In this study, a three-dimensional model based on RANS, slender-body theory and Newton-Euler dynamics is established to study the number concentration, one of the most important fluidization characteristics of cylindr...In this study, a three-dimensional model based on RANS, slender-body theory and Newton-Euler dynamics is established to study the number concentration, one of the most important fluidization characteristics of cylindrical particles. Also, the effects of interaction between cylindrical particles are taken into account by introducing the rigid collision dynamics. To validate the model, the fluidization experiments of cylindrical particles in a cold-state fluidized bed are carried out. The number concentration characteristics of cylindrical particles are obtained from computational fluid dynamics (CFD) simulation. It is found that cylindrical particles arriving at the exit of the riser the earliest come from the near-wall regions, the horizontal transfer of so many cylindrical particles from the radial centre regions to the near-wall regions is evident. Meanwhile, there is no distinct relationship between the number concentration and inlet wind velocity.展开更多
The sedimentations of two cylindrical particles in three different initial relative po- sitions are numerically simulated using the lattice Boltzmann method.The movement characteristics and particle interactions durin...The sedimentations of two cylindrical particles in three different initial relative po- sitions are numerically simulated using the lattice Boltzmann method.The movement characteristics and particle interactions during their sedimentation are presented and discussed in detail.The results show that,(i)if the two particles are released parallel but separated horizontally,they push away each other,rotate inwards and separate horizontally as they fall;(ii)if the two particles are released par- allel but separated vertically,the sedimentation behavior can be classified into three stages:trailing, tumbling and separating;(iii)if the two particles are released perpendicular but separated vertically, the sedimentation behavior can be characterized as:trailing and rotating,touching and sliding.In order to validate our simulation,experiments were also conducted and the results agree well with the numerical ones.展开更多
The orientation distribution function of cylindrical particle suspensions was deduced and numerically simulated, and an application was taken in a wedge-shaped flow field. The relationship between the orientation dist...The orientation distribution function of cylindrical particle suspensions was deduced and numerically simulated, and an application was taken in a wedge-shaped flow field. The relationship between the orientation distribution function and particle orientation angles was obtained. The results show that comparing with the most probable angle distribution which comes to being in short time, the distribution of the steady state doesn't vary much. in range; the main difference is the anti-clockwise rotation in the right and upper field, that is, particles rotate more at the points where the velocity gradients are larger. The most probable orientations are close to the direction of local streamlines. In the direction of streamlines, with poleradius decreasing, the most probable angles increase, but the angles between their orientations and the local streamlines decrease.展开更多
Based on the momentum and constitutive equations, the modified Orr_Sommerfeld equation describing the flow stability in a cylindrical particle two_phase flow was derived.For a cylindrical particle two_phase boundary l...Based on the momentum and constitutive equations, the modified Orr_Sommerfeld equation describing the flow stability in a cylindrical particle two_phase flow was derived.For a cylindrical particle two_phase boundary layer, the neutral stability curves and critical Reynolds number were given with numerical simulation. The results show that the cylindrical particles have a suppression effect on the flow instability, the larger the particle volume fraction and the particle aspect_ratio are, the more obvious the suppression effect is.展开更多
With the help of the method of separation of variables and the Debye-Hüchel approximation, the Poisson-Boltzmann equation that describes the distribution of the potential in the electrical double layer of a cylin...With the help of the method of separation of variables and the Debye-Hüchel approximation, the Poisson-Boltzmann equation that describes the distribution of the potential in the electrical double layer of a cylindrical particle with a limited length has been firstly solved under a very low potential condition. Then with the help of the functional analysis theory this equation has been further analytically solved under general potential conditions and consequently, the corresponding surface charge densities have been obtained. Both the potential and the surface charge densities cointide with those results obtained from the Debye-Hüchel approximation when the very low potential of zeψ〈〈kT is introduced.展开更多
Discrete element method simulations of granular shear flows of frictional cylindrical particles are performed. From the simulations, solid-phase pressure, shear stress, and bulk friction coefficient μ can be measured...Discrete element method simulations of granular shear flows of frictional cylindrical particles are performed. From the simulations, solid-phase pressure, shear stress, and bulk friction coefficient μ can be measured, allowing the investigation of the effects of particle properties on the macroscopic flow behaviors. Thus, the inertial number I based rheological models, which were frequently used for the spherical particles in the previous work, are examined for the applicability to cylindrical particles in the present study. It is found that the particle aspect ratio, interparticle friction coefficient, and particle size polydispersity all affect the bulk friction coefficient-inertial number correlation and the solid volume fraction-inertial number correlation, and their effects vary in different flow regimes, which exhibit different mechanical behaviors.展开更多
