In this work,computational fuid dynamics(CFD)is used to study elbow erosion due to a gas-solid two-phase fow.In particular,the direct simulation Monte Carlo(DSMC)method is used to study the impact of inter-particle co...In this work,computational fuid dynamics(CFD)is used to study elbow erosion due to a gas-solid two-phase fow.In particular,the direct simulation Monte Carlo(DSMC)method is used to study the impact of inter-particle collision on the erosion behavior.The two-way coupled Euler-Lagrange method is used to solve the gas-solid fow,and the DSMC method is used to consider the collision behavior between particles.The efects of key factors,such as the particle concentration distribution and inter-particle collision,on the erosion ratio are evaluated and discussed.The efectiveness of the method is verifed from experimental data.The results show that the inter-particle collision signifcantly infuences the particle movement path and erosion ratio.When the inter-particle collision is considered,the maximum erosion position is ofset.The erosion model proposed by Oka et al.,who used the DSMC method,agrees best with the experimental data,and the average percentage error decreases from 39.2 to 27.4%.展开更多
During the process of landslide, its dynamic mechanism is important to understand and predict these kinds of natural hazard. In this paper, a new method, based on concepts of complex networks, has been proposed to inv...During the process of landslide, its dynamic mechanism is important to understand and predict these kinds of natural hazard. In this paper, a new method, based on concepts of complex networks, has been proposed to investigate the evolution of contact networks in mesoscale during the sliding process of slope. A slope model was established using the discrete element method (DEM), and influences of inter-particle frictional coefficients with four different values on?dynamic landslides were studied. Both macroscopic analysis on slope?landslide?and mesoanalysis on structure evolution of contact networks, including the?average degree, clustering coefficient?and N-cycle, were done during the process?of landslide. The analysis results demonstrate that: 1) with increasing inter-particle?frictional coefficients, the displacement of slope decreases and the stable angle of slope post-failure increases, which is smaller than the peak internal frictional angle;2) the average degree decreases with the increase of inter-particle frictional coefficient. When the displacement at the toe of the slope is smaller,?the average degree there changes more greatly with increasing inter-particle?frictional coefficient;3) during the initial stage of landslide, the clustering coefficient?reduces sharply, which may leads to easily slide of slope. As the landslide?going?on, however, the clustering coefficient?increases denoting increasing stability?with?increasing inter-particle frictional coefficients. When the inter-particle?frictional coefficient is smaller than 0.3, its variation can affect the clustering coefficient?and stable inclination of slope post-failure greatly;and 4) the number of?3-cycle increases, but 4-cycle and 5-cycle decrease with increasing inter-particle frictional coefficients.展开更多
The mechanism of erosion of a riverbank is not easy to analyze and each sediment particle is under influence of number of forces. Among all these forces, force of cohesion between the particles plays a very dominant a...The mechanism of erosion of a riverbank is not easy to analyze and each sediment particle is under influence of number of forces. Among all these forces, force of cohesion between the particles plays a very dominant and significant role, and, till date, not much progress has been made to analyze this force in a deterministic manner. A particle is bound to its neighboring particles under this force of cohesion. In this paper, the analysis of forces acting on a particle on a riverbank has been made with a model called the Truncated Pyramid Model. A particle requires a certain velocity to escape from the riverbank and determination of the escape velocity can pave the way for finding out other parameters like entrainment rate, erosion coefficient and so on. Calculation and estimation of riverbank erosion rate is an important aspect of river basin management. In this paper it has been shown that the escape velocity is dependent on certain micro-level parameters like inter-particle distance and volume of the water bridge between two adjacent particles. Also, for saline water the particle requires less velocity to escape compared to the pure-water scenario. The findings of the present paper exactly fall in line with the results of another paper where the researchers showed that cohesive force between the particles decreases as water turns from pure to impure.展开更多
This study explores the magnetohydrodynamic(MHD)boundary layer flow of a water-based Boger nanofluid over a stretching sheet,with particular focus on the influences of nanoparticle diameter,nanolayer effects,and therm...This study explores the magnetohydrodynamic(MHD)boundary layer flow of a water-based Boger nanofluid over a stretching sheet,with particular focus on the influences of nanoparticle diameter,nanolayer effects,and thermal radiation.The primary aim is to examine how variations in nanoparticle size and nanolayer thickness affect the hydrothermal behavior of the nanofluid.The model also incorporates the contributions of viscous dissipation and Joule heating within the heat transfer equation.The governing momentum and energy equations are converted into dimensionless partial differential equations(PDEs)using appropriate similarity variables and are numerically solved using the finite element method(FEM)implemented in MATLAB.Extensive validation of this method confirms its reliability and accuracy in numerical solutions.The findings reveal that increasing the diameter of copper nanoparticles significantly enhances the velocity profile,with a more pronounced effect observed at wider inter-particle spacings.A higher solvent volume fraction leads to decreased velocity and temperature distributions,while a greater relaxation time ratio improves velocity and temperature profiles due to the increased elastic response of the fluid.Moreover,enhancements in the magnetic parameter,thermal radiation,and Eckert number lead to an elevation in temperature profiles.Furthermore,higher nanolayer thickness reduces the temperature profile,whereas particle radius yields the opposite outcome.展开更多
