapex angle is 45° without the mutilation element, which means the funnel flow of the particle swarm is relatively stable. By introducing a conical modulating element above the discharge port, the unstable funnel flow of the particle swarm could be transformed to an overall uniform flow. The modelling results indicate that the installation height of the modulation element has the greatest influence on the pulsation degree. The optimized parameters for the conical modulation element based on numerical modelling tests are 70° for the vertex angle, 35 mm for the length of the flank and 70 mm for the installation heigh.

Abrasive flow jet machining (ASJM) is modern manufacturing technique which uses comparatively low-pressure abrasive flow jet for machining various machined surfaces like holes, channels and intricate shapes which is not possible from conventional machining processes. The effect of abrasive particle concentration on the impacting slurry velocity on the surface was examined in the present CFD simulation, resulting in target surface erosion. To predict the impact velocity of abrasive particles hitting the surface, a 2D CFD model was used. The depth of machined surface, surface irregularity and surface removal rate at normal incidence mainly depend on the KE of particle, impact angle, etc. in line with previously published research work on highly pressurised air and water driven abrasive jet. In the present work CFD simulation is performed to predict the effect of solid particle concentration on the impacting slurry jet velocity at the target surface and also turbulence kinetic energy near the surface is studied. As per the CFD results the simulation model predictions the velocity of impacting particle goes on decreasing due to internal frictional resistance between solid and liquid phase and it shows scope of further parametric analysis in this area.

There are computation time constraints caused by the number and size of particles in the powder packing simulation using DEM. In this paper, newly suggested packing model transforms a general packing sequence –particle generation, stack, and compression – into particle generation and packing by growing particles. To verify the new packing model, it was compared using three contact models widely used in DEM, in terms of Radial Distribution Function, porosity, and Coordination Number. As a result, contact between particles showed a similar trend, and the pore distribution was also similar. Using the new packing model can reduce simulation time by 400% compared to the normal packing model without any other coarse graining methods. This model has only been applied to particle packing simulations in this paper, but it can be expanded to other simulations with complex domain based on DEM.

In many energy and combustion applications, particles experience large temperature gradients, which can affect the coagulation process due to thermophoresis. This study presents a rigorous theory of thermophoretically modified Brownian coagulation in the entire particle size regime. The theoretical derivations are based on the kinetic theory for the free-molecular regime and the harmonic mean method for the transition regime. The coagulation kernels in different size regimes can be expressed as the basic Brownian coagulation kernel times an enhancement factor. The enhancement factor represents the coagulation rate enhancement induced by thermophoresis and is a function of specific dimensionless numbers. Based on the enhancement factor, the thermophoretic enhancement effects on particle coagulation are further analyzed under a wide range of gas and particle conditions. The results show that thermophoretic enhancement effects are ignorable in the free-molecular regime, but need to be considered in the continuum regime and the transition regime. In addition, the enhancement effects increase significantly with increase of gas temperature and temperature gradient while decrease with increase of gas pressure. The present study can improve understanding of thermophoretic effects on Brownian coagulation in the entire size regime and provide a useful tool to calculate the coagulation rates in presence of thermophoresis.

Granular matter can exhibit solid or liquid behavior, which contains complex physical mechanisms. In this work, we experimentally investigated the structural relaxation and avalanche dynamics of particle piles under vertical vibration. The influence of vibration parameters on the avalanche process was studied. The morphological features of avalanches were recorded and classified using high-speed camera. The effects of vibration parameters and particle properties on the relaxation mode are obtained. It is found that the evolution of particle pile height with time can be described by an exponential decay function. The relaxation rate and avalanche characteristics of four types of particles with different sizes are discussed. At the same acceleration level, for two larger particles, a smaller amplitude (A = 0.025 mm) leads to a faster relaxation rate, while for two smaller particles, a large amplitude (A = 0.500 mm) leads to a faster relaxation rate. The analogy powder surface tension is introduced to address the cohesion and flowability evolution of particles under vibration.

We report a joint experimental and numerical study on the global thermal performance of a novel windowless vortex-based cavity receiver for potential thermal processing of suspended particles. This systematic study assesses the coupled influence of particle loading, Froude and Stokes number through variation of the inlet mass flowrate, particle size and loading on the global performance of the Solar Expanding Vortex Receiver-Reactor (SEVR) under steady-state conditions. The experiments employ polydispersed CARBO CP ceramic particles that are heated with an 18-kWel Metal Halide three-lamp solar simulator. A numerical study was also performed using computational fluid dynamics (CFD) software ANSYS/CFX 2019 R1. It was found that the particle volumetric loading and Froude number have primary controlling influence, while the Stokes number has a secondary influence on the global performance for these conditions. An overall thermal efficiency of 67% was obtained under high particle loading and Froude numbers.

Various impeded flow particle receivers were proposed to prolong the particle residence time but always faced the risk of thermal deterioration and the difficulty of real-time particle velocity control. Herein, we reported a novel impeded flow particle receiver to solve above problems and further have the potential to control the particle velocity distribution, which could provide a heat source with better stability, better uniformity and higher temperature for subsequent thermal power generation and other thermal applications. In this receiver, the friction along the path and the gate valves at outlet act as the obstruction structures to allow the particles to move slowly and controllably in the form of a sliding-bed, which is why we call this receiver a sliding-bed receiver. The sliding-bed receiver's structural validity and operational characteristics at different working conditions were detailly investigated with both experimental and numerical methods. Experimental results showed that the outlet particle temperature and efficiency could reach 847 °C and 77.2% under a solar simulator of 4 kW. An optical and thermal coupling model was developed and revealed an improved particle temperature of 1350 °C and efficiency of 82% under higher incident power. The effects of the effects of the incident power distribution, the particle velocity distribution and the quartz glass on aperture on the receiver performance were detailly analyzed, which could also help optimize the design and operation of other particle receivers such as free-falling particle receivers.