With consideration of the Stokes drag and virtual mass force, the equationsfor mean and fluctuating velocities in rotation and translation were given for rigid cylindricalparticles moving in a turbulent flow. Then the...With consideration of the Stokes drag and virtual mass force, the equationsfor mean and fluctuating velocities in rotation and translation were given for rigid cylindricalparticles moving in a turbulent flow. Then the rotational and translational dispersion coefficientsof particle were derived. The relationships between the dispersion, coefficients and flow lengthscale as well as particle characteristic parameters were analyzed. The resulting dispersioncoefficients were proved to decrease as the particle length increases. The conclusions are helpfulfor the further research on the motion of cylindrical particles in turbulent flows.展开更多
Particle packing is widely applied in organic pollutant adsorption,catalytic reaction.biomass combustion,nuclear cooling,and other scenarios.Due to the complexity of the shape,the studies on the void fraction of the c...Particle packing is widely applied in organic pollutant adsorption,catalytic reaction.biomass combustion,nuclear cooling,and other scenarios.Due to the complexity of the shape,the studies on the void fraction of the cylindrical particles are not as thorough as the spherical particles.This study investigated the influence of the flling rate,material properties and sphericity on the void fraction of cylinders through experiments and simulation.DEM(discrete element method)was validated by the internal structures of the packing obtained by CT(computed tomography).Based on the logarithmic correlation between the void fraction and flling rate,an ingenious framework for predicting the void fraction of cylindrical particles was presented with two intermediate coefficients.By correlating the coefficients with the material property and sphericity,a novel void-fraction prediction model was established with R-squared of 0.996.The mechanism of void fraction under random loose packing for cylinders was eventually found in this study.展开更多
Systematic physical experiments examining the packing densification of mono-sized cylindrical parti- cles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration ti...Systematic physical experiments examining the packing densification of mono-sized cylindrical parti- cles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration time, frequency, amplitude, vibration strength, container size, and the aspect ratio and spheric- ity of the particle on the packing density were analyzed and discussed. For each initial packing density with a certain aspect ratio, operating parameters were optimized to achieve much denser packing. The results indicate that the packing density initially increases with vibration time and then remains con- stant. The effects of vibration frequency and amplitude on the packing densification have similar trends, i.e. the packing density first increases with the vibration frequency or amplitude to a high value and then decreases; too large or small frequency or amplitude does not enhance densification. Increasing the container size can reduce container wall effects and help achieve a high packing density. Varying the particle aspect ratio and sphericity can lead to different dense random packing structures. Overall, based on results of the examined systems, the highest random packing density obtained in an infinite sized container can reach 0.73, which agrees well with corresponding numerical and analytical results in the literature.展开更多
The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work, particle oscillation and effect of particle on the fluid are considered, and the ...The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work, particle oscillation and effect of particle on the fluid are considered, and the torque exerted on a particle when viscous fluid flow around a particle is got through experiment and included in the numerical simulation. The computational results showed that the sedimentation velocities of particle increase slowly with the increase of particle aspect ratio . For disk like particle, when the motion direction of particle is parallel to axis of particle, particle falls more slowly than the case of perpendicular to axis of particle; while for rod like particle, it is inverse. For sedimentation of a crowd of high frequency oscillating cylindrical particles with arbitrary initial orientation, both vertical velocity and horizontal velocity oscillate dramatically, the degree of oscillation of the former is stronger than the later. A crowd of particles fall more quickly than an isolated particle. Particles tend to strongly align in the direction of gravity. The computational results agreed well with the experimental ones and helpful for controlling of pollutant particles.展开更多
A new method, i.e. the iterative method in functional theory, was introduced to solve analytically the nonlinear Poisson-Boltzmann （PB） equation under general potential ψ condition for the electric double layer of ...A new method, i.e. the iterative method in functional theory, was introduced to solve analytically the nonlinear Poisson-Boltzmann （PB） equation under general potential ψ condition for the electric double layer of a charged cylindrical colloid particle in a symmetrical electrolyte solution. The iterative solutions of ψ are expressed as functions of the distance from the axis of the particle with solution parameters： the concentration of ions c, the aggregation number of ions in a unit length m, the dielectric constant e, the system temperature T and so on. The relative errors show that generally only the first and the second iterative solutions can give accuracy higher than 97%. From the second iterative solution the radius and the surface potential of a cylinder have been defined and the corresponding values have been estimated with the solution parameters, Furthermore, the charge density, the activity coefficient of ions and the osmotic coefficient of solvent were also discussed,展开更多
Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density ε and termina...Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density ε and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted “T” structure were observed, the pollutant particles for high ε and large ReT scattered wider than that for low ε and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on ε and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to ε. The orientation distributions of pollutant particles depended on ReT and ε, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on ε and ReT.展开更多
Motion of fibres in sheared fibre suspensions is simulated numerically by using the lattice Boltzmann method. The orientational distributions of the fibres are presented for different Reynolds numbers, Stokes numbers,...Motion of fibres in sheared fibre suspensions is simulated numerically by using the lattice Boltzmann method. The orientational distributions of the fibres are presented for different Reynolds numbers, Stokes numbers, shear rate and fibre aspect ratio. Some computational results are compared with the experimental data of pipe flow, and the qualitative agreement is achieved. The results show that the orientational distributions are greatly affected by the Reynolds numbers, while relatively insensitive to the fibre aspect ratio. The Stokes number and shear rate have obvious influence on the orientation distribution.展开更多
The equation of probability distribution function for mean fibre orientation in a turbulent boundary layer is derived, in which the correlation terms of the fluctuating velocity, fluctuating angular velocity with the ...The equation of probability distribution function for mean fibre orientation in a turbulent boundary layer is derived, in which the correlation terms of the fluctuating velocity, fluctuating angular velocity with the fluctuating probability distribution function are related to the gradient of mean probability distribution function and the dispersion coefficients in order to make the equation be solvable. The finite-difference method is used to solve the equation numerically. The results show that the fibres tend to align with the streamline, which is in agreement qualitatively with the experimental result given by visualization. The fibre aspect-ratio has a significant effect on the orientation distribution of fibres, while the effect of the distance from the wall is negligible.展开更多
The study of cylindrical particulate flows has wide industrial applicability and hence received much attention. The purpose of the present paper is to provide a review on the motion of cylindrical particles in shear l...The study of cylindrical particulate flows has wide industrial applicability and hence received much attention. The purpose of the present paper is to provide a review on the motion of cylindrical particles in shear layer, converging channel and jet flows, the dynamic of cylindrical particles sedimentation in a Newtonian fluid, the characterization of turbulent cylindrical particulate flows, the property of interaction between the particles, the structural feature and rheology of suspensions, the analysis of hydrodynamic instability of cylindrical particle suspensions. Finally, the concluding remarks are given.展开更多
基金Supported by the Natural Science Fund for Colleges and Universities in Jiangsu Province(2011112TSJ0149)Jiangsu Key Laboratory of Process Enhancement & New Energy Equipment Technology at Nanjing University of Technology,China
文摘In this study, a three-dimensional model based on RANS, slender-body theory and Newton-Euler dynamics is established to study the number concentration, one of the most important fluidization characteristics of cylindrical particles. Also, the effects of interaction between cylindrical particles are taken into account by introducing the rigid collision dynamics. To validate the model, the fluidization experiments of cylindrical particles in a cold-state fluidized bed are carried out. The number concentration characteristics of cylindrical particles are obtained from computational fluid dynamics (CFD) simulation. It is found that cylindrical particles arriving at the exit of the riser the earliest come from the near-wall regions, the horizontal transfer of so many cylindrical particles from the radial centre regions to the near-wall regions is evident. Meanwhile, there is no distinct relationship between the number concentration and inlet wind velocity.
基金The project supported by the National Natural Science Foundation of China for Distinguished Scholars(19925210)
文摘The sedimentations of two cylindrical particles in three different initial relative po- sitions are numerically simulated using the lattice Boltzmann method.The movement characteristics and particle interactions during their sedimentation are presented and discussed in detail.The results show that,(i)if the two particles are released parallel but separated horizontally,they push away each other,rotate inwards and separate horizontally as they fall;(ii)if the two particles are released par- allel but separated vertically,the sedimentation behavior can be classified into three stages:trailing, tumbling and separating;(iii)if the two particles are released perpendicular but separated vertically, the sedimentation behavior can be characterized as:trailing and rotating,touching and sliding.In order to validate our simulation,experiments were also conducted and the results agree well with the numerical ones.