An interfacial force microscope （IFM） was employed to measure the inter-particle forces between two individual glass beads with diameters varying from 8 to 20 μm. With the feedback function of IFM turned off, attra...An interfacial force microscope （IFM） was employed to measure the inter-particle forces between two individual glass beads with diameters varying from 8 to 20 μm. With the feedback function of IFM turned off, attractive forces were obtained. The forces varied in the range of 0.1-0.34 μN, and their validity was confirmed by a theoretical analysis of the van der Waals force between the same glass beads. With the feedback function switched on, no attractive forces between particles were detected by the IFM when the probe approached the sample substrate. This may be attributed to the dramatic change of the attractive forces within a very short separation distance and/or the relatively poor signal-to-noise ratio of the IFM.展开更多
This article investigates the role of the specularity coefficient(φ,the extent of the energy dissipation due to particle-wall collisions),inter-particle restitution coefficient(e_(pp),the extent of the energy dissipa...This article investigates the role of the specularity coefficient(φ,the extent of the energy dissipation due to particle-wall collisions),inter-particle restitution coefficient(e_(pp),the extent of the energy dissipation due to inter-particle collisions),and four combinations of these variables on the hydrodynamics,and the pressure recovery of the dilute gas-solid suspension in a diffuser.The investigation applies the two-fluid modeling approach along with the kinetic theory of the granular flow.The present investigation’s findings indicate that an increase inφor a reduction in e_(pp) reduces the pressure recovery by weakening the reverse momentum transfer phenomenon,which is recognized as the primary means for the pressure recovery.Besides,in a gas-solid flow system,a higherφor smaller e_(pp) enhances the particles’trapping in the recirculation zone.The recirculation zone’s strength and size increase asφincreases or e_(pp) reduces.Moreover,an increase in the wall-particle and inter-particle interactions strengthens the sidewise displacement of the particles.The effect of the wall-particle and inter-particle interactions are insignificant for extremely small solid loading.展开更多
There exist big gaps between measurements and modeling predictions on solids holdup and pressure drop in dense solids transport, such as those occuring in the bottom sections of gas-solids risers. The inability of clo...There exist big gaps between measurements and modeling predictions on solids holdup and pressure drop in dense solids transport, such as those occuring in the bottom sections of gas-solids risers. The inability of closing this gap by common modeling approaches indicates certain missing and/or misrepresentation of some controlling mechanisms in modeling the transport. Previous research efforts show that the gap can not be effectively narrowed by simply modifying the drag force formulations without inclusion of the collision effect. This paper explores the origin of some controlling mechanisms that might have been overlooked in previous modeling approaches, and recommends how to make the model dense solids transport better. Our analysis shows the presence of a resistant force arising from inter-particle collision when the solids are accelerated in dense-phase transport. This may be caused by non-equilibrium collision during solids acceleration, which differs from local-equilibrium assumptions on which the current kinetic theory modeling of granular particles is based. A complete modeling of this collision-induced resistance calls for a total revision of the kinetic theory, with the inclusion of non-equilibrium collisions and offcenter collisions in dense solids transport.展开更多
The oxide scale present on the feedstock particles is critical for inter-particle bond formation in the cold spray(CS)coating process,therefore,oxide scale break-up is a prerequisite for clean metallic contact which g...The oxide scale present on the feedstock particles is critical for inter-particle bond formation in the cold spray(CS)coating process,therefore,oxide scale break-up is a prerequisite for clean metallic contact which greatly improves the quality of inter-particle bonding within the deposited coating.In general,a spray powder which contains a thicker oxide scale on its surface(i.e.,powders having high oxygen content)requires a higher critical particle velocity for coating formation,which also lowers the deposition efficiency(DE)making the whole process a challenging task.In this work,it is reported for the first time that an artificially oxidized copper(Cu)powder containing a high oxygen content of 0.81 wt.%with a thick surface oxide scale of 0.71μm.,can help achieve an astonishing increment in DE.A transition of surficial oxide scale evolution starting with crack initiations followed by segmenting to peeling-off was observed during the high velocity particle impact of the particles,which helps in achieving an astounding increment in DE.Single-particle deposit observations revealed that the thick oxide scale peels off from most of the sprayed powder surfaces during the high-velocity impact,which leaves a clean metallic surface on the deposited particle.This makes the successive particles to bond easily and thus leads to a higher DE.Further,owning to the peeling-off of the oxide scale from the feedstock particles,very few discontinuous oxide scale segments are retained at inter-particle boundaries ensuring a high electrical conductivity within the resulting deposit.Dependency of the oxide scale threshold thickness for peeling-off during the high velocity particle impact was also investigated.展开更多
Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in stu...Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in studying the CES.In the present work,a bi-scale impedance transmission line model(TLM)is firstly developed for a single pore to a porous electrode.Not only the TLM of the single pore is reparameterized but also the particle packing compactness is defined in the bi-scale.Subsequently,the CES properties are identified by FRA,focused on rate capability vs.characteristic frequency,peak power vs.equivalent series resistance,and energy density vs.low frequency limiting capacitance for a single pore to a porous electrode.Based on these relationships,the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length,intra-particle pore diameter,inter-particle pore diameter,electrolyte conductivity,interfacial capacitance&exponent factor,electrode thickness,electrode apparent surface area,and particle packing compactness.Finally,the experimental diagnosis of four supercapacitors(SCs)with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore.The calculating results suggest,to some extent,the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode.Hence,in order to design a better porous electrode,more attention should be given to the inter-particle pore.展开更多
Inter-particle and molecular forces are of most important forces affecting fines migration. Investigating the impact of these types of forces requires information about electrical properties of constitutive component ...Inter-particle and molecular forces are of most important forces affecting fines migration. Investigating the impact of these types of forces requires information about electrical properties of constitutive component and Nano-sized solids. Surface potential is a well-known parameter, which can be used to measure aforementioned forces. The force balance among electrical, gravity, drag and buoyance forces tracing on a particle can be estimated using fluid properties and physical properties of reservoir such as surface potential, pore size distribution and fine size distribution. The task is to set these forces at conditions that fine migration does not take place. This paper investigates the impact of several parameters that could influence pertinent forces. Effect of ionic strength of flowing fluid is taken into account to evaluate Debye length that determines double layer forces. The impact of injection rate on a parameter named erosion number is?also studied. The results of this study show that how introducing salts and injection rate can affect stability of fines on their locations.展开更多
The aim of this paper is to obtain relevant sets of collision cross sections of the parent ions in low pressure discharges in argon, oxygen, and nitrogen, i.e., Ar＋ in Ar, O2＋ in O2 and N2＋ in N2. These ion data ar...The aim of this paper is to obtain relevant sets of collision cross sections of the parent ions in low pressure discharges in argon, oxygen, and nitrogen, i.e., Ar＋ in Ar, O2＋ in O2 and N2＋ in N2. These ion data are first discussed and then validated from comparisons between the calculated transport coefficients and those measured in the literature. The elastic momentum transfer collision cross sections are determined from a semi-classical approximation for the phase shift calculation based on a 12-6-4 inter-particle potential while ion transport coefficients are determined versus the reduced electric field from Monte Carlo simulations.展开更多
A simplified model is proposed for an easy understanding of the coarse-grained technique and for achieving a first approximation to the behavior of gases. A mole of a gas substance, within a cubic container, is repres...A simplified model is proposed for an easy understanding of the coarse-grained technique and for achieving a first approximation to the behavior of gases. A mole of a gas substance, within a cubic container, is represented by six particles symmetrically moving. The impacts of particles on container walls, the inter-particle collisions, as well as the volume of particles and the inter-particle attractive forces, obeying a Lennard-Jones curve, are taken into account. Thanks to the symmetry, the problem is reduced to the nonlinear dynamic analysis of a SDOF oscillator, which is numerically solved by a step-by-step time integration algorithm. Five applications of proposed model, on Carbon Dioxide, are presented: 1) Ideal gas in STP conditions. 2) Real gas in STP conditions. 3) Condensation for small molar volume. 4) Critical point. 5) Iso-kinetic energy curves and iso-therms in the critical point region. Results of the proposed model are compared with test data and results of the Van der Waals model for real gases.展开更多
Fines migration is defined as separation of a Nano-sized particle by fluid flow in porous media and its migration along some distances and its entrapment in a narrow pore throat or its settlement on pore wall. Althoug...Fines migration is defined as separation of a Nano-sized particle by fluid flow in porous media and its migration along some distances and its entrapment in a narrow pore throat or its settlement on pore wall. Although this phenomenon happens in scales of Nano-meters, it can lead to sever irretrievable damages. This damage includes permeability reduction that causes drastic oil recovery reduction. There are several forces impacting a fine that is placed on a pore wall. Some of most important forces affecting settlement of a fine in porous media in presence of a fluid are electrical forces. Electrical forces consist of several long and short range forces. This study focuses on a long range force called Double Layer Force (DLF) that beside Van der Waals is one of most powerful electrical forces. DLF is a repulsive force that can repel a particle from pore wall and result separation of a Nano-sized solid which subsequently moves along with flowing fluid and clogs a throat. The DLF depends on the solid material (reservoir rock and fine) and fluid properties (i.e. ionic strength, pH). This study investigates how each of these parameters affects DLF and introduces proper conditions for reservoir water flooding for controlling fines migration.展开更多