The discrete element method (DEM) is widely used in the realistic simulation of the shapes of particles. Researchers have considered the simplification of particle shapes owing to the high computational cost of such simulation. In this regard, the modeling of calibrated particles is a major challenge owing to the simultaneous effects of particle properties. The angle-of-repose test is a standard test method used to calibrate the bulk behavior of simulated particles. In the present study, the hollow-cylinder (slump) test was modeled for the verification of discrete element simulations. In this regard, a sensitivity analysis was conducted for all effective parameters, namely the static friction, rolling friction, restitution coefficient, sphericity, roundness, particle size distribution, and number of ballast particles. The results indicate that the rolling friction, roundness, number of particles, and size of particles are the most important parameters in the determination of the angle of repose (AOR). For particles in the range of ballast (20–60 mm), the effect of the number of particles on the angle of repose is reduced when the number is greater than 426. Additionally, it is concluded that angular particles can be replaced with sub-angular particles (R ≈ 0.2–0.45) with a higher rolling friction coefficient (μr > 0.14).

Experimental study of particle-laden turbulent reacting flow was conducted on a test facility for swirl combustor. The Three-Dimension Particle Dynamic Analyzer (PDA) was employed to measure the gas and particle instantaneous velocities. The measured results provide the distributions of time-averaged axial and tangential velocities, root mean square of axial and tangential fluctuating velocities, and correlation moments of axial-tangential fluctuating velocities for both gas and particle phases and the distribution of particle mean diameter. The Probability Density Functions (PDF) for the instantaneous particle axial and tangential velocities are also obtained at each measuring location. The gas and particle axial and tangential velocities as well as axial and tangential fluctuating velocities are large in the upstream central region of the combustor. Differences are found evidently between the gas and particle fluctuating velocity components.

The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na2SO4 circulating fluidized bed evaporator. The particle collision signals are analyzed with standard deviation by varying the amount of added particles e (1%–3%), circulation flow velocity u (0.37–1.78 m·s–1), and heat flux q (7.29–12.14 kW·m–2). The results show that the enhancement factor reach up to 14.6% by adding polytetrafluoroethylene particles at e = 3%, u= 1.78 m·s–1, and q= 7.29 kW·m–2. Both the standard deviation of the particle collision signal and enhancement factor increase with the increase inthe amount of added particles. The standard deviation increases with the increase in circulation flow velocity; however, the enhancement factor initially decreases and then increases. The standard deviationslightly decreases with the increase in heat flux at low circulation flow velocity, but initially increases and then decreases at high circulation flow velocity. The enhancement factor decreases with the increase in heat flux. The enhancement factor in Na2SO4 solution is superior to that in water at high amount of added particles. The empirical correlation for heat transfer is established, and the model results agree well with the experimental data.

Several authors have studied the effect of particle shape and size on cuttings transport and have reported different, often contradictory, results. The thixotropic nature of the drilling is seldom considered. This study investigates the effects of particle shape and size on cuttings carrying capability of thixotropic fluids in an attempt to better understand the underlying process. Flow equations are based on the mixture approach and are numerically solved using the CFD methodology. Turbulence is modeled using the buoyant k-epsilon model. A relative velocity equation is developed to model the slip between non-spherical particles and thixotropic fluid. It is concluded that in horizontal annuli, cuttings transport does not have a one to one relationship with particle size and/or particle shape. Instead, cuttings transport has a power-law relationship with the ratio of the product of particle shape and flow rate, and particle size i.e. (sphericity x velocity)/particle diameter.

The purpose of this study is to show the validity of the simulation result for particle charge and trajectory in an ESP with multiple wire electrodes.The ESP in this study has wires-and-plates configuration composed of three high-voltage application wire electrodes placed between grounded plate electrodes with a gap of 15 mm. The potential, the electric field intensity and the negative ion density were calculated by coupled analysis of Poison’s and current- continuity equations. The fundamental equation of flow field considering the ionic gas flow was a k-ω turbulence flow model. The charge of the particles was calculated from the differential equations of the electric and diffusion charging equations, taking into account the temporal and spatial electric field and ion density. The charged particle trajectory in the ESP was analyzed by an equation of motion considering fluid drag force and Coulomb’s force. In the measurement of the charged particle trajectory, oil mist as the tracer particle was mixed into the gas flow, and analyzed by a particle image velocimetry (PIV) using the software.As a result, the analysis value of the current density distribution on the surface of the grounded plate electrode agreed with the experimental value. The analysis results of the particle trajectory showed that the particle velocity increased, and moved toward the grounded plate electrode as the discharge power increased. The x and y components of particle velocity measured using PIV almost agreed with the simulated result. These results indicated the validity of the simulation result for charged particle trajectory, which was calculated by fitting the analyzed corona current to the experimental value, in the gas flow considering the ionic flow in an ESP with multiple wire electrodes.