文摘The orientation distribution function of cylindrical particle suspensions was deduced and numerically simulated, and an application was taken in a wedge-shaped flow field. The relationship between the orientation distribution function and particle orientation angles was obtained. The results show that comparing with the most probable angle distribution which comes to being in short time, the distribution of the steady state doesn't vary much. in range; the main difference is the anti-clockwise rotation in the right and upper field, that is, particles rotate more at the points where the velocity gradients are larger. The most probable orientations are close to the direction of local streamlines. In the direction of streamlines, with poleradius decreasing, the most probable angles increase, but the angles between their orientations and the local streamlines decrease.
文摘Based on the momentum and constitutive equations, the modified Orr_Sommerfeld equation describing the flow stability in a cylindrical particle two_phase flow was derived.For a cylindrical particle two_phase boundary layer, the neutral stability curves and critical Reynolds number were given with numerical simulation. The results show that the cylindrical particles have a suppression effect on the flow instability, the larger the particle volume fraction and the particle aspect_ratio are, the more obvious the suppression effect is.
基金Supported by the National Natural Science Foundation of China(No.20473034) the Taihu Scholar Foundation of SouthernYangtze University(2003).
文摘With the help of the method of separation of variables and the Debye-Hüchel approximation, the Poisson-Boltzmann equation that describes the distribution of the potential in the electrical double layer of a cylindrical particle with a limited length has been firstly solved under a very low potential condition. Then with the help of the functional analysis theory this equation has been further analytically solved under general potential conditions and consequently, the corresponding surface charge densities have been obtained. Both the potential and the surface charge densities cointide with those results obtained from the Debye-Hüchel approximation when the very low potential of zeψ〈〈kT is introduced.
基金The National Natural Science Foundation of China(grant numbers 11872333,11272061,91852205)the Natural Science Foundation of Zhejiang Province(grant number LR19A020001)the Fundamental Research Funds for Central Universities(grant number 2017ZY37)are acknowledged for financial supports.
文摘Discrete element method simulations of granular shear flows of frictional cylindrical particles are performed. From the simulations, solid-phase pressure, shear stress, and bulk friction coefficient μ can be measured, allowing the investigation of the effects of particle properties on the macroscopic flow behaviors. Thus, the inertial number I based rheological models, which were frequently used for the spherical particles in the previous work, are examined for the applicability to cylindrical particles in the present study. It is found that the particle aspect ratio, interparticle friction coefficient, and particle size polydispersity all affect the bulk friction coefficient-inertial number correlation and the solid volume fraction-inertial number correlation, and their effects vary in different flow regimes, which exhibit different mechanical behaviors.
文摘With consideration of the Stokes drag and virtual mass force, the equationsfor mean and fluctuating velocities in rotation and translation were given for rigid cylindricalparticles moving in a turbulent flow. Then the rotational and translational dispersion coefficientsof particle were derived. The relationships between the dispersion, coefficients and flow lengthscale as well as particle characteristic parameters were analyzed. The resulting dispersioncoefficients were proved to decrease as the particle length increases. The conclusions are helpfulfor the further research on the motion of cylindrical particles in turbulent flows.
基金This work was supported by the China National Key R&D Program during the 13th Five-year Plan Period(grant number 2018YFC0705300)the National Natural Science Foundation of China(grant number 52078354).
文摘Particle packing is widely applied in organic pollutant adsorption,catalytic reaction.biomass combustion,nuclear cooling,and other scenarios.Due to the complexity of the shape,the studies on the void fraction of the cylindrical particles are not as thorough as the spherical particles.This study investigated the influence of the flling rate,material properties and sphericity on the void fraction of cylinders through experiments and simulation.DEM(discrete element method)was validated by the internal structures of the packing obtained by CT(computed tomography).Based on the logarithmic correlation between the void fraction and flling rate,an ingenious framework for predicting the void fraction of cylindrical particles was presented with two intermediate coefficients.By correlating the coefficients with the material property and sphericity,a novel void-fraction prediction model was established with R-squared of 0.996.The mechanism of void fraction under random loose packing for cylinders was eventually found in this study.
基金We are grateful to the financial support of National Natural Science Foundation of China （No. 51374070） and Fundamental Research Funds for the Central Universities of China （N120202001, N130102001）.
文摘Systematic physical experiments examining the packing densification of mono-sized cylindrical parti- cles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration time, frequency, amplitude, vibration strength, container size, and the aspect ratio and spheric- ity of the particle on the packing density were analyzed and discussed. For each initial packing density with a certain aspect ratio, operating parameters were optimized to achieve much denser packing. The results indicate that the packing density initially increases with vibration time and then remains con- stant. The effects of vibration frequency and amplitude on the packing densification have similar trends, i.e. the packing density first increases with the vibration frequency or amplitude to a high value and then decreases; too large or small frequency or amplitude does not enhance densification. Increasing the container size can reduce container wall effects and help achieve a high packing density. Varying the particle aspect ratio and sphericity can lead to different dense random packing structures. Overall, based on results of the examined systems, the highest random packing density obtained in an infinite sized container can reach 0.73, which agrees well with corresponding numerical and analytical results in the literature.