Discrete element modeling requires the proper quantification of the behavior of grains at their contacts including the normal force-displacement and tangential force-displacement relationships to be used as input for ...Discrete element modeling requires the proper quantification of the behavior of grains at their contacts including the normal force-displacement and tangential force-displacement relationships to be used as input for contact modeling purposes.This paper reports on recent advances in soil mechanics experimentation which allowed measuring the grain contact behavior of small sand particles quantifying friction and stiffness with sliding tests of a force-controlled or displacement-controlled type.The particular focus of this work is on the micromechanical behavior of quartz type grains of size between about 1 and 5 mm.A description of the developed micromechanical apparatus at City University of Hong Kong is first discussed and its important different capabilities with previously developed apparatus is briefly reviewed.Subsequently,a limited set of new data is reported and discussed along with a review of recently acquired results published in the literature associated with the contact behavior of quartz sand grains.These sliding tests have covered a wider range of normal contact forces from about 0.5 to 8 N,and the results indicated that,for this range of confining forces,there is not any notable change of the inter-particle coefficient of friction.展开更多
This paper establishes a lattice Boltzmann equation-discrete element method (LBE-DEM) coupled simulation method under the Eulerian-Lagrangian framework at first, and applies it to simulating a two-dimensional gas-soli...This paper establishes a lattice Boltzmann equation-discrete element method (LBE-DEM) coupled simulation method under the Eulerian-Lagrangian framework at first, and applies it to simulating a two-dimensional gas-solid two-phase cross jet. The gas phase is simulated by the lattice-Boltzmann method via the TD2G9 model; the solid phase is traced by the Lagrangian method and the inter-particle collision is calculated by the DEM method. Three values of the Stokes number St=10, 25, and 50 are simulated under the same mass loading. This paper focuses on the characteristics of vortex structure, particle distribution, and the reverse-flow/rebounding rate in cross jets. We analyze the characteristics of fluid vortex motion, particle cluster distribution, rebounding rate of particles and the influencing factors for them. The results show the existence of joint distribution of discrete clusters and discrete particles in cross jets. Meanwhile, it shows that a larger concentration of particles in the early stage of jet evolution or a smaller Stokes number under the same mass loading can produce a larger rebounding rate. However, the rebounding rate of particles at the late stage, in general, is stable.展开更多
In the past few decades,multi-scale numerical methods have been developed to model dense gas-solidflow in fluidized beds with different resolutions,accuracies,and efficiencies.However,ambiguity needsto be clarified in...In the past few decades,multi-scale numerical methods have been developed to model dense gas-solidflow in fluidized beds with different resolutions,accuracies,and efficiencies.However,ambiguity needsto be clarified in the multi-scale numerical simulation of fluidized beds:(i)the selection of the submodels,parameters,and numerical resolution;(ii)the multivariate coupling of operating conditions,bed configurations,polydispersity,and additional forces.Accordingly,a state-of-the-art review is performed to assess the applicability of multi-scale numerical methods in predicting dense gas-solid flow influidized beds at specific fluidization regimes(e.g.,bubbling fluidization region,fast fluidization regime),with a focus on the inter-particle collision models,inter-phase interaction models,collision parameters,and polydispersity effect.A mutual restriction exists between resolution and efficiency.Higherresolution methods need more computational resources and thus are suitable for smaller-scale simulations to provide a database for closure development.Lower-resolution methods require fewercomputational resources and thus underpin large-scale simulations to explore macro-scale phenomena.Model validations need to be further conducted under multiple flow conditions and comprehensivemetrics(e.g.,velocity profiles at different heights,bubbles,or cluster characteristics)for furtherimprovement of the applicability of each numerical method.展开更多
Carbon nanotubes (CNTs) can be fluidized in the form of fluidlike agglomerates made of many three-dimensional sub-agglomerates, having a multi-stage agglomerate (MSA) structure and containing large amounts of twisting...Carbon nanotubes (CNTs) can be fluidized in the form of fluidlike agglomerates made of many three-dimensional sub-agglomerates, having a multi-stage agglomerate (MSA) structure and containing large amounts of twisting CNTs of micrometer magnitude.展开更多
Three physicalmechanismswhichmay affect dispersion of particle’smotion in wall-bounded turbulent flows,including the effects of turbulence,wall roughness in particle-wall collisions,and inter-particle collisions,are ...Three physicalmechanismswhichmay affect dispersion of particle’smotion in wall-bounded turbulent flows,including the effects of turbulence,wall roughness in particle-wall collisions,and inter-particle collisions,are numerically investigated in this study.Parametric studies with differentwall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach.A low-Reynolds-number k−ǫturbulence model is applied for the solution of the carrier-flow field,while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion.It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles.Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particleladen flow.Since the investigated particles are associated with large Stokes numbers,i.e.,larger than O(1),in the test problem,the effects of turbulence on particle dispersion aremuch less considerable,as expected,in comparison with another two physical mechanisms investigated in the study.展开更多
A new model that combines Eulerian and Lagrangian approach is set up. with inter-particle interaction being taken account of through kinetic theory. The numerical algorithm is included. In the end, comparison with the...A new model that combines Eulerian and Lagrangian approach is set up. with inter-particle interaction being taken account of through kinetic theory. The numerical algorithm is included. In the end, comparison with the experimental results of Barlow and Morrison [1] is make, and a good agreement is reached.展开更多
基金The authors acknowledge the fnancial support by the National Natural Science Foundation of China(No.51874340)by the Shandong Provincial Natural Science Foundation,China(No.ZR2018MEE004).