Isobaric surface is a characteristic feature generated during particle motion in the hydrocyclone. Its pattern and position can directly affect the separation performance, which has rarely been studied. In this study, the isobaric surface and flow field in the hydrocyclone with different apex/vortex ratios were investigated in-depth via numerical analysis, and the effects of air core on axial velocity and tangential velocity were explored. On that basis, the effect of apex/vortex ratio on the hydrocyclone's separation performance was analyzed. The results showed that both pressure and tangential velocity increased with the increasing apex/vortex ratio. Through theoretical study and numerical analysis, the isobaric surface in the forced- and free-vortexes showed parabolic and hyperbolic patterns, respectively. As the apex/vortex ratio increased, the isobaric surface moved towards the center of hydrocyclone, suggesting the expansion of free-vortex region, the shrinkage of the forced-vortex region, and thus the failure in particle gradation and separation. Air core can lead to the fluctuation of both axial and tangential velocities. The fluctuation frequentness increased with the apex/vortex ratio, causing the disorder of flow field and the reduction of separation efficiency. At an apex/vortex ratio of 3/2, fluid can only move downwards and the hydrocyclone no longer played the role of gradation. As the apex/vortex ratio increased, the content of fine particles in the underflow increased drastically, and most of coarse particles were discharged from the underflow port. In contrary, the cutting capability and separation precision increased with the decline of the apex/vortex ratio. Therefore, in order to obtain high-quality product, the apex/vortex ratio should be as small as possible under the premise of satisfying the separation requirement.

The flow behavior of polydisperse particles in rolling mode rotating drum is important in industry, but it is still not clear. In this work, the discrete element method (DEM) is used to explore the flow of particles in the three-dimensional drum. After the accuracy of simulation verified by the experimental data from literature, the particle bed is divided into active layer and passive layer. The flow behavior of polydisperse particles was revealed by studying the particle velocity, residence time, mixing and axial dispersion in different regions in the drum. By exploring the parameters such as rotation speed, filling level and the shape and position of the lifter, some ideas are provided for improving the performance of the rolling mode rotating drum. In addition, the difference of flow behavior between polydisperse particles and monodisperse particles is also given, which can provide some reference for the industrial application of complex particle system.

The particle manipulation technology based on standing surface acoustic waves (SSAW) has been widely used with high efficiency and low consumption. However, it is difficult to study particle motion at the microscopic scale with experimental methods and conventional continuous methods. In this paper, computational fluid dynamics (CFD) and the discrete element method (DEM) are used to describe the fluid-particle flow, and the effect of the acoustic field is calculated according to Gorkov's theory. The established model is validated by the particle separation in micro-channel under SSAWs as the simulation results are in good agreement with experiments in publication. The consistency between the numerical simulation results and the experimental results in separation time and separation distance confirms the merits of model. The particle motion, space distribution, velocity field, force analysis and particle collision have been conducted thoroughly to reveal the mechanism of the separation.

Sedimentation of particle suspensions in a channel flow into a cavity is analysed numerically using a lattice Boltzmann method coupled with a discrete element method. The work focuses on the entrapment of particles inside a confined cavity and the particle dynamics after entrapment. A close examination of the particle motions reveals three distinct dynamic behaviours: i) resuspension, ii) circulation in the central vortex and iii) deposition to the rear edge of the cavity. The effects of fluid inertia, particle density and cavity size on the infiltration and resuspension behaviours are systematically investigated. The results show that decreasing the Reynolds number, and increasing the length and depth of the cavity all lead to an increase in the trap efficiency. Three distinctive regimes with respect to the trap efficiency were then identified by deriving an empirical dimensionless trap number Tp: a resuspension regime when Tp 2.5.

Presence of mucus layer and inlet air temperature variations can significantly affect the extent of particle transport and deposition in the mouth-throat airway for aerosol drug delivery applications. In addition, higher inlet air temperature can lead to thermal injuries as well. The main goal of the present paper is to investigate these effects in a highly idealized mouth-throat geometry in detail. Large eddy simulation was performed to accurately predict the air flow-fields and a Lagrangian particle tracking model has been employed to capture the particle deposition efficiencies and patterns. The effects of three different inlet air temperatures (15 °C, 26.7 °C and 45 °C) and three different particle sizes (3 μm, 5 μm and 6 μm) have been studied for inlet flow rates of 15 L/min and 30 L/min with and without mucus layer in the present investigation. Detailed velocity and temperature fields, as well as, particle deposition efficiencies and patterns were analyzed and it has been found out that (a) the particle deposition efficiencies varied significantly with changes in inlet air temperature and flow rates, particle diameters and in the presence of mucus layer, (b) the presence of recirculation zones and secondary vortices determined the rate of particle deposition at different inhalation flow rates and inlet air temperatures, and (c) the changes in temperature distribution near the mouth-throat wall in the presence of mucus layer have a dominant effect on particle deposition as compared to inertial deposition. The findings of the present work will provide useful information in understanding the heat transfer effects on particle transport and deposition for the design of pulmonary drug delivery devices under the influence of various environmental and human factors.

This paper presents the flow fields and aerodynamic loading of a two bladed H‐type vertical axis wind turbine with active variable pitch for load and circulation control. Particle Image Velocimetry is used to capture flow fields at six azimuthal positions of the blades during operation, three upwind and three downwind. Flow phenomena such as dynamic stall and tower shadow are captured in the flow fields. The phase‐averaged velocity fields and their time and spatial derivatives are used to calculate the normal and tangential loading at each position for each pitching configuration using the Noca formulation of the flux equations. The results show the effect of load shifting from the upwind to downwind region of the actuator using pitch and the effects of dynamic stall on the blades. The results also provide an unique database for model validation.