基金TheNationalNaturalSciencesFoundationforOutstandingYouthofChina (No .1 992 52 1 0 )
文摘The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work, particle oscillation and effect of particle on the fluid are considered, and the torque exerted on a particle when viscous fluid flow around a particle is got through experiment and included in the numerical simulation. The computational results showed that the sedimentation velocities of particle increase slowly with the increase of particle aspect ratio . For disk like particle, when the motion direction of particle is parallel to axis of particle, particle falls more slowly than the case of perpendicular to axis of particle; while for rod like particle, it is inverse. For sedimentation of a crowd of high frequency oscillating cylindrical particles with arbitrary initial orientation, both vertical velocity and horizontal velocity oscillate dramatically, the degree of oscillation of the former is stronger than the later. A crowd of particles fall more quickly than an isolated particle. Particles tend to strongly align in the direction of gravity. The computational results agreed well with the experimental ones and helpful for controlling of pollutant particles.
基金Project supported by the National Natural Science Foundation of China （Nos. 20676051, 20573048 and 20473034） and the 0pen Project Program of the Key Laboratory of Industrial Biotechnology, Ministry of Education （No. KLIB-KF200504）.
文摘A new method, i.e. the iterative method in functional theory, was introduced to solve analytically the nonlinear Poisson-Boltzmann （PB） equation under general potential ψ condition for the electric double layer of a charged cylindrical colloid particle in a symmetrical electrolyte solution. The iterative solutions of ψ are expressed as functions of the distance from the axis of the particle with solution parameters： the concentration of ions c, the aggregation number of ions in a unit length m, the dielectric constant e, the system temperature T and so on. The relative errors show that generally only the first and the second iterative solutions can give accuracy higher than 97%. From the second iterative solution the radius and the surface potential of a cylinder have been defined and the corresponding values have been estimated with the solution parameters, Furthermore, the charge density, the activity coefficient of ions and the osmotic coefficient of solvent were also discussed,
文摘Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density ε and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted “T” structure were observed, the pollutant particles for high ε and large ReT scattered wider than that for low ε and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on ε and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to ε. The orientation distributions of pollutant particles depended on ReT and ε, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on ε and ReT.
基金Supported by the Key Project of the National Natural Science Foundation of China under Grant No 10632070.
文摘Motion of fibres in sheared fibre suspensions is simulated numerically by using the lattice Boltzmann method. The orientational distributions of the fibres are presented for different Reynolds numbers, Stokes numbers, shear rate and fibre aspect ratio. Some computational results are compared with the experimental data of pipe flow, and the qualitative agreement is achieved. The results show that the orientational distributions are greatly affected by the Reynolds numbers, while relatively insensitive to the fibre aspect ratio. The Stokes number and shear rate have obvious influence on the orientation distribution.
基金Supported by the National Natural Science Foundation of China under Grant No 10372090, and the Doctoral Program of Higher Education in China under Grant No 20030335001.
文摘The equation of probability distribution function for mean fibre orientation in a turbulent boundary layer is derived, in which the correlation terms of the fluctuating velocity, fluctuating angular velocity with the fluctuating probability distribution function are related to the gradient of mean probability distribution function and the dispersion coefficients in order to make the equation be solvable. The finite-difference method is used to solve the equation numerically. The results show that the fibres tend to align with the streamline, which is in agreement qualitatively with the experimental result given by visualization. The fibre aspect-ratio has a significant effect on the orientation distribution of fibres, while the effect of the distance from the wall is negligible.
基金*Project supported by the National Natural Science Foundation of China (Grant No: 10372090).
文摘The study of cylindrical particulate flows has wide industrial applicability and hence received much attention. The purpose of the present paper is to provide a review on the motion of cylindrical particles in shear layer, converging channel and jet flows, the dynamic of cylindrical particles sedimentation in a Newtonian fluid, the characterization of turbulent cylindrical particulate flows, the property of interaction between the particles, the structural feature and rheology of suspensions, the analysis of hydrodynamic instability of cylindrical particle suspensions. Finally, the concluding remarks are given.