文摘In this work,computational fuid dynamics(CFD)is used to study elbow erosion due to a gas-solid two-phase fow.In particular,the direct simulation Monte Carlo(DSMC)method is used to study the impact of inter-particle collision on the erosion behavior.The two-way coupled Euler-Lagrange method is used to solve the gas-solid fow,and the DSMC method is used to consider the collision behavior between particles.The efects of key factors,such as the particle concentration distribution and inter-particle collision,on the erosion ratio are evaluated and discussed.The efectiveness of the method is verifed from experimental data.The results show that the inter-particle collision signifcantly infuences the particle movement path and erosion ratio.When the inter-particle collision is considered,the maximum erosion position is ofset.The erosion model proposed by Oka et al.,who used the DSMC method,agrees best with the experimental data,and the average percentage error decreases from 39.2 to 27.4%.
文摘During the process of landslide, its dynamic mechanism is important to understand and predict these kinds of natural hazard. In this paper, a new method, based on concepts of complex networks, has been proposed to investigate the evolution of contact networks in mesoscale during the sliding process of slope. A slope model was established using the discrete element method (DEM), and influences of inter-particle frictional coefficients with four different values on?dynamic landslides were studied. Both macroscopic analysis on slope?landslide?and mesoanalysis on structure evolution of contact networks, including the?average degree, clustering coefficient?and N-cycle, were done during the process?of landslide. The analysis results demonstrate that: 1) with increasing inter-particle?frictional coefficients, the displacement of slope decreases and the stable angle of slope post-failure increases, which is smaller than the peak internal frictional angle;2) the average degree decreases with the increase of inter-particle frictional coefficient. When the displacement at the toe of the slope is smaller,?the average degree there changes more greatly with increasing inter-particle?frictional coefficient;3) during the initial stage of landslide, the clustering coefficient?reduces sharply, which may leads to easily slide of slope. As the landslide?going?on, however, the clustering coefficient?increases denoting increasing stability?with?increasing inter-particle frictional coefficients. When the inter-particle?frictional coefficient is smaller than 0.3, its variation can affect the clustering coefficient?and stable inclination of slope post-failure greatly;and 4) the number of?3-cycle increases, but 4-cycle and 5-cycle decrease with increasing inter-particle frictional coefficients.
文摘The mechanism of erosion of a riverbank is not easy to analyze and each sediment particle is under influence of number of forces. Among all these forces, force of cohesion between the particles plays a very dominant and significant role, and, till date, not much progress has been made to analyze this force in a deterministic manner. A particle is bound to its neighboring particles under this force of cohesion. In this paper, the analysis of forces acting on a particle on a riverbank has been made with a model called the Truncated Pyramid Model. A particle requires a certain velocity to escape from the riverbank and determination of the escape velocity can pave the way for finding out other parameters like entrainment rate, erosion coefficient and so on. Calculation and estimation of riverbank erosion rate is an important aspect of river basin management. In this paper it has been shown that the escape velocity is dependent on certain micro-level parameters like inter-particle distance and volume of the water bridge between two adjacent particles. Also, for saline water the particle requires less velocity to escape compared to the pure-water scenario. The findings of the present paper exactly fall in line with the results of another paper where the researchers showed that cohesive force between the particles decreases as water turns from pure to impure.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.D5000230061)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2025A1515011192).