A three-dimensional high-fidelity particle-scale computational fluid dynamics (CFD) modeling of a selective parallel dual-laser melting (SPDLM) process is developed, on which dynamics behavior of molten pools of Nickel-based superalloy during SPDLM is simulated. The phenomena of wetting, necking, and pores near the overlapping region in the parallel dual-laser molten pools are especially investigated. The simulated results show that the SPDLM process improves the re-melting rate of the molten pool and the wettability of the overlapping region of the SPDLM molten pool, reducing the probability of defects, especially the probability of lack of fusion. Due to the uniform temperature distribution in the overlapping region of the two tracks and the complete melting, the product quality at the overlapping region of the two molten pools can be better guaranteed when the interval between the parallel dual lasers is 2.5 times of the laser beam radius. The results suggest that the SPDLM technique together with appropriate process parameters can not only increase the printing efficiency, but also improve the surface quality of the overlapping area of the two molten pools. The simulated results also reveal the formation mechanisms of pore defects during the selective multi-laser melting process on a mesoscopic scale. This study shows that the proposed particle-scale CFD model provides a high fidelity approach to characterize the molten pool in the SPDLM process and, therefore, is helpful for the optimal process design for the selective multi-laser melting.

The accuracy of the particle parameter settings directly affects the reliability of the simulation results. The discrete element method used a repose angle test to address incorrect particle parameter settings when throwing straw particles thrown by a chaff cutter. The tests calibrated the static and rolling friction coefficients using the repose angle of a mixture of maize stalk internodal tissue, pith, and nodal tissue particles as response indicators. Physical tests measured particle materiality parameters and contact parameters to provide data for the simulation tests. A Plackett-Burman design was performed to test the significance of the parameters to be calibrated. The results show that the static friction coefficient of Rind-Node, the rolling friction coefficient of Rind-Rind, the rolling friction coefficient of Pith-Pith, and the rolling friction coefficient of Pith-Iron have a significant effect on the repose angle. The purpose of the steepest ascent test is to narrow down the optimization range of the parameters. The central composite design was used to determine the DEM parameters' levels and quantify their effects. The central composite design test modeled a second-order polynomial regression equation for the repose angle and significance parameters. The physical test values were used as the target values for the optimization solution to obtain a calibrated and better combination of simulation parameters. The two-sample heteroskedasticity t-test showed no significant difference between the simulated and experimental values. The maximum relative error was 1.75%, the mean relative error was only 0.29%, verifying the reliability and authenticity of the simulation test. These parameters provide a basis for future work, such as the design of a corn stalk processing machine and the discrete-element study on the motion of corn stalk particles inside such machines.

The particle-laden turbulent flow over a two-dimensional dune bathymetry is studied by means of Large Eddy Simulation (LES). The 4-way coupling regime for particle–particle and particle-flow interactions is applied and an appropriate empirical formula is used to estimate the bedload transport. The flow conditions correspond to river flow in laboratory scale at a Reynolds number equal to 17 , 500 with respect to the maximum water depth and bulk velocity. The dune-shaped bed is introduced within a Cartesian grid by means of the Immersed Boundary Method. A particle cloud consisting of spherical particles is released within the carrier fluid under the influence of the Stokes drag and gravity forces. Three different types of particles are examined: acrylic, glass and steel particles. The particle volume fraction is significant and a hard-sphere model is deployed to account for particle–particle collisions in a 4-way coupling regime. Closure parameters for the collision model have been adopted for each type of the examined particles, based on experimental works in literature. Results focus on the effect of the particle inertia on their kinematics, the velocity field and the shear stress along the dune bed which modifies bedload transport. Using the numerical simulations presented, it can be observed that when larger particle-to-fluid density ratios were examined, larger slip velocities between the fluid and particle phases were recorded.

The steady low-Reynolds-number rotation of a spherical soft particle (a hard core coated with a permeable porous layer) in a viscous fluid within a nonconcentric spherical cavity about their common diameter is semi-analytically studied. To solve the Stokes and Brinkman equations for the fluid velocity, a solution is constituted by the general solutions in two spherical coordinate systems originated from the particle and cavity centers and the boundary conditions are satisfied by a collocation technique. Numerical results of the hydrodynamic torque on the soft sphere are obtained as a function of the core-to-particle radius ratio, particle-to-cavity radius ratio, relative center-to-center distance of the particle and cavity, and ratio of the particle radius to the permeation length in the porous layer over the entire ranges. The effect of the cavity on the torque of a rotating soft particle is weaker than that of a corresponding hard particle (or soft one with lower permeability or thinner thickness of its porous layer). While the normalized torque of a soft sphere in general is an increasing function of the particle-to-cavity radius ratio, a weak minimum of it (surprisingly, less than the value of an unconfined particle) may occur for a particle with a small to mediate core-to-particle radius ratio and a high permeability inside a nonconcentric cavity at a moderate value of the particle-to-cavity radius ratio. Also, this torque in general is an increasing function of the eccentricity of the particle location, but it may decrease slightly with an increase in the eccentricity for a particle with a small to mediate core-to-particle radius ratio and a high permeability.

Based on the basic principles and improved algorithms of the smoothed particle hydrodynamics method, a corresponding surface tension model and latent heat model are proposed for the heat exchange phase transition problem of droplets impinging on a low temperature wall surface. This research establishes a novel smoothed particle hydrodynamics model of the impinging wall of droplets accompanied by the phase transition process. This work also includes simulations cov?ering the spreading flow and phase transition process of droplets under different impingement regimes. Moreover, the icing patterns of the droplet impingement spreading process are provided and a comparative analysis with related experi?mental results. The improved smoothed particle hydrodynamics model is verified by experiments and its ability to solve droplet impingement icing problems.

We investigate the microphysics of contrail formation behind commercial aircraft by means of the particle-based LCM (Lagrangian Cloud Module) box model. We extend the original LCM to cover the basic pathway of contrail formation on soot particles being activated into liquid droplets that soon after freeze into ice crystals. In our particle-based microphysical approach, simulation particles are used to represent different particle types (soot, droplets, ice crystals) and properties (mass/radius, number). The box model is applied in two frameworks. In the classical framework, we prescribe the dilution along one average trajectory in a single box model run. In the second framework, we perform a large ensemble of box model runs using 25 000 different trajectories inside an expanding exhaust jet as simulated by the LES (large-eddy simulation) model FLUDILES. In the ensemble runs, we see a strong radial dependence of the temperature and relative humidity evolution. Droplet formation on soot particles happens first near the plume edge and a few tenths of a second later in the plume centre. Averaging over the ensemble runs, the number of formed droplets and ice crystals increases more smoothly over time than for the single box model run with the average dilution. Consistent with previous studies, contrail ice crystal number varies strongly with atmospheric parameters like temperature and relative humidity near the contrail formation threshold. Close to this threshold, the apparent ice number emission index (product of freezing fraction and soot number emission index) strongly depends on the geometric-mean dry core radius and the hygroscopicity parameter of soot particles. The freezing fraction of soot particles slightly decreases with increasing soot particle number, particularly for higher soot number emissions. This weakens the increase of the apparent ice number emission index with rising soot number emission index. Comparison with box model results of a recent contrail formation study by Lewellen (2020) (using similar microphysics) shows a later onset of our contrail formation due to a weaker prescribed plume dilution. If we use the same dilution data, our evolution and Lewellen's evolution in contrail ice nucleation show an excellent agreement cross-verifying both microphysics implementations. This means that differences in contrail properties mainly result from different representations of the plume mixing and not from the microphysical modelling. Using an ensemble mean framework instead of a single trajectory does not necessarily lead to an improved scientific outcome. Contrail ice crystal numbers tend to be overestimated since the interaction between the different trajectories is not considered. The presented aerosol and microphysics scheme describing contrail formation is of intermediate complexity and thus suited to be incorporated in an LES model for 3D contrail formation studies explicitly simulating the jet expansion. Our box model results will help interpret the upcoming, more complex 3D results.

Direct impingement (DI) erosion testing of steel and cobalt-based alloys is conducted with particles entrained in air and water. The tests are performed using 75- and 300-μm silica particles with three particle velocities and five impact angles. The mass loss results are used to develop an empirical equation that contains an explicit exponential term for the particle size effect. The erosion equation obtained from the gas jet experiments is implemented into a CFD solver with Lagrangian particle tracking for the liquid-submerged geometry. The CFD-based erosion predictions agree fairly with the experimental measurement for both particles. Strong effect has been observed for the exponential correction term in the erosion equation for liquid-solid flow cases; particularly with small particles at low impact velocities.

The coefficient of restitution describes the energy dissipation resulting from particle-particle and particle–surface interactions in solid–fluid flows. The energy loss depends on the mechanical characteristics of the solid phase, therefore, to correctly predict the behavior of these systems it is necessary to use reliable coefficient values based on the properties of the particles. This paper investigated the energy dissipation in particle–surface collisions using 7 types of particles with a wide range of mechanical properties (Young's modulus between 1.38 × 104 and 2.83 × 109 Pa). Three empirical equations have been proposed to calculate the coefficient of restitution based on the impact velocity and the compressional wave velocity. The experimental results presented an inverse relation between the impact velocity and the coefficient of restitution. This effect was more pronounced for less elastic particles. The models presented an accurate fit to the experimental data and statistical analysis showed that the Power model presented the greater capacity to predict the coefficient of restitution from generic data. The experimental results showed the predominant effect of mechanical characteristics on the coefficient of restitution. In addition, the proposed equations are proved to be precise tools for predicting particle coefficients of restitution with a wide range of elasticity modulus at low velocities.

Velocity fields in flow in permeable media are of great importance to many subsurface processes such as geologic storage of CO2 , oil and gas extraction, and geothermal systems. Steady-state flow is characterized by velocity fields that do not change significantly over time. The flow field transitions to a new steady state once it experiences a disturbance such as a change in flow rate or in pressure gradient. This transition is often assumed to be instantaneous, which justifies the expression of constitutive relations as functions of instantaneous phase saturations. This work examines the evolution of velocity fields in a surrogate quasi-2D permeable medium using a microfluidic device, a microscopy system, and a high-speed camera. Tracer particles are injected into the medium along with Deionized water. The evolution of the velocity field is examined by tracing these particles in the captured images using the standard high-density particle image velocimetry algorithm founded on cross-correlation. The results suggest that the transition between steady states for an incompressible fluid takes a finite and non-negligible amount of time that is independent of the magnitude of the change in pressure gradient. The existence of transient states and the nature of the response during these states are readily interpreted by the principle of least action where flow gradually establishes an optimal configuration such that energy dissipation is minimized. The findings provide evidence against the applicability of the assumption that flowing phases relax instantaneously to their steady states and, hence, against the accuracy of the classical multiphase extension of Darcy’s law. Cited as: Sun, J., Li, Z., Furtado, F., Aryana, S. A. A microfluidic study of transient flow states in permeable media using fluorescent particle image velocimetry. Capillarity, 2021, 4(4): 76-86, doi: 10.46690/capi.2021.04.03