文摘This study explores the magnetohydrodynamic(MHD)boundary layer flow of a water-based Boger nanofluid over a stretching sheet,with particular focus on the influences of nanoparticle diameter,nanolayer effects,and thermal radiation.The primary aim is to examine how variations in nanoparticle size and nanolayer thickness affect the hydrothermal behavior of the nanofluid.The model also incorporates the contributions of viscous dissipation and Joule heating within the heat transfer equation.The governing momentum and energy equations are converted into dimensionless partial differential equations(PDEs)using appropriate similarity variables and are numerically solved using the finite element method(FEM)implemented in MATLAB.Extensive validation of this method confirms its reliability and accuracy in numerical solutions.The findings reveal that increasing the diameter of copper nanoparticles significantly enhances the velocity profile,with a more pronounced effect observed at wider inter-particle spacings.A higher solvent volume fraction leads to decreased velocity and temperature distributions,while a greater relaxation time ratio improves velocity and temperature profiles due to the increased elastic response of the fluid.Moreover,enhancements in the magnetic parameter,thermal radiation,and Eckert number lead to an elevation in temperature profiles.Furthermore,higher nanolayer thickness reduces the temperature profile,whereas particle radius yields the opposite outcome.
文摘An interfacial force microscope （IFM） was employed to measure the inter-particle forces between two individual glass beads with diameters varying from 8 to 20 μm. With the feedback function of IFM turned off, attractive forces were obtained. The forces varied in the range of 0.1-0.34 μN, and their validity was confirmed by a theoretical analysis of the van der Waals force between the same glass beads. With the feedback function switched on, no attractive forces between particles were detected by the IFM when the probe approached the sample substrate. This may be attributed to the dramatic change of the attractive forces within a very short separation distance and/or the relatively poor signal-to-noise ratio of the IFM.
文摘This article investigates the role of the specularity coefficient(φ,the extent of the energy dissipation due to particle-wall collisions),inter-particle restitution coefficient(e_(pp),the extent of the energy dissipation due to inter-particle collisions),and four combinations of these variables on the hydrodynamics,and the pressure recovery of the dilute gas-solid suspension in a diffuser.The investigation applies the two-fluid modeling approach along with the kinetic theory of the granular flow.The present investigation’s findings indicate that an increase inφor a reduction in e_(pp) reduces the pressure recovery by weakening the reverse momentum transfer phenomenon,which is recognized as the primary means for the pressure recovery.Besides,in a gas-solid flow system,a higherφor smaller e_(pp) enhances the particles’trapping in the recirculation zone.The recirculation zone’s strength and size increase asφincreases or e_(pp) reduces.Moreover,an increase in the wall-particle and inter-particle interactions strengthens the sidewise displacement of the particles.The effect of the wall-particle and inter-particle interactions are insignificant for extremely small solid loading.
文摘There exist big gaps between measurements and modeling predictions on solids holdup and pressure drop in dense solids transport, such as those occuring in the bottom sections of gas-solids risers. The inability of closing this gap by common modeling approaches indicates certain missing and/or misrepresentation of some controlling mechanisms in modeling the transport. Previous research efforts show that the gap can not be effectively narrowed by simply modifying the drag force formulations without inclusion of the collision effect. This paper explores the origin of some controlling mechanisms that might have been overlooked in previous modeling approaches, and recommends how to make the model dense solids transport better. Our analysis shows the presence of a resistant force arising from inter-particle collision when the solids are accelerated in dense-phase transport. This may be caused by non-equilibrium collision during solids acceleration, which differs from local-equilibrium assumptions on which the current kinetic theory modeling of granular particles is based. A complete modeling of this collision-induced resistance calls for a total revision of the kinetic theory, with the inclusion of non-equilibrium collisions and offcenter collisions in dense solids transport.
基金supported financially by the National Natural Science Foundation of China(No.51875443)the Guangdong Basic and Applied Basic Research Foundation(Nos.2019B1515120016 and 202002030290)+3 种基金the Shaanxi Co-Innovation Projects(No.2015KTTSGY03-03)the Shaanxi Natural Science Foundation(No.2015JQ5200)the Open Project from The Key Lab of Guangdong for Modern Surface Engineering Technologyfinancial support by Guangdong Academy of Sciences’Project of Constructing First-class Domestic Research Institutions(Nos.2019GDASYL-0503006,2020GDASYL-20200302011)。
文摘The oxide scale present on the feedstock particles is critical for inter-particle bond formation in the cold spray(CS)coating process,therefore,oxide scale break-up is a prerequisite for clean metallic contact which greatly improves the quality of inter-particle bonding within the deposited coating.In general,a spray powder which contains a thicker oxide scale on its surface(i.e.,powders having high oxygen content)requires a higher critical particle velocity for coating formation,which also lowers the deposition efficiency(DE)making the whole process a challenging task.In this work,it is reported for the first time that an artificially oxidized copper(Cu)powder containing a high oxygen content of 0.81 wt.%with a thick surface oxide scale of 0.71μm.,can help achieve an astonishing increment in DE.A transition of surficial oxide scale evolution starting with crack initiations followed by segmenting to peeling-off was observed during the high velocity particle impact of the particles,which helps in achieving an astounding increment in DE.Single-particle deposit observations revealed that the thick oxide scale peels off from most of the sprayed powder surfaces during the high-velocity impact,which leaves a clean metallic surface on the deposited particle.This makes the successive particles to bond easily and thus leads to a higher DE.Further,owning to the peeling-off of the oxide scale from the feedstock particles,very few discontinuous oxide scale segments are retained at inter-particle boundaries ensuring a high electrical conductivity within the resulting deposit.Dependency of the oxide scale threshold thickness for peeling-off during the high velocity particle impact was also investigated.