This paper develops a novel approach for evaluating charged particles' collision probability in the external electric field of a regular two-stage electrostatic precipitator based on Lagrangian particle tracking method, which overcomes itself difficulties and that of the Eulerian method. The numerical simulation aims to obtain the particles' accumulated displacement which is a parameter to reflect the efficiency of particle collision. The effect factors of frequency, gas velocity, plate spacing and applied voltage are also considered. Results indicate that the external electric field of R-AC is more beneficial to particle collision compared to the other waveforms of AC. Besides, frequency and plate spacing are not found to have obvious or regular effect on collision probability, but the promotion effect of applied voltage on it was obtained. The dimensionless coefficient analysis provides extremely useful information for the optimization of working conditions in different types of the external electric field.

Flow of cohesive granular materials with different moisture contents was examined in a four-bladed mixer via the discrete element method (DEM). Firstly, the mixer diameter (D) was increased while keeping the particle diameter (d) constant. It was observed that when the mixer diameter to the particle diameter ratio (D/d) was larger than a certain critical size (D/d ≥ 75), granular flow behaviors and mixing kinetics followed simple scaling relations. For D/d ≥ 75, flow patterns and mixing kinetics were found to be independent of system size, and velocities of particles scaled linearly with the tip speed of the impeller blades and particle diffusivities scaled with the tip speed of the blades and mixer diameter. These results suggest that past a certain system size the flow and mixing of cohesive particles in large-scale units can be predicted from smaller systems. Secondly, system size was kept constant and particle diameter was changed and it was observed that by keeping the Bond number constant (by changing the level of cohesion) the flow behavior and mixing patterns did not change, showing that larger particles can be used to simulate flow of smaller cohesive particles in a bladed mixer by matching the Bond numbers.

Particle-laden turbulent flow under saturated electrostatic field in 90-degree bend pipe at Reb = 58000 is investigated using one-way coupled Large Eddy Simulation (LES) with a Lagrangian particle tracking technique. Drag, lift, buoyancy, gravity, and electrostatic force are considered. Three particle sizes (dp = 5, 10, 50 μm, St = 5.47, 21.91, 547) are considered. The results show that particle concentration is higher in outer bend than that in inner bend and the concentration increases with particle size. At the stagnation point of Dean vortices near the inner arc of bend, particle concentration is significantly increased under the synergy effect of electrostatics and secondary flow. In addition, particles trapped in the viscous layer are difficult to resuspend under electrostatic effect. Particle concentration near the wall under the presence of electrostatics is larger than that under the absence of electrostatics. However, at the bend, particle concentration in the core region under the presence of electrostatics is lower than that in the absence of electrostatics. For particle behavior, drag force plays the most important role in the core region while electrostatic force dominates the near wall region and causes particles to accumulate there.

In this paper, a numerical simulation is applied to statistic the particle velocity and coordination number of the surface layer under the slumping regime in a rotating drum. We find that the particle velocity distribution under different coordination numbers in the avalanche always satisfies Maxwell distribution and exponential distribution. This indicated that the distribution of coordination number is the main factor causing uneven avalanche. Furthermore, the mathematical model of particle velocity and coordination number is established, and a novel method for calculating the kinetic energy of particle system is proposed. It is observed that the maximum kinetic energy of particles in different regions during the uneven avalanche is positively correlated with the avalanche duration. These results reveal the particle flow regular in the rotating drum, which provides reference data for improving the control technology of particle material flow and the heat transfer in industry.

Particle transport in a vertical nonplanar fracture is a typical but poorly understood element in hydraulic fracturing. Particle-fluid flow in a nonplanar fracture with a narrowing width is investigated experimentally by a laboratory-scale slot, and the relevant transport mechanisms are compared with that in the planar slot. The effects of fluid flow rate, particle density, particle size, and particle volume fraction on particle distribution are investigated. The results indicate that the narrowing width complicates the slurry flow and lowers the bed coverage area. The vortex flow appears at the contraction of the cross-section as the bed grows to a threshold height and resuspends more particles further into the slot. An irregular bed with a descending stepped surface is formed due to non-uniform placement. Smaller size sands injected at a high flow rate and a low particle volume fraction build up a smaller bed. Larger and denser particles would reverse the trend. A rational model expressed by four dimensionless numbers is developed by the linear regression method to predict the coverage percentage of the particle bed. The model and experimental results provide directions to quantitatively evaluate the particle transport and distribution in a nonplanar fracture.

Numerical simulations of steady and unsteady viscous flows are presented by adopting two different numerical methodologies: the Smoothed Particle Hydrodynamics formulation implemented in the open-source code DualSPHysics and an in-house lattice Boltzmann code based on a concise central-moments scheme. Both methods employ a weakly compressible assumption to simulate incompressible flow, which means the fluid is assumed barotropic and the density and pressure are related through an equation of state. The accuracy of the two approaches is evaluated against well-defined and consolidated benchmark tests. Advantages and disadvantages of the two methodologies are discussed and substantiated by quantitative comparisons that focus on accuracy and efficacy of the two methodologies against other well-established computational methods. Overall, both formulations proposed herein are able to capture the relevant flow physics with a good level of accuracy when compared to other more affirmed techniques. Remarkably, this is observed in spite of the proposed two methods lacking key strategies commonly used in grid-based methods, such as adaptive mesh refinement.

An approach for particle breakage simulation based on the framework of discrete element method was proposed in the current study. Convex polyhedron blocks were adopted as elementary particles for the complex particle shapes, and the variability of particle breakage strength is modeled using the invertible function method. Additionally, the traditional modified “Brazilian” criterion was adopted as the breakage criterion. Under the assumption that the eventual fractures within a particle can be determined according to the contact points and the centroid of the particle, once a target particle fulfilled the breakage criterion, it was cut into several fragments by a series of virtual cutting faces, which are consistent with the eventual fractures. With this, the production of local stress and the non-conservation of mass and volume can be avoided. A pre-defined fragmentation mode was also unnecessary for this approach. A series of numerical triaxial tests adopting this new presented approach was then conducted according to the configurations reported in the literature and comparisons made with experimental results. It revealed that while the presented approach is capable of reproducing the macroscopic shear responses and particle breakage characteristics of breakable particle assemblies, some fragmentation modes of particles such as surface grinding and corner abrasion cannot be captured using this approach, presenting an area for future investigation.

Particle damping materials convert the kinetic energy of the system into other forms of energy through friction and collision between particles and between the particles and container wall. Gear transmission is advancing toward higher speeds, heavier loads, and lower noise. In order to reduce the vibration in the gear transmission without changing the original structure, particle damping is used in the paper. The equivalent displacement mapping of the gear contact load from the non-continuous domain to continuous element nodes was realized using the combined gear dynamics and discrete element method (DEM). Furthermore, the bidirectional transfer of load boundary conditions in the continuous domain and displacement boundary conditions in the discrete element domain were realized in the same calculation model. At low rotating speeds, the best vibration reduction occurred at the particle friction coefficient of approximately 0.43. At high rotating speeds, the best vibration reduction occurred at the particle friction coefficient of approximately 0.22. The vibration acceleration of the gear decreases significantly after the particle damper is added, confirming its vibration damping effect. This research has significant potential for vibration and noise reduction in gear transmission systems.

A deep understanding of the gasification behavior of porous char particle is the premise of the reactor-scale modeling, but there are few studies on the gasification characteristics in supercritical water. Thus, a numerical model for porous char particle gasification in supercritical water was developed in this work, and the effects of particle size, inflow temperature and inflow velocity were studied. Simulation results showed that gasification of the small particle of 0.1 mm lay in zone I regime where the particle radius kept unchanged due to uniform reactions inside the particle and the effectiveness factor increased rapidly after the gasification began due to easy accessibility of supercritical water into the particle. The gasification of the large particle of 1 mm showed typical characteristics in zone II regime that the particle began to shrink at a certain conversion degree, and smaller effectiveness factor was observed due to larger supercritical water concentration gradient inside the particle. As the increase of temperature and particle size, ambient fluid became difficult to flow through the unreacted core, and the Stefan flow was observed to obviously modify the hydrodynamic boundary layer at low Reynolds number. Besides, it is unreasonable to assume isothermal particle for gasification with large particle and high temperature because of the significantly overestimated particle consumption rate.

Taking regolith samples by unmanned equipment is a popular method to understand the outerspace in aerospace exploration. The electrostatic sampler can drive the charged particles to move or be transported by strong electric intensity, and its driving ability is extraordinarily powerful in the low gravity environment. The amount of charge acquired by a particle is vital to understand its dynamic behaviour in an electric field. In this study, the model of contact charging for a single particle is discussed to present its detailed behaviour during its charging process. Further, a suspension balancing method (SBM) is proposed for measuring the charges of a single particle. The experimental result fits well with the amended single-particle charging model. The experimental and simulation results prove that the charging source of a particle dynamically approaching the electrode can be attributed not only to the contact electrification but also to the air discharge.

Elastic waves have different attenuation laws when propagating in various materials, which is one of the important challenges in the application of non-destructive testing methods, such as acoustic emission (AE) technology in geotechnical engineering. The study presented in this paper investigated the influence mechanism of concrete composition materials and parameters on the propagation law of elastic waves using concrete specimens produced in six different particle sizes of sand or gravel. The burst AE signal was generated through the lead-breaking experiment, and ceramic piezoelectric sensors were used to record the signal waveform at different propagation distances. Through parameter analysis, spectrum analysis, and pattern recognition techniques, the influence of the concrete aggregate particle size on AE wave propagation and attenuation was revealed. The results show that the attenuation of elastic wave amplitude, energy spectral density, and frequency all were positively correlated with the aggregate particle size, and the elastic wave spectrum center of gravity generally decreased with the propagation distance. The ring count gradually decreased with the propagation distance, and the specimens with a larger aggregate particle size underwent a relatively faster ring count attenuation rate. The rise time increased rapidly with the propagation of the elastic wave, and the specimens with a larger aggregate particle size experienced a relatively rapid increase in rise time. In addition, in the feature spaces of ring count-amplitude and rise time–amplitude, the size of aggregate has an obvious influence on the distribution of these feature vector.