基金financial support from the National Science Foundation of China(22078190)the National Key R&D Plan of China(2020YFB1505802)。
文摘Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in studying the CES.In the present work,a bi-scale impedance transmission line model(TLM)is firstly developed for a single pore to a porous electrode.Not only the TLM of the single pore is reparameterized but also the particle packing compactness is defined in the bi-scale.Subsequently,the CES properties are identified by FRA,focused on rate capability vs.characteristic frequency,peak power vs.equivalent series resistance,and energy density vs.low frequency limiting capacitance for a single pore to a porous electrode.Based on these relationships,the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length,intra-particle pore diameter,inter-particle pore diameter,electrolyte conductivity,interfacial capacitance&exponent factor,electrode thickness,electrode apparent surface area,and particle packing compactness.Finally,the experimental diagnosis of four supercapacitors(SCs)with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore.The calculating results suggest,to some extent,the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode.Hence,in order to design a better porous electrode,more attention should be given to the inter-particle pore.
文摘Inter-particle and molecular forces are of most important forces affecting fines migration. Investigating the impact of these types of forces requires information about electrical properties of constitutive component and Nano-sized solids. Surface potential is a well-known parameter, which can be used to measure aforementioned forces. The force balance among electrical, gravity, drag and buoyance forces tracing on a particle can be estimated using fluid properties and physical properties of reservoir such as surface potential, pore size distribution and fine size distribution. The task is to set these forces at conditions that fine migration does not take place. This paper investigates the impact of several parameters that could influence pertinent forces. Effect of ionic strength of flowing fluid is taken into account to evaluate Debye length that determines double layer forces. The impact of injection rate on a parameter named erosion number is?also studied. The results of this study show that how introducing salts and injection rate can affect stability of fines on their locations.
文摘The aim of this paper is to obtain relevant sets of collision cross sections of the parent ions in low pressure discharges in argon, oxygen, and nitrogen, i.e., Ar＋ in Ar, O2＋ in O2 and N2＋ in N2. These ion data are first discussed and then validated from comparisons between the calculated transport coefficients and those measured in the literature. The elastic momentum transfer collision cross sections are determined from a semi-classical approximation for the phase shift calculation based on a 12-6-4 inter-particle potential while ion transport coefficients are determined versus the reduced electric field from Monte Carlo simulations.
文摘A simplified model is proposed for an easy understanding of the coarse-grained technique and for achieving a first approximation to the behavior of gases. A mole of a gas substance, within a cubic container, is represented by six particles symmetrically moving. The impacts of particles on container walls, the inter-particle collisions, as well as the volume of particles and the inter-particle attractive forces, obeying a Lennard-Jones curve, are taken into account. Thanks to the symmetry, the problem is reduced to the nonlinear dynamic analysis of a SDOF oscillator, which is numerically solved by a step-by-step time integration algorithm. Five applications of proposed model, on Carbon Dioxide, are presented: 1) Ideal gas in STP conditions. 2) Real gas in STP conditions. 3) Condensation for small molar volume. 4) Critical point. 5) Iso-kinetic energy curves and iso-therms in the critical point region. Results of the proposed model are compared with test data and results of the Van der Waals model for real gases.
文摘Fines migration is defined as separation of a Nano-sized particle by fluid flow in porous media and its migration along some distances and its entrapment in a narrow pore throat or its settlement on pore wall. Although this phenomenon happens in scales of Nano-meters, it can lead to sever irretrievable damages. This damage includes permeability reduction that causes drastic oil recovery reduction. There are several forces impacting a fine that is placed on a pore wall. Some of most important forces affecting settlement of a fine in porous media in presence of a fluid are electrical forces. Electrical forces consist of several long and short range forces. This study focuses on a long range force called Double Layer Force (DLF) that beside Van der Waals is one of most powerful electrical forces. DLF is a repulsive force that can repel a particle from pore wall and result separation of a Nano-sized solid which subsequently moves along with flowing fluid and clogs a throat. The DLF depends on the solid material (reservoir rock and fine) and fluid properties (i.e. ionic strength, pH). This study investigates how each of these parameters affects DLF and introduces proper conditions for reservoir water flooding for controlling fines migration.