Laminar fluid-particle flows in bend geometries are present in many industrial, pharmaceutical, and biomedical applications. Particle deposition has been studied extensively; however, little attention has been paid to the effect of particle sedimentation on particle position and deposition in different pipe geometry combinations. This study presented a comprehensive analysis of sedimentation effects on particle flow behaviour in 90{\deg} circular pipe bends of micron particles in laminar pipe flows. Pipe geometry combinations consisted of eight pipe diameters, nine bend radii, and 30 particle diameters in a range of 1 to 100 {\mu}m. The results demonstrated the locations of particles that sedimented to the bottom half of the straight pipe section, and the particle positions upstream from the pipe bend entrance, which was no longer in a fully developed profile. These new locations represent the effects of gravity, pulling the particles down. While obtaining these positions can be found through CFD analysis, we proposed an analytical solution to predict the particle trajectory from different release locations that would help to identify the initial particle distribution at locations upstream to the bend, to obviate the need for long upstream straight pipe sections in the CFD analysis., Comment: In-Press

In this study, experiments and numerical simulations are performed where a hollow particle with a uniaxial through–hole is dropped freely in water, and its behavior is investigated. The distribution of falling particle trajectories reveals significant deviation in the direction perpendicular to the through–hole of the particle. In addition, the pressure distribution at the particle surface and the vorticity field of the wake of the particle are distributed asymmetrically in the plane perpendicular to the through–hole of the particle. Conversely, this pressure distribution and vorticity field are distributed symmetrically with respect to the direction parallel to the through–hole of the particle. Thus, this study clarifies that the movement of the particle in the direction parallel to the through–hole is suppressed. These results provide valuable novel insights into the control of particle motion.

Ribbon mixers are used in various industries for the mixing of particle matter. The discrete element method (DEM) is used to investigate the effects of the particle size and density on particle mixing in a laboratory-scale ribbon mixer. The mixer consists of a ribbon impeller with spokes and a horizontal cylindrical vessel. The particle size varies from 5 to 15 mm, and density from 417 to 2500 kg/m3. A particle-scale index is used to analyse the mixing state, and the impeller torque is used to evaluate the mixer's mechanical performance. The results show that the mixing rate generally becomes slower at a given density when the particle size is reduced with the fill-level fixed. For small particle sizes, the density effect was negligible, and the particle-size effect was described by an empirical equation, which was also extrapolated for much smaller particles. Effects of particle size and density on the impeller torque were also investigated.

This work describes a unique technique to simulate continuously and directly coupled fluid flow and moving particles including both mechanical and thermal interactions between the flow, particles, and flow paths. The particles/flow paths are discretized within a computational fluid dynamics flow domain so that the local flow and temperature field conditions surrounding each particle or other solid body are known along with the local temperature distribution within the particle and other solids. Contact conduction between solid bodies including contact resistance, conjugate heat transfer at the fluid–solid interfaces, and even radiation exchanges between solid surfaces and between solid surfaces and the fluid are incorporated in the thermal interactions and a soft collision model simulates the solid body mechanical contact. The ability to capture these local flow and thermal effects removes reliance on correlations for fluid forces and for heat transfer coefficients/exchange and removes restrictions on the flow regime and particle size and volume fraction considered. Larger particle sizes and higher particle concentration conditions can be studied with local effects captured. The method was tested for a range of particle thermal and mechanical properties, driving pressures, and for limited radiation parameters. The results reveal important information about the basic thermal and flow phenomena that cannot be obtained in standard modeling methods and demonstrate the utility of the modeling method. The technique can be applied to examine phenomena dependent on local thermal conditions such as chemical reactions, material property variation, agglomerate formation, and phase change. The methods can also be used as a basis for machine learning algorithm development for flows with large particle counts so that more detailed phenomena can be considered compared to those provided by standard techniques with reduced computational costs compared to those with fully resolved particles in the flow.

The general expression is derived for the diffusiophoretic velocity of a large spherical colloidal particle of radius a in a concentration gradient of general electrolytes of Debye-Huckel parameter κ. On the basis of this expression, simple approximate analytic expressions for the diffusiophoretic velocity correct to the order of (1/κa)0 are derived, which can be applied for large particles with κa ≥ 50 at arbitrary values of the particle zeta potential with negligible errors.

The discrete element method (DEM) coupled with computational fluid dynamics (CFD) is a powerful tool for exploring the detailed behaviors of dense particle–fluid interaction problems such as fluidized beds. Coarse-graining models have been proposed to decrease the computational cost by increasing the model particle size. In this study, we examine the influence of the model particle size and the spatial resolution on the average size and number of bubbles in coarse-graining DEM-CFD calculations of bubbling fluidized beds. Calculation results indicate that the bubble size is scaled by the model particle size if parameters are following similarity laws defined in a particle scale, as well as the geometric similarity of the whole system is maintained. The usage of coarse spatial resolution increases the bubble size and decreases the number of bubbles. The countervailing influence of the model particle size and the spatial resolution in a practical coarse-graining scenario results in nearly the same bubble size.

An electric virtual impactor with a capability of sampling fine and ultrafine particles was developed and its performance was evaluated both numerically and experimentally. The electric virtual impactor was provided with metallic electrodes, to which electric voltage in the range of 75–9000 V was applied for creating an electric field within the virtual impactor. Particle electric mobility was utilized to sample ultrafine particles at the major outflow section, while particle inertia was employed to collect fine particles at the minor outflow section. Silver nanoparticles with known charge level and Arizona test dust were used to experimentally validate the performance of the electric virtual impactor. Numerical and experimental outcomes agreed well with each other. The upper cutoff size of the electric virtual impactor was fixed at about 2.6 μm, while the lower cutoff size varied from 7 nm to 110 nm depending on the applied electric voltage. As a result, the proposed electric virtual impactor was able to sample both fine and ultrafine particles of a desired particle size range.