基金The work described in this paper was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region,China(Project No.CityU 8779012).
文摘Discrete element modeling requires the proper quantification of the behavior of grains at their contacts including the normal force-displacement and tangential force-displacement relationships to be used as input for contact modeling purposes.This paper reports on recent advances in soil mechanics experimentation which allowed measuring the grain contact behavior of small sand particles quantifying friction and stiffness with sliding tests of a force-controlled or displacement-controlled type.The particular focus of this work is on the micromechanical behavior of quartz type grains of size between about 1 and 5 mm.A description of the developed micromechanical apparatus at City University of Hong Kong is first discussed and its important different capabilities with previously developed apparatus is briefly reviewed.Subsequently,a limited set of new data is reported and discussed along with a review of recently acquired results published in the literature associated with the contact behavior of quartz sand grains.These sliding tests have covered a wider range of normal contact forces from about 0.5 to 8 N,and the results indicated that,for this range of confining forces,there is not any notable change of the inter-particle coefficient of friction.
基金supported by the National Natural Science Foundation of China (Grant No. 51106180)the research funds of China University of Petroleum, Beijing (Grant No. BJ-2010-03)
文摘This paper establishes a lattice Boltzmann equation-discrete element method (LBE-DEM) coupled simulation method under the Eulerian-Lagrangian framework at first, and applies it to simulating a two-dimensional gas-solid two-phase cross jet. The gas phase is simulated by the lattice-Boltzmann method via the TD2G9 model; the solid phase is traced by the Lagrangian method and the inter-particle collision is calculated by the DEM method. Three values of the Stokes number St=10, 25, and 50 are simulated under the same mass loading. This paper focuses on the characteristics of vortex structure, particle distribution, and the reverse-flow/rebounding rate in cross jets. We analyze the characteristics of fluid vortex motion, particle cluster distribution, rebounding rate of particles and the influencing factors for them. The results show the existence of joint distribution of discrete clusters and discrete particles in cross jets. Meanwhile, it shows that a larger concentration of particles in the early stage of jet evolution or a smaller Stokes number under the same mass loading can produce a larger rebounding rate. However, the rebounding rate of particles at the late stage, in general, is stable.
基金This work was supported by the National Natural ScienceFoundation of China(No.51925603)the Fundamental ResearchFunds for the Central Universities(No.2022ZFJH004).
文摘In the past few decades,multi-scale numerical methods have been developed to model dense gas-solidflow in fluidized beds with different resolutions,accuracies,and efficiencies.However,ambiguity needsto be clarified in the multi-scale numerical simulation of fluidized beds:(i)the selection of the submodels,parameters,and numerical resolution;(ii)the multivariate coupling of operating conditions,bed configurations,polydispersity,and additional forces.Accordingly,a state-of-the-art review is performed to assess the applicability of multi-scale numerical methods in predicting dense gas-solid flow influidized beds at specific fluidization regimes(e.g.,bubbling fluidization region,fast fluidization regime),with a focus on the inter-particle collision models,inter-phase interaction models,collision parameters,and polydispersity effect.A mutual restriction exists between resolution and efficiency.Higherresolution methods need more computational resources and thus are suitable for smaller-scale simulations to provide a database for closure development.Lower-resolution methods require fewercomputational resources and thus underpin large-scale simulations to explore macro-scale phenomena.Model validations need to be further conducted under multiple flow conditions and comprehensivemetrics(e.g.,velocity profiles at different heights,bubbles,or cluster characteristics)for furtherimprovement of the applicability of each numerical method.
文摘Carbon nanotubes (CNTs) can be fluidized in the form of fluidlike agglomerates made of many three-dimensional sub-agglomerates, having a multi-stage agglomerate (MSA) structure and containing large amounts of twisting CNTs of micrometer magnitude.
基金support by National Science Council,R.O.C.under Grant No.NSC 98-2221-E006-132.
文摘Three physicalmechanismswhichmay affect dispersion of particle’smotion in wall-bounded turbulent flows,including the effects of turbulence,wall roughness in particle-wall collisions,and inter-particle collisions,are numerically investigated in this study.Parametric studies with differentwall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach.A low-Reynolds-number k−ǫturbulence model is applied for the solution of the carrier-flow field,while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion.It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles.Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particleladen flow.Since the investigated particles are associated with large Stokes numbers,i.e.,larger than O(1),in the test problem,the effects of turbulence on particle dispersion aremuch less considerable,as expected,in comparison with another two physical mechanisms investigated in the study.
文摘A new model that combines Eulerian and Lagrangian approach is set up. with inter-particle interaction being taken account of through kinetic theory. The numerical algorithm is included. In the end, comparison with the experimental results of Barlow and Morrison [1] is make, and a good agreement is reached.